Thriving in extremes: harnessing the potential of pH-resilient algal strains for enhanced productivity and stability

Abstract

Algal biomass can play a multifaceted role in advancing the sustainable developmental goals (SDGs) as a means of carbon sequestration and waste mitigation. Outdoor algal cultivation, typically conducted in open raceway ponds, while a cost-effective approach for biofuel and bioproduct production, suffers from several challenges, including weather variability, contamination, nutrient mixing, and challenges in harvesting and dewatering. Notably, large-scale cultivation of neutrophilic algae grown at pH 7 necessitates pH stabilization measures due to fluctuations induced by CO₂ uptake, nutrient concentration, photosynthesis, and competing microbial activity, resulting in significant operating costs. The exploitation of pH-resilient algae encompassing acidophilic, acid-tolerant, alkaliphilic, and alkali-tolerant strains can maximize growth and productivity across a wide range of pH from acidic to alkaline. As a result, the repertoire of water sources used for cultivation can be expanded to include wastewater treatment and industrial effluents, reducing use of scarce freshwater and dependence on costly pH regulation measures. Extremophilic strains possess the intrinsic capacity to withstand pH fluctuations that limit invaders, hence minimizing culture crashes. In the present review we highlight the unique adaptations of pH-resilient algal strains that can strengthen the resilience of large-scale algal cultivations and overcome the challenges of outdoor operations. We delve into the pH adaptation mechanism of extremophilic algae and their applicability in diverse fields of bioremediation, carbon capture, and bioproduct manufacture. Recent strides in strain improvement for enhancing the metabolic prowess of pH-resilient algae have been discussed, emphasizing their critical role towards shaping the future of a sustainable bioeconomy.