A total of 33 strains of fast-growing soybean rhizobia isolated from soil and soybean nodules collected in China and 25 strains belonging to the genera Rhizobium, Bradyrhizobium, and Agrobacteriurn were compared by numerical taxonomic techniques, using 240 different characters, Our results indicated that all of the strains of fast-growing soybean rhizobia which we examined are closely related (guanine-plus-cytosine content, 59.9 to 63.8 mol%) and are separated from Rhizobium and Bradyrhizobium at the generic level. Based on numerical taxonomy, deoxyribonucleic acid (DNA) base ratio determinations, DNA-DNA hybridization data, serological analysis data, the composition of extracellular gum, bacteriophage typing data, and soluble protein patterns, we propose that the fast-growing soybean rhizobia represent members of a new genus rather than a species of Rhizobium (Rhizobium fredii); we propose Sinorhizobium gen. nov. as an appropriate generic name.
(4). Rhizobium includes three species, Rhizobium meliloti,Rhizobium loti, and Rhizobium leguminosarum. Bradyrhizobium has only one species, Bradyrhizobium japonicum, and includes strains that are capable of nodulating lupines, soybeans, and certain other legumes (4).Recently, a new group of fast-growing soybean rhizobia was identified from soil and soybean nodules collected in the People's Republic of China by Chinese and American scientists (6, 25). The taxonomic status of these bacteria was uncertain, but they may represent a transitional group falling between the genera Rhizobium and Bradyrhizobium (4).Scholla and Elkan (13) proposed a new species name for this group, Rhizobium fredii, based mainly on deoxyribonucleic acid (DNA) hybridization comparisons of five strains of these bacteria with representatives of the genera Rhizobium and Brudyrhizobium and on a review of some of the characteristics of 11 strains of fast-growing soybean rhizobia.To extend the current information on the fast-growing soybean bacteria, we performed a numerical taxonomic study of a large number of strains. We propose that they be assembled in a new genus that includes two species.
MATERIALS AND METHODSOrganisms. A total of 58 strains were used in this study (Table 1); 33 strains were fast-growing soybean rhizobia isolated from soil and soybean nodules collected in the People's Republic of China, and the other 25 strains were representatives of Rhizobium, ~r u d y r~i z o~i u m , and Agrobacterium.Features. Each of the 58 strains was characterized by determining 240 different coding features. The following features were considered: (i) utilization as sole carbon sources (0.1%) of cellobiose, D-mannose, salicin, ammonium tartrate, casein hydrolysate, fructose, sodium acetate, sorbose, riffinose, D-melezitose monohydrate, hexose 6-phos- (iv) tolerance to dyes (0.1%, wt/vol), such as sudan 1, erythrosin A, picrocarmine, safranine T, orcein, rosanilin, brilliant cresyl blue, gentian violet, bromthymol blue, bromophenol blue, methyl red, bromocresol purple, neutral red, auramine O.B.S, light gree...