Effect of pH and salinity on biofilm-like phenotypes of yeasts isolated from fermented olives

The yeast biofilm-like phenotypes such as media invasiveness and mat colony are considered mechanisms to colonize and persist in environmental niches. In table olive fermentation, pH and salinity are two hurdles that yeasts have to overcome to succeed in developing a stable population. Eight yeast strains - among which Candida, Pichia, and Wickerhamomyces genera - isolated from table olive fermentations, and the two control strains of Saccharomyces cerevisiae Σ1278b and BY4742 were tested in YPD agar either carbon-rich (glucose 2%) or -deficient (glucose 0.1%) media also modified both for pH (4.3) and salinity (NaCl 5%) to simulate the brine. Conventional (2%) and low (0.3%) agar concentrations were used to study invasiveness and mat colony formation, respectively. The majority of the strains showed bigger mat colonies with 2% of glucose than 0.1%. Three strains exhibited an increase in area colonies growing in the modified media. The pH and salinity modifications determined invasive growth for six and two strains in the presence of either 2% or 0.1% of glucose, respectively. Two strains were unable to invade media. A wide diversity was observed among the strains and media; moreover, some of the strains displayed the two biofilm-like phenotypes in dissociated way. The observed phenotypic diversity could confer strain advantage during the olive fermentation process. Our results may be taking into account to select strains to drive fermentation process.