Abstract
BackgroundXylitol accumulation is a major barrier for efficient ethanol production through heterologous xylose reductase-xylitol dehydrogenase (XR-XDH) pathway in recombinant Saccharomyces cerevisiae. Mutated NADH-preferring XR is usually employed to alleviate xylitol accumulation. However, it remains unclear how mutated XR affects the metabolic network for xylose metabolism. In this study, haploid and diploid strains were employed to investigate the transcriptional responses to changes in cofactor preference of XR through RNA-seq analysis during xylose fermentation.ResultsFor the haploid strains, genes involved in xylose-assimilation (XYL1, XYL2, XKS1), glycolysis, and alcohol fermentation had higher transcript levels in response to mutated XR, which was consistent with the improved xylose consumption rate and ethanol yield. For the diploid strains, genes related to protein biosynthesis were upregulated while genes involved in glyoxylate shunt were downregulated in response to mutated XR, which might contribute to the improved yields of biomass and ethanol. When comparing the diploids with the haploids, genes involved in glycolysis and MAPK signaling pathway were significantly downregulated, while oxidative stress related transcription factors (TFs) were significantly upregulated, irrespective of the cofactor preference of XR.ConclusionsOur results not only revealed the differences in transcriptional responses of the diploid and haploid strains to mutated XR, but also provided underlying basis for better understanding the differences in xylose metabolism between the diploid and haploid strains.
Highlights
Xylitol accumulation is a major barrier for efficient ethanol production through heterologous xylose reductase-xylitol dehydrogenase (XR-Xylitol dehydrogenase (XDH)) pathway in recombinant Saccharomyces cerevisiae
The NADPH/ NADH ratios of HX62W and B were greater than 1, while those of HX57D and A were less than 1, which demonstrated that the cofactor preference of Xylose reductase (XR)(K270R/N272D) was altered from NADPH to NADH
The higher activities of both XR and XDH in the haploid strains might contribute to the improved xylose utilization, which was consistent with previous studies [22, 23]
Summary
Xylitol accumulation is a major barrier for efficient ethanol production through heterologous xylose reductase-xylitol dehydrogenase (XR-XDH) pathway in recombinant Saccharomyces cerevisiae. Mutated NADH-pre‐ ferring XR is usually employed to alleviate xylitol accumulation. It remains unclear how mutated XR affects the metabolic network for xylose metabolism. Haploid and diploid strains were employed to investi‐ gate the transcriptional responses to changes in cofactor preference of XR through RNA-seq analysis during xylose fermentation. Xie et al Microb Cell Fact (2020) 19:211 and the native host metabolism [8, 9], but how mutated XR affects the xylose metabolism remains unclear. Several studies have reported that ploidy changes have a notable effect on stress tolerance and ethanol productivity when fermenting glucose [15,16,17]. Metabolomic and transcriptomic analyses have been carried out to compare diploid with haploid during glucose fermentation [18, 19], but the molecular basis for the distinct xylose fermentation capability of haploid and diploid strains remains obscure
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