(588d) Quantification of [Fe-Fe]-Hydrogenase, MrcA and FTHFS Gene In Mixed Anaerobic Cultures During Dark Hydrogen Fermentation

Energy security, climatic change and decreasing fossil fuel inventories are major issues driving researchers to develop technologies to produce cheap and dependable energy supplies. Hydrogen (H2) is a promising potential energy carrier for meeting future energy needs because it is eco-friendly, it has a high heating value (2.75 times higher energy content than hydrocarbon fuels) and it can be converted into electricity via fuel cells (Benemann, 1996; Momirlan and Vezrioglu, 2002). Currently, H2 is mainly produced from fossil fuel-based feedstock (Oil/naptha reforming, coal gasfication, methane steam reforming etc.,) chemicals because many commercial petrochemical processes are cost effective (Ewan and Allen, 2005). However, the dark fermentation process is emerging as a practical route for producing H2 because of fast reaction rates, technical simplicity and less area (1-5%)  requirements compared to the direct photolysis or indirect photolysis or photo fermentation (Levin et al., 2004; Li and Fang 2007).

The successful operation of the dark fermentation process requires a good understanding of how mixed microbial cultures behave under a variety of operating conditions. Identifying microbial communities can provide descriptions of the interaction between different groups; however, this approach may not provide sufficient information about the function of the communities. Noticeable changes in the microbial community composition within the H2 fermenting reactor is expected during operation. Quantifying the gene expression and monitoring fluctuations within the community structure will provide an understanding of the changes linked to the operation of bioreactors. This approach can possibly serve as a rapid tool for bioprocess monitoring.

In the present study, genes responsible for H2 production and H2 consumption were monitored as a means of establishing changes within the microbial community structure. The Fe-Fe hydrogenase gene is monitored because it is related to H2 production. Methanogens and acetogens are major H2 consumers and monitoring includes examination of the McrA gene and formyltetrahydrofolate synthetase (FTHFS) gene, respectively. A monitoring protocol for three different sources of cultures (A, B and C) at pH 5.5 and 37oC was developed using qRT-PCR. Terminal Restriction Fragment Length Polymorphism (T-RFLP) analysis was also performed to characterize changes in the community. The results indicated that the expression levels of [Fe-Fe]-hydrogenase, MrcA and FTHFS gene varied with the culture source. The [Fe-Fe]-hydrogenase gene expression was shown to correlate with H2 production. Increasing MrcA expression as well as increasing FTHFS and [Fe-Fe]-hydrogenase activity was correlated with low H2 yields of approximately 1.65±0.25 mol.mol-1 glucose in culture B. In comparison, cultures A and C with lower FTFHS and higher [Fe-Fe]-hydrogenase activities had higher H2 yields of 2.4±0.12 and 2.5±0.23 mol.mol-1 glucose, respectively. This data clearly suggest that monitoring the [Fe-Fe]-hydrogenase gene alone is insufficient to gain an understanding of how mixed cultures function and genes related to H2-consumers (MrcA and FTHFS) should be monitored and down regulated to achieve higher H2 yields.

References

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Ewan, B.C.R., Allen, R.W.K. 2005. A figure of merit assessment of the routes to hydrogen. Int. J. Hydrogen Energ. 30 (8), 809-819.

Levin, D.B., Pitt, L., Love, M. 2004. Biohydrogen production: prospects and limitations to practical application. Int. J. Hydrogen Energ. 29 (2), 173-185.

Li. C., Fang, H.H.P. 2007. Fermentative hydrogen production from wastewater and solid wastes by mixed cultures. Crit. Rev. Env. Sci. Tec. 37 (1), 1-39.

Momirlan, M., Veziroglu, T.N. 2002. Current status of hydrogen energy. Renew. Sust. Energ. Rev. 6 (1-2), 141-179.