Heyndrickxia coagulans as a next-generation probiotic: current evidence and future perspectives

Abstract

Heyndrickxia coagulans, a spore-forming probiotic, has garnered significant attention due to its exceptional tolerance to gastric acid and heat, alongside its multifaceted therapeutic potential. This review systematically delineates the unique biological characteristics of this bacterium, which include high survivability mediated by its spore form (retaining 73% viability after microwave treatment at 260 °C), dual lactate fermentation pathways, and plasticity in ATP synthesis that depends on pH and growth rate. Clinical evidence supports its efficacy in managing metabolic disorders (e.g., type 2 diabetes and non-alcoholic fatty liver disease), gastrointestinal conditions (e.g., constipation and irritable bowel syndrome), and neuropsychiatric disorders (e.g., depression and Alzheimer's disease). The underlying mechanisms involve the production of short-chain fatty acids (SCFAs), modulation of the TLR4/MyD88/NF-κB signaling pathway, and suppression of oxidative stress. Notably, therapeutic effects are strain-specific: H. coagulans MTCC 5856 (2 × 10¹⁰ CFU day⁻¹) significantly reduces abdominal distension (P < 0.01), while the strain Unique IS-2 alleviates anxiety-like behaviors by upregulating hippocampal BDNF. Although toxicological assessments establish a no observed adverse effect level (NOAEL) of >1000 mg kg⁻¹ in rodent models, its limited capacity for intestinal colonization presents a clinical challenge. Future research should prioritize large-scale clinical trials, multi-omics mechanistic investigations, and the development of synbiotic formulations to fully realize its potential as a next-generation therapeutic agent.

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1 Introduction

The human gut harbors a diverse and abundant microbial community, known as the gut microbiota, which colonizes the intestine shortly after birth and is subsequently enriched through dietary and other factors. This community performs numerous physiological and biochemical functions within the host. By producing metabolites such as short-chain fatty acids (SCFAs), enzymes, and antimicrobial substances, the gut microbiota modulates and maintains a stable intestinal microenvironment, thereby protecting against pathogen invasion. Furthermore, it enhances host immune function by regulating immune responses, influences sleep, mood, and cognitive functions via the gut–brain axis, and impacts cardiometabolic health and disorders such as obesity by modulating substance metabolism. Consequently, maintaining intestinal homeostasis is crucial for overall health.^1–3

Probiotics primarily include yeasts, Actinobacteria, Bacillus spp., Bifidobacterium, Clostridium butyricum, and Lactobacillus.⁴ They are non-pathogenic and do not produce or release toxic substances in humans. Probiotics play vital roles in maintaining gut microbiome homeostasis. Dietary supplementation with probiotics enhances metabolite production, protects the intestinal mucosal barrier, inhibits intestinal inflammation, and maintains microbial equilibrium, thereby promoting gut health and bolstering immunity. Additionally, certain probiotics have applications in improving aquaculture water quality and meat quality.^5–8

However, the harsh conditions of the human digestive system, particularly gastric acid and other secretions, inactivate many probiotics before they reach the intestine. Only a small minority survive to exert beneficial effects. H. coagulans, a Gram-positive, spore-forming, facultative anaerobic bacterium within the phylum Firmicutes, demonstrates exceptional tolerance to high temperatures, acid, and bile salts. This resilience allows it to survive transit to the gut, making it one of the few viable probiotic species upon arrival and enabling its application in products like candies and biscuits. H. coagulans benefits the gut ecosystem by consuming free oxygen and undergoing lactic acid fermentation, thereby creating an anaerobic environment favorable for obligate anaerobes such as lactobacilli and bifidobacteria and helping to restore gut microbial balance. Moreover, it possesses an extensive enzymatic system capable of producing various enzymes that enhance intestinal nutrient absorption and metabolism. These improvements facilitate nutrient utilization from food, boost immunity and disease resistance, and reduce the incidence of intestinal disorders.^9–11

H. coagulans currently exhibits promising research and application prospects; however, more robust scientific evidence to support its medical applications is required. This review aims to comprehensively examine the biological characteristics and recent medical applications of H. coagulans, evaluate research progress across various medical fields, and propose future research directions for researchers and healthcare practitioners. While the therapeutic potential of H. coagulans is evident, its application is constrained by an insufficient understanding of strain-specific effects, unclear long-term colonization dynamics, and a lack of large-scale clinical validation. This review not only synthesizes current evidence but also critically identifies these knowledge gaps. By highlighting the mechanistic heterogeneity among strains and the limitations of existing studies, we provide a compelling rationale for future research aimed at developing precision probiotic therapies.

2 Introduction of bacteria

2.1 The biological properties of H. coagulans

H. coagulans was first isolated by Hammer in 1915 from spoiled canned milk. It is a Gram-positive bacterium within the phylum Firmicutes. The cells are rod-shaped and produce terminal spores but lack flagella. The cell wall exhibits a unique structure, with lipids representing up to 12.6% of its cell wall content—significantly higher than the 1–2% found in many other Gram-positive bacteria. However, unlike many other probiotic bacilli, the teichoic acids of H. coagulans lack amino acid substituents.⁹

The stability and protection of the cell membrane rely heavily on lipids, primarily phospholipids, which constitute its major structural framework. Lipids also provide thermal insulation, a feature that may significantly contribute to the bacterium's robust stress tolerance and thermostability. Lipoteichoic acid (LTA), a crucial component of the Gram-positive bacterial cell wall, plays vital biological roles, including mediating immune responses, facilitating host–microbe interactions, and enabling pathogen recognition. It regulates host immune responses, participates in cellular adhesion and invasion during infection, and can activate host immune pathways. Amino acid substituents on teichoic acids, particularly D-alanine (D-Ala), are critical for their function. The absence of these substituents likely impairs the bacterium's adhesion and colonization capabilities within the gut, thereby hindering its long-term persistence.

H. coagulans exhibits an optimal growth temperature between 45 °C and 50 °C and an optimal pH range of 6.6 to 7.0.¹² It grows under anaerobic and microaerophilic conditions and demonstrates high tolerance to acids and bile salts. Through lactic acid fermentation, H. coagulans produces L-lactic acid, thereby lowering the intestinal pH. This acidity inhibits the growth of harmful bacteria and promotes the proliferation of beneficial bacteria such as Bifidobacterium. These characteristics underscore the significant application potential of H. coagulans in the probiotic field.

2.1.1 Safety. Safety is a primary criterion for evaluating whether a probiotic can be approved for production and application. The core safety requirements include the absence of toxicity, no promotion of antibiotic resistance gene transfer, no induction of infections, and no adverse effects on the immune system.

For the patented formulation H. coagulans, seven toxicological studies were conducted to systematically assess its safety. The bacterial reverse mutation (Ames) test showed that the formulation did not exhibit mutagenic activity in any of the tested strains.¹³

In a mouse micronucleus test, no signs of toxicity were observed even at doses as high as 1 × 10¹² CFU kg⁻¹ day⁻¹. Peripheral blood micronucleus testing detected no evidence of toxicity, indicating no induction of bone marrow toxicity within this dose range. An in vitro chromosomal aberration test further confirmed that H. coagulans did not induce significant chromosomal aberrations in Chinese hamster ovary cells, irrespective of the presence of a metabolic activation system.¹³

An acute oral toxicity study in rats demonstrated that H. coagulans did not induce significant pathological changes in any organs. In a subsequent 13-week subchronic toxicity study, daily administration of up to 5 × 10¹¹ CFU kg⁻¹ for 90 days produced no treatment-related macroscopic or microscopic lesions, and no adverse effects on hematology, clinical biochemistry, or organ weights were observed. The no-observed-adverse-effect level (NOAEL) was established at greater than 1000 mg kg⁻¹ day⁻¹ (equivalent to 95.2 × 10¹¹ CFU for a 70 kg human body weight). All test animals survived the study period.¹³

An acute irritation test in rabbits indicated that H. coagulans produced mild to moderate ocular irritation, but the symptoms resolved completely within 72 hours. Skin contact resulted only in mild, transient erythema without edema, which subsided within 24 hours. These findings indicate that H. coagulans causes only mild and reversible irritant effects.

Based on the above tests, H. coagulans did not demonstrate mutagenicity, genotoxicity, or cytogenetic damage, nor did it cause significant skin or eye irritation. The results from multiple genotoxicity tests confirm its safety for long-term human consumption.¹³

Furthermore, in vitro evaluation of H. coagulans CGI314 on sheep blood agar plates demonstrated a negative result (gamma-hemolysis), indicating no hemolytic activity. Its cell-free supernatant, upon co-culture with HT-29 and HepG2 cells for 20 hours, did not significantly affect epithelial cell viability. Antibiotic susceptibility testing conducted per European Food Safety Authority (EFSA) guidelines indicated that the strain was susceptible to all tested antibiotics (including vancomycin and gentamicin), with minimum inhibitory concentrations ranging from 0.125 to 2 mg L⁻¹, which are within the EFSA-defined acceptable range.¹⁴ These traditional safety indicators—the absence of hemolysis and cytotoxicity, coupled with susceptibility to all EFSA-recommended antibiotics—collectively affirm the high safety profile of the strain H. coagulans CGI314 and support the safety of the H. coagulans species in general.¹⁴

2.1.2 Survival, colonization capacity, and stability. While most probiotics can exert beneficial effects on the human gut microbiota, the harsh conditions of the gastrointestinal tract, particularly gastric acid, pose a significant challenge to their survival and passage to the intestine. Techniques such as microencapsulation and refrigeration are often employed to enhance probiotic stability and facilitate intestinal colonization, albeit at an increased cost.¹⁵

Spore-forming probiotics possess a natural advantage in this regard. A comparative evaluation of the thermostability and gastrointestinal (GI) survival of probiotic H. coagulans MTCC 5856 revealed that its spores exhibited superior heat resistance compared to tested Lactobacillus species and Bacillus strains, with a D-value of 35.71 minutes at 90 °C. Moreover, when exposed to simulated gastric fluid (SGF) at pH 1.3, 1.5, and 2.0, the H. coagulans strains demonstrated significantly higher tolerance than the Lactobacillus strains.^16,17

