Aspects moléculaires de l'assimilation du tréhalose chez Saccharomyces cerevisiae

Trehalose is a non reducing disaccharide of glucose considered a storage carbohydrate for yeast, as well as glycogen. Trehalose is also widespread in plants and that makes it an alternative carbon source for microorganisms. In this work, we showed that Saccharomyces cerevisiae is able to grow on trehalose using two distinct pathways. Applying the invertase assay (on whole cells) to trehalase, we firstly showed that more than 90% of acid trehalase activity of Ath1p is periplasmic, splitting of the disaccharide into glucose. A throughput screening performed on a 4500-mutant collection then completed our understanding of this major pathway. We also found that the second, independent pathway corresponds to a coupling between the Agt1p-mediated trehalose transport and the hydrolysis of the disaccharide by the cytosolic neutral trehalase Nth1p. Nevertheless this pathway is only an alternative route because of several constraints such as the control of AGT1 expression by the MAL system or the inactivation/degradation process of Agt1p exhibited during growth on trehalose. Our results also suggest that the Nth2p protein whose function has not been identified yet displays a neutral trehalase activity. The atypical trehalose consumption profile during stationary phase seems to be related to the Nth2p activation. In batch cultivation, we also observed oscillations, probably favoured by the purely oxidative metabolism exhibited during growth on trehalose. We then described two types of oscillations that can occur simultaneously or consecutively during the culture, and show that these phenomena do not occur in the absence of active neutral trehalase in the cells