Influence of Energy and Electron Availability on In Vivo Methane and Hydrogen Production by a Variant Molybdenum Nitrogenase
ABSTRACT The anoxygenic phototrophic bacteriumRhodopseudomonas palustrisproduces methane (CH4) from carbon dioxide (CO2) and hydrogen (H2) from protons (H+) when it expresses a variant form of molybdenum (Mo) nitrogenase that has two amino acid substitutions near its active site. We examined the influence of light energy and electron availability onin vivoproduction of these biofuels. Nitrogenase activity requires large amounts of ATP, and cells exposed to increasing light intensities produced increasing amounts of CH4and H2. As expected for a phototroph, intracellular ATP increased with increasing light intensity, but there was only a loose correlation between ATP content and CH4and H2production. There was a much stronger correlation between decreased intracellular ADP and increased gas production with increased light intensity, suggesting that the rate-limiting step for CH4and H2production byR. palustrisis inhibition of nitrogenase by ADP. Increasing the amounts of electrons available to nitrogenase by providing cells with organic alcohols, using nongrowing cells, blocking electrons from entering the Calvin cycle, or blocking H2uptake resulted in higher yields of H2and, in some cases, CH4. Our results provide a more complete understanding of the constraints on nitrogenase-based production of biofuels. IMPORTANCEA variant form of Mo nitrogenase catalyzes the conversion of CO2and protons to the biofuels CH4and H2. A constant supply of electrons and ATP is needed to drive these reduction reactions. The bacteriumR. palustrisgenerates ATP from light and has a versatile metabolism that makes it ideal for manipulating electron availability intracellularly. We therefore explored its potential as a biocatalyst for CH4and H2production. We found that intracellular ADP had a major effect on biofuel production, more pronounced than the effect caused by ATP. This is probably due to inhibition of nitrogenase activity by ADP. In general, the amount of CH4produced by the variant nitrogenasein vivowas affected by electron availability much less than was the amount of H2produced. This study shows the nature of constraints onin vivobiofuel production by variant Mo nitrogenase.
- Research Organization:
- Energy Frontier Research Centers (EFRC) (United States). Center for Biological Electron Transfer and Catalysis (BETCy); Montana State Univ., Bozeman, MT (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES)
- DOE Contract Number:
- SC0012518
- OSTI ID:
- 1566725
- Journal Information:
- Applied and Environmental Microbiology, Vol. 85, Issue 9; ISSN 0099-2240
- Publisher:
- American Society for Microbiology
- Country of Publication:
- United States
- Language:
- English
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