Xylose and xylose/glucose co-fermentation by recombinant Saccharomyces cerevisiae strains expressing individual hexose transporters

• Published in: Enzyme and microbial technology 2014-09, Vol.63, p.13-20
• Main Authors: Gonçalves, Davi L., Matsushika, Akinori, de Sales, Belisa B., Goshima, Tetsuya, Bon, Elba P.S., Stambuk, Boris U.
• Format: Article
• Language: English
• Subjects: Aldehyde Reductase - genetics; Aldehyde Reductase - metabolism; Anaerobiosis; Bioethanol; D-Xylulose Reductase - genetics; D-Xylulose Reductase - metabolism; Ethanol - metabolism; Fermentation; Glucose - metabolism; Glucose/xylose co-fermentation; HXT transporters; Industrial Microbiology - methods; Monosaccharide Transport Proteins - deficiency; Monosaccharide Transport Proteins - genetics; Monosaccharide Transport Proteins - metabolism; Phosphotransferases (Alcohol Group Acceptor) - genetics; Phosphotransferases (Alcohol Group Acceptor) - metabolism; Recombinant Proteins - metabolism; Saccharomyces cerevisiae; Saccharomyces cerevisiae - enzymology; Saccharomyces cerevisiae - genetics; Saccharomyces cerevisiae Proteins - genetics; Saccharomyces cerevisiae Proteins - metabolism; Xylose - metabolism; Xylose fermentation
• ISSN: 0141-0229; 1879-0909
• DOI: 10.1016/j.enzmictec.2014.05.003

•The HXT1 permease allowed production of ethanol in xylose/glucose co-fermentations.•The HXT5 permease did not allow significant xylose uptake by the yeast cells.•The HXT2 permease allowed xylose or glucose uptake and fermentation with same rates.•The HXT7 permease allowed efficient fermentations, but preferred glucose over xylose.•HXT overexpression for bioethanol production should consider sugar syrup composition. Since the uptake of xylose is believed to be one of the rate-limiting steps for xylose ethanol fermentation by recombinant Saccharomyces cerevisiae strains, we transformed a hxt-null strain lacking the major hexose transporters (hxt1Δ-hxt7Δ and gal2Δ) with an integrative plasmid to overexpress the genes for xylose reductase (XYL1), xylitol dehydrogenase (XYL2) and xylulokinase (XKS1), and analyzed the impact that overexpression of the HXT1, HXT2, HXT5 or HXT7 permeases have in anaerobic batch fermentations using xylose, glucose, or xylose plus glucose as carbon sources. Our results revealed that the low-affinity HXT1 permease allowed the maximal consumption of sugars and ethanol production rates during xylose/glucose co-fermentations, but was incapable to allow xylose uptake when this sugar was the only carbon source. The moderately high-affinity HXT5 permease was a poor glucose transporter, and it also did not allow significant xylose uptake by the cells. The moderately high-affinity HXT2 permease allowed xylose uptake with the same rates as those observed during glucose consumption, even under co-fermentation conditions, but had the drawback of producing incomplete fermentations. Finally, the high-affinity HXT7 permease allowed efficient xylose fermentation, but during xylose/glucose co-fermentations this permease showed a clear preference for glucose. Thus, our results indicate that approaches to engineer S. cerevisiae HXT transporters to improve second generation bioethanol production need to consider the composition of the biomass sugar syrup, whereby the HXT1 transporter seems more suitable for hydrolysates containing xylose/glucose blends, whereas the HXT7 permease would be a better choice for xylose-enriched sugar streams.