Bradyrhizobium

Abstract Bra.dy.rhi.zo'bi.um. Gr. masc. adj. bradys , slow; N.L. neut. n. Rhizobium , a bacterial generic name; N.L. neut. n. Bradyrhizobium , the slow (growing) Rhizobium. Pseudomonadota / Alphaproteobacteria / Hyphomicrobiales / Nitrobacteraceae / Bradyrhizobium Cells are rod‐shaped, 0.3–1.0 μm wide × 0.7–7.0 μm long. They are often pleomorphic under stress and contain poly‐β‐hydroxybutyrate granules that are microscopically visible . Gram‐stain‐negative and non‐spore‐forming. Motile, typically with polar or subpolar flagella, though some species are non‐motile. Most are aerobic, but some strains perform denitrification, making them facultative anaerobes . Colonies are usually circular, convex, translucent or opaque, light pink to pearl white, ranging between 0.8–1.0 mm in diameter in 5–9 days of growth on Yeast Mannitol Agar (YMA) medium. Some species present an extra slow growing rate (10–14 days). Generation time varies from 6 to 23 hours. Turbidity develops after 3–7 days in shaken broth. In general, do not grow on Luria Bertani (LB) medium. They are usually urease‐positive. Some species tolerate 1% NaCl or higher concentrations. Optimum temperature is 25–30°C, but several species grow from 14 to 37°C. Growth between 4–12°C and 40–60°C is usually limited. Optimum pH is 6.0–7.0, but several species can grow at 4.0–5.0 and 8.0–9.0. Chemoorganotrophic, capable of using a wide range of pentoses, hexoses, sugar alcohols, and dicarboxylic acids as sole carbon sources. Rarely metabolize disaccharides. They often produce extracellular polysaccharide slime. They can use ammonium salts or nitrate and amino acids as a sole nitrogen source and typically do not require vitamins. Usually produces an alkaline reaction in mineral salts medium containing mannitol and/or other carbohydrates . Some strains can grow chemolithotrophically in the presence of H 2 , CO 2 , and low levels of O 2 . Few species have photosynthetic ability. Predominant fatty acids are C 16:0 and C 18:1 ω6 c /C 18:1 ω7 c (summed feature 8) . Their antibiotic tolerance varies; however, they are generally resistant to chloramphenicol, erythromycin, nalidixic acid, ampicillin, penicillin, bacitracin, polymyxin B, and cloxacillin; and susceptible to streptomycin, neomycin, cefuroxime, kanamycin, d ‐serine, and guanidine HCl. Most species fix atmospheric nitrogen (N 2 ) in symbiosis with leguminous plants, inducing nodules primarily on roots and, occasionally, on stems. In addition to the nodules, isolation from root tumors, soils, water, and a cave wall was also reported. Few species are free‐living nitrogen fixers. The genus has large genomes (average 8.5 Mb ), generally does not carry plasmids, and their symbiosis genes are typically organized in genomic islands. The genus currently has 22 symbiovars. DNA G + C content (mol%) : 59.9–65.4. Type species : Bradyrhizobium japonicum Jordan 1982 VP (basonym: “ Rhizobacterium japonicum ” Kirchner 1896, synonym: Rhizobium japonicum Buchanan 1926 AL ).