The XylR variant (R121C and P363S) releases arabinose-induced catabolite repression on xylose fermentation and enhances coutilization of lignocellulosic sugar mixtures

Microbial production of fuels and chemicals from lignocellulosic biomass provides a promising alternative to conventional petroleum-derived routes. However, the heterogeneous sugar composition of lignocellulose prevents efficient microbial sugar co-fermentation due to carbon catabolite repression, which negatively affects production metrics. We previously discovered that a mutant copy of the transcriptional regulator XylR (P363S and R121C; denoted as XylR*) in Escherichia coli has a higher DNA-binding affinity than wild-type XylR, leading to a stronger activation of the d-xylose catabolic genes and a release from glucose-induced repression on xylose fermentation. Here, we showed that XylR* also releases l-arabinose-induced repression on xylose fermentation through altered transcriptional control, enhancing co-fermentation of arabinose-xylose sugar mixtures in wild-type E. coli. Integrating xylR* into an ethanologenic E. coli resulted in the coutilization of 96% of the provided glucose-xylose-arabinose mixtures (120 g/L total sugars supplied) with an ethanol yield higher than 90% of the theoretical maximum by simple batch fermentations.