Biochemical Characterization of Fast- and Slow-Growing Rhizobia That Nodulate Soybeans

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Abstract
Fast-growing, acid-producing soybean rhizobia were examined to determine their biochemical relatedness to each other, to typical slow-growing Rhizobium japonicum strains and to other fast-growing Rhizobium spp. Although both the fast- and slow-growing soybean rhizobia were positive for catalase, urease, oxidase, nitrate reductase and penicillinase, the fast-growing strains grouped with other fast-growing Rhizobium spp. in that they tolerated 2% NaCl, were capable of growth at pH 9.5, utilized a large variety of carbohydrates (notably disaccharides) and produced serum zones in litmus milk. These fast-growing strains were similar to other fast-growing Rhizobium spp. in that they produced appreciable levels of .beta.-galactosidase and NAD phosphate-linked 6-phosphogluconate dehydrogenase, but had no detectable hydrogenase activity. The fast-growing soybean rhizobia share symbiotic host specificity with Bradyrhizobium japonicum, but appear to be related biochemically to the other fast-growing Rhizobium spp.