title: Rhizobium sp. strain ORS571 ammonium assimilation and nitrogen fixation.
abstract: Among rhizobia studied, Rhizobium sp. strain ORS571 alone grew unambiguously on N2 as sole N source. In ORS571 , only the glutamine synthetase (GS)-glutamate synthase ( GOGAT ) pathway assimilated ammonium. However, ORS571 exhibited two unique physiological aspects of this pathway: ORS571 had only GS I, whereas all other Rhizobiaceae studied had both GS I and GS II, and both NADPH- and NADH-dependent GOGAT activities were present. ORS571 GS-affected and NADPH- GOGAT -affected mutant strains were defective in both ammonium assimilation (Asm-) and N2 fixation (Nif-) in culture and in planta ; NADH- GOGAT mutants were Asm- but Nif+. "Bacteroid" GS activity was essentially nil, suggesting symbiotic ammonium export. Physiological studies on effects of glutamine, ammonium, methionine sulfoximine, and diazo-oxo-norleucine on nitrogenase induction in culture implied a regulatory role for the intracellular glutamine pool.
mesh_terms: D000641:Ammonia / Q000378:metabolism*; D005970:Glutamate Synthase / Q000378:metabolism*; D005974:Glutamate-Ammonia Ligase / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009154:Mutation; D009586:Nitrogen Fixation; D009713:Nucleotidyltransferases / Q000378:metabolism; D012231:Rhizobium / Q000235:genetics / Q000378:metabolism*; D013045:Species Specificity; D000637:Transaminases / Q000378:metabolism*
chemical_list: D000641:Ammonia; D005970:Glutamate Synthase; D000637:Transaminases; D009713:Nucleotidyltransferases; C020658:glutamine-synthetase adenylyltransferase; D005974:Glutamate-Ammonia Ligase