RESUMEN
Sixty-eight new rhizobial isolates were obtained from root-nodules of Medicago laciniata and from Mediterranean soils in Tunisia and France. All of them were identified as Sinorhizobium meliloti on the basis of PCR-RFLP analyses of 16S rDNA and the intergenic spacer sequence between 16S and 23S rDNAs. DNA/DNA hybridization, phenotypic characterization and 16S rRNA gene sequencing led to the conclusion that they belong the same taxon. All new isolates shared the ability to nodulate and fix nitrogen with M. laciniata except 11 of them not capable of fixing nitrogen with this plant and originating from French soils containing no efficiently adapted symbionts with M. laciniata. The nitrogen-fixing rhizobia on M. laciniata differed markedly from the other S. meliloti or Sinorhizobium medicae isolates and references in their symbiotic traits such as nifDK RFLP diversity, nodA sequences and nitrogen effectiveness with tree other different annual Medicago species (M. truncatula, M. polymorpha and M. sauvagei). Two infrasubspecific (biovar) divisions are therefore proposed within S. meliloti: bv. medicaginis for Sinorhizobium efficient on M. laciniata and bv. meliloti for the classically known S. meliloti group represented by the strains ATCC9930(T) and RCR 2011 efficient on M. sativa.
Asunto(s)
Medicago/microbiología , Fijación del Nitrógeno/fisiología , Sinorhizobium meliloti/clasificación , Aciltransferasas/química , Aciltransferasas/genética , Proteínas Bacterianas/química , Proteínas Bacterianas/genética , Secuencia de Bases , ADN Bacteriano/química , ADN Bacteriano/genética , ADN Espaciador Ribosómico/química , ADN Espaciador Ribosómico/genética , Francia , Variación Genética , Datos de Secuencia Molecular , Hibridación de Ácido Nucleico , Fenotipo , Filogenia , Reacción en Cadena de la Polimerasa , Polimorfismo de Longitud del Fragmento de Restricción , ARN Ribosómico 16S/química , ARN Ribosómico 16S/genética , Nódulos de las Raíces de las Plantas/microbiología , Análisis de Secuencia de ADN , Sinorhizobium meliloti/genética , Sinorhizobium meliloti/aislamiento & purificación , Sinorhizobium meliloti/metabolismo , Simbiosis/fisiología , TúnezRESUMEN
Bacterial strains from Zn-Pb mine tailings were isolated by trapping with Anthyllis vulneraria, a legume-host suitable for mine substratum phytostabilisation. Sequence analysis of the 16S rRNA gene and three housekeeping genes (atpD, dnaK and recA) showed that they were related to those of the genus Aminobacter. DNA-DNA relatedness of representative isolates supported the placement of novel strains in Aminobacter as a new species. Phenotypic data emphasize their differentiation from the other related species of Aminobacter and Mesorhizobium. Aminobacter isolates exhibited nodA sequences tightly related with M. loti as the closest nodA relative. By contrast, their nodA sequences were highly divergent from those of M. metallidurans, another species associated with A. vulneraria that carries two complete copies of nodA. Therefore, the novel bacterial strains efficient on A. vulneraria represented the first occurrence of legume symbionts in the genus Aminobacter. They represent a new species for which the name Aminobacter anthyllidis sp. nov. is proposed (type strain STM4645(T)=LMG26462(T)=CFBP7437(T)).
Asunto(s)
Fabaceae/microbiología , Phyllobacteriaceae/clasificación , Phyllobacteriaceae/genética , Aciltransferasas/genética , Proteínas Bacterianas/genética , Técnicas de Tipificación Bacteriana , Composición de Base , Secuencia de Bases , ADN Bacteriano/genética , ADN Ribosómico/genética , Plomo , Minería , Datos de Secuencia Molecular , Phyllobacteriaceae/aislamiento & purificación , Phyllobacteriaceae/metabolismo , Filogenia , ARN Ribosómico 16S/análisis , ARN Ribosómico 16S/genética , Rec A Recombinasas/genética , Nódulos de las Raíces de las Plantas/microbiología , Análisis de Secuencia de ADN , ZincRESUMEN
A polyphasic taxonomic approach was used to characterize 31 rhizobial isolates obtained from Anthyllis vulneraria, a metallicolous legume species, growing close to a zinc mine in the south of France (Saint Laurent le Minier). Comparative analysis of nearly full-length 16S rRNA gene sequences showed that these Gram-negative bacteria belonged to the genus Mesorhizobium and that they were related most closely to Mesorhizobium tianshanense ORS 2640(T). The phylogenetic relationships of these isolates with other Mesorhizobium species were confirmed by sequencing and analysis of the recA and atpD genes, which were used as alternative chromosomal markers. These novel mesorhizobial strains tolerated high concentrations of heavy metals: 16-32 mM Zn and 0.3-0.5 mM Cd. DNA-DNA hybridizations revealed >73 % relatedness between the strains isolated from A. vulneraria, but only 19-33 % relatedness between these and the type strains of M. tianshanense and Mesorhizobium mediterraneum. These results, together with other phenotypic characteristics, support the conclusion that these isolates represent a single, novel species of the genus Mesorhizobium, for which the name Mesorhizobium metallidurans sp. nov. is proposed. The type strain is STM 2683(T) (=CFBP 7147(T)=LMG 24485(T)).