Behaviour of Kloeckera apiculata flocculent strain in coculture with Saccharomyces cerevisiae

Abstract

The behaviour of the flocculent Kloeckera apiculata strain in coculture with the nonflocculent Saccharomyces cerevisiae strain, both yeasts isolated from wine, has been analyzed. Pure culture of Kloeckera apiculata (apiculate yeast) exhibits 75 % flocculation in the yeast extract/peptone/glucose (containing 20 g/L of glucose, YPG20) medium after 24-hour incubation at 28 °C. This yeast expresses a weak flocculent phenotype in glucose-poor medium (10 % of flocculated cells). Increasing the glucose concentrations in this medium induces yeast flocculation. When the apiculate yeast was co-inoculated with a nonflocculent strain of Saccharomyces cerevisiae (elliptic yeast), an increase of the number of elliptic cells that settled at the bottom of the culture was observed. Electron microscopy observations of the aggregates formed in the mixed culture confirmed that apiculate and elliptic yeasts can interact and establish a binding between them through homogeneous mucus. However, a lower percentage of Kloeckera apiculata flocculation with respect to the pure cultures was observed, this behaviour being correlated with a higher rate of glucose consumption by Saccharomyces cerevisiae. The prompt coflocculation of Kloeckera apiculata with Saccharomyces strains and the induction of this phenomenon by glucose could be considered an important biotechnological tool for the early decreasing of indigenous saccharomycetic flora from the media, before the inoculation of a selected sta rter strain to carry out a more controlled alcohol fermentation.