Su Yi-Kai, Willis Laura B, Jeffries Thomas W
Department of Biological Systems Engineering, University of Wisconsin, Madison, Wisconsin; DOE Great Lakes Bioenergy Research Center, University of Wisconsin, Madison, 53703, Wisconsin.
Biotechnol Bioeng. 2015 Mar;112(3):457-69. doi: 10.1002/bit.25445.
Spathaspora passalidarum 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 S. passalidarum NN245 and Scheffersomyces (Pichia) stipitis 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 S. passalidarum 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 O2 /L h. Increasing the OTR to 4.27 mmol O2 /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. S. passalidarum secreted lower amounts of polyols compared to S. stipitis under most circumstances. In addition, the composition of polyols differed: S. passalidarum accumulated mostly xylitol and R,R-2,3-butanediol (BD) whereas S. stipitis accumulated mostly xylitol and ribitol when cultivated in xylose or a mixture of 12% xylose and 3% glucose. R,R-2,3-BD accumulation by S. passalidarum during xylose fermentation can be as much as four times of that by S. stipitis, and R,R-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.
嗜木生斯帕塔酵母NN245（NRRL - Y27907）是一种子囊菌酵母，其木糖发酵比葡萄糖发酵具有更高的比发酵速率。先前的研究表明，随着通气量降低，其木糖发酵能力增强而细胞产量降低。通气优化对于从木质纤维素水解物中最大化生物乙醇产量起着关键作用。在此，我们比较了嗜木生斯帕塔酵母NN245和树干毕赤酵母（Scheffersomyces）NRRL Y - 7124在四种不同通气条件下发酵15%葡萄糖、15%木糖或12%木糖加3%葡萄糖的动力学。嗜木生斯帕塔酵母的最大比发酵速率为0.153 g乙醇/g细胞干重·h，在氧气传递速率为2.47 mmol O2/L·h时，从150 g/L木糖的产率为0.448 g/g。将氧气传递速率提高到4.27 mmol O2/L·h，木糖乙醇产率从0.46降至0.42 g/g，同时体积乙醇生产率从0.52提高到0.8 g/L·h。两种酵母在木糖上生长时的细胞产量均低于在葡萄糖上生长时，乙醇产量则更高。两种菌株的乙酸积累量与通气量增加呈正相关。在大多数情况下，嗜木生斯帕塔酵母分泌的多元醇量低于树干毕赤酵母。此外，多元醇的组成不同：嗜木生斯帕塔酵母在木糖或12%木糖与3%葡萄糖的混合物中培养时，主要积累木糖醇和R,R - 2,3 - 丁二醇（BD），而树干毕赤酵母主要积累木糖醇和核糖醇。嗜木生斯帕塔酵母在木糖发酵过程中R,R - 2,3 - BD的积累量可达树干毕赤酵母的四倍，且R,R - 2,3 - BD也是仅次于木糖醇的最丰富副产物。讨论了两种酵母在不同通气条件下积累的多元醇比例以及这些观察结果对菌株和工艺工程的意义。
