Transport and Utilization of Hexoses and Pentoses in the Halotolerant Yeast Debaryomyces hansenii

Abstract

Debaryomyces hansenii is a yeast species that is known for its halotolerance. This organism 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 pentoses and hexoses in mixtures and as single carbon sources. Growth parameters were calculated for batch aerobic cultures containing pentoses, hexoses, and mixtures of both types of sugars. Growth on pentoses was slower than growth on hexoses, but the values obtained for biomass yields were very similar with the two types of sugars. Furthermore, when mixtures of two sugars were used, a preference for one carbon source did 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 had two distinct high-affinity transport systems for glucose and xylose. The sensitivity of labeled glucose and xylose transport to dissipation of the transmembrane proton gradient by the protonophore carbonyl cyanidem-chlorophenylhydrazone allowed us to consider these transport systems as proton symports, although the cells displayed sugar-associated proton uptake exclusively in the presence of NaCl or KCl. When the V max values of transport systems for glucose and xylose were compared with glucose- and xylose-specific consumption rates during growth on either sugar, it appeared that transport did not limit the growth rate.

Physiological studies on long-term adaptation to salt stress in the extremely halotolerant yeast CBS 4019 (syn. )

“…Concomitantly, the variation in V max observed according to external pH in the presence of either TPP or CCCP suggested glycerol symport to be essentially pH-dependent. Moreover, K i and C min for ethanol are comparable with values published for other symporters [22,27,32]. To support these results, glycerol accumulated inside the cell against the chemical gradient.…”

“…Intracellular concentrations of sugars, organic acids and polyols were determined by HPLC using the internal standard method as described by Nobre et al [22]. When samples were obtained from media containing NaCl, enzymatic determinations were made instead.…”

“…Another agent with a recognised uncoupling e¡ect is ethanol. It is current practice [26,27] to use the inhibitory e¡ect of ethanol on uptake to distinguish between nonmediated and mediated substrate entry, the inhibitory effect being generally stronger on active transporters, which depend on pmf, than on equilibrating-type transporters as facilitated di¡usion [22,26,27,32]. The experiments were performed so as to allow the determination of the ethanol exponential inhibition constant (K i ).…”

XYLHencodes a xylose/H+symporter from the highly related yeast speciesDebaryomyces fabryiandDebaryomyces hansenii

“…The physiology of xylose transport has been assessed in several yeast species. A common pattern was reported in C. shehatae (Lucas & van Uden, 1986), S. stipitis (Kilian & van Uden, 1988;Does & Bisson, 1989), Rhodotorula glutinis (H€ ofer & Misra, 1978), P. heedii (Does & Bisson, 1989), C. utilis (Kilian et al, 1993), D. hansenii (Nobre et al, 1999), Kluyveromyces marxianus (Stambuk et al, 2003) and C. intermedia (G ardonyi et al, 2003). Under glucose repression, cells display a xylose/glucose low-affinity transporter operating by facilitated diffusion, while cells cultivated on xylose and/or glucose-starved display a high-affinity sugar/proton symporter.…”

“…Our group previously characterized the xylose transport mechanisms and regulation, on CCMI 941 yeast strain that consumes xylose very efficiently (Amaral-Colac ßo et al, 1989;Nobre et al, 1999) and that has been proposed for the industrial production of xylitol (Carvalheiro et al, 2006). This yeast, previously assigned as D. hansenii, was subsequently assigned as variety fabryi from D. hansenii.…”