tailieunhanh - Báo cáo hóa học: "A mutated xylose reductase increases bioethanol production more than a glucose/xylose facilitator in simultaneous fermentation and co-fermentation of wheat straw"

Tuyển tập báo cáo các nghiên cứu khoa học quốc tế ngành hóa học dành cho các bạn yêu hóa học tham khảo đề tài: A mutated xylose reductase increases bioethanol production more than a glucose/xylose facilitator in simultaneous fermentation and co-fermentation of wheat straw | Olofsson et al. AMB Express 2011 1 4 http content 1 1 4 o AMB Express a SpringerOpen Journal ORIGINAL ARTICLE Open Access A mutated xylose reductase increases bioethanol production more than a glucose xylose facilitator in simultaneous fermentation and co-fermentation of wheat straw Kim Olofsson1 David Runquist2 3 Barbel Hahn-Hagerdal2 Gunnar Lidén1 Abstract Genetically engineered Saccharomyces cerevisiae strains are able to ferment xylose present in lignocellulosic biomass. However better xylose fermenting strains are required to reach complete xylose uptake in simultaneous saccharification and co-fermentation SSCF of lignocellulosic hydrolyzates. In the current study haploid Saccharomyces cerevisiae strains expressing a heterologous xylose pathway including either the native xylose reductase XR from P. stipitis a mutated variant of XR mXR with altered co-factor preference a glucose xylose facilitator Gxf1 from Candida intermedia or both mXR and Gxf1 were assessed in SSCF of acid-pretreated nondetoxified wheat straw. The xylose conversion in SSCF was doubled with the S. cerevisiae strain expressing mXR compared to the isogenic strain expressing the native XR converting 76 and 38 respectively. The xylitol yield was less than half using mXR in comparison with the native variant. As a result of this the ethanol yield increased from to g g-1 when the native XR was replaced by mXR. In contrast the expression of Gxf1 only slightly increased the xylose uptake and did not increase the ethanol production. The results suggest that ethanolic xylose fermentation under SSCF conditions is controlled primarily by the XR activity and to a much lesser extent by xylose transport. Introduction The yeast Saccharomyces cerevisiae has been extensively engineered for ethanolic fermentation of the pentose sugar xylose either by introducing genes encoding xylose reductase XR and xylitol dehydrogenase XDH or by introducing the gene encoding xylose isomerase XI