Revealing the Draft Genome Sequence of Bradyrhizobium sp. Strain USDA 3458, an Effective Symbiotic Diazotroph Isolated from Cowpea (Vigna unguiculata) Genotype IT82E-16

Pairing plants with plant growth-promoting bacteria is critical to the future of agriculture. Bradyrhizobium sp. strain USDA 3458 isolated from Vigna unguiculata (cowpea) paired with cowpea genotype IT82E-16 represents a novel combination in arid regions. Here, we report the draft genome sequence of strain USDA 3458.

Elucidation of the Genome of Bradyrhizobium sp. Strain USDA 3456, a Historic Agricultural Diazotroph from Cowpea (Vigna unguiculata)

Bradyrhizobium sp. strain USDA 3456 is a historic strain from the United States Department of Agriculture (USDA) Agricultural Research Service (ARS) National Rhizobium Germplasm Collection isolated from Vigna unguiculata (cowpea) in 1966. Strain USDA 3456 has been utilized in global agricultural applications, including improving soil nitrogen fertility. The draft genome sequence here provides a genetic reference of a novel diazotroph.

Revision of the taxonomic status of type strains of Mesorhizobium loti and reclassification of strain USDA 3471T as the type strain of Mesorhizobium erdmanii sp. nov. and ATCC 33669T as the type strain of Mesorhizobium jarvisii sp. nov.

The species Mesorhizobim loti was isolated from nodules of Lotus corniculatus and its type strain deposited in several collections. Some of these type strains, such as those deposited in the USDA and ATCC collections before 1990, are not coincident with the original strain, NZP 2213T, deposited in the NZP culture collection. The analysis of the 16S rRNA gene showed that strains USDA 3471T and ATCC 33669T formed independent branches from that occupied by Mesorhizobium loti NZP 2213T and related to those occupied by Mesorhizobium opportunistum WSM2075T and Mesorhizobium huakuii IFO 15243T, respectively, with 99.9 % similarity in both cases. However, the analysis of concatenated recA, atpD and glnII genes with similarities lower than 96, 98 and 94 %, respectively, between strains USDA 3471T and M. opportunistum WSM2075T and between strains ATCC 33669T and M. huakuii IFO 15243T, indicated that the strains USDA 3471T and ATCC 33669T represent different species of the genus Mesorhizobium . These results were confirmed by DNA–DNA hybridization experiments and phenotypic characterization. Therefore, the two strains were reclassified as representatives of the two species Mesorhizobium erdmanii sp. nov. (type strain USDA 3471T = CECT 8631T = LMG 17826t2T) and Mesorhizobium jarvisii sp. nov. (type strain ATCC 33669T = CECT 8632T = LMG 28313T).

Symbiotic properties of Bradyrhizobium sp. (Lupinus) assayed on serradella plants

Physiological and symbiotic properties of <i>Bradyrhizobium</i> sp. (<i>Lupinus</i>) nodule isolates were compared to the standard slow-growing <i>Bradyrhizobium</i> sp. (<i>Lupinus</i>) strain USDA 3045. Lupine nodules isolates showed typical characteristics for bradyrhizobial strains and nodulated small seed legume, serradella (<i>Ornithopus sativus</i>), in tube test. We observed a permanent physiological segregation of the effective (Fix') and ineffective (Fix-) symbiotic phenotype for all tested bradyrhizobial strains during the growth of serradella in plant tube test. The ultrastructural differences between Fix* and Fix serradella nodules were observed. Rapid and visible nodulation as well as easy assay of the reduction of acetylene make serradella a convenient system for studies of <i>Bradyrhizobium</i> sp. (<i>Lupinus</i>) strains in laboratory conditions.

Polyphasic evidence supporting the reclassification of Bradyrhizobium japonicum group Ia strains as Bradyrhizobium diazoefficiens sp. nov.

Bradyrhizobium japonicum was described from soybean root-nodule bacterial isolates. Since its description, several studies have revealed heterogeneities among rhizobia assigned to this species. Strains assigned to B. japonicum group Ia have been isolated in several countries, and many of them are outstanding soybean symbionts used in inoculants worldwide, but they have also been isolated from other legume hosts. Here, we summarize published studies that indicate that group Ia strains are different from the B. japonicum type strain USDA 6T and closely related strains, and present new morphophysiological, genotypic and genomic evidence to support their reclassification into a novel species, for which the name Bradyrhizobium diazoefficiens sp. nov. is proposed. The type strain of the novel species is the well-studied strain USDA 110T ( = IAM 13628T = CCRC 13528T = NRRL B-4361T = NRRL B-4450T = TAL 102T = BCRC 13528T = JCM 10833T = TISTR 339T = SEMIA 5032T = 3I1B110T = ACCC 15034T = CCT 4249T = NBRC 14792T = R-12974T = CNPSo 46T).

Purification and Characterization of an α-Glucosidase from Rhizobium sp. (Robinia pseudoacacia L.) Strain USDA 4280

ABSTRACT A novel α-glucosidase with an apparent subunit mass of 59 ± 0.5 kDa was purified from protein extracts of Rhizobium sp. strain USDA 4280, a nodulating strain of black locust (Robinia pseudoacacia L), and characterized. After purification to homogeneity (475-fold; yield, 18%) by ammonium sulfate precipitation, cation-exchange chromatography, hydrophobic chromatography, dye chromatography, and gel filtration, this enzyme had a pI of 4.75 ± 0.05. The enzyme activity was optimal at pH 6.0 to 6.5 and 35°C. The activity increased in the presence of NH4 +and K+ ions but was inhibited by Cu2+, Ag+, Hg+, and Fe2+ ions and by various phenyl, phenol, and flavonoid derivatives. Native enzyme activity was revealed by native gel electrophoresis and isoelectrofocusing-polyacrylamide gel electrophoresis with fluorescence detection in which 4-methylumbelliferyl α-glucoside was the fluorogenic substrate. The enzyme was more active with α-glucosides substituted with aromatic aglycones than with oligosaccharides. This α-glucosidase exhibited Michaelis-Menten kinetics with 4-methylumbelliferyl α-d-glucopyranoside (Km , 0.141 μM; V max, 6.79 μmol min−1 mg−1) and withp-nitrophenyl α-d-glucopyranoside (Km , 0.037 μM; V max, 2.92 μmol min−1 mg−1). Maltose, trehalose, and sucrose were also hydrolyzed by this enzyme.