| As a kind of important chemical raw material, 2,3-butanediol has been widely used in many fields including food, medicine, chemical industries and aerospace industry.Microbiological production of 2,3-butanediol offers a cheaper and environmentally friendly method than traditional synthesis, which can utilize the cheap lignocellulose biomass instead of fossil oil. It is accord with the demand of sustainable development. As xylose is the only monosaccharide less than glucose in lignocellulose hydrolyzate, increasing the utilization rate of xylose not only can improve the conversion rate of raw materials but also can relieve the inhibition of xylose on hydrolases and reduce the production cost of 2,3-butanediol. By studying the effects of different xylose transporters and genes related to xylose metabolism on the growth of Enterobacter cloacae, xylose utilization and 2,3-butanediol production, the aim of this study was to improve the utilization rate of xylose and relieve the inhibition of glucose. The effects of different xylose transporters and genes related to xylose metabolism on the growth of Enterobacter cloacae, xylose utilization and 2,3-butanediol were studied, aiming to improve the utilization rate of xylose and relieve the inhibition of glucose.We tried to increase the specifiity transport of xylose by overexpressing different kind of sugar transporters including xylose ABC transporter protein xylFGH, arabinose transporter araE, proton-linked symporters xylE and galactose transporter gatC. The growth rate of the mutant strains was slightly decreased compared with the original strain and the utilization rate of xylose was lower than that of the original strain in the medium with xylose as a sole carbon source, but the production of xylose utilization rate and 2,3-butanediol were higher than the original strain in the fermentation medium with 30 g/L glucose and 30 g/L xylose, especially 1011-xylE of which increased by 50.6% and 18.4%compared with the original strain. The production of 2,3-butanediol of 1011-xylE was increased by 18.6% than the original strain in the medium with 50 g/L xylose.By expressing the genes related to xylose metabolism xylAK (xylose isomerase and xylulokinase), rperpiA (D-ribulose-5-phosphate epimerase and ribose-5-phosphate isomerase ) and taltkt (transaldolase and transketolase) we contructed 1011-xylAK?1011-rperpiA and1011-taltkt. The results showed that when xylose was sole carbon source,the over expression of xylose metabolic genes on the growth of several strains and xylose utilization were not promoted, but 2,3- butanediol production has increased, the most significant increase is 1011-taltkt with 50g/L xylose ,which 2,3- butanediol production was 20.1% higher than the original strain; when carbon source was glucose and xylose, rate of xylose utilization of 1011-xylAK and 1011-taltkt were 18.7% and 6.7% higher than the original strain, 2,3- butanediol yield increased 18.3% and 6.1% than the original strain, in different medium xylose utilization rate and 2,3- butanediol yield of 1011-rperpiA were lower than that of the original strain.Thus, by overpress genes about xylose transport and xylose metabolic genes in Enterobacter cloacae, we could relieve the inhibition of glucose utilization of in a certain extent, and improve the 2,3- butanediol yield and conversion rate. Therefore, this study constructed and overexpressed ABC xylose transporter transporter encoding gene xylFGH and xylose isomerase and xylulokinase gene encoding xylAK mutant strain 1011-xylFGHAK. When 1011-xylFGHAK was fermented with 50 g/L xylose, the utilization rate of xylose was lower than the original strain, but 2,3-butanediol was 20.9%higher , and was higher than 1011-xylFGH and 1011-xylAK. The utilization rate of xylose was 26.2% higher than the original strain when fermented with mixed carbon source,slightly higher than 1011-xylFGH and 1011-xylAK, but the yield of 2,3-butanediol was not significantly improved. |
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