GLUCOSE-METABOLISM IN THE YEAST SCHWANNIOMYCES-CASTELLII - ROLE OF PHOSPHORYLATION SITE-I AND AN ALTERNATIVE RESPIRATORY PATHWAY

Glucose metabolism in a Crabtree-negative yeast, Schwanniomyces castel lii, and a cytochrome b-deficient mutant of this strain was investigat ed in chemostat culture. The wild-type and mutant strains exhibited th e same behavior. Oxidative metabolism was observed when the substrate uptake rate (qS) was low, Fermentative metabolites were excreted when the qS value was higher than 0.40 g.g(-1).h(-1), indicating the occurr ence of a respirofermentative metabolism; however, the respiratory quo tient (RQ) remained near 1. When fermentation occurred, the cytochrome pathway was repressed but not the salicylhydroxamic acid (SHAM)-sensi tive pathway, The presence of an alternative SHAM-sensitive respirator y pathway and the presence of phosphorylation site I in all metabolic conditions explained the RQ value of I and accounted for high biomass yields in oxidative metabolism conditions (0.62 g.g(-1) for the wild-t ype strain and 0.31 g.g(-1) for the cytochrome b-deficient mutant stra in).