Properties of Three Ferredoxins from the Photosynthetic Bacterium Rhodobacter Capsulatus: Studies on their Possible Role in Nitrogen Fixation

Abstract

Rhodobacter capsulatus is a facultative phototroph endowed with a very versatile metabolism. This bacterium is able to thrive under various conditions including fermentative, heterotrophic and autotrophic type of growth, in either light or darkness. It is able to metabolize various organic and inorganic nitrogen sources including molecular dinitrogen. These remarkable properties make such a microorganism a valuable tool for studies on nitrogen fixation and assimilation. Regulation of nitrogen fixation was investigated both at the enzymatic and genetic levels in R. capsulatus (reviewed in Vignais et al. 1985). Synthesis of nitrogenase, the enzyme which catalyzes N2-fixation, is repressed by NH4 + and O2 as in other diazotrophic bacteria (Hallenbeck et al. 1982 b). In addition, nitrogenase synthesis was found to be closely dependent on light intensity (Jouanneau et al. 1984, 1985). Besides, nitrogenase is subjected to a feedback inhibition by NH4 +. This short-term regulation involves the covalent modification by ADP-ribosylation of the component 2 of nitrogenase (Jouanneau et al. 1983,1989).