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 flocculation conditions. The flocculation ability of strain NCYC 1195, recently classified in the literature as the NewFlo phenotype, was more sensitive to growth temperature than Flo1 phenotype strains (NCYC 869 and NRRL Y265). The initial pH of the culture medium did not affect the flocculation ability of Flo1 phenotype strains but in the case of strain NCYC 1195 flocculation was repressed when the initial pH of the culture 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 poor buffering capacity of the defined medium. All strains showed strong flocculation when grown in glucose, but were nonflocculent in glycerol. It was clearly demonstrated that the phenotypic expression of flocculation could be induced or repressed by changing cultural and nutritional conditions. Two distinct behaviours were also displayed with regard to the effect of the cultural conditions upon flocculation, namely the effect of pH. These different behaviours can be used to distinguish the two flocculation phenotypes.