Specifically, H. coagulans MTCC 5856 retained 73% viability after exposure to microwave cooking at 260 °C for 300 seconds and 98.52% viability after pasteurization at 72 °C for 420 minutes in milk and fruit juice.^5,16 In simulated gastric fluid viability comparisons, initial counts of approximately 10.20 log₁₀ CFU mL⁻¹ were recorded. After 2 hours of incubation at pH 1.3, 1.5, and 2.0: Lactobacillus casei ATCC 393 counts dropped to 5.01, 5.21, and 5.55 log₁₀ CFU mL⁻¹, respectively (reduction >4 log CFU). Lactobacillus rhamnosus NRRL B-442 (at pH 1.3) and Lactobacillus helveticus NRRL B-734 (at pH 1.3) counts decreased from ∼10.1 log₁₀ CFU mL⁻¹ to 6.2 and 5.1 log₁₀ CFU mL⁻¹, respectively, indicating poor acid resistance. H. coagulans MTCC 5856 and ATCC 31284 maintained counts of 9.3, 9.3, and 9.8 log₁₀ CFU mL⁻¹ at pH 1.3, 1.5, and 2.0, respectively (reduction <1 log CFU), demonstrating significantly higher survival rates than the Lactobacillus strains upon prolonged exposure to low-pH SGF. This resistance extended to the presence of digestive enzymes (such as pepsin), confirming its high tolerance to GI environmental stressors.^16,17

Food serves not only as a delivery vehicle providing buffering for probiotic transit but also modulates probiotic colonization. Cereal flours can aid passage through the GI tract and enhance colonization. Studies on the viability of H. coagulans MTCC 5856 under food cooking conditions showed survival rates of 88.94% in pancakes and 94.56% in noodles post-cooking, highlighting its exceptional resistance to food processing temperatures and GI stress, enabling stability even without encapsulation.¹⁸ Another study assessing the stability of H. coagulans MTCC 5856 spores in brewed tea and coffee and subsequent survival under simulated GI conditions found that viability did not decrease further after 10 minutes in coffee at 70–80 °C. When added to tea and stored refrigerated (4 ± 2 °C) for 72 hours, viability remained high (94.56%, 93.64%, 94.55%), demonstrating the remarkable environmental resistance and stability of the spores.¹⁹

These findings collectively demonstrate that Heyndrickxia coagulans MTCC 5856 possesses outstanding stability, thermotolerance, and gastric acid resistance. These properties make it particularly advantageous for incorporation into functional foods that undergo high-temperature processing and ensure high survival rates after ingestion to support intestinal colonization. Consequently, it represents an ideal probiotic strain for developing thermally processed foods with varying shelf-life requirements.

2.2 Impact of spores on H. coagulans

Similar to other Bacillus species, sporulation in H. coagulans can be triggered by factors such as nutrient depletion, environmental stresses, and physical treatments. Unlike Bacillus cereus and Clostridium sporogenes, H. coagulans does not possess a loose, flexible exosporium at any stage of spore development.^7,9 Following sporulation, the structure of a mature H. coagulans spore differs markedly from its vegetative cell. The mature spore comprises a core, inner membrane, cortex, and spore coat(s).⁹ Under suitable environmental conditions, H. coagulans spores can survive in a dormant state for years. However, they can germinate rapidly upon receiving appropriate stimuli.

Owing to its spore-forming capability, H. coagulans is one of the few probiotic species that survives transit to the intestine, exhibiting superior survival rates and stability. This characteristic provides a significant advantage over traditional probiotic bacteria in exerting beneficial effects within the gut. H. coagulans spores typically germinate within 4–6 hours after ingestion, with up to 85% of administered spores successfully passing through the digestive system to germinate and proliferate in the intestine.²⁰ However, due to weak adhesion to intestinal epithelial cells, the bacterium generally cannot persist long-term in the gut naturally. Consequently, it remains transiently in the intestinal tract and is typically excreted in feces within 4 to 7 days. Therefore, regular supplementation with H. coagulans preparations is necessary to ensure sufficient intestinal colonization and sustained probiotic efficacy.¹¹

2.3 The spore advantage: industrial and clinical implications over non-spore-forming probiotics

Compared to non-spore-forming probiotics—which are characterized by poor stress resistance, low viability, short shelf life, high storage and transportation costs, susceptibility to inactivation, and a tendency for strain degeneration requiring frequent subculturing—spore-forming bacteria such as H. coagulans benefit from their unique endospore structure. This structure enables them to withstand high temperatures, ultraviolet radiation, chemical disinfectants, desiccation, and ionizing radiation. In their spore state, they can be stored at room temperature for several years without cold chain logistics, offering exceptional stability for biocontrol and industrial applications. Additionally, spores are highly resistant to gastric and bile acids, allowing them to reach the intestines safely and germinate, which provides a significant advantage for oral administration. Furthermore, the spore structure facilitates easy preservation and revival, and spores are efficient at secreting substantial amounts of proteins and enzymes, which is beneficial for downstream extraction.^21–25

2.4 Metabolic characteristics of H. coagulans and analysis of ATP production pathways

A study constructed a high-quality genome-scale metabolic model (GEM) of H. coagulans, designated iBag597, providing deep insights into its complex metabolic network. This network encompasses key areas including carbohydrate, amino acid, nucleotide, cofactor, vitamin, terpenoid, and polyketide metabolism. Notably, carbohydrate and amino acid metabolism play central roles in the physiological activities of this bacterium, while energy metabolism and glycan biosynthesis and metabolism are relatively less prominent. The study revealed that H. coagulans possesses two distinct glucose fermentation pathways: heterolactic fermentation and homolactic fermentation (Fig. 1a). These pathways enable the bacterium to flexibly select the optimal metabolic route depending on environmental conditions. Furthermore, H. coagulans harbors two pentose fermentation pathways (such as for xylose), a characteristic similar to traditional lactic acid bacteria (LAB).^26,27

Fig. 1 Schematic diagrams of metabolic pathways and ATP synthesis in Heyndrickxia coagulans 36D1. (a) Schematic diagram of H. coagulans 36D1 glucose metabolism. (b) Schematic diagram of H. 36D1 pyruvate metabolism. (c) ATP synthesis path 1 of H. coagulans 36D1. (d) ATP synthesis path 2 of H. coagulans 36D1. ADP: adenosine diphosphate; ACK: acetate kinase; Acetyl-CoA: acetyl coenzyme A; Acetyl-P: acetyl phosphate; ADHA: alcohol dehydrogenase A; ALD: acetoin dehydrogenase; ALS: acetolactate synthase; ATP: adenosine triphosphate; DHAP: dihydroxyacetone phosphate; E4P: erythrose-4-phosphate; FDH: formate dehydrogenase; F6P: fructose-6-phosphate; F16BP: fructose-1,6-bisphosphate; G3P: glyceraldehyde-3-phosphate; G6P: glucose-6-phosphate; 6PGL: 6-phosphogluconolactone; 6PGC: 6-phosphogluconate; L-lactate: L-lactate; NAD: nicotinamide adenine dinucleotide; NADH: nicotinamide adenine dinucleotide (reduced); PEP: phosphoenolpyruvate; PFL: pyruvate formate lyase; PTA: phosphotransacetylase; RL5P: ribulose-5-phosphate; R5P: ribose-5-phosphate; X5P: xylulose-5-phosphate.

Pyruvate metabolism is another notable feature of H. coagulans (Fig. 1b). The bacterium converts pyruvate to acetyl-CoA via either the pyruvate dehydrogenase complex (PDH) or pyruvate formate lyase (PFL). Notably, formate generated by the PFL reaction may be further degraded to carbon dioxide by formate dehydrogenase (FDH), a process that differs from some other lactic acid bacteria (LAB). Additionally, under aerobic conditions, H. coagulans 36D1 lacks the gene encoding NADH oxidase, preventing NAD⁺ regeneration through this pathway as in traditional LAB. Instead, it oxidizes NADH via an electron transport chain (ETC) consisting of NADH dehydrogenase, cytochrome oxidase, and ATP synthase. This mechanism not only regenerates NAD⁺ but also generates ATP concurrently, underscoring the unique metabolic adaptation of H. coagulans in energy metabolism.²⁷

Research identified three primary ATP generation pathways in H. coagulans 36D1 under microaerobic conditions: 1. Via the complete Embden–Meyerhof–Parnas (EMP) glycolytic pathway, producing lactate and ATP (Fig. 1c). 2. Through heterolactic fermentation coupled with the lower section of the EMP pathway, yielding lactate, acetate, and ATP (Fig. 1d). 3. Via an electron transport chain that recovers excess NADH while concomitantly producing ATP. The activation of these pathways responds to specific growth rates and pH conditions.²⁷

When the specific growth rate (μ) of H. coagulans increases from 0.1 h⁻¹ to 0.25 h⁻¹, its primary ATP production shifts from Pathway 1 (lower ATP yield) to Pathway 2 (higher ATP yield). However, this higher growth rate reduces lactate yield and adversely impacts homolactic fermentation. At the lowest specific growth rate tested (0.05 h⁻¹), corresponding to low lactate production, Pathway 3 is activated. This pathway utilizes the ETC to enhance ATP generation and achieves the maximum ATP yield per mole of glucose consumed. Consequently, Pathway 3 is activated under very low extracellular glucose concentrations.

Comparative analysis revealed that although Pathway 2 offers higher ATP yield, its proteomic cost (the cellular resources required for enzyme synthesis) is slightly higher than that of Pathway 1.^16,17,28,29 Despite this, the proteomic efficiency (ATP produced per unit protein synthesized) of Pathways 1 and 2 is very similar. This indicates that H. coagulans can obtain roughly equivalent amounts of ATP for a similar proteomic investment. Therefore, while the bacterium can switch to a higher ATP yield mode (Pathway 2) at high growth rates, the transition between these pathways might be governed by mechanisms beyond proteomic constraints.²⁷

2.5 Nutritional requirements

2.5.1 Carbon source utilization. A study investigating the metabolic impact of different carbon sources on H. coagulans revealed that while the bacterium possesses a phosphotransferase system (PTS) for sucrose and galactose uptake, it lacks lactase responsible for lactose transport and metabolism. Consequently, H. coagulans cannot utilize lactose as a sole carbon source. In contrast, it efficiently metabolizes and utilizes most other carbon sources, including fructose, maltose, and mannose.²⁷

A complementary analysis using the Biolog GEN III system with H. coagulans LMG S-24828 demonstrated its capacity to metabolize 39 out of 71 tested substrates, including 7 monosaccharides, 6 disaccharides, 3 oligosaccharides, and 4 polyols (Fig. 2). Notably, the strain exhibited robust growth with lactulose (4-O-β-D-galactopyranosyl-D-fructose) as the sole carbon source, indicating its ability to hydrolyze β(1 → 4) glycosidic bonds. Subsequent enzymatic profiling via the API ZYM kit confirmed β-galactosidase activity and revealed the expression of six additional enzymes: esterase (C4-specific), leucine arylamidase, acid phosphatase, naphthol-AS-BI-phosphohydrolase, α-galactosidase, and β-galactosidase (Fig. 2).^30,31

Fig. 2 Phenotypic and enzymatic characteristics of Heyndrickxia coagulans LMG S-24828; metabolic substrates are highlighted in green, −, negative (no activity detected); ±, weak activity; +, positive; ++, strongly positive.

2.5.2 Amino acid requirements. Unlike most LAB, which typically require multiple amino acids for growth – a requirement that often varies substantially between strains of the same species – H. coagulans can synthesize all 20 proteinogenic amino acids via its endogenous metabolic pathways.²⁷ However, valine deprivation significantly impairs its biomass production.³²

2.5.3 Vitamin requirements. Growth studies of 14 laboratory-isolated H. coagulans strains in semi-synthetic media (containing enzymatic casein hydrolysate, glucose, and mineral salts) at 37 °C identified critical vitamin dependencies. All tested strains showed no significant growth in the absence of biotin and thiamine (vitamin B₁).

Furthermore, the simultaneous omission of both folate and para-aminobenzoic acid (PABA) substantially reduced growth. In contrast, the individual elimination of either folate or PABA had negligible effects on growth kinetics. These findings demonstrate that H. coagulans requires biotin, thiamine, and either folate or PABA for optimal proliferation.^33–38

2.6 Factors influencing metabolism

2.6.1 Effect of pH on metabolism. H. coagulans exhibits an optimal growth pH range of 6.6–7.0. Variations in pH significantly alter the metabolic phenotype of H. coagulans.^39–41 Studies indicate that under acidic fermentation conditions, acetate and citrate production increases, whereas lactate production and glucose uptake decrease markedly.⁴² Simulations further reveal that ATP production rates are higher at pH 6.0 than at pH 5.5. Therefore, optimizing the culture pH during fermentation can enhance lactate yield in H. coagulans.²⁷

2.6.2 Effect of growth rate on metabolism. Genome-scale metabolic models (GEMs) were employed to estimate the growth-associated (GAM) and non-growth-associated (NGAM) ATP maintenance values during H. coagulans growth. By constraining the models with measured exchange rates and specific growth rates, the maximal ATP production rates were computed under various chemostat conditions. The analysis demonstrated that the ATP demand per unit of biomass decreases at high specific growth rates. However, compared to certain other LAB, H. coagulans exhibits higher GAM and NGAM values, indicating greater ATP requirements for cellular maintenance and growth.²⁷

Flux balance analysis (FBA) and flux variability analysis (FVA) were applied to map the flux distributions of key reactions in the central carbon metabolism (CCM) across specific growth rates. Carbon flux analysis revealed that the upper Embden–Meyerhof–Parnas (EMP) pathway—represented by glucose-6-phosphate isomerase (PGI)—dominates across all growth rates, confirming homolactic fermentation in H. coagulans 36D1.

2.6.3 Impact of growth rate on metabolism. The growth-associated maintenance (GAM) and non-growth-associated maintenance (NGAM) ATP requirements in H. coagulans were estimated using genome-scale metabolic models (GEMs). These models were constrained with measured exchange rates and the specific growth rate to calculate the maximum ATP production rate under various chemostat conditions. The relationship between the ATP production rate and the specific growth rate was then computed and plotted over the course of growth. Analysis revealed that H. coagulans exhibits a lower ATP demand per unit of biomass at high specific growth rates. However, a comparative assessment indicated that H. coagulans has higher GAM and NGAM values than several other LAB, reflecting a greater overall ATP requirement for cellular maintenance and growth.

Furthermore, flux balance analysis (FBA) and flux variability analysis (FVA) were employed to map the fluxes of key reactions within the central carbon metabolism (CCM) of H. coagulans across varying specific growth rates. Analysis of carbon flux distributions relative to the specific growth rate demonstrated that reactions in H. coagulans are predominantly governed by the upper Embden–Meyerhof–Parnas (EMP) pathway, exemplified by phosphoglucose isomerase (PGI), at any given specific growth rate. Consequently, H. coagulans 36D1 exclusively exhibits homolactic fermentation, irrespective of the specific growth rate.

Furthermore, flux balance analysis (FBA) and flux variability analysis (FVA) were employed to map the flux distributions of key reactions in the central carbon metabolism (CCM) of H. coagulans across different growth rates. Carbon flux distribution analysis revealed that the central carbon metabolism in H. coagulans is predominantly governed by the upper Embden–Meyerhof–Parnas (EMP) pathway, as exemplified by phosphoglucose isomerase (PGI), across all growth rates. Consequently, H. coagulans 36D1 displays exclusively homolactic fermentation across all growth rates.

Analysis of metabolic reactions across different specific growth rates revealed that at low rates (approaching 0 to 0.05 h⁻¹), the glucose uptake rate directed toward the LDH reaction was relatively low. In contrast, at a specific growth rate near 0.1 h⁻¹, the glucose uptake rates for both the LDH and PYK reactions were higher, promoting an increased flux toward lactate production. However, within the specific growth rate range of 0.1 to 0.25 h⁻¹, the glucose uptake rates for these two reactions progressively decreased. These findings collectively indicate that, under the studied conditions, moderate growth rates are optimal for achieving a high lactate yield in H. coagulans 36D1.²⁷

Additionally, studies investigating the impact of various specific growth rates under glucose-limited chemostat conditions at different dilution rates demonstrated that as the specific growth rate increased: the specific glucose uptake rate and the specific lactate production rate of H. coagulans increased initially and then reached a plateau; the specific production rates of various by-products, including acetate, citrate, and pyruvate, increased proportionally with the specific growth rate; and the specific uptake rates of amino acids such as glutamate (Glu), threonine (Thr), and tyrosine (Tyr) also increased.

3 Probiotic effects

3.1 Intestinal probiotic effects, improved nutrient absorption and digestion

H. coagulans facilitates the establishment of an anaerobic and acidic intestinal environment by consuming free oxygen in the gastrointestinal tract, thereby reducing the redox potential. This environment inhibits the growth of various pathogens and effectively counteracts dysbiosis caused by multiple factors. Furthermore, H. coagulans secretes a range of antimicrobial compounds, including bacteriocins, lactic acid, and acetic acid. Consequently, compared to other non-lactic acid-producing bacilli, H. coagulans demonstrates a superior capacity for restoring gastrointestinal microecological balance.^9,43

Benefiting from its ability to produce various enzymes, H. coagulans germinates in the upper small intestine and collaborates with other members of the gut microbiota. This cooperation enhances intestinal nutrient absorption and availability, thereby improving the utilization of nutrients derived from food. Under intestinal conditions, the strain GBI-30, 6086 produces active digestive enzymes, such as alkaline protease, which assist in the digestion and absorption of carbohydrates and proteins. Additionally, it amplifies the benefits of prebiotics by promoting the production of SCFAs—which are essential for intestinal health—and by stimulating the proliferation of beneficial bacteria.^44–48 Moreover, H. coagulans GBI-30, 6086 enhances the health of intestinal epithelial cells by reducing inflammation. This creates optimal conditions for the development of the villi absorptive surface, thereby improving nutrient absorption and enhancing the uptake and recovery of certain amino acids (Fig. 3).

Fig. 3 Probiotic effects of Heyndrickxia coagulans.

3.2 Reduction of exercise-induced muscle damage

Oral administration of H. coagulans GBI-30, 6086 has been shown to mitigate exercise-induced muscle damage and enhance recovery capacity. Research indicates that supplementation with this strain, in combination with a slowly digested protein, may improve athletic performance. A comparative study involving resistance-trained individuals examined protein intake during a resistance training program. Compared to consuming 20 grams of casein twice daily, supplementation with 20 grams of casein plus 500 million CFU of H. coagulans GBI-30, 6086 demonstrated a trend toward increased vertical jump power (p = 0.10) and suggested potential benefits for peak power and fat mass. However, no significant differences were observed in body composition or other performance metrics.^44,49

Another study investigating the effects of H. coagulans GBI-30, 6086 on muscle damage, performance, and recovery following a muscle-damaging exercise bout also found beneficial effects. Participants performed a unilateral muscle-damaging exercise. Post-exercise measurements included strength, power, muscle soreness, perceived recovery, and markers of hypertrophy and muscle damage. The group receiving protein alone exhibited significantly increased muscle soreness and reduced perceived recovery. In contrast, co-administration of H. coagulans GBI-30, 6086 with casein significantly reduced participant-reported pain and increased perceived recovery. This indicates that consuming protein alongside H. coagulans GBI-30, 6086 may help reduce exercise-induced muscle damage^44,49 (Fig. 3).

3.3 Improvement and protection of the intestinal mucosal barrier

Antibiotic treatment can disrupt the gut microbiome, resulting in antibiotic-associated diarrhea.⁵⁰ A study utilizing the Mucosal Simulator of the Human Intestinal Microbial Ecosystem (M-SHIME®), an in vitro gut model, assessed the effects of a probiotic formulation (MegaDuo™) containing H. coagulans SC208 and Bacillus subtilis HU58 on intestinal permeability and immune markers. Treatment with MegaDuo™ promoted microbial community recovery after antibiotic exposure by rapidly reducing Enterobacteriaceae and increasing SCFA-producing Bacteroidetes and Firmicutes. It also enhanced intestinal barrier integrity, reduced levels of pro-inflammatory cytokines including TNFα, MCP1, and IL-6, and mitigated lipopolysaccharide (LPS)-induced barrier damage, thereby restoring intestinal barrier function.⁵¹

Moreover, recent studies reveal that H. coagulans not only alleviates intestinal mucosal damage in immunosuppressed mice⁵² but also upregulates the transcription of genes encoding key barrier proteins, including TJP1 (ZO-1), CLDN1 (Claudin-1), CLDN2 (Claudin-2), MUC2 (Mucin 2), and OCLN (Occludin). Claudin-1 is a critical tight junction protein, and MUC2 is the major component of the intestinal mucus layer; their increased expression helps maintain barrier integrity and enhances the thickness and stability of the mucus layer. Furthermore, H. coagulans was shown to reduce serum levels of D-lactate (D-LA) and diamine oxidase (DAO) in chicks infected with Salmonella Pullorum, thereby further enhancing intestinal mucosal barrier integrity. qRT-PCR analysis demonstrated that H. coagulans MF-06 promotes intestinal epithelial regeneration, particularly the proliferation of intestinal stem cells (ISCs), in chicks infected with Salmonella Enteritidis. This effect was achieved by increasing the expression of C-MYC in the intestinal epithelium and upregulating the transcription of genes associated with the Wnt/β-catenin signaling pathway, including Wnt3, β-catenin, TCF4, C-MYC, LGR5, and BMI1.⁵³ Additionally, evaluation of proliferating cell nuclear antigen (PCNA)—a marker of intestinal epithelial cell (IEC) proliferation—and mucosal epithelial repair capacity revealed a significant increase in PCNA expression. This suggests that H. coagulans MF-06 may promote IEC proliferation within the crypts, facilitating subsequent migration along the crypt–villus axis.⁵⁴ The elevated PCNA levels indicate an enhanced rate of cell division, which contributes to the maintenance of intestinal mucosal barrier integrity.⁵⁵

Another study investigating the protective mechanisms of H. coagulans—using H&E staining, immunofluorescence, and 16S rRNA analysis—found that it protects against Klebsiella pneumoniae-induced intestinal barrier damage in rabbits. The treatment improved intestinal morphology, increased goblet cell numbers and PCNA protein expression, and modulated MUC1 and MUC2 expression to reinforce the chemical barrier. It also suppressed the TLR4/MyD88/NF-κB signaling pathway by downregulating the expression of inflammatory cytokines TNF-α, IL-1β, and IL-6, thereby attenuating inflammation. Furthermore, H. coagulans strengthened the mechanical barrier by upregulating the expression of tight junction (TJ) proteins Occludin, Claudin-1, and ZO-1.⁵⁶

Collectively, these findings demonstrate that H. coagulans enhances the intestinal mucosal barrier by improving its mechanical, chemical, biological, and immune components. The underlying mechanism for this protective effect likely involves the modulation of key inflammatory pathways (Fig. 3).

4 Clinical research on related medical applications

The following sections synthesize the current evidence for the medical applications of H. coagulans. A crucial distinction must be made between findings from preclinical models, which elucidate potential mechanisms and therapeutic hypotheses (summarized in Table 1), and those from controlled human clinical trials, which provide evidence for efficacy and safety in humans. While animal and in vitro studies are invaluable for understanding fundamental biology, their controlled conditions (e.g., standardized diet, genetics) do not fully replicate the complexity of the human gut microbiome and its interactions with diverse environmental factors. Therefore, the clinical trial data presented in Table 1 represent the most direct and relevant evidence for human applications.

Table 1 Comprehensive overview of research types, key findings, main effects, and mechanisms of action for different H. coagulans strains

Strain name	Research type	Key findings	Main effects	Mechanisms of action
MTCC5856	In vitro clinical	High thermostability (retains 73% viability after microwave treatment at 260 °C); significantly alleviates abdominal distension (P < 0.01)	Improves gastrointestinal function, reduces bloating and abdominal distension	Inhibits gas-producing microorganisms; modulates gut microbiota (increases Actinobacteria and Firmicutes, decreases Bacteroidetes, Proteobacteria, etc.)
Unique IS-2	Animal	Exerts anxiolytic and antidepressant-like effects; alleviates examination stress	Improves neuropsychiatric symptoms, anti-anxiety and antidepressant effects	Modulates gut microbiota–brain axis; upregulates hippocampal BDNF; regulates inflammatory factors (CRP, IL-1β, TNF-α)
GBI-30, 6086	Animal clinical	Reduces exercise-induced muscle damage and enhances recovery capacity; improves non-alcoholic fatty liver disease (NAFLD)	Improves exercise recovery, treats NAFLD	Produces alkaline protease and other digestive enzymes; promotes SCFA production; secretes antimicrobial peptide coagulin
BC01	Animal	Improves functional constipation; increases beneficial bacteria abundance and diversity	Alleviates constipation	Affects neurotransmitter and gastrointestinal hormone secretion; regulates gene expression (COX-2, NF-κB); produces SCFAs to lower intestinal pH
SNZ 1969	Clinical	Improves intestinal motility and constipation perception in patients with mild intermittent constipation	Alleviates constipation	Modulates gut microbiota (increases Lactobacillales, decreases Clostridium); produces lactic acid and SCFAs; stimulates mucin and gastrointestinal hormone secretion
FCYS 01	Animal	Synergistically with chitooligosaccharides attenuates DSS-induced colitis severity	Treats ulcerative colitis	Modulates IL-10 expression; influences host gut microbiota's SCFA production capacity
TL3	Animal	Inhibits LPS-induced cecal oxidative stress and inflammatory injury	Treats LPS-induced intestinal damage	Modulates TLR4/MyD88/NF-κB and Nrf2 signaling pathways; regulates gut microbiota (increases Akkermansia muciniphila)
MZY531	Animal	Alleviates cyclophosphamide-induced intestinal mucosal damage; modulates gut microbiota; enhances immune function	Protects intestinal mucosa, anti-inflammatory	Downregulates TLR4/MyD88 signaling pathway; increases IL-10; modulates immunoglobulins and cytokines
JA845	Animal	Alleviates D-galactose/AlCl3-induced neurodegeneration; improves cognitive function	Treats Alzheimer's disease	Modulates Nrf2/HO-1 and MyD88/TRAF6/NF-κB signaling pathways; enhances antioxidant enzyme activity; reduces Aβ and tau protein deposition
BCP92™	Animal	Improves depression- and anxiety-like behaviors; modulates neurotransmitters and inflammatory factors	Antidepressant, anti-anxiety	Modulates microbiota–immune–neural axis; increases 5-HT, DA, NA levels in prefrontal cortex; decreases TNF-α, IL-1β, CRP expression
JBI-YZ6.31	In vitro	Direct immune-activating properties under non-inflammatory conditions; anti-inflammatory properties under inflammatory conditions	Immunomodulation	Cell wall fraction activates NF-κB and MAPK signaling pathways via TLR-2; metabolite fraction induces antioxidant response element (ARE) and modulates inflammatory cell signaling pathways
BACO-17	Animal	Alleviates collagen antibody-induced arthritis (CAIA) symptoms; protects joint cartilage and synovium	Treats rheumatoid arthritis	Downregulates inflammatory cytokines TNF-α, IL-6, IL-17; inhibits MMP2, MMP9, MMP13 expression
T242	In vitro	Inhibits lipid peroxidation; scavenges free radicals; activates Nrf2 signaling pathway	Antioxidant	Activates Nrf2/Keap1 pathway; upregulates HO-1; decreases IL-6, IL-8, TNF-α
CGI314	In vitro	No hemolytic activity; non-cytotoxic to epithelial cells; susceptible to all tested antibiotics	Safety assessment	No hemolytic activity, no cytotoxicity, antibiotic susceptibility
SANK 70258	Clinical	Improves colonic transit time, intestinal environment, defecation frequency, and stool characteristics	Alleviates constipation	Modulates intestinal environment; promotes intestinal motility
LMG S-24828	In vitro	Metabolizes 39 out of 71 tested substrates, including 7 monosaccharides, 6 disaccharides, 3 oligosaccharides, and 4 polyols	Nutritional metabolic characteristics	Broad substrate utilization capacity; expresses multiple enzymes (esterase, leucine arylamidase, acid phosphatase, etc.)

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4.1 Treatment of metabolic diseases and antioxidant effects

4.1.1 Therapy for acute intermittent porphyria (AIP). Acute intermittent porphyria (AIP) is an autosomal dominant disorder caused by deficient activity of porphobilinogen deaminase (PBGD; also known as hydroxymethylbilane synthase, HMBS). This deficiency leads to the accumulation of porphyrin precursors, δ-aminolevulinic acid (ALA) and porphobilinogen (PBG). The toxic effects of these compounds can manifest as abdominal pain, neuropsychiatric symptoms, and potentially life-threatening complications.^57,58 Current therapeutic strategies include conventional approaches such as high-carbohydrate therapy and intravenous hemin therapy (IHT), alongside emerging modalities like gene therapy and enzyme replacement therapy.⁵⁹ However, high-carbohydrate therapy may increase intestinal permeability, promote bacterial product translocation, and induce insulin resistance. Murine studies demonstrate that while wild-type (WT) mice induce hepatic glycogen catabolism to restore glucose homeostasis, AIP mice exhibit insulin deficiency. This results in the activation of ketogenesis and gluconeogenesis, leading to increased ketone bodies as an alternative energy source. When ketone body production exceeds utilization, accumulation occurs, culminating in ketonemia, glucose intolerance, and hyperinsulinemia.^60,61

Murine investigations revealed that AIP mice harbor higher intestinal abundances of Odoribacter laneus and Bacteroides faecichinchillae compared to WT mice. Notably, high levels of Turicibacter sanguinis were exclusively detected in fecal samples from aged WT and AIP mice. Furthermore, young AIP mice exhibited a gut microbiota characterized by elevated Bacteroides abundance. Administration of H. coagulans significantly reduced the levels of Lachnoanaerobaculum umeaense (FJ967000) and Lachnospiraceae bacterium (KC311366) in both WT and AIP mice, concurrently enhancing fecal microbiome diversity. These findings suggest that H. coagulans modulates intestinal metabolism in AIP mice by altering the relative abundance of gut bacteria.^61–65

Moreover, H. coagulans significantly enhanced glucose uptake in the skeletal muscle of AIP mice, with only marginal effects observed in the liver and brain. It also induced brain-specific expression of GLUT1 and GLUT3 transporters and the InsRβ chain, thereby modulating factors associated with insulin resistance. Additionally, H. coagulans increased hepatic heme content, restoring it to near-normal levels in AIP mice. Following 12 weeks of continuous consumption of H. coagulans spore-supplemented water, AIP mice demonstrated improved glucose metabolism, ameliorated hyperinsulinemia, altered gut microbial composition, and stimulated lipid handling in adipose tissue.^61,66 Collectively, these results indicate that H. coagulans represents a potentially safe and cost-effective therapeutic approach for managing hyperinsulinemia and glucose metabolic disorders in AIP patients harboring PBGD mutations (Fig. 4).

Fig. 4 Medical applications of Heyndrickxia coagulans.

4.1.2 Alleviation and treatment of type 2 diabetes mellitus (T2DM). Type 2 diabetes mellitus (T2DM) is a metabolic disorder characterized by hyperglycemia, primarily resulting from relative insulin deficiency and insulin resistance. This condition is influenced by multiple factors, including genetics, environment, and lifestyle.^67,68 T2DM poses significant health risks, with milder manifestations including weight loss and wasting, while severe disease can lead to hypertension, atherosclerosis, and various macrovascular and microvascular complications. These complications may result in blindness, renal failure progressing to uremia, and even limb disability.^69–71 Current primary treatments involve insulin and hypoglycemic agents, both of which may cause adverse effects. Research indicates that synbiotic supplements containing H. coagulans, Lactobacillus rhamnosus, Lactobacillus acidophilus, and fructooligosaccharides can improve glycemic control and reduce inflammation in diabetic patients. Notably, these supplements showed no significant effects on blood lipids or systolic blood pressure. Furthermore, they demonstrated beneficial effects on glycemic indices, insulin resistance, high-sensitivity C-reactive protein (hs-CRP) levels, and diastolic blood pressure in individuals with T2DM⁷¹ (Fig. 4).

4.1.3 Treatment of NAFLD and associated inflammation. Non-alcoholic fatty liver disease (NAFLD) is a chronic liver condition characterized by metabolic stress and closely associated with insulin resistance (IR) and genetic susceptibility. NAFLD not only causes liver damage that may progress to cirrhosis and hepatocellular carcinoma but is also strongly linked to a higher incidence of metabolic syndrome (MetS), type 2 diabetes mellitus (T2DM), atherosclerotic cardiovascular disease, and colorectal tumors, which can be fatal in severe cases. Currently, there are no established pharmacological or surgical cures. Relevant research highlights a strong association between the gut microbiota and both the development and progression of NAFLD.⁷²

A double-blind, placebo-controlled clinical trial investigating the effects of H. coagulans in NAFLD patients found that 12-week supplementation with a mixture of inulin and H. coagulans GBI-30 reduced insulin resistance and lowered serum cholesterol and triglyceride concentrations in diabetic patients,⁷³ The treatment also stimulated the production of SCFAs, lactate, and bacteriocins. Notably, H. coagulans GBI-30 secretes a bacteriocin named coagulin, which is active against multiple pathogenic gut bacteria.⁷⁴ This activity helps reduce pathogenic bacteria, decrease intestinal barrier permeability, and prevent bacterial translocation. Additionally, it reduces the production and systemic translocation of lipopolysaccharide (LPS), thereby minimizing hepatocyte exposure to LPS and ameliorating NAFLD-associated inflammation,⁷⁵ without significantly affecting relevant cardiovascular risk factors. These findings suggest that H. coagulans could represent a potential future therapeutic strategy for NAFLD⁷⁶ (Fig. 4).

4.1.4 Treatment of obesity and weight loss potential. H. coagulans and its metabolites demonstrate beneficial effects on obesity and related metabolic disorders. In high-fat diet (HFD)-induced obese mice, Curezyme—LAC—a fermented multi-grain mixture derived from H. coagulans metabolites—dose-dependently reduced body weight, fat mass, plasma lipids, and fasting blood glucose, while also lowering inflammatory cytokines and improving glucose tolerance.⁷⁷ In human subjects, it decreased visceral fat area, body weight, waist circumference, and modulated plasma adipokine and inflammatory cytokine levels, independent of dietary or physical activity changes.⁷⁸

In another study, a heat-processed vinegar beverage supplemented with H. coagulans counteracted HFD-induced reductions in fasting serum glucagon-like peptide-1 (GLP-1) levels. This effect was mediated by bacterial metabolite-derived SCFAs activating GPR43, which enhanced GLP-1 secretion.^79,80 The same beverage also reduced circulating leptin and C-peptide levels, improved insulin sensitivity, and attenuated weight gain and hepatic steatosis in obese mice, suggesting a synergistic effect between the vinegar and H. coagulans in restoring leptin sensitivity.⁸¹

Moreover, the H. coagulans-vinegar combination downregulated hepatic CD36 expression, reducing lipid uptake and accumulation, and ameliorated systemic inflammation and insulin resistance.⁸⁴ It also suppressed overexpression of IL-1β, IL-6, and key lipogenic transcription factors SREBP and LXR, leading to improved serum lipid profiles and reduced hepatic fat content.⁸² It also suppressed overexpression of IL-1β, IL-6, and key lipogenic transcription factors SREBP and LXR, leading to improved serum lipid profiles and reduced hepatic fat content.^83,84

By elevating intestinal acetate and butyrate, H. coagulans enhanced the vinegar's beneficial effects on lipid metabolism and steatosis. Similarly, Curezyme—LAC reduced inflammatory markers and improved body composition in obese subjects.⁷⁸ Together, these findings support the potential of H. coagulans in managing obesity and metabolic syndrome^85–87 (Fig. 4).

4.1.5 Protective effects against cellular oxidative damage and antioxidant potential. Studies have shown that the probiotic strain H. coagulans T242 can inhibit lipid peroxidation and scavenge free radicals.^88–90 It also increases antioxidant enzyme levels, enhances cellular antioxidant capacity, and exhibits significant chemical antioxidant activity, including ABTS radical scavenging and lipid peroxidation inhibition.^91–93

Another study investigated the protective effects of H. coagulans T242 against 2,2′-azobis(2-amidinopropane) dihydrochloride (AAPH)-induced oxidative damage in HT-29 cells. The bacterium exerted its antioxidant effects by activating the Nrf2 signaling pathway and quenching oxygen radicals. Specifically, H. coagulans T242 significantly enhanced the activity of antioxidant enzymes and upregulated the expression of proteins in the Nrf2/Keap1 pathway, including Nrf2, Keap1 (Kelch-like ECH-associated protein 1), and HO-1 (heme oxygenase-1). It also reduced the expression of the pro-inflammatory cytokines IL-6, IL-8, and TNF-α in HT-29 cells, thereby protecting them from AAPH-induced oxidative damage. Due to its ability to inhibit lipid peroxidation, its reducing power, and its oxygen radical scavenging capacity, H. coagulans T242 effectively suppressed lipid peroxidation in HT-29 cells. It also significantly reduced the malondialdehyde (MDA) content—a major product of lipid peroxidation and a key biomarker of oxidative damage—in AAPH-treated HT-29 cells. These findings highlight the potential of H. coagulans T242 as a natural antioxidant agent in food products^93,94 (Fig. 4).

4.2 Treatment of gastrointestinal disorders

4.2.1 Treatment of bloating. Small intestinal bacterial overgrowth (SIBO), alterations in the gut microbiota, food intolerances, and functional dyspepsia can lead to intestinal distension and bloating. Visceral hypersensitivity, abnormal intestinal gas transit, and impaired gas evacuation also contribute to functional bloating.^95,96 Persistent bloating can result in malnutrition and anemia, while also compromising immune function and disease resistance. Current primary treatments for bloating involve dietary modifications or the administration of antibiotics, prokinetics, probiotics, antispasmodics, and neuromodulators. These aim to reduce the accumulation of gas, air, water, and feces within the intestinal lumen and decrease excessive gas production by colonic or small intestinal bacteria, thereby alleviating symptoms.^97–99 However, these approaches often fail to address the natural course of the problem and may cause adverse effects. Relevant studies indicate that adequate probiotic intake can effectively alleviate bloating symptoms with a favorable safety profile and minimal adverse reactions.¹⁰⁰

Although H. coagulans produces acid in the gut, its glucose fermentation does not generate gas. It has been shown to significantly reduce symptoms of flatulence, bloating, and abdominal distension in patients with functional bloating without other serious gastrointestinal disorders. A study evaluating the efficacy of H. coagulans MTCC 5856 (at a dose of 2 billion CFU per day) for managing functional gas and bloating symptoms found that this strain improves gut microbiota ecology by inhibiting gas-producing microorganisms, positively upregulating the abundance of beneficial bacteria such as Actinobacteria and Firmicutes, and downregulating potentially detrimental phyla like Bacteroidetes, Proteobacteria, Streptococcaceae, and Verrucomicrobia. This modulation significantly reduced symptoms of flatulence, bloating, and abdominal distension in the target patient group. Furthermore, H. coagulans MTCC 5856 administered at 2 billion CFU per day for 30 consecutive days was well-tolerated, with no reported adverse effects, demonstrating high safety and promising application potential¹⁰¹ (Fig. 4).

4.2.2 Alleviation and treatment of constipation. Chronic constipation, characterized by prolonged retention of feces in the intestines, can lead to the accumulation of harmful bacteria and toxin production. Subsequent reabsorption of these toxins into systemic circulation may exert long-term detrimental effects on both overall health and intestinal function.¹⁰² Symptoms include abdominal pain, bloating, headaches, nausea, and loss of appetite. In severe cases, it may contribute to pelvic organ prolapse, psychological distress, and increased risks of obesity, enteritis, and colorectal cancer.¹⁰³

Given the diverse and complex etiology of chronic constipation, effective treatment remains challenging. Conventional strategies such as increased dietary fiber intake or laxative use (e.g., osmotic or stimulant types) can promote bowel movements but are often accompanied by adverse effects like abdominal distension and diarrhea.^104–106 Recent studies highlight the potential of probiotics in constipation management due to their efficacy and favorable safety profile.^107–112

Studies in mouse models of functional constipation have shown that oral administration of H. coagulans BC01 enriches beneficial bacteria, increases microbial abundance and diversity, and corrects constipation-associated dysbiosis.¹¹² This strain modulates gut function through multiple mechanisms: it influences the secretion of neurotransmitters and gastrointestinal hormones (e.g., substance P, motilin, vasoactive intestinal peptide, somatostatin, and endothelin-1); regulates the expression of genes such as COX-2 and NF-κB; and produces SCFAs that lower intestinal pH, thereby accelerating intestinal motility and improving small intestinal transit.^113,114 Furthermore, H. coagulans BC01 alleviates constipation by upregulating the c-Kit/SCF signaling pathway, which is critical for the proliferation and phenotypic maintenance of Interstitial Cells of Cajal (ICCs).¹¹⁵

Additional findings indicate that this strain significantly elevates serum levels of pro-kinetic neurotransmitters SP and MTL while reducing levels of VIP, SS, and ET-1, which slow intestinal transit. These effects are more pronounced at higher doses,^111,116,117 underscoring its potential as a novel therapeutic agent for constipation.

Another strain, H. coagulans SNZ1969, has also demonstrated efficacy in alleviating constipation. Daily supplementation modulates the gut microbiota by enriching Bacillales and Lactobacillales while reducing harmful bacteria such as Clostridium.^17,24 It produces lactic acid and SCFAs, which lower colonic pH, enhance peristalsis, and shorten colonic transit time. Additionally, it stimulates mucin and gastrointestinal hormone secretion, maintaining intestinal lubrication and further promoting bowel movements, with a favorable safety profile.^{9,110,118–120}

Other relevant studies include the combination of H. coagulans Unique IS2 with the osmotic laxative lactulose, which was found to accelerate constipation relief compared to lactulose alone.^116,119 Similarly, H. coagulans SANK70258, isolated from green malt, improved colonic transit time, intestinal environment, defecation frequency, and stool characteristics, demonstrating therapeutic value in constipation management¹¹⁶ (Fig. 4).

4.3 Treatment of inflammatory diseases

4.3.1 Treatment of ulcerative colitis (UC). Ulcerative colitis (UC) is a chronic inflammatory disease triggered by gut dysbiosis, leading to intestinal barrier dysfunction and immune system dysregulation. It manifests with symptoms such as abdominal pain, bloody stools, and vomiting, and can lead to complications including toxic megacolon, intestinal perforation, and an increased risk of colorectal cancer. Current primary treatments involve surgery and pharmacological interventions, both of which are associated with significant side effects and risks, such as increased bacterial resistance and further disruption of the gut microbiota, potentially precipitating other intestinal disorders. Probiotic therapy represents a promising alternative, offering improved safety and demonstrated efficacy.

A study investigating the effects of H. coagulans FCYS01 spores combined with chitooligosaccharides (COSs) in a mouse model of dextran sulfate sodium (DSS)-induced colitis demonstrated that the probiotic not only modulated IL-10 expression under inflammatory conditions but also enhanced the gut microbiota's capacity to produce SCFAs, thereby attenuating UC-related inflammation. Importantly, the combination of H. coagulans FCYS01 and COS acted synergistically to alleviate colitis severity, restore intestinal barrier function, and improve immune responses, with no observed adverse effects.^121–123 These results support the therapeutic potential of H. coagulans FCYS01 in ulcerative colitis management^66,124 (Fig. 4).

4.3.2 Treatment of LPS-induced cecal oxidative stress and inflammatory injury. Recent research demonstrated that administration of H. coagulans TL3 significantly enhanced the expression of tight junction (TJ) proteins—Claudin-1, Occludin, and zonula occludens-1 (ZO-1)—in LPS-treated rats, thereby preserving intestinal barrier integrity and reducing permeability. Furthermore, H. coagulans TL3 significantly decreased the relative abundance of harmful Enterobacteriaceae (e.g., Escherichia coli and Shigella spp.), while increasing that of the beneficial mucin-degrading bacterium Akkermansia muciniphila (phylum Verrucomicrobia). A. muciniphila adheres to intestinal epithelial cells, produces SCFAs, and enhances epithelial monolayer integrity in vitro, collectively supporting barrier restoration in damaged intestines.¹²⁵ These microbiota modulations helped improve gut ecology, aiding the immune system in preventing infection and reducing inflammation-associated tissue damage. Together, these mechanisms confer protection against LPS-induced intestinal injury and effectively alleviate cecal oxidative stress and inflammatory damage¹²⁶ (Fig. 4).

4.3.3 Amelioration of CYP-induced intestinal mucosal damage and inflammation. A study examined the effects of H. coagulans MZY531 on cyclophosphamide (CYP)-induced intestinal mucosal damage, inflammation, and gut microbiota alterations in mice. Treatment with H. coagulans MZY531 not only reduced harmful bacteria but also significantly increased the relative abundance of beneficial taxa, including the phylum Firmicutes and the genera Prevotella and Bifidobacterium, thereby correcting gut microbiota dysbiosis and improving microbial ecology.¹²⁷ Additionally, H. coagulans MZY531 downregulated the TLR4/MyD88 signaling pathway and increased IL-10 levels, while elevating IFN-γ, IL-4, and immunoglobulins (IgG, IgM, IgA, IgE). It also reduced pro-inflammatory cytokine levels, collectively restoring immune balance and enhancing anti-inflammatory capacity.¹²⁸

Furthermore, H. coagulans MZY531 significantly mitigated CYP-induced intestinal mucosal damage, reduced villus shedding and endothelial cell edema, and increased crypt depth, effectively alleviating intestinal endothelial damage and inflammation¹²⁹ (Fig. 4).

4.4 Treatment of neurological and psychiatric disorders

4.4.1 Anxiolytic and antidepressant effects. Recent studies indicate that modulating the gut microbiota ecosystem through prebiotics, probiotics, postbiotics, or fecal microbiota transplantation (FMT) can ameliorate clinical depression and anxiety. Specifically, the strain H. coagulans Unique IS-2 has been shown to mitigate examination-related stress in students and exhibit anxiolytic and antidepressant-like phenotypes in preclinical models of depression.^130–136

Pro-inflammatory cytokines play a key role in the pathogenesis of depression. A six-week treatment with H. coagulans Unique IS-2 normalized elevated levels of CRP, IL-1β, and TNF-α in the hippocampus and/or frontal cortex.^137–139 It also ameliorated neurobehavioral abnormalities, including the anhedonia-like phenotype observed in sucrose preference tests in stressed rats.¹³⁶ Furthermore, the treatment restored serotonin (5-HT) levels in both sexes and hippocampal brain-derived neurotrophic factor (BDNF) levels in males in a maternal separation (MS) plus chronic unpredictable mild stress (CUMS) mouse model.^3,139–141

Patients with depression show a reduced abundance of Firmicutes and increased Actinobacteria. H. coagulans Unique IS-2 restored CUMS-altered gut histology, significantly increased levels of acetate, butyrate, propionate, and total SCFAs—which are reduced in the MS + CUMS group—and thereby activated mood-elevating processes. It also decreased Actinobacteria and increased Bacteroidetes abundance in male MS + CUMS mice, promoting the growth of beneficial bacterial strains.^139,142 These findings suggest that H. coagulans Unique IS-2 exerts antidepressant effects via regulation of systemic inflammation and the gut microenvironment, positioning it as a potential therapeutic option for depression¹³⁹ (Fig. 4).

In another study, a rat model of depression was established using maternal separation (MS) and chronic unpredictable mild stress (CUMS). Rats were administered H. coagulans BCP92™ at 2 billion CFU per day for six weeks. Behavioral tests—including sucrose preference, forced swimming, elevated plus maze, and open field tests—were used to assess depression- and anxiety-like behaviors. Brain, intestinal, and fecal samples were collected for neurobiochemical, molecular, and histopathological analyses.

Results showed that depressive model rats treated with H. coagulans BCP92™ exhibited significant improvements in anhedonia (sucrose preference test), reduced behavioral despair (forced swimming test), enhanced autonomous activity (open field test), and alleviated anxiety-like behavior (elevated plus maze). The treatment also restored prefrontal cortex levels of serotonin (5-HT), dopamine (DA), and norepinephrine (NA); reduced brain expression of TNF-α, IL-1β, and CRP; normalized elevated doublecortin levels; and increased BDNF and glial fibrillary acidic protein (GFAP), thereby promoting neural plasticity. These multi-pathway effects indicate that H. coagulans BCP92™ modulates the microbiota-immune-neural axis, supporting its potential as a probiotic intervention for depression via the gut–brain axis.¹⁴³

The gut–brain axis effects of H. coagulans are also closely linked to neurotransmitter balance. Notably, many lactic acid bacteria from food sources can safely and efficiently produce GABA (γ-aminobutyric acid), a major inhibitory neurotransmitter whose deficiency is associated with anxiety and depression. It is plausible that specific strains of H. coagulans may similarly stimulate GABAergic activity,^201,202 potentially acting synergistically with BDNF upregulation and inflammatory modulation to mediate anxiolytic and antidepressant effects. Therefore, establishing standardized strain libraries and phenotypic databases, along with expanding relevant in vivo and cellular models, will be essential to validate such GABAergic mechanisms and other strain-specific functions.

4.4.2 Treatment of Alzheimer's disease. A study investigating the therapeutic efficacy of H. coagulans JA845 in D-galactose/AlCl₃-induced neurodegeneration demonstrated that this strain attenuates neuroinflammation and oxidative damage by modulating the Nrf2/HO-1 and MyD88/TRAF6/NF-κB signaling pathways, thereby protecting against brain injury and cognitive decline and ameliorating Alzheimer's disease (AD)-related symptoms.¹⁴⁴

In D-gal/AlCl₃-induced AD model mice, researchers observed reduced antioxidant enzyme activity and elevated oxidative markers.¹⁴⁵ Expression of MyD88, TRAF6, and NF-κB was significantly increased, while nuclear factor erythroid 2-related factor 2 (Nrf2)—a master regulator of redox homeostasis with neuroprotective effects—was decreased in AD-relevant brain regions.^145,146 Nrf2 deficiency not only reduces HO-1 expression but also exacerbates AD pathology.¹⁴⁷ AD progression involves cognitive decline, extracellular amyloid-beta (Aβ) deposition, intracellular accumulation of hyperphosphorylated tau, neuronal loss, neurofibrillary tangle formation, and neuroinflammation.^147,148 Neurofibrillary tangles composed of hyperphosphorylated tau correlate with dementia severity and duration,¹⁴⁹ while misfolded Aβ triggers innate immune activation and excessive pro-inflammatory cytokine secretion, accelerating disease progression.¹⁴⁸ Both Aβ and tau pathologies induce neurotoxicity, oxidative damage, and synaptic impairment, which are central to neurodegeneration.¹⁵⁰

Supplementation with H. coagulans JA845 effectively suppressed the expression of MyD88, TRAF6, and NF-κB in AD model mice. It significantly enhanced the activities of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and catalase (CAT), while reducing serum levels of malondialdehyde (MDA) and nitric oxide (NO). The treatment increased nuclear expression of Nrf2, activating the Nrf2-mediated induction of the phase II enzyme HO-1. This Nrf2/HO-1 pathway activation elicited antioxidant effects, bolstering antioxidant capacity and protecting cells against oxidative damage.¹⁵⁰Furthermore, supplementation reduced hippocampal deposits of hyperphosphorylated tau protein and amyloid-beta in D-gal/AlCl₃-induced AD mice, prevented cognitive decline and AD-like pathological features, significantly mitigated inflammation and oxidative stress, attenuated Aβ accumulation and tau pathology, and delayed AD onset. It also increased IL-6 levels and decreased serum levels of the pro-inflammatory cytokines TNF-α and IL-1β in the AD model, thereby alleviating neuroinflammation. By ameliorating neuropathological lesions in the hippocampus, improving Aβ and tau pathologies, and attenuating AD-induced oxidative stress and inflammation via the Nrf2/HO-1 and MyD88/TRAF6/NF-κB pathways, H. coagulans JA845 demonstrates significant therapeutic potential for Alzheimer's disease¹⁵¹ (Fig. 4).

4.5 Treatment of cancer

4.5.1 Treatment of breast cancer. Breast carcinoma (BC) ranks among the four most prevalent cancers worldwide, accounting for approximately one-quarter of common cancers in women. It is the second leading cause of cancer-related mortality globally, after lung cancer. Current treatments include radiotherapy, chemotherapy, hormone therapy, and surgery. While these approaches can partially eliminate tumor tissue, they often damage healthy tissues; for example, chemotherapy may induce drug resistance in cancer cells and harm normal cells.^152,153

A study investigating the inhibitory effect of H. coagulans on MCF-7 breast cancer cells revealed that its bacterial supernatant significantly inhibits the proliferation of these cells. Treatment with 1 mg mL⁻¹ and 2 mg mL⁻¹ of the supernatant for 48 hours inhibited 30% and 40% of MCF-7 cells, respectively, while normal cell viability remained unaffected under the same conditions. This indicates that the H. coagulans supernatant exerts dose-dependent anti-proliferative effects with low cytotoxicity toward normal cells.

The supernatant appears to activate apoptosis through both extrinsic and intrinsic pathways. It promotes mitochondrial membrane permeabilization, facilitating cytochrome c release, and consequently increases the expression of caspase-3 and caspase-9, key executors of apoptosis. Furthermore, the supernatant downregulates the anti-apoptotic Bcl-2 gene. Since Bcl-2 normally inhibits the accumulation of pro-apoptotic Bax and Bak proteins, its downregulation enhances mitochondrial membrane permeabilization, cytochrome c release, and caspase activation, collectively promoting cancer cell death.

In summary, the H. coagulans supernatant shows significant cytotoxicity against MCF-7 cells with minimal effects on normal cells. It induces apoptosis via the mitochondrial pathway by upregulating pro-apoptotic genes and downregulating anti-apoptotic genes, suggesting its potential as a future therapeutic strategy for breast cancer^154–156 (Fig. 4 and 5).

Fig. 5 Intrinsic apoptosis pathway of Heyndrickxia coagulans.

4.5.2 Therapeutic applications in colorectal cancer. Colorectal cancer (CRC) represents a significant global health challenge, with conventional chemotherapeutic agents like 5-fluorouracil (5-FU) often encountering drug resistance. Oncolytic viruses and probiotics have emerged as promising novel cancer therapeutic modalities. Recent investigations have highlighted an avian Paramyxovirus type I, Newcastle disease virus (NDV), which has demonstrated efficacy in inducing cancer cell death via the intrinsic apoptotic pathway against various malignancies, including lymphoma, glioblastoma, and hepatocellular carcinoma. Notably, NDV can also target cancer stem cells and dormant tumor cells.^157,158 Concurrently, metabolites released in probiotic supernatants have garnered attention due to their ease of use, stability, and multifaceted properties, such as anti-inflammatory, cytotoxic, antioxidant, and immunomodulatory effects specifically against cancer cells, establishing them as an active area of investigation in cancer therapy.^159,160

A study evaluating the growth inhibitory effects of NDV and H. coagulans, both individually and in combination, on the HT29 cell line revealed that NDV provides a potent death signal through endoplasmic reticulum stress and syncytia formation, triggering immunogenic cell death. Simultaneously, metabolites from H. coagulans compromised mitochondrial integrity by modulating Bcl-2 family proteins. The combined regimen of NDV, H. coagulans, and 5-FU—the latter inducing DNA damage by interfering with DNA synthesis—synergistically enhanced the intrinsic apoptotic pathway, significantly amplifying tumor cell killing.¹⁶⁰

Another study found that inactivated forms of the probiotic H. coagulans Hammer, along with its derivatives—extracellular vesicles (EVs) and cell-free supernatant (CFS)—could significantly upregulate the expression of the pro-apoptotic gene Bax while downregulating the anti-apoptotic gene Bcl-2. This mitochondrial perturbation led to the release of apoptotic signals and subsequent upregulation of the initiator caspase, Caspase-9, and the executioner caspase, Caspase-3, irreversibly committing cells to apoptosis and exerting anticancer activity.¹⁶¹

Furthermore, a study utilizing human embryonic kidney cells (HEK 293T) as a non-cancerous control assessed the anti-proliferative effects of heat-inactivated culture supernatant (HSUP) from H. coagulans Unique IS2 on colon carcinoma (COLO 205), cervical carcinoma (HeLa), and chronic myeloid leukemia (K562) cell lines. Consistently, the HSUP was observed to promote apoptosis by upregulating the pro-apoptotic protein Bax, downregulating the anti-apoptotic protein Bcl-2, consequently increasing the Bax/Bcl-2 ratio. This disrupted the mitochondrial membrane potential, facilitated cytochrome c release, activated the caspase cascade, promoted PARP cleavage, and culminated in DNA fragmentation, ultimately executing apoptosis and inhibiting tumor proliferation¹⁶² (Fig. 4 and 5).

4.5.3 Therapeutic applications in hepatocellular carcinoma. Research on the inhibitory effect of H. coagulans MZY531 on murine H22 hepatoma cells demonstrated that this strain induces apoptosis by downregulating phosphorylation of the PI3K/AKT/mTOR signaling pathway, thereby reducing cancer cell viability. It was also shown to promote apoptosis through the Bax/Bcl-2/Caspase-3 axis, indicating a dual mechanism of cell death induction. Complementary assays, including CCK-8, confirmed that MZY531 significantly inhibits H22 cell proliferation in a concentration-dependent manner. In addition, TUNEL staining and flow cytometry verified the effective induction of apoptosis in H22 cells by MZY531. These findings support the potential of H. coagulans as a future therapeutic strategy for liver cancer¹⁶² (Fig. 4 and 5).

4.5.4 Synergistic therapy for other cancers. While conventional anticancer therapies such as chemotherapy and radiotherapy remain predominant, the emergence of novel approaches—including bacteria-mediated antitumor therapy (BMAT), chemodynamic therapy (CDT), and immunotherapy—has opened new therapeutic prospects. However, the efficacy of monotherapies is often limited by insufficient treatment response and drug resistance, leading to suboptimal outcomes. Consequently, there is a pressing need for combinatorial strategies to enhance antitumor efficacy.^163–165

A recent study discovered that the spore shell (SS) of H. coagulans exhibits excellent tumor-targeting capability and adjuvant activity. Leveraging this, a biomimetic spore nanoplatform was developed to synergize CDT, BMAT, and antitumor immunity. The platform was constructed by mechanically isolating SS from H. coagulans, encapsulating hemoglobin (Hb), glucose oxidase (GOx), and the BRD4 inhibitor JQ1 within liposomes (Lipo) to form Lipo/Hb/GOx/JQ1, and then attaching SS to the surface via electrostatic adsorption, yielding the SS@Lipo/Hb/GOx/JQ1 nanoplatform.¹⁶⁶

In this system, GOx consumes intratumoral glucose to generate H₂O₂. Fe²⁺ from Hb then catalyzes the Fenton reaction, converting H₂O₂ into highly toxic hydroxyl radicals (˙OH), which activate the ROS/NLRP3 inflammasome pathway to induce pyroptosis and release damage-associated molecular patterns (DAMPs) such as HMGB1 and calreticulin (CRT), thereby enhancing tumor immunogenicity. Concurrently, JQ1 inhibits BRD4, downregulating PD-L1 expression on tumor cells, which blocks CD8⁺ T cell exhaustion and reduces regulatory T cell (Treg) infiltration, alleviating immune suppression. Hb also ameliorates the tumor hypoxic microenvironment (TME) and downregulates HIF-1α. SS modification significantly enhanced nanoparticle accumulation and uptake in tumor cells, effectively elevating intracellular ROS levels, inducing lipid peroxidation and pyroptosis, and substantially improving tumor-targeting and killing efficacy. Furthermore, supernatant from tumor cells treated with this nanoplatform effectively promoted dendritic cell (DC) maturation. In tumor-bearing mouse models, the treatment reduced Treg populations while significantly increasing infiltration of mature DCs and cytotoxic T lymphocytes (CTLs), and promoting secretion of immunostimulatory cytokines such as IFN-γ, thereby fostering immune activation. The nanoplatform also demonstrated excellent efficacy in inhibiting tumor growth and preventing lung metastasis, with no significant systemic toxicity observed, indicating considerable promise for future cancer therapy.¹⁶⁷

4.6 Eradication of Helicobacter pylori

Numerous studies have identified the antagonistic effects of probiotics against Helicobacter pylori (H. pylori). Probiotic administration can mitigate side effects associated with conventional antibiotic therapy, improve patient compliance and H. pylori eradication rates, and reduce H. pylori-induced damage.¹⁶⁸

A study evaluating the efficacy and safety of Clostridium butyricum and H. coagulans as monotherapy for H. pylori infection found that H. coagulans can reduce and eradicate H. pylori by secreting lactic acid to lower the local pH and inhibiting urease activity, thereby creating an unfavorable environment for H. pylori growth. Concurrently, H. coagulans modulates the host immune system by activating human immune cells and altering the production of immune-activating and anti-inflammatory cytokines and chemokines. This action reduces the secretion of multiple inflammatory mediators while enhancing immune activation and anti-inflammatory responses, thereby inhibiting H. pylori infection and preventing symptom exacerbation.

Moreover, H. coagulans demonstrates a significant capacity to eradicate H. pylori to a considerable extent, along with a favorable safety profile. This supports its potential as an effective therapeutic option for individuals with H. pylori infection who are unsuitable for antibiotic treatment or exhibit antibiotic resistance^169–171 (Fig. 4).

4.7 Immunomodulatory effects and treatment of immune-related disorders

4.7.1 Immunomodulation. Recent studies indicate that H. coagulans JBI-YZ6.31 exhibits direct immune-activating properties under non-inflammatory conditions and anti-inflammatory properties under inflammatory conditions. Both its cell wall and secreted metabolites contribute to these immunomodulatory effects.¹⁷²

In the absence of inflammation, the cell wall and metabolite fractions of H. coagulans JBI-YZ6.31 induce immune activation, as evidenced by upregulation of CD25 and CD69 activation markers and increased production of pro-inflammatory cytokines such as TNF-α, IL-17, IL-6, and IL-1β. The immunostimulatory effect of the cell wall fraction is mediated by peptidoglycan binding to Toll-like receptor 2 (TLR-2), leading to activation of NF-κB and MAPK signaling pathways.^173–175 In contrast, the immune activation induced by the secreted metabolite fraction appears to involve synergistic actions of various components. This direct immunostimulatory property likely arises from multiple distinct, non-overlapping mechanisms: one involving gene regulation via the induction of the antioxidant response element (ARE),^93,176,177 and another involving modulation of inflammatory cell signaling pathways.¹⁷²

Under inflammatory conditions, the cell wall fraction enhances immune cell activation while increasing production of the anti-inflammatory cytokine IL-10 and decreasing TNF-α. The metabolite fraction modulates immunity by stimulating IL-10 and reducing levels of the pro-inflammatory chemokine MCP-1.

Previous studies have confirmed that cell wall and metabolite fractions of H. coagulans GBI-30, 6086 support maturation of antigen-presenting immune cells and modulate gut inflammatory processes by reducing pro-inflammatory cytokines.^178,179 Furthermore, a recent study found that ProBC Plus, a product containing H. coagulans (LMG S-31876), significantly improves immune status and shows promise in providing measurable immunomodulatory and stress-reducing benefits.¹⁷² Collectively, these findings highlight the immunomodulatory potential of H. coagulans (Fig. 4).

4.7.2 Alleviation of allergic reactions. Allergic reactions are commonly triggered by a combination of environmental and genetic factors. Recent studies highlight the crucial role of gut microbiota in the development of mucosal immune tolerance. For instance, spores of H. coagulans exert specific immunomodulatory effects by enhancing IL-10 secretion and reducing IL-8 production in human cell lines.¹⁸⁰ They also upregulate inflammatory cytokines such as IL-6, IL-17A, TNF-α, and IL-1α, thereby modulating immune responses and alleviating allergy.^7,181

Shellfish, while nutritious and widely consumed, are a common food allergen. Their major antigen, tropomyosin (TM), can induce IgE-mediated allergic reactions, leading to gastrointestinal and cutaneous disturbances and, in severe cases, life-threatening anaphylaxis. Research indicates that yogurt-derived probiotic bacteria (YSPB) can mitigate food allergy by restoring gut microbiota, modulating intestinal metabolism, and regulating mucosal immunity. Specifically, Bifidobacterium longum (Bi) and H. coagulans (Hc) within YSPB alleviate TM-induced allergy through dendritic cell-dependent induction of regulatory T cells (Tregs) and suppression of mTOR signaling.^7,182–186

To investigate the mechanisms underlying YSPB-mediated protection against TM-induced allergy, a food allergy mouse model was established. Female mice exhibited higher sensitivity to TM sensitization than males. Experimental groups included control (Ctrl), adjuvant (Ad), and TM-sensitized (TM) groups. TM sensitization induced intestinal infiltration of CD4⁺ T cells, eosinophils, and mast cells, along with enterocyte apoptosis and goblet cell hyperplasia—pathological changes alleviated by either Bi or Hc treatment. Both probiotics counteracted TM-induced reductions in weight gain, allergic symptoms, serum histamine, and IgE levels, and reduced TM-specific IgE and IgG2a production. Notably, H. coagulans administration significantly increased IL-17A and decreased IL-13 production in splenocytes, suggesting a shift toward inflammatory Th17 differentiation and suppression of allergic Th2 responses, thereby mitigating TM-related allergy.¹⁸⁷

Amino acid metabolism, particularly involving arginine and proline, plays a key role in gut mucosal homeostasis and inflammation. Compared to the Ad group, the TM group showed significant downregulation of precursor metabolic pathways such as alanine, aspartate, and glutamate metabolism. YSPB treatment restored TM-induced metabolic disturbances by modulating arginine and proline metabolism. H. coagulans supplementation not only regulated metabolic homeostasis during food allergy but also restored these precursor pathways.

In summary, under TM sensitization, H. coagulans alleviated immune cell infiltration, enterocyte apoptosis, and goblet cell hyperplasia; reduced allergy-related symptoms and serum biomarkers; and modulated immune polarization and metabolic pathways, demonstrating its anti-allergic potential.^187–189

In a study on canine allergic contact dermatitis, probiotic supplementation prevented intestinal infections, improved immunity, and controlled dermatitis symptoms.^190,191 Comparisons among groups receiving Bacillus subtilis and H. coagulans, prednisolone, or a combination of both revealed that the probiotic group achieved symptom improvement comparable to the combined group, with a faster response.^192,193 Between days 21 and 35 of treatment, the probiotic mixture increased anti-trypsin activity and reduced lysosomal enzyme activity, myeloperoxidase (MPO), and alternative and classical complement pathway activity, ameliorating clinical signs of DNCB-induced dermatitis. These results support the potential of H. coagulans, especially in combination with Bacillus subtilis, in managing canine allergic contact dermatitis.¹⁹⁴ These findings indicate that the combination of H. coagulans and Bacillus subtilis can alleviate, treat, or maintain treatment in larger animal groups or clinical cases of canine ACD, further demonstrating the potential of H. coagulans to reduce allergic reactions (Fig. 4).

4.7.3 Treatment of rheumatoid arthritis (RA). Emerging research suggests that gut microbiota dysbiosis is a key factor in the development of rheumatoid arthritis (RA).^195,196 Subsequent experimental data confirm that alterations in gut microbiota composition contribute significantly to systemic immune abnormalities in RA patients.^197–199 Modulating the gut microbiota to restore a balanced ecosystem therefore represents a promising therapeutic strategy. H. coagulans, known for its probiotic benefits in regulating gut flora and managing intestinal disorders, is a candidate for such interventions.

An experimental study using the collagen antibody-induced arthritis (CAIA) mouse model demonstrated that treatment with the H. coagulans strain BACO-17 downregulated TNF-α expression and reduced plasma levels of IL-6 and Th17 cells.^200,201 This treatment protected joint cartilage and synovium from RA-induced damage, significantly reduced paw swelling, arthritis scores, and paw thickness, and improved bone structure by mitigating cartilage damage and osteophyte formation.

Furthermore, the BACO-17 strain dose-dependently suppressed TNF-α-induced mRNA and protein expression of MMP2, MMP9, and MMP13.²⁰² These matrix metalloproteinases (MMPs)—particularly MMP2, MMP9, and MMP13, which degrade cartilage and bone extracellular matrix—are strongly implicated in joint destruction during RA.^203,204 BACO-17 also dose-dependently inhibited TNF-α-induced expression of IL-1β, IL-6, and IL-17 by reducing phosphorylation of p85, Akt, and p65.²⁰² IL-17, a pro-inflammatory cytokine, plays a significant role in RA-related joint damage.

Methotrexate (MTX), one of the most commonly used disease-modifying antirheumatic drugs (DMARDs) for RA,^205,206 was found to reduce IL-17 expression more effectively when combined with H. coagulans BACO-17^202,207 (Fig. 4).

5. Challenges, heterogeneity, and future perspectives

The extensive research compiled in this review underscores the considerable therapeutic potential of H. coagulans. However, translating this potential from bench to bedside—and ultimately to the market—requires a clear and integrated understanding of its developmental pathway. As summarized in Fig. 6, this pathway begins with the unique biological properties of specific strains and culminates in diverse health applications, navigating challenges at every step. Building on this framework, the foremost challenge remains the strain-specific functional heterogeneity.

Fig. 6 From strain to outcome: the translational pathway of Heyndrickxia coagulans.

5.1. Strain-specific heterogeneity

As summarized in Table 1, the functional properties of H. coagulans exhibit significant strain-specific heterogeneity. Different strains display distinct therapeutic specializations: for example, MTCC 5856 and SNZ 1969 primarily address gastrointestinal issues such as bloating and constipation, respectively; Unique IS-2 and BCP92™ show potential in neuropsychiatric disorders, demonstrating anxiolytic and antidepressant-like activities; whereas JA845 and BACO-17 are effective in models of Alzheimer's disease and rheumatoid arthritis.^{101,120,139,143,144,207}

5.1.1. Heterogeneity in immunomodulatory mechanisms. A deeper analysis reveals striking differences in how various strains interact with the host immune system. The immunomodulatory effects are not uniform but are highly pathway-specific. For instance: (1) Strains TL3 and MZY531 primarily exert their anti-inflammatory effects by significantly downregulating the TLR4/MyD88/NF-κB signaling pathway, a key driver of systemic inflammation.⁵² (2) In contrast, JBI-YZ6.31 exhibits a more complex, context-dependent immunomodulatory profile. Its cell wall fraction acts as a direct immune activator under non-inflammatory conditions by binding to TLR-2 and activating NF-κB and MAPK pathways, whereas its metabolite fraction shows anti-inflammatory properties.¹⁷² (3) Meanwhile, strain Unique IS-2 demonstrates a systemic anti-inflammatory capability, normalizing levels of IL-1β and TNF-α in the brain, which is central to its antidepressant effects.^20,27 This spectrum of activity—from direct immune activation and TLR2-mediated effects to systemic suppression of the TLR4/NF-κB axis and neuroinflammation—highlights that different strains can be selectively employed to modulate distinct immune pathways.

5.1.2. Heterogeneity in metabolic activity and nutritional requirements. Beyond immunomodulation, significant metabolic heterogeneity exists among strains, which directly influences their probiotic functionality. Although lactic acid production is a common feature, the spectrum of secreted enzymes and metabolites varies considerably. GBI-30, 6086 is distinguished by its production of alkaline protease to support protein digestion and the bacteriocin coagulin to inhibit pathogens.^44,46–48 LMG S-24828 exhibits a broad substrate utilization capacity, metabolizing 39 different carbon sources and expressing enzymes such as β-galactosidase. As detailed in Section 2.3, the metabolic model iBag597 for strain 36D1 reveals sophisticated, growth-rate and pH-dependent plasticity in ATP synthesis. Such metabolic flexibility remains uncharacterized in most other strains, suggesting that energetic strategies and resulting metabolic byproducts may differ substantially.³⁰

5.2. Mechanistic black box and translational bottlenecks

At the fundamental research level, the molecular mechanisms behind many of its benefits remain a “black box”. Advanced tools like CRISPR-based gene editing and single-cell transcriptomics are urgently needed to systematically decrypt the spatiotemporal dynamics of spore germination, immunomodulatory signaling (e.g., TLR4/MyD88/NF-κB, Nrf2), and gut–brain-axis communication. Future efforts should prioritize the development of novel delivery systems, such as nanocarrier encapsulation and biofilm-inspired surface modifications, to enhance gut residency.

5.3. Toward personalized probiotic therapy

The future of H. coagulans research lies in embracing its inherent heterogeneity rather than overlooking it. We propose a paradigm shift toward strain-specific, mechanism-driven applications: (1) Establishing standardized resources: creating globally accessible, well-characterified strain repositories and phenotypic databases is imperative for enabling robust comparative studies. (2) Developing synergistic formulations: exploring synergies with prebiotics (e.g., inulin), conventional therapeutics, and other probiotics will be essential for designing effective synbiotic and combinatorial regimens. (3) Leveraging multi-omics and AI: integrating genomics, metabolomics, and metagenomics with clinical metadata will help decipher the complex “strain–host–environment” interaction network. Coupling this with artificial intelligence can predict optimal strain–indication pairing, ultimately paving the way for truly personalized probiotic medicine.

Author contributions

Sihan Ke: writing – original draft, review & editing, investigation, formal analysis. Zixia Chen: writing – original draft, investigaion, formal analysis. Yutong Qi: writing – original draft, investigation, formal analysis. Jiantang Zhang: writing – original draft, visualization. Qizhu Chen: writing – original draft, review & editing, visualization. Jun Chen: writing – review & editing, supervision, project administration, conceptualization. Huaben Bo: writing – review & editing, supervision, project administration, conceptualization.

Conflicts of interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Data availability

No data was used for the research described in the article.

Acknowledgements

This work was supported by the National Natural Science Foundation of China [grant number 82104514], Guangdong Undergraduate Innovation and Entrepreneurship Training Program Project [grant number 202210573064 and 202210573053], Project on Traditional Chinese Medicine in Guangdong Province, [grant number 20241174].

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