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

BACKGROUND During wine making, 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 would be 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 involved mechanisms, influences of acid and ethanol stresses on O. oeni SD-2a were detected in this study to gain a better understanding of the cross-protection responses. RESULTS The results showed that acid and ethanol stress both caused the damage of cell membrane and decreased cellular ATP concentration. At the same time, acid stress increased the uptake of GSH, while ethanol stress led to cell depolarization. The results of comparative proteomic analysis highlighted that heat shock protein (Hsp20) was induced with almost all acid and ethanol stresses. In addition, the expression of stress relevant genes (hsp20, clpP, trxA, ctsR, recO, usp) increased highly with ethanol and acid stress treatments. Finally, the viability of O. oeni was improved with acid and ethanol pretreatments after freeze-drying. CONCLUSION 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 the lyophilized cells. This article is protected by copyright. All rights reserved.