Contrary to S. cerevisiae, P. stipitis is able to naturally utilize L-arabinose and/or D-xylose and efficiently ferments xylose to ethanol, being the gene donor of the xylose catabolic pathway successfully expressed in S. cerevisae. It has also been considered for fermentation of hemicellulose hydrolysates to ethanol [78-80]. Several auxotrophic mutants with higher fermentation capacities and improved xylose utilization have been developed in order to obtain suitable P. stipitis strains for further hemicellulose-to-ethanol metabolic engineering [78]. P. stipitis is, however, unable to grow anaerobically and is more sensitive to ethanol and inhibitors than S. cerevisiae. The S. cerevisiae gene that confers the ability to grow under anaerobiosis (URA1, encoding the dihydroorotate dehydrogenase) was successfully expressed in P. stipitis, allowing anaerobic fermentation of glucose to ethanol [170]. In addition, the disruption of the cytochrome c gene increased xylose fermentation and consequently, ethanol yield [169]. In an evolutionary engineering approach, P. stipitis was adapted in hemicellulose hydrolysate con­taining glucose, xylose, and arabinose, improving tolerance to acetic acid and pH [131]. In a CBP perspective, xylan conversion into ethanol was enhanced by the heterologous expression of fungal xylanases in P. Stipitis [38]. The recent progress in genomic and transcriptomic characterization of P. stipitis [80] opened new perspectives for metabolic engineering towards efficient hemicellulose fermentation.