Multi-omics analysis reveals the response mechanism of Pichia kudriavzevii to high-concentration lactic acid stress.

Pichia kudriavzevii tolerance mechanisms are not well understood, even though strong-flavor Baijiu fermentation places a heavy burden on yeast metabolism due to the accumulation of lactic acid (LA). This study utilized growth kinetics, electron mi-croscopy, antioxidant tests, and integrated metabolomic-transcriptomic studies to an-alyze strain Y2-1, which was isolated from Baijiu pit yellow water. Y2-1 showed a de-layed biphasic growth pattern and could withstand up to 80 g/L of LA. It appears that morphological adaptation plays a role in stress resistance, as scanning electron mi-croscopy showed that cells elongated significantly at high LA levels. Enrichment in pyruvate metabolism, glutathione metabolism, and ABC transporter pathways was among the 1,125 differentially expressed genes and 817 different metabolites found using multi-omics analysis. In order to maintain membrane integrity, ergosterol homeo-stasis, and mitochondrial function, mechanistically speaking, LA tolerance entailed three strategies: (i) activating pyruvate metabolism, which channeled lactate into energy metabolism and mitigated proton imbalance; (ii) enhancing the glutathione antioxidant system, which included spermidine synthase upregulation and improved ROS scavenging and intracellular pH buffering; and (iii) induction of ABC transporters (SNQ2, ABCB7). Molecular insights into yeast acid tolerance and a foundation for creating robust strains to boost Baijiu fermentation efficiency are offered by these findings, which indicate a metabolic-transport-linked defense strategy.