Influences of acid and ethanol stresses on Oenococcus oeni SD-2a and its proteomic and transcriptional responses

BACKGROUND During winemaking, malolactic fermentation (MLF) is usually induced by Oenococcus oeni owing to its high resistance to wine stress factors. To ensure a controlled and efficient MLF process, starter cultures are inoculated in wine. In previous studies, O. oeni strains with sub-lethal acid or ethanol stresses showed higher freeze-drying vitality and better MLF performance. To explore the mechanisms involved, influences of acid and ethanol stresses on O. oeni SD-2a were investigated in this study to gain a better understanding of the cross-protection responses. RESULTS The results showed that acid and ethanol stresses both caused damage to cell membranes and decreased cellular adenosine triphosphate concentration. At the same time, acid stress increased the uptake of glutathione, while ethanol stress led to cell depolarization. The results of comparative proteomic analysis highlighted that heat shock protein was induced with almost all acid and ethanol stresses. In addition, the expression of stress-relevant genes (hsp20, clpP, trxA, ctsR, recO, usp) increased greatly with ethanol and acid stress treatments. Finally, the viability of O. oeni was improved with acid and ethanol pretreatments after freeze-drying. CONCLUSIONS This study demonstrated that acid and ethanol stresses had mixed influences on O. oeni SD-2a. Some physiological and molecular changes would contribute to a more stress-tolerant state of O. oeni, thereby improving the viability of lyophilized cells. (c) 2020 Society of Chemical Industry

Automated summary

Acid and ethanol stresses had mixed influences on Oenococcus oeni SD-2a, with changes in cell membrane damage and ATP concentration. Acid stress increased glutathione uptake while ethanol stress led to cell depolarization. Heat shock protein induction, along with increased expression of stress-relevant genes, was observed with both acid and ethanol stresses. The viability of O. oeni improved after acid and ethanol pretreatments.