Transport and utilization of hexoses and pentoses in the halotolerant yeast Debaryomyces hansenii

Abstract

Debaryomyces hansenii is a yeast species well known for its halotolerance. It has seldom been mentioned as a pentose consumer. In the present work, a strain of this species was investigated with respect to the utilization of mixtures of pentoses and hexoses. Growth parameters were calculated from batch aerobic cultures with pentoses, hexoses and mixtures of both sugars as carbon sources. Growth on pentoses was slower than on hexoses, but the values obtained for biomass yields were very similar in both type of sugars. Furthermore, in mixtures of both sugars, the preference for one carbon source does not inhibit consumption of the other. Glucose and xylose were transported by cells grown on glucose, via a specific low-affinity facilitated diffusion system. Cells derepressed by growth on xylose exhibiteded two distinct high-affinity transport systems for glucose and xylose. The characterization of these transport systems allowed us to consider them as proton symports, although they displayed sugar associated proton uptake exclusively only in the presence of NaCl or KCl. When the individual sugar uptake rates during cultivation and the Vmax of transport systems for glucose and xylose were compared, transport appeared not to limit the growth rate on either sugar.