In bacterial system, direct conversion of xylose to xylonic acid is mediated through NAD-dependent xylose dehydrogenase (xylB) and xylonolactonase (xylC) genes. Heterologous expression of these genes from Caulobacter crescentus into recombinant Corynebacterium glutamicum ATCC 13032 and C. glutamicum ATCC 31831 (with an innate pentose transporter, araE) resulted in an efficient bioconversion process to produce xylonic acid from xylose. Process parameters including the design of production medium was optimized using a statistical tool, Response Surface Methodology (RSM). Maximum xylonic acid of 56.32 g/L from 60 g/L xylose, i.e. about 76.67% of the maximum theoretical yield was obtained after 120 h fermentation from pure xylose with recombinant C. glutamicum ATCC 31831 containing the plasmid pVWEx1 xylB. Under the same condition, the production with recombinant C. glutamicum ATCC 13032 (with pVWEx1 xylB) was 50.66 g/L, i.e. 69% of the theoretical yield. There was no significant improvement in production with the simultaneous expression of xylB and xylC genes together indicating xylose dehydrogenase activity as one of the rate limiting factor in the bioconversion. Finally, proof of concept experiment in utilizing biomass derived pentose sugar, xylose, for xylonic acid production was also carried out and obtained 42.94 g/L xylonic acid from 60 g/L xylose. These results promise a significant value addition for the future bio refinery programs.

中文翻译：

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谷氨酸棒杆菌中木糖向木糖酸生物转化的基因的异源表达和生物过程的优化。

在细菌系统中，木糖直接转化为木糖酸是通过NAD依赖性木糖脱氢酶（xylB）和木糖醇内酯酶（xylC）基因介导的。这些基因从新月形杆菌到重组谷氨酸棒杆菌ATCC 13032和谷氨酸棒杆菌ATCC 31831（具有先天戊糖转运蛋白araE）的异源表达导致从木糖生产木糖酸的有效生物转化过程。使用统计工具“响应表面方法”（RSM）对包括生产介质设计在内的工艺参数进行了优化。用含有质粒pVWEx1 xylB的重组谷氨酸棒杆菌ATCC 31831从纯木糖发酵120小时后，从60g / L木糖中得到最大木糖醛酸56.32g / L，即最大理论产率的约76.67％。在相同条件下 重组谷氨酸棒杆菌ATCC 13032（带有pVWEx1 xylB）的产量为50.66 g / L，即理论产量的69％。xylB和xylC基因同时表达在一起，表明木糖脱氢酶活性是生物转化中的限速因子之一，生产没有明显改善。最后，还进行了利用生物质衍生的戊糖木糖生产木糖醛酸的概念实验，并从60 g / L木糖中得到42.94 g / L木糖酸。这些结果有望为未来的生物炼制计划带来巨大的附加值。xylB和xylC基因同时表达在一起，表明木糖脱氢酶活性是生物转化中的限速因子之一，生产没有明显改善。最后，还进行了利用生物质衍生的戊糖木糖生产木糖醛酸的概念实验，并从60 g / L木糖中得到42.94 g / L木糖酸。这些结果有望为未来的生物炼制计划带来巨大的附加值。xylB和xylC基因同时表达在一起，表明木糖脱氢酶活性是生物转化中的限速因子之一，生产没有明显改善。最后，还进行了利用生物质衍生的戊糖木糖生产木糖醛酸的概念实验，并从60 g / L木糖中得到42.94 g / L木糖酸。这些结果有望为未来的生物炼制计划带来巨大的附加值。