RESUMEN
Strains of Bradyrhizobium spp. form nitrogen-fixing symbioses with many legumes, including soybean. Although inorganic sulfur is preferred by bacteria in laboratory conditions, sulfur in agricultural soil is mainly present as sulfonates and sulfur esters. Here, we show that Bradyrhizobium japonicum and B. elkanii strains were able to utilize sulfate, cysteine, sulfonates, and sulfur-ester compounds as sole sulfur sources for growth. Expression and functional analysis revealed that two sets of gene clusters (bll6449 to bll6455 or bll7007 to bll7011) are important for utilization of sulfonates sulfur source. The bll6451 or bll7010 genes are also expressed in the symbiotic nodules. However, B. japonicum mutants defective in either of the sulfonate utilization operons were not affected for symbiosis with soybean, indicating the functional redundancy or availability of other sulfur sources in planta. In accordance, B. japonicum bacteroids possessed significant sulfatase activity. These results indicate that strains of Bradyrhizobium spp. likely use organosulfur compounds for growth and survival in soils, as well as for legume nodulation and nitrogen fixation.
Asunto(s)
Proteínas Bacterianas/metabolismo , Bradyrhizobium/genética , Bradyrhizobium/metabolismo , Genes Bacterianos , Glycine max/microbiología , Compuestos de Azufre/metabolismo , Proteínas Bacterianas/genética , Bradyrhizobium/crecimiento & desarrollo , Perfilación de la Expresión Génica , Regulación Bacteriana de la Expresión Génica , Oxigenasas de Función Mixta/genética , Oxigenasas de Función Mixta/metabolismo , Familia de Multigenes , Mutación , Fijación del Nitrógeno/genética , Operón , Nodulación de la Raíz de la Planta/genética , Glycine max/genética , Glycine max/metabolismo , Sulfatasas/genética , Sulfatasas/metabolismo , SimbiosisRESUMEN
Concatenated sequence analysis with 16S rRNA, rpoB and fusA genes identified a bacterial strain (IRBG74) isolated from root nodules of the aquatic legume Sesbania cannabina as a close relative of the plant pathogen Rhizobium radiobacter (syn. Agrobacterium tumefaciens). However, DNA:DNA hybridization with R. radiobacter, R. rubi, R. vitis and R. huautlense gave only 44%, 5%, 8% and 8% similarity respectively, suggesting that IRBG74 is potentially a new species. Additionally, it contained no vir genes and lacked tumour-forming ability, but harboured a sym-plasmid containing nifH and nodA genes similar to those in other Sesbania symbionts. Indeed, IRBG74 effectively nodulated S. cannabina and seven other Sesbania spp. that nodulate with Ensifer (Sinorhizobium)/Rhizobium strains with similar nodA genes to IRBG74, but not species that nodulate with Azorhizobium or Mesorhizobium. Light and electron microscopy revealed that IRBG74 infected Sesbania spp. via lateral root junctions under flooded conditions, but via root hairs under non-flooded conditions. Thus, IRBG74 is the first confirmed legume-nodulating symbiont from the Rhizobium (Agrobacterium) clade. Cross-inoculation studies with various Sesbania symbionts showed that S. cannabina could form fully effective symbioses with strains in the genera Rhizobium and Ensifer, only ineffective ones with Azorhizobium strains, and either partially effective (Mesorhizobium huakii) or ineffective (Mesorhizobium plurifarium) symbioses with Mesorhizobium. These data are discussed in terms of the molecular phylogeny of Sesbania and its symbionts.
Asunto(s)
Rhizobium/genética , Nódulos de las Raíces de las Plantas/microbiología , Sesbania/microbiología , Aciltransferasas/análisis , Aciltransferasas/genética , Proteínas Bacterianas/análisis , Proteínas Bacterianas/genética , ADN Bacteriano/análisis , ADN Bacteriano/genética , Fijación del Nitrógeno , Oxidorreductasas/análisis , Oxidorreductasas/genética , Factor G de Elongación Peptídica/análisis , Factor G de Elongación Peptídica/genética , Filogenia , Plásmidos/análisis , Plásmidos/genética , ARN Ribosómico 16S/análisis , ARN Ribosómico 16S/genética , Rhizobium/ultraestructura , Nódulos de las Raíces de las Plantas/ultraestructura , Alineación de Secuencia , Análisis de Secuencia de ADN , Sesbania/ultraestructura , Especificidad de la Especie , SimbiosisRESUMEN
Anabaena PCC 7120 genome contains three elements, which get excised out during late stages of heterocyst differentiation by a site-specific recombination process. The XisA protein, which excises the nifD element, shows sequence homology with the integrase family of tyrosine recombinase. The 11 bp target site of XisA CGGAGTAATCC contains a 3 bp inverted repeat. Here, we report restriction endonuclease activity of XisA by specific loss of plasmids containing single or double target sites. The pMX25 plasmid containing two target sites demonstrated endonuclease activity proportional to excision frequency. Different plasmid substrates containing one base pair mutation in the inverted repeat of the target site were monitored for endonuclease activity. Mutation of A4C retained endonuclease activity, while other modifications lost endonuclease activity. The presence of an additional copy of the target site enhanced endonuclease activity. These results suggest that the XisA protein could be an IIE type of restriction endonuclease in addition to being a recombinase.