Influence of Energy and Electron Availability on In Vivo Methane and Hydrogen Production by a Variant Molybdenum Nitrogenase

A variant form of Mo nitrogenase catalyzes the conversion of CO 2 and protons to the biofuels CH 4 and H 2 . A constant supply of electrons and ATP is needed to drive these reduction reactions. The bacterium R. palustris generates 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 CH 4 and H 2 production. 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 CH 4 produced by the variant nitrogenase in vivo was affected by electron availability much less than was the amount of H 2 produced. This study shows the nature of constraints on in vivo biofuel production by variant Mo nitrogenase.