Kinetics and regulation of fructose and glucose transport systems are responsible for fructophily in Zygosaccharomyces bailii

Abstract

A strain of Zygosscchammyces bailii was selected for studies on fructose and glucose transport to determine the basis of the fructophilic behaviour of this species. Fructose was transported by a specific low-aff inity, high-capacity transport system with a Km of 65.6 mM and a Vmu of 6 7 mmol g-l h-' for cells grown on 2% (w/v) fructose, while the transport of glucose showed a Km of 7 mM and a Vmu of 1.7 mmol g-1 h-l for cells grown on 2 % (w/v) glucose. The transporter of glucose also accepted fructose as a substrate. Fructose inactivated the glucose transporter; inactivation was faster at higher concentrations. Both transporters were partially inductive. Measurements of metabolic fluxes and respiration and fermentation rates supported the general features identified by transport measurements. The kinetics and regulation of transport of the two sugars confirm the fructophilic behaviour previously described by other authors.

The High-Capacity Specific Fructose Facilitator ZrFfz1 Is Essential for the Fructophilic Behavior of Zygosaccharomyces rouxii CBS 732T

“…Fructose transport is thus privileged, mainly at high sugar concentrations. Three mechanisms seem to be responsible for this behavior: (i) fructose is transported by a specific transport system with high capacity, (ii) fructose competes with glucose for the hexose transport system, and (iii) high fructose concentrations inactivate the glucose facilitator system (10). Similar results were also found for Z. rouxii (11).…”

“…In the glucophilic yeast S. cerevisiae, glucose not only is an energy and carbon source, it also has an important role as a global regulator of metabolism and growth. In the fructophilic yeasts Z. bailii and Z. rouxii, this critical regulatory role seems to be played by fructose, as fructose regulates and inactivates the glucose transporter system, especially at high fructose concentrations, since glucose transport is completely abolished subsequent to addition of 10% fructose to 2% glucose-grown cells after 4 h of incubation in Z. bailii (10) and in Z. rouxii (11).…”

“…Fructose uptake in Z. bailii was shown to be mediated by a specific facilitator system with high capacity and low affinity and by a low-capacity and high-affinity facilitator system that also transports glucose (10). Fructose transport is thus privileged, mainly at high sugar concentrations.…”

Ffz1, a new transporter specific for fructose from Zygosaccharomyces bailii

“…In contrast with most yeasts, and in particular with S. cerevisiae, Z. bailii consumes fructose faster than glucose, deserving the designation of a fructophilic yeast. This behaviour was explained by Sousa-Dias et al (1996) by taking into account the kinetics of hexose uptake observed in this yeast. Fructose is taken up by a high-capacity, low-affinity transporter, specific for fructose (no other sugar inhibits fructose uptake); a second transporter takes up glucose, fructose and 2-deoxyglucose in a low-capacity and high-affinity manner.…”

Isolation and sequence analysis of the gene encoding triose phosphate isomerase from Zygosaccharomyces bailii

“…In contrast to S. cerevisiae, which always prefers glucose as carbon source, Z. bailii exhibits the phenomenon of so-called fructophily. In fact, when glucose and fructose are both available in the medium, Z. bailii incorporates fructose more rapidly (Sousa-Dias et al, 1996). However, sugar metabolism in this microorganism has not so far been extensively studied.…”