Induction of Xylose Reductase and Xylitol Dehydrogenase Activities in Pachysolen tannophilus and Pichia stipitis on Mixed Sugars

Abstract

The induction of xylose reductase and xylitol dehydrogenase activities on mixed sugars was investigated in the yeasts Pachysolen tannophilus and Pichia stipitis. Enzyme activities induced on D-xylose served as the controls. In both yeasts, D-glucose, D-mannose, and 2-deoxyglucose inhibited enzyme induction by D-xylose to various degrees. Cellobiose, L-arabinose, and D-galactose were not inhibitory. In liquid batch culture, P. tannophilus utilized D-glucose and D-mannose rapidly and preferentially over D-xylose, while D-galactose consumption was poor and lagged behind that of the pentose sugar. In P. stipitis, all three hexoses were used preferentially over D-xylose. The results showed that the repressibility of xylose reductase and xylitol dehydrogenase may limit the potential of yeast fermentation of pentose sugars in hydrolysates of lignocellulosic substrates.

Fermentation of the Straw Material Paja Brava by the Yeast <i>Pichia stipitis</i> in a Simultaneous Saccharification and Fermentation Process

“…The con- version of cellobiose also increased in the fed-batch process, although to a lesser extent. The simultaneous assimilation of sugars suggest that the xylose-metabolizing enzymes, xylose reductase (XR) and xylitol dehydrogenase (XDH), were not repressed by cellobiose and arabinose, which is consistent with the report by Bicho et al [33] on induction of these enzymes in P. stipitis in mixed sugar solutions.…”

Mutants of the pentose‐fermenting yeast Pichia stipitis with improved tolerance to inhibitors in hardwood spent sulfite liquor

“…One of the problems associated with fermentation of mixed sugars in lignocellulosic hydrolyzates is glucose repression of xylose utilization, resulting in sequential glucose-xylose utilization (Bicho et al, 1988;Lee, 1992). While the P. stipitis mutants isolated in this study continued to exhibit a sequential pattern of glucose-xylose utilization (Fig.…”

“…However, wild-type (WT) strains of this yeast cannot utilize or ferment the pentoses in lignocellulosic hydrolysates to ethanol. Naturally occurring pentose-fermenting yeasts such as Pichia stipitis, Candida shehatae, and Pachysolen tannophilus ferment both glucose and xylose to ethanol (Bicho et al, 1988;Du Preez and Prior, 1985). In particular, strains of P. stipitis can convert xylose almost exclusively to ethanol with no other significant byproducts (Slininger et al, 1985).…”

“…In particular, strains of P. stipitis can convert xylose almost exclusively to ethanol with no other significant byproducts (Slininger et al, 1985). However, pentose-fermenting yeasts generally suffer from hexose repression (Bicho et al, 1988), low ethanol tolerance (Barbosa et al, 1990) and they perform poorly in the presence of hydrolysate inhibitors (Lohmeier-Vogel et al, 1998).…”

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

“…Plenty of yeasts consume xylose (Barnett et al, 2000), although only a few are able to ferment this pentose, namely Scheffersomyces stipitis (previously Pichia stipitis) and Candida shehatae (Dupreez et al, 1986), or Pachysolen tannophilus (Bicho et al, 1988). This is not the case for Saccharomyces cerevisiae.…”