Bradyrhizobium

Bra.dy.rhi.zo' bi.um. Gr. adj.bradusslow; M.L. neut. n.Rhizobiuma bacterial generic name; M.L. neut. n.Bradyrhizobiumthe slow (growing) rhizobium.Proteobacteria / Alphaproteobacteria / Rhizobiales / Bradyrhizobiaceae / BradyrhizobiumRods 0.5–0.9 × 1.2–3.0 µm.Commonly pleomorphic under adverse growth conditions. Usually contain granules of poly‐β‐hydroxybutyrate that are refractile by phase‐contrast microscopy.Nonsporeforming.Gram negative.Motile by one polar or subpolar flagellum. Fimbriae have not been described.Aerobic,possessing a respiratory type of metabolism with oxygen as the terminal electron acceptor.Optimal temperature 25–30°C. Optimal pH, 6–7, although lower optima may be exhibited by strains from acid soils. Colonies are circular, opaque, rarely translucent, white, and convex, and tend to be granular in texture; they do not exceed 1.0 mm in diameter in less than 5–6 days incubation on A1EG medium.Turbidity develops only after 3–4 days in agitated broth.Generation times are 9–18 h. Chemoorganotrophic, utilizing a range of carbohydrates and salts of organic acids as carbon sources, without gas formation; arabinose and other pentoses are preferred carbon sources. Cellulose and starch are not utilized. Produce an alkaline reaction in mineral salts medium containing mannitol and/or many other carbohydrates.Growth on carbohydrate media is usually accompanied by extracellular polysaccharide slime production particularly with glycerol,gluconate,or mannitol. Some strains can grow chemolithotrophically in the presence of H2, CO2, and low levels of O2. Ammonium salts, usually nitrates, and some amino acids, can serve as nitrogen sources. Peptone is poorly utilized (except for strains isolated fromLotononis). Casein and agar are not hydrolyzed. There is usually no requirement for vitamins with the rare exception of biotin, which also may be inhibitory to some strains. 3‐Ketoglycosides are not produced (Bernaerts and De Ley, 1963).The organisms are characteristically able to enter the root hairs of tropical‐zone and some temperate‐zone leguminous plants(family Leguminosae)and incite the production of root nodules,in which the bacteria occur as intracellular nitrogen‐fixing symbionts. Some strains, especiallyB.elkanii, fix nitrogen in the free‐living state when examined under special conditions.The mol%G+C of the DNA is: 61–65.Type species:Bradyrhizobium japonicum(Kirchner 1896) Jordan 1982, 137 (“Rhizobacterium japonicum” Kirchner 1896, 221;Rhizobium japonicum(Kirchner 1896) Buchanan 1926, 90.)