Colony dimorphism associated with stress resistance in Oenococcus oeni VP01 cells during stationary growth phase

Abstract

The resistance to stresses as starvation, the presence of ethanol, sulfite and low pH, is a fundamental prerequisite for starter cultures used to induce malolactic fermentation in wine. In order to evaluate stress resistance of cells undergone starvation, cells viability in laboratory cultures of Oenococcus oeni VP01 strain was monitored during prolonged stationary growth phase. Once entered the stationary phase, strain VP01 showed 99% reduction of cell viability within 4 days. The remaining cells population maintained viability over 70 days and, when plated on agar medium, generated small colonies. The occurrence of this phenomenon was associated to stress resistance, since 10-day-old cells resulted more resistant than 3-day-old cells to ethanol and low pH conditions. No genomic mutations were revealed by pulse-field gel electrophoresis (PFGE) analysis in aged cultures. Total protein analysis by bidimensional electrophoresis highlighted differential protein expression in cultures differentially aged. It was demonstrated that O. oeni starving cultures at the stationary phase are constituted by dynamic cell populations. These results offer interesting perspective for a better understanding of cells behavior when inoculated in wine.