Diversity of ethanol stress responses in Oenococcus oeni strains.

Oenococcus (O.) oeni is the lactic acid bacteria (LAB) species most resistant to the hostile environment of wine in which various physical-chemical factors affect the LAB growth responsible for the malolactic fermentation (MLF). Although several studies analyzed few mechanisms that enable O. oeni to withstand stress conditions, more information about the mechanisms involved in the adaptation of O. oeni to stress conditions is required, particularly under winemaking conditions. In this study, late-exponential phase cells of O. oeni strains were exposed to different ethanol stresses (concentrations of 7, 12 and 13%) to investigate the diversity of their responses. The changes in total proteins expression and the expression products of different genes were evaluated by a proteomic strategy combining 2-DE with peptide mass fingerprinting (PMF) MALDI-TOF mass spectrometry analysis. A 2-DE reference map obtained for cells grown in optimal conditions was compared with those obtained after ethanol stresses at 7, 12 and 13% concentrations. A significant decrease in protein synthesis was observed in response to 12 and 13% ethanol concentrations, while O. oeni response to a lowering ethanol concentration stress was not associated to substantial variations in the 2-D map. Protein identification using PMF was performed by MASCOT search engine against the NCBI non-redundant protein database and Swiss Prot database. Proteins up/down regulation measurements demonstrated that the response to different environmental stimuli can involve the contribution of unique as well as combined physiological mechanisms. These results provide a better comprehension of biochemical processes related to stress resistance in O. oeni, allowing a better knowledge of stress physiology that may be useful to optimize survival and selection of potential starter cultures.