The deletion of YLR042c improves ethanolic xylose fermentation by recombinant Saccharomyces cerevisiae

In a recent study combining transcriptome analyses of a number of recombinant laboratory and industrial S. cerevisiae strains with improved xylose utilization and their respective control strains, the ORF YLR042c was identified as a downregulated gene and it was shown that the gene deletion improved aerobic growth on xylose in the tested strain background. In the present study, the influence of deleting YLR042c on xylose fermentation was investigated in two different xylose-fermenting strains: TMB3001, which expresses genes from the initial xylose catabolizing pathway, including heterologous xylose reductase (XR) and xylitol dehydrogenase (XDH) and endogenous xylulokinase (XK); and TMB3057, which, in addition to the initial xylose catabolizing pathway, overexpresses the endogenous genes encoding the non-oxidative pentose phosphate pathway enzymes. The deletion of YLR042c led to improved aerobic growth on xylose in both strain backgrounds. However, the effect was more significant in the strain with the poorer growth rate on xylose (TMB3001). Under anaerobic conditions, the deletion of YLR042c increased the specific xylose consumption rate and the ethanol and xylitol yields. In strain TMB3057, xylose consumption was also improved at low concentrations and during co-fermentation of xylose and glucose. The effect of the gene deletion and overexpression was also tested for different carbon sources. Altogether, these results suggest that YLR042c influences xylose and the assimilation of carbon sources other than glucose, and that the effect could be at the level of sugar transport or sugar signalling.