Increased formate-dependent H2 production from xylose in Enterobacter sp. CN1 transformed with a formate hydrogenlyase activator gene

Abstract

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 H2 yield in Enterobacter sp. CN1. The result showed that H2 could be produced from formate alone and the yields were positively correlated with formate concentrations. Moreover, the yield of H2 from xylose was significantly increased in the presence of formate, revealing that formate is not only a good carbon source but also promotes H2 production from xylose in strain CN1. The production of H2 from formate was not affected by pH; however, H2 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, H2 production from pyruvate was inhibited completely when sodium hypophosphate (HPP) was present, but formate-dependent H2 production was mostly not affected. In addition, H2 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 H2 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 H2 production per gram of xylose and per gram of cells by 10.5% and 18.8%, respectively, in the presence of xylose.