代谢改造热带假丝酵母发酵木糖母液生产木糖醇

Metabolic Engineering of Candida tropicalis for Xyltiol Production from Xylose Mother Liquor

木糖醇是一种在食品、医药、轻工等领域具有广泛用途的多元醇,目前主要通过酸水解木聚糖获得木糖并进一步化学催化加氢方法制备。提取木糖过程中会产生大量的木糖母液副产物,其中含有一定浓度的葡萄糖、木糖、阿拉伯糖等碳源,以及少量的糠醛、四氢呋喃等物质。研究微生物转化木糖母液生产高附加值化学品不仅能够提高木糖母液的利用价值,而且能够减少环境污染。热带假丝酵母不仅能够利用葡萄糖,也具有高效的木糖代谢途径。首先利用代谢工程技术删除了热带假丝酵母菌株的木糖醇脱氢酶基因,获得能够转化木糖积累木糖醇的突变株。在此基础上,评价了突变株在木糖母液培养基中的发酵性能。通过单因素优化实验确定了突变株发酵生产木糖醇较优的发酵工艺:培养基组成为木糖母液300g/L,玉米浆5g/L;最佳发酵条件为:发酵温度35℃,初始p H为5.0,接种量15%,200r/min摇床培养140h。利用优化后的发酵工艺,木糖醇产量达到83.01g/L。初步建立了转化木糖母液生产木糖醇的工艺,为进一步利用木糖母液奠定了基础。

As one of polyol, xylitol has been extensively used in the food, pharmaceutical and other light industries. Presently, xylitol is produced by the reduction of D-xylose derived from hemicellulosic hydrolysate in the presence of Raney nickel catalysts. In the process of extracting xylose, a large amount of xylose mother liquor as by-product will be generated. Xylose mother liquor contains in a certain concentration of glucose, xylose, arabinose and other carbon sources, and a small amount of furfural, tetrahydrofuran and other substances. Production of biochemical from xylose mother liquor via microbial transformation can improve economic value of xylose mother liquor and reduce the environmental pollution. Candida tropicalis can not only use glucose, but also has a highly efficient xylose metabolic pathway. Two allelic genes of xylitol dehydrogenase gene from C. tropicalis was deleted by genetic technique, and the resulting mutant strain was obtained, which can not use xylitol as carbon source. The fermentation performance of the mutant in xylose mother liquor medium was evaluated. The fermentation conditions of xylitol fermentation process was optimized. The optimal fermentation conditions were as follows： 300g/L xylose mother liquor, 5g/L corn steep liquor, fermentation temperature 35℃, initial pH 5. 0, inoculate volume 15%, under 200r/min for 140h. Using the optimized fermentation process, xylitol yield reached 83.01g/L.