Lignocellulosic feedstocks are considered to be of great economic and environmental significance for future biotechnological production processes. For cost-effective and efficient industrial processes, complete and fast conversion of all sugars derived from these feedstocks is required. Hence, simultaneous or fast sequential fermentation of sugars would greatly contribute to the efficiency of production processes. One of the main challenges emerging from the use of lignocellulosics for the production of ethanol by the yeast Saccharomyces cerevisiae is efficient fermentation of D-xylose and L-arabinose, as these sugars cannot be used by natural S. cerevisiae strains. In this study, we present the first engineered S. cerevisiae strain (IMS0003), capable of fermenting mixtures of glucose, xylose and arabinose at a high ethanol yield of 0.43 g g(-1) of total sugar, without formation of the side-products xylitol and arabinitol. Kinetics of anaerobic fermentation of glucose-xylose-arabinose mixtures were greatly improved by the application of a novel evolutionary engineering strategy. The strategy encompassed a regime of repeated batch cultivation with repeated cycles of consecutive growth in three different medium compositions (glucose-xylose-arabinose, xylose-arabinose and only arabinose) and allowed for the rapid selection of an evolved strain (IMS0010) exhibiting improved specific consumption rates for xylose and arabinose. This evolution strategy led to a 40 % reduction of the time required to completely ferment a mixture of 30 g l(-1) glucose, 15 g l(-1) xylose and 15 g l(-1) arabinose.
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