Fast-Growing Rhizobia Isolated from Root Nodules of Soybean

Abstract

Fast-growing rhizobia have been isolated from soybean root nodules collected in China. These new isolates are physiologically distinct from slow-growing soybean rhizobia. They formed effective nitrogen-fixing associations with wild soybean and an unbred soybean cultivar from China, but were largely ineffective as nitrogen-fixing symbionts with common commercial cultivars of soybeans.

Rhizobium fredii synthesizes an array of lipooligosaccharides, including a novel compound with glucose inserted into the backbone of the molecule

“…We have not yet examined the biological activities of the new LCOs, so we do not know if the differing arrays of compounds contribute to the observed patterns of cultivar specificity [4,5] of the producing strains. Our observations raise another interesting issue as well: how does R. fredii insert glucose into the center of the oligochitin backbone of one of its LCOs?…”

“…At subnanomolar concentrations, these molecules can substitute for intact Rhizobium cells in inducing a number of host nodulation responses, in a manner that matches the specificity of the producing Rhizobium strain. We previously characterized the LCOs of R. fredii USDA257, a strain that originally was isolated from nodules of wild soybean, Glycine soja [4]. This organism has a wide host range for legume species, but it is specific for certain cultivars of soybean [4,5].…”

“…We previously characterized the LCOs of R. fredii USDA257, a strain that originally was isolated from nodules of wild soybean, Glycine soja [4]. This organism has a wide host range for legume species, but it is specific for certain cultivars of soybean [4,5]. The LCOs of strain USDA257 comprise a series of 13-1,4-1inked oligomers of N-acetyl-o-glucosamine, with degrees of polymerization ranging from three to five [7].…”

The soybean cultivar specificity gene noIX is present, expressed in a nodD-dependent manner, and of symbiotic significance in cultivar-nonspecific strains of Rhizobium (Sinorhizobium) fredii

“…Rhizobium (now Sinorhizobium) fredii is a nitrogenfixing bacterial symbiont of several dozen legume species, including the soybean (Keyser et al, 1982;Krishnan & Pueppke, 1994b). Like other rhizobia, it stimulates cortical cells of host roots to divide and it enters root hairs by means of tubular infection threads (Heron & Pueppke, 1984;Chatterjee et al, 1990).…”

Pulsed-field gel electrophoresis studies of Rhizobiaceae

“…both of which are capable of nodulating and fixing dinitrogen in symbiosis with certain genotypes of G. max (Keyser et al, 1982). Based on numerical taxonomy studies, Chen et al (1988) proposed that R. fredii should be reclassified as Sinorhizobium.…”