Xylitol Production by Genetically Engineered Trichoderma reesei Strains Using Barley Straw as Feedstock

Xylitol, a naturally occurring five-carbon sugar alcohol derived from d-xylose, is currently in high demand by industries. Trichoderma reesei, a prolific industrial cellulase and hemicellulase producing fungus, is able to selectively use d-xylose from hemicelluloses for xylitol production. The xylitol production by T. reesei can be enhanced by genetic engineering of blocking further xylitol metabolism in the d-xylose pathway. We have used two different T. reesei strains which are impaired in the further metabolism of xylitol including a single mutant in which the xylitol dehydrogenase gene was deleted (?xdh1) and a double mutant where additionally l-arabinitol-4-dehydrogenase, an enzyme which can partially compensate for xylitol dehydrogenase function, was deleted (?lad1?xdh1). Barely straw was first pretreated using NaOH and Organosolv pretreatment methods. The highest xylitol production of 6.1 and 13.22 g/L was obtained using medium supplemented with 2 % Organosolv-pretreated barley straw and 2 % d-xylose by the ?xdh1 and ?lad1?xdh1 strains, respectively.