Enhancement effect of l-cysteine on lactic acid fermentation production.

BACKGROUND: Environmental stress resistance is still a bottleneck for economical process for l-lactic acid fermentation. Chronological lifespan (CLS) extension has represented a promising strategy for improving stress resistance of microbial cell factories. MAIN METHODS AND MAJOR RESULTS: In this study, addition of anti-aging drug cysteine, a kind of extending CLS of microbial cell factories, was systematically evaluated on cell viability and l-lactic acid production in Bacillus coagulans CICC 23843. The results revealed that 16 mm l-cysteine supplement significantly improved l-lactic acid titer in B. coagulans. The enhanced total antioxidant capacity (T-AOC) and key enzymes activities involving in glycolytic pathway as well as differentially expressed genes involved in cysteine synthesize and cysteine precursor synthesize pathways, and fatty acid degradation pathway may help to further understand the relative mechanism of l-cysteine effect on improving l-lactic acid accumulation. Finally, based on 16 mm l-cysteine supplement, a final l-lactic acid titer of 130.5 g L-1 with l-lactic acid productivity of 4.07 g L-1  h-1 and the conversion rate of 0.94 g g-1 total sugar was achieved in a 5 L bioreactor. CONCLUSIONS AND IMPLICATIONS: This study provided a valuable option for engineering lactic acid bacteria lifespan for enhancement of lactic acid yield.