Characterization of fast-growing rhizobia from nodulated soybean [Glycine max (L) Merr] in Vietnam

We have examined six fast-growing Rhizobium strains isolated from nodulated soybean [Glycine max (L.) Merr.] plants growing in Vietnam, with special emphasis on two of them, SMX11 and SMH12. The abilities of strains SMX11 and SMH12 to utilize II carbon sources were indistinguishable from that of control Sinorhizobium fredii strains USDA257 and HH103, but their growth rates in standard media were considerably more rapid. The Vietnamese strains also were more salt-tolerant and antibiotic-resistant than the S. fredii reference strains, and their LPS banding patterns were less complex. Weak immunological cross-reactivity between the Vietnamese strains and S. fredii was evident. RFLP patterns of a series of nodulation genes and a repetitive sequence from S. fredii matched those of the Vietnamese strains, as did the sequence of a portion of a 16S rRNA gene. Analysis of cellular fatty acids was consistent with the assignment of strain SMH12 and four other Vietnamese strains to S. fredii, bur it aligned strain SMX11 more closely to other related groups of rhizobia. The Vietnamese strains have broad lost ranges for nodulation of legumes, and their abilities to fix nitrogen in association with five soybean cultivars are equivalent to or surpass that of S. Fredii.