초록
<P><B>Background</B></P><P>Understanding the effects of oxygen levels on yeast xylose metabolism would benefit ethanol production. In this work, xylose fermentative capacity of <I>Scheffersomyces stipitis</I>, <I>Spathaspora passalidarum</I>, <I>Spathaspora arborariae</I> and <I>Candida tenuis</I> was systematically compared under aerobic, oxygen-limited and anaerobic conditions.</P><P><B>Results</B></P><P>Fermentative performances of the four yeasts were greatly influenced by oxygen availability. <I>S. stipitis</I> and <I>S. passalidarum</I> showed the highest ethanol yields (above 0.44 g g<SUP>−1</SUP>) under oxygen limitation. However, <I>S. passalidarum</I> produced 1.5 times more ethanol than <I>S. stipitis</I> under anaerobiosis. While <I>C. tenuis</I> showed the lowest xylose consumption rate and incapacity to produce ethanol, <I>S. arborariae</I> showed an intermediate fermentative performance among the yeasts. NAD(P)H xylose reductase (XR) activity in crude cell extracts correlated with xylose consumption rates and ethanol production.</P><P><B>Conclusions</B></P><P>Overall, the present work demonstrates that the availability of oxygen influences the production of ethanol by yeasts and indicates that the NADH-dependent XR activity is a limiting step on the xylose metabolism. <I>S. stipitis</I> and <I>S. passalidarum</I> have the greatest potential for ethanol production from xylose. Both yeasts showed similar ethanol yields near theoretical under oxygen-limited condition. Besides that, <I>S. passalidarum</I> showed the best xylose consumption and ethanol production under anaerobiosis.</P>