Comparative metabolic profiling revealed limitations in xylose-fermenting yeast during co-fermentation of glucose and xylose in the presence of inhibitors.

During lignocellulosic ethanol fermentation, yeasts are exposed to various lignocellulose-derived inhibitors, which disrupt the efficiency of hexose and pentose co-fermentation. To understand the metabolic response of fermentation microbes to these inhibitors, a comparative metabolomic investigation was performed on a xylose-fermenting Saccharomyces cerevisiae 424A (LNH-ST) and its parental strain 4124 with and without three typical inhibitors (furfural, acetic acid, and phenol). Three traits were uncovered according to fermentation results. First, the growth of strain 424A (LNH-ST) was more sensitive to inhibitors than strain 4124. Through metabolomic analysis, the variance of trehalose, cadaverine, glutamate and g-aminobutyric acid (GABA) suggested that strain 424A (LNH-ST) had a lower capability to buffer redox changes caused by inhibitors. Second, lower ethanol yield in glucose and xylose co-fermentation than glucose fermentation was observed in strain 424A (LNH-ST), which was considered to be correlated with the generation of xylitol, as well as the reduced levels of lysine, glutamate, glycine and isoleucine in strain 424A (LNH-ST). Accumulation of glycerol, galactinol and mannitol was also observed in strain 424A (LNH-ST) during xylose fermentation. Third, xylose utilization of strain 424A (LNH-ST) was more significantly disturbed by inhibitors than glucose utilization. Through the analysis of fermentation and metabolomic results, it was suggested that xylose catabolism and energy supply, rather than xylose uptake, were the limiting steps in xylose utilization in the presence of inhibitors.