Effects of aeration on growth, ethanol and polyol accumulation by Spathaspora passalidarum NRRL Y‐27907 and Scheffersomyces stipitis NRRL Y‐7124

Abstract

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.

Fermentation strategy for second generation ethanol production from sugarcane bagasse hydrolyzate by Spathaspora passalidarum and Scheffersomyces stipitis

“…It is noteworthy that ethanol concentration was not higher than 23.3 g · L −1 due to sugar availability during fermentation. In the literature, Su et al () presents results of 60 g · L −1 of ethanol for the fermentation of a mixture of xylose and glucose by S. passalidarum . It is important emphasize that low concentrations of ethanol were obtained in the present work, and this is an important parameter for process viability.…”

“…One challenge for ethanol production from xylose by wild pentose fermenting yeasts is the control of oxygen supply to maximize ethanol production. Excess of oxygen leads to an aerobic cell growth and low ethanol yield; on the other hand, insufficient oxygen supply decreases the rate of fermentation, increases xylitol accumulation, and decrease ethanol productivity (Su et al, ). This control is difficult to achieve.…”

“…There are few results reported for S. passalidarum xylose fermentation on literature. According to Table , Su et al () have used glucose and xylose in flasks fermentations to produce ethanol by S. passalidarum Y‐27907 and obtained 58.3 g L −1 of ethanol, 0.42 g g −1 of conversion yield and 0.65 g L −1 h −1 of productivity. Hou, have worked with S. passalidarum MYA‐4345 in a fermentation using flasks with glucose and xylose as carbon sources, and obtained 25 g L −1 of ethanol, 0.41 g g −1 of conversion yield and 1.04 g L −1 h −1 for productivity.…”

Ethanol production improvement driven by genome-scale metabolic modeling and sensitivity analysis in Scheffersomyces stipitis

“…On the other hand, [23] reported an OTR of 1.8 mmol O 2 L −1 ⋅h −1 as optimal to reach a yield of 0.40 g⋅g −1 . [28] suggested an OTR range between 2.5 and 4.7 mmol O 2 L −1 ⋅h −1 to achieve a yield of 0.39 g⋅g −1 . In the present work rotenone addition allowed to increase yield from 0.16 g⋅g −1 to 0.20 g⋅g −1 at an OTR of 5.857 mmol O 2 L −1 ⋅h −1 and from 0.32 g⋅g −1 to 0.38 g⋅g −1 at an OTR of 3.514 mmol O 2 L −1 ⋅h −1 .…”

“…Culture conditions associated to high yield in S. stipitis are in a narrow range of oxygen concentrations, so that an effective control of oxygen supply is required [22–28]. S. stipitis has the proton translocating NADH dehydrogenase complex I (NDH1) and an alternative oxidase (AOX) in the respiratory chain, both absent in the Crabtree-positive yeast Saccharomyces cerevisiae [29].…”