Effect of cultural and nutritional conditions on the control of flocculation expression of Saccharomyces cerevisiae

Abstract

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.

Nous avons etudie chez trois souches de Saccharomyces cerevisiae l'effet de conditions de culture (temperature et pH) et de conditions nutritives (source d'azote et de carbone) sur !'expression de la flocculation. Ce phenomene a ete etudie plairant Jes cellules en phase stationnaire dans des conditions habitue!les de flocculation. La temperature de croissance a eu plus d'influence sur le pouvoir de flocculation de la souche NCYC 1195, classee recernrnent dans la Iitterature comme phenotype NewFlo, que chez Jes souches NCYC 869 et NRRL Y265 de phenotype Flo I. Le pH initial du milieu de culture n 'avail pas d 'influence sur la flocculation des souches du phenotype Flo 1, mais dans le cas de la souche NCYC 1194 une repression etait observee lorsque le pH etait inferieur a 3,5. Cette repression de la flocculation chez la souche NCYC 1195 a aussi ete observee dans un milieu de culture defini. Cette inhibition n 'etait pas reliee a un besoin specifique d 'azote mais a un foible pouvoir tampon de ce milieu defini. Toutes Jes souches ont fortement floccule lorsque cultivees dans le glucose mais pas dans le glycerol. II est clairement demontre que !'expression phenotypique de Ja flocculation pouvait etre induite OU reprirnee par Un changernent des conditions de culture ou de nutrition. Nous avons observe deux comporternents distincts consequents a l'effet des conditions de culture sur la flocculation, particulierernent du pH. Ces comporternents differents pourraient servir a distinguer deux phenotypes de flocculation.