Induction of Xylose Reductase and Xylitol Dehydrogenase Activities in Pachysolen tannophilus and Pichia stipitis on Mixed Sugars |
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Authors: | Bicho Paul A Runnals P Lynn Cunningham J Douglas Lee Hung |
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Institution: | Department of Environmental Biology, University of Guelph, Guelph, Ontario, Canada N1G 2W1. |
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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. |
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