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Cooperative response of Pichia kudriavzevii and Saccharomyces cerevisiae to lactic acid stress in Baijiu fermentation.

Lactic acid is a universal metabolite, as well as a growth inhibitor of ethanol producers in Baijiu fermentation. Revealing the mechanism of lactic acid tolerance is essential for the yield of fermented foods. Here, we employed RT-qPCR to explore the degradation mechanism of lactic acid, based on the co-culture of Pichia kudriavzevii and Saccharomyces cerevisiae. Under high lactic acid stress, P. kudriavzevii decreased lactic acid from 40.00 to 35.46 g L-1 within 24 hours. Then, S. cerevisiae restored its capacity to degrade lactic acid. Finally, lactic acid decreased to 26.29 g L-1. Co-culture significantly enhanced lactic acid consumption compared to the mono-culture of P. kudriavzevii (90% higher) or S. cerevisiae (209% higher). We found lactate catabolism, H+ extrusion and glycerol transport were the lactic acid tolerance pathways in yeasts. This study reveals the novel acid tolerance mechanisms of microbiota and would provide new strategies for ethanol production under acid stress.