RESUMEN
Qinghai-Tibet plateau is the highest place in the world and the environment in that plateau is hard for animals and plants, with low temperature, low concentration of oxygen and high solar radiation. In this study, 61 root nodule isolates from Vicia, Oxytropis, Medicago, Melilotus and Onobrychis species grown in Qinghai-Tibet plateau and in loess plateau were comparatively characterized. Based upon the results of numerical taxonomy, ARDRA, AFLP, DNA-DNA hybridization and 16S rDNA sequencing, the isolates were classified as Rhizobium leguminosarum, Sinorhizobium meliloti, Sinorhizobium fredii, Mesorhizobium sp., Phyllobacterium sp., Stenotrophomonas sp. and two non-symbiotic groups related to Agrobacterium and Enterobacteriaceae. The strains isolated from Qinghai-Tibet plateau and from the loess plateau were mixed in these species or groups. Oxytropis spp. and Medicago archiducis-nicolai grown in Qinghai-Tibet plateau were recorded as new hosts for R. leguminosarum, as well as Oxytropis glabra and Medicago lupulina for S. fredii. In addition, strains resistant to high alkaline (pH 11) and high concentration of NaCl (3-5%, w/v) were found in each of the rhizobial species. This was the first systematic study of rhizobia isolated from Qinghai-Tibet plateau.
Asunto(s)
Fabaceae/microbiología , Rhizobiaceae/clasificación , Microbiología del Suelo , China , ADN Bacteriano/genética , ADN Ribosómico/genética , Fabaceae/fisiología , Concentración de Iones de Hidrógeno , Raíces de Plantas/microbiología , ARN Ribosómico 16S/genética , Rhizobiaceae/genética , Rhizobiaceae/aislamiento & purificación , Rhizobiaceae/fisiología , Simbiosis , TibetRESUMEN
We studied the genetic structure of 176 bacterial isolates from nodules of Medicago sativa, M. lupulina and M. polymorpha in fifteen sites distributed in three localities in Mexico. The strains were characterized by multilocus enzyme electrophoresis, plasmid profiles, PCR restriction fragment length polymorphism of 16S rRNA genes and of the intergenic spacer between 16S and 23S rRNA genes, and partial sequences of glnII, recA and nodB. Most of the strains were classified as Sinorhizobium meliloti, and a high genetic diversity was recorded. Six strains were classified as Sinorhizobium medicae, with no genetic variation. Phylogenetic and population genetic analyses revealed evidence of frequent recombination and migration within species.
Asunto(s)
Medicago sativa/microbiología , Sinorhizobium meliloti/genética , Sinorhizobium/genética , Microbiología del Suelo , Proteínas Bacterianas/genética , ADN Bacteriano/genética , ADN Ribosómico/genética , ADN Espaciador Ribosómico/genética , Enzimas/genética , Evolución Molecular , Variación Genética , Desequilibrio de Ligamiento , México , Filogenia , Plásmidos/genética , ARN Ribosómico 16S/genética , Nódulos de las Raíces de las Plantas/microbiologíaRESUMEN
Ninety-five rhizobial strains isolated from Astragalus adsurgens growing in the northern regions of China were classified into three main groups, candidate species I, II and III, based on a polyphasic approach. Comparative analysis of full-length 16S rRNA gene sequences of representative strains showed that candidate species I and II were Mesorhizobium, while candidate species III, which consisted of non-nodulating strains, was closely related to Agrobacterium tumefaciens. The phylogenetic relationships of the three candidate species and some related strains were also confirmed by the sequencing of glnA genes, which were used as an alternative chromosomal marker. The DNA-DNA relatedness was between 11.3 and 47.1 % among representative strains of candidate species I and II and the type strains of defined Mesorhizobium species. Candidate III had DNA relatedness of between 4.3 and 25.2 % with type strains of Agrobacterium tumefaciens and Agrobacterium rubi. Two novel species are proposed to accommodate candidate species I and II, Mesorhizobium septentrionale sp. nov. (type strain, SDW014(T)=CCBAU 11014(T)=HAMBI 2582(T)) and Mesorhizobium temperatum sp. nov. (type strain, SDW018(T)=CCBAU 11018(T)=HAMBI 2583(T)), respectively. At least two distinct nodA sequences were identified among the strains. The numerically dominant nodA sequence type was most similar to that from the Mesorhizobium tianshanense type strain and was identified in strains belonging to the two novel species as well as other, as yet, undefined genome types. Host range studies indicate that the different nodA sequences correlate with different host ranges. Further comparative studies with the defined Agrobacterium species are needed to clarify the taxonomic identity of candidate species III.
Asunto(s)
Alphaproteobacteria/clasificación , Alphaproteobacteria/aislamiento & purificación , Planta del Astrágalo/microbiología , Aciltransferasas/genética , Proteínas Bacterianas/genética , Técnicas de Tipificación Bacteriana , China , ADN Bacteriano/química , ADN Bacteriano/aislamiento & purificación , ADN Ribosómico/química , ADN Ribosómico/aislamiento & purificación , Genes de ARNr , Genotipo , Glutamato-Amoníaco Ligasa/genética , Datos de Secuencia Molecular , Filogenia , ARN Bacteriano/genética , ARN Ribosómico 16S/genética , Rhizobium/genética , Análisis de Secuencia de ADNRESUMEN
Forty-six Mesorhizobium strains associated with the leguminous plants Leucaena leucocephala and Sesbania herbacea in an uncultivated Mexican field were characterized using a polyphasic approach. The strains were identified as Mesorhizobium plurifarium based upon the close relationships with the reference strains for this species in PCR-based restriction fragment length polymorphism analyses, sequencing of 16S rRNA genes, multilocus enzyme electrophoresis, and DNA-DNA hybridization. Although the strains isolated from both plants formed the same group in multilocus enzyme electrophoresis and cross-nodulations were observed in the laboratory, different electrophoretic types were obtained from the two plants grown in natural soils, indicating the existence of a preferable association between the plants and the rhizobia. The M. plurifarium strains from Mexico and the reference strains from Africa and Brazil formed different phenotypic clusters in a numerical taxonomy. The Mexican strains did not grow at 37 degrees C and were sensitive to salty-alkaline conditions, while the reference strains from Africa and Brazil grew at 42 degrees C and were more resistant to salty-alkaline conditions. These results demonstrate that both the plants and environmental factors affected the evolution of rhizobia and that the Mexican strains had adapted to the neutral soils and the cool climate where they were isolated.
Asunto(s)
Alphaproteobacteria/clasificación , Alphaproteobacteria/aislamiento & purificación , Biodiversidad , Fabaceae/microbiología , Microbiología del Suelo , Adaptación Biológica , Alphaproteobacteria/crecimiento & desarrollo , Proteínas Bacterianas/análisis , Proteínas Bacterianas/aislamiento & purificación , Evolución Biológica , ADN Ribosómico/química , ADN Ribosómico/aislamiento & purificación , Variación Genética , Concentración de Iones de Hidrógeno , México , Datos de Secuencia Molecular , Hibridación de Ácido Nucleico , Presión Osmótica , Filogenia , Polimorfismo de Longitud del Fragmento de Restricción , ARN Ribosómico 16S/genética , Análisis de Secuencia de ADN , Homología de Secuencia de Ácido Nucleico , Cloruro de Sodio , TemperaturaRESUMEN
Legume species belonging to the genus Lespedeza are annual or perennial herb or shrub plants that grow in the northern hemisphere. They are known for the formation of root nodules, but little information is available about their microsymbionts. In this study, 58 root-nodule isolates from Lespedeza spp., obtained from China and the USA, were characterized using numerical taxonomic analysis of phenotypic features, SDS-PAGE analysis of whole-cell proteins, DNA-DNA hybridization, 16S rRNA gene sequence