Increased formate-dependent H-2 production from xylose in Enterobacter sp. CN1 transformed with a formate hydrogenlyase activator gene

摘要

Finding bacterial strains for effective hydrogen production and optimization of the fermentative conditions are two major approaches to promoting commercial application of bio-hydrogen. In the present study, we carried out experiments to examine factors that affected H-2 yield in Enterobacter sp. CN1. The result showed that H-2 could be produced from formate alone and the yields were positively correlated with formate concentrations. Moreover, the yield of H-2 from xylose was significantly increased in the presence of formate, revealing that formate is not only a good carbon source but also promotes H-2 production from xylose in strain CN1. The production of H-2 from formate was not affected by pH; however, H-2 production from xylose at pH 7 was higher than that at pH 6, no matter if formate is presence or absence in the medium. Further, H-2 production from pyruvate was inhibited completely when sodium hypophosphate (HPP) was present, but formate-dependent H-2 production was mostly not affected. In addition, H-2 production from glucose or xylose was dramatically reduced but sill detectable in the presence of HPP, suggesting that formate hydrogenlyase is the main pathway responsible for H-2 production from xylose in Enterobacter sp. CN1. To confirm the above hypothesis, the formate hydrogenlyase activator (fhlA) gene was cloned and over-expressed in strain CN1. Compared with the wild-type, recombinant CN1 strain increased H-2 production per gram of xylose and per gram of cells by 10.5% and 18.8%, respectively, in the presence of xylose.

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