Flocculation onset, growth phase and genealogical age in Saccharomyces cerevisiae

Abstract

Flocculation onset, the time during the fermentative cycle at which the strains of Saccharomyces cerevisiae become flocculent, is an important factor in the brewing industry. The flocculation ability of Flo 1 phenotype (strain NCYC 869) remained practically unchanged throughout the growth and seems to be insensitive to the presence of nutrients of the culture medium. On the contrary, the flocculation of NewFlo phenotype (strain NCYC 1195) exhibited a cyclic behaviour. It was found that the loss of flocculation in the early growth was the result of two combined effects: the dismantling of the flocculation mechanism of the cells coming from the inoculum and the nonflocculent state of the new cells produced after growth has started. The onset of flocculation of strain NCYC 1195 in the cultural conditions used in this work coincided with the end of the exponential growth, when the minimum glucose level in the culture medium was attained. It was demonstrated that it is possible to manipulate the flocculation onset by changing the initial glucose concentration in the culture medium.

: Le seuil de flocculation. soit le moment oil. durant le cycle de fermentation, Jes souches de Saccharomyces cere1·esiae commencent a flocculer, est un parametre important dans I "industrie du brassage de la biere. La capacite de flocculation du phenotype Flo! (souche NCYC 869) demeure pratiquement intacte au cours de la croissance et ne semble pas influencee par Jes elements nutritifs presents dans le milieu de culture. Par contre, chez le phenotype NewFlo (souche ~CYCI 195), la flocculation apparait de fa~on clyclique. La perte de la capacite de flocculation en debut de croissance semble due a deux effets combines: l"alteration du mecanisme de flocculation des ce!lules qui viendrait de l'inoculum et l'etat de non-flocculation des nouvelles cellules produites apres le demarrage de la croissance. Dans !es conditions de culture utilisees dans le present travail, le seuil de flocculation de la souche NCYCI 195 co"incide avec la fin de la phase exponentielle de croissance au moment ou la concentration de glucose dans le milieu de culture atteint sont minimum. II a ete demontre qu"il est possible de modifier le seuil de flocculation en changeant la concentration initiale du glucose dans le milieu de culture.