EFFECT OF CULTURAL AND NUTRITIONAL CONDITIONS ON THE CONTROL OF FLOCCULATION EXPRESSION IN SACCHAROMYCES-CEREVISIAE

The effect of cultural (temperature and pH) and nutritional conditions (nitrogen and carbon source) on the flocculation expression of three strains was studied. The strains' flocculation ability was determined by placing the cells in a stationary phase of growth in standard flocc ulation conditions. The flocculation ability of strain NCYC 1195, rece ntly classified in the literature as the NewFlo phenotype, was more se nsitive to growth temperature than Flo 1 phenotype strains (NCYC 869 a nd NRRL Y265). The initial pH of the culture medium did not affect the flocculation ability of Flo 1 phenotype strains but in the case of st rain NCYC 1195 flocculation was repressed when the initial pH of the c ulture medium was below 3.5. Flocculation in strain NCYC 1195 was also repressed in defined culture medium; this inhibition was not related to a deficiency in any particular nitrogen source, but rather to the p oor buffering capacity of the defined medium. All strains showed stron g flocculation when grown in glucose, but were nonflocculent in glycer ol. It was clearly demonstrated that the phenotypic expression of floc culation could be induced or repressed by changing cultural and nutrit ional conditions. Two distinct behaviours were also displayed with reg ard to the effect of the cultural conditions upon flocculation, namely the effect of pH. These different behaviours can be used to distingui sh the two flocculation phenotypes.