Promotion of protein utilization from corn by-product via calcium-dependent growth stimulation of Streptomyces sp. SCUT-3

Abstract

Calcium signaling plays fundamental roles in growth and development in plants and animals, yet its functional significance in prokaryotes remains poorly understood. In this study, calcium carbonate was identified as a potent growth stimulant for Streptomyces sp. SCUT-3, accompanied by a significant increase in intracellular Ca²⁺ levels, suggesting a previously underappreciated calcium-responsive physiological process in actinomycetes. Leveraging this insight, CaCO₃-rich shrimp shell waste (SSW) was employed as an adjuvant to improve the bioconversion of recalcitrant corn gluten meal (CGM). By blending 20% SSW with CGM in a solid-state fermentation system, SCUT-3 achieved a 94.8% solubilized protein fraction (13.2-fold higher than CGM alone), yielding 27.6 g free amino acids and 23.3 g soluble peptides per 100 g substrate, with 91.1% of peptides below 2 kDa. The fermented product exhibited 83.6% in vitro digestibility (3.5-fold improvement), and significantly enhanced antioxidant activity. The strategy was successfully extended to distillers dried grains with solubles (DDGS), achieving a 92.7% solubilized protein fraction and 53.7% in vitro digestibility. These findings expand the conceptual scope of calcium-associated regulation in actinomycetes and provide a potential strategy for designing high-efficiency biomass degradation processes.