Comparison of colony morphology, salt tolerance, and effectiveness in Rhizobium japonicum

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Abstract
Four strains of R. japonicum, 2 of which produce slimy and non-slimy colony types and 2 others which produce large and small colony types, were isolated and cloned. All were infective and nodulated Lee soybean host plants. Each colony type was characterized as to its salt sensitivity to Na+ and K+, relative level of symbiotic N2 fixation and relative level of free-living N2 fixation. Growth studies performed in the presence of salts demonstrated that the non-slimy or small colony types were sensitive to salt with significantly depressed growth rates and cell yields. Growth rates and cell yields of slimy, large, colony tpyes were relatively unaffected salt. Both symbiotic and free-living (non-associative) N2 fixation analyses (by acetylene reduction) revealed that the non-slimy, small colonies were significantly more effective than slimy, large colonies.