Regulation of Inorganic Nitrogen Metabolism in the Phototrophic Bacterium Rhodobacter Capsulatus E1F1

Abstract

The phototrophic bacterium Rhodobacter capsulatus E1F1 utilizes oxidized, inorganic nitrogen compounds such as dinitrogen, nitrate or nitrite, as well as reduced nitrogen sources such as amino acids, urea or ammonium for phototrophic growth. Although nitrogen fixation is wide-spread among Rhodospirillaceae, only few strains are able to reduce and/or assimilate nitrate (Ferguson et al. 1987). R. capsulatus E1F1 reduces nitrate (Moreno-Vivian et al. 1982) and nitrite (Kerber et al. 1981) to ammonium only under anaerobic conditions in the light and exhibits an ammonium-sensitive nitrate reductase (Moreno-Vivian et al. 1982). Ammonium is also the end product of nitrogen fixation, a process regulated by light intensity, nitrogen compounds and oxygen. In R. capsulatus E1F1, assimilation of ammonium derived from nitrate or dinitrogen reduction takes place mainly by the GS/GOGAT cycle (Moreno-Vivian et al. 1983), and the nitrogen flux through this pathway is regulated at the level of both glutamine synthetase activity (Caballero et al. 1985) and synthesis (Caballero et al. 1989 b).