Nitrate Photo-Assimilation by the Phototrophic Bacterium Rhodopseudomonas capsulata EjFj

Rhodopseudomonas capsulata bacteria photo-assimilated nitrate under anaerobic condi­ tions, but were incapable of reducing it in the dark. The bacteria utilized dissolved N 2 as nitrogen source, but the growth in the presence of nitrate was 5-fold higher. Nitrite was excreted to the medium, but not stoichiometrically with respect to nitrate consumption. Nitrate reductase is particulate and used reduced viologens or flavins as electron donors for nitrate reduction. The enzyme was inhibited in vitro by KCN, NaN3, dithioerythritol and mercurials. Ammonia and other sources of reduced nitrogen repressed nitrate reductase synthesis.