modC is part of a set of genes, modABC, which encode the bacterial molybdate ABC transporter. ModC comprises the ATPase. Of the three structural Mod proteins, ModC has received the least attention, believed to be little different from ATPases of other ABC complexes. However, findings of multiple copies of modC in A. vinelandii and identification of a potential molybdate-binding domain in the C-terminal of ModC may point to a more complex role. ORF10 is one of three copies of modC in A. vinelandii; atypically, ORF10 is not found with genes encoding the other ABC transporter components but is instead found as part of the nif gene cluster, encoding molybdenum nitrogenase. The role of ORF10 is investigated here via sequence analysis and comparison of growth of a ORF10- A. vinelandii strain with wild type growth. Findings imply ORF10 optimizes growth under conditions requiring nitrogenixation, specifically under those conditions where molybdate-availability is limited.

Hydrogen has an extensive potential as a clean and renewable energy source. Photosynthetic, non-sulphur, purple bacteria, Rhodobacter sphaeroides O.U.001 produces molecular hydrogen by nitrogenase enzyme. Nitrogenase enzyme is encoded by nifHDK genes and expression of the structural genes, nifHDK, is controlled by NifA which is encoded by nifA gene. The transcription of nifA is under the control of Ntr system and product of prrA gene. Relationship between the genes that have roles in nitrogenase synthesis should be understood well to increase biological hydrogen production. In this work, expression levels of nitrogenase encoding nifH and control genes nifA, prrA were examined at different physiological conditions. In addition to modifications in expression levels, changes in hydrogen production and growth capacity were also investigated in response to different concentrations of ammonium source, oxygen and different light intensities. In this study, it was found that increasing concentrations of ammonium chloride caused decrease in hydrogen production. Glutamate containing medium had the capacity for higher hydrogen production. The expression levels of nifH and nifA genes decreased with the increase in concentrations of ammonium chloride. There was a negative correlation between the expression levels of prrA gene and its target, nifA gene. Hydrogen production was observed even in aerobic conditions of the same media compositions. It was observed that different culture media had changing growth and hydrogen production capabilities at different light intensities. There was no direct proportion between the expression levels of nifH gene and amount of hydrogen at different light intensities.