Lignocellulosic material is mainly composed of cellulose, hemicellulose and lignin, where hemicellulose is a heteropolymer of hexoses and pentoses (xylose and arabinose). Baker’s yeast Saccharomyces cerevisiae can rapidly convert hexose sugars to ethanol with high yield and high productivity. In addition, it displays a good tolerance to several fermentation-inhibiting compounds present in lignocellulosic derived media. However, S. cerevisiae is not able to utilize pentose sugars, which may constitute a significant portion of the lignocellulosic feedstock.

Since optimal process economy demands exhaustive substrate utilization, the feasibility of the forthcoming switch from oil- to biomass-derived raw materials for the fabrication of fuels and chemicals is strongly dependent on the development of a fermenting micro-organism with a broad range of substrates. Construction of a substrate-broadened S. cerevisiae strain entails the introduction of heterologous genes encoding D-xylose and L-arabinose metabolizing enzymes, respectively.

Essentially, two different pathways are available in nature for the catabolism of C5 aldoses: isomerization based pathways and reduction/oxidation based pathways and several metabolic engineering studies showed that their introduction in yeast allows xylose and arabinose utilization to different extent.

For the present study, mixed sugars fermenting S. cerevisiae strains were constructed by combining optimized xylose and arabinose utilisation pathways. Comparative evaluation of the different strains capacity of aerobic growth on pentose sugars is presented, as well as substrate consumption rates and products distribution in anaerobic mixed sugars fermentation.