NITROGEN FIXATION BY PHOTOSYNTHETIC BACTERIA

Abstract

Previous research by the Wisconsin group had suggested a possible role of hydrogenase in biological N fixation, a view strengthened by the recent discovery of Kamen and Gest (Science 109: 560. 1949) that Rhodospirillum rubrum, a purple nonsulfur photo-synthetic bacterium, fixes molecular nitrogen. The critical points of the finding have been fully confirmed: (a) that R. rubrum does fix No and that the fixation is associated with photoreduction of CO2; (b) that evolution of H2 by R. rubrum is inhibited by N2. On the basis of these results it was predicted that other photo-synthetic bacteria and possibly other organisms that contain hydrogenase may fix N2. Previous tests with Escherichia coli, Proteus vulgarls and Scenedesmus (alga with hydrogenase) had been negative. In a note added to the proof it was announced that spp. of the green sulfur photosynthetic bacteria (Chloro-bacterium) and the purple sulfur photosynthetic bacteria (Chromatium) had given positive results in preliminary N2-fixing expts.