초록
<P><B>ABSTRACT</B></P><P><I>Spathaspora passalidarum</I> NN245 (NRRL‐Y27907) is an ascomycetous yeast that displays a higher specific fermentation rate with xylose than with glucose. Previous studies have shown that its capacity for xylose fermentation increases while cell yield decreases with decreasing aeration. Aeration optimization plays a crucial role in maximizing bioethanol production from lignocellulosic hydrolysates. Here, we compared the kinetics of <I>S. passalidarum</I> NN245 and <I>Scheffersomyces</I> (<I>Pichia</I>) <I>stipitis</I> NRRL Y‐7124 fermenting 15% glucose, 15% xylose, or 12% xylose plus 3% glucose under four different aeration conditions. The maximum specific fermentation rate for <I>S. passalidarum</I> was 0.153 g ethanol/g CDW · h with a yield of 0.448 g/g from 150 g/L xylose at an oxygen transfer rate of 2.47 mmol O<SUB>2</SUB>/L h. Increasing the OTR to 4.27 mmol O<SUB>2</SUB>/L h. decreased the ethanol yield from 0.46 to 0.42 g/g xylose while increasing volumetric ethanol productivity from 0.52 to 0.8 g/L h. Both yeasts had lower cells yields and higher ethanol yields when growing on xylose than when growing on glucose. Acetic acid accretions of both strains correlated positively with increasing aeration. <I>S. passalidarum</I> secreted lower amounts of polyols compared to <I>S. stipitis</I> under most circumstances. In addition, the composition of polyols differed: <I>S. passalidarum</I> accumulated mostly xylitol and <I>R,R‐</I>2,3‐butanediol (BD) whereas <I>S. stipitis</I> accumulated mostly xylitol and ribitol when cultivated in xylose or a mixture of 12% xylose and 3% glucose. <I>R,R</I>‐2,3‐BD accumulation by <I>S. passalidarum</I> during xylose fermentation can be as much as four times of that by <I>S. stipitis</I>, and <I>R,R‐</I>2,3‐BD is also the most abundant byproduct after xylitol. The ratios of polyols accumulated by the two species under different aeration conditions and the implications of these observations for strain and process engineering are discussed. Biotechnol. Bioeng. 2015;112: 457–469. © 2014 Wiley Periodicals, Inc.</P>