Mesorhizobium

Abstract

Me.so.rhi.zo' bi.um . Gr. adj. mesos middle; M.L. neut. n. Rhizobium bacterial generic name; M.L. neut. n. Mesorhizobium the meso ‐growing rhizobium, referring to the growth rate intermediate between those of the genera Rhizobium and Bradyrhizobium . Proteobacteria / Alphaproteobacteria / Rhizobiales / Phyllobacteriaceae / Mesorhizobium Rods 0.4–0.9 × 1.2–3.0 μm. Commonly pleomorphic under adverse growth condition or in the root nodules as bacteroids . Usually contain granules of poly‐β‐hydroxybutyrate, which are refractile by phase‐contrast microscopy. Nonsporeforming. Gram negative. Motile by one polar or subpolar flagellum or by peritrichous flagella. Aerobic, possessing a respiratory type of metabolism with oxygen as the terminal electron acceptor. Optimal temperature 25–30°C. Optimal pH 6–8. Growth in yeast extract–mannitol agar (YMA) 1 produces colonies that are circular, convex, semitranslucent, raised, and mucilaginous, 2–4 mm diameter within 5–6 d for some species or 1 mm after a 7‐d incubation for other species. The generation times of Mesorhizobium strains range from 4–15 h . Chemoorganotrophic, utilizing a wide range of carbohydrates and salts of organic acids as carbon sources without gas production. Cellulose and starch are not utilized. Produces an acidic reaction in YMA . Ammonium salts, nitrates, urea, and most amino acids are utilized as nitrogen sources. Peptone is poorly utilized. Mesorhizobium strains are only weakly proteolytic, but can produce a slow digestion in litmus milk; some strains form a clear serum zone. Some strains require thiamin, nicotinamide, and riboflavin for growth. The organisms are characteristically able to invade the root hairs of a wide range of temperate, subtropical, and tropical leguminous plants, inciting production of root nodules where the bacteria reduce atmospheric nitrogen into a combined form available for the host plants . All strains exhibit host specificity. The mol % G + C of the DNA is : 59–64. Type species : Mesorhizobium loti (Jarvis, Pankhurst, and Patel 1982) Jarvis, van Berkum, Chen, Nour, Fernandez, Cleyet‐Marel and Gillis 1997, 898 ( Rhizobium loti Jarvis, Pankhurst, and Patel 1982, 378.)