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Lignocellulosic biomass is an attractive sustainable platform for fuel ethanol production. Xylose is a second after glucose most abounded sugar in lignocellulosic hydrolysates. Effective conversion of xylose to ethanol is one of key prerequisite for the development of an efficient conversion of biomass to ethanol. Engineered Saccharomyces cerevisiae strains are able to xylose fermentation. However, the yield and productivities of xylose fermentation remains lower in comparison with glucose fermentation. In this work, we studied impact of transcription factors Znf1, Sip4, Adr1, Tup1, and Hap4 on xylose catabolism. We have isolated znf1Δ, adr1Δ, tup1Δ and hap4Δ mutants, and strains overexpressing SIP4, ADR1 and HAP4 genes on the background of xylose-fermenting strain of S. cerevisiae aiming to explore involvement of these transcription factors in regulation of xylose growth and fermentation. It was shown that hap4Δ reveal 1.8-fold increase of ethanol production from xylose as compared to that of parental strain. The hap4Δ mutant accumulates 10.38 g l -1 of ethanol with an overall ethanol yield reaching 0.41 g g -1 of consumed xylose. While the other constructed strains revealed a decrease in ethanol production from this pentose., (© 2021. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

Glucose is a preferred carbon source for most living organisms. The metabolism and regulation of glucose utilization are well studied mostly for Saccharomyces cerevisiae. Xylose is the main pentose sugar released from the lignocellulosic biomass, which has a high potential as a renewable feedstock for bioethanol production. The thermotolerant yeast Ogataea (Hansenula) polymorpha, in contrast to S. cerevisiae, is able to metabolize and ferment not only glucose but also xylose. However, in non-conventional yeasts, the regulation of glucose and xylose metabolism remains poorly understood. In this study, we characterize the role of transcriptional factors Mig1, Mig2, Tup1 and Hap4 in the natural xylose-fermenting yeast O. polymorpha. The deletion of MIG1 had no significant influence on ethanol production either from xylose or glucose, however the deletion of both MIG1 and MIG2 reduced the amount of ethanol produced from these sugars. The deletion of HAP4-A and TUP1 genes resulted in increased ethanol production from xylose. Inversely, the overexpression of HAP4-A and TUP1 genes reduced ethanol production during xylose alcoholic fermentation. Thus, HAP4-A and TUP1 are involved in repression of xylose metabolism and fermentation in yeast O. polymorpha and their deletion could be a viable strategy to improve ethanol production from this pentose., (© The Author(s) 2021. Published by Oxford University Press on behalf of FEMS.)

Xylose is a second-most abounded sugar after glucose in lignocellulosic hydrolysates and should be efficiently fermented for economically viable second-generation ethanol production. Despite significant progress in metabolic and evolutionary engineering, xylose fermentation rate of recombinant Saccharomyces cerevisiae remains lower than that for glucose. Our recent study demonstrated that peroxisome-deficient cells of yeast Ogataea polymorpha showed a decrease in ethanol production from xylose. In this work, we have studied the role of peroxisomes in xylose alcoholic fermentation in the engineered xylose-utilizing strain of S. cerevisiae. It was shown that peroxisome-less pex3Δ mutant possessed 1.5-fold decrease of ethanol production from xylose. We hypothesized that peroxisomal catalase Cta1 may have importance for hydrogen peroxide, the important component of reactive oxygen species, detoxification during xylose alcoholic fermentation. It was clearly shown that CTA1 deletion impaired ethanol production from xylose. It was found that enhancing the peroxisome population by modulation the peroxisomal biogenesis by overexpression of PEX34 activates xylose alcoholic fermentation., (© 2020 International Federation for Cell Biology.)