Xylose metabolism was inhibited by ethanol: effects and an in situ removel process

Efficient utilization of xylose is critical for production of fuels and chemicals from biomass hydrolysate. Most microbes prefer glucose over xylose because of carbon catabolite repression. Using the engineered strain Saccharomyces cerevisiae W32N55, which can use xylose anaerobically, the effect of ethanol on xylose utilization was investigated. It was shown that xylose catabolism was significantly inhibited upon addition of ethanol, and xylose catabolism was resumed once ethanol was removed from the broth. It indicated that ethanol was an inhibitor for xylose catabolism. Based on these results, a fermentation- pervaporation coupling process was developed for cellulosic ethanol production. After in situ removal of ethanol, 150 g/L glucose and 31 g/L xylose from corn stover hydrolysate were consumed in 72 h, providing a total of 76 g/L ethanol and an over yield of 0.42 g/g. These results provide new insights into the xylose catabolism for efficient production of cellulosic ethanol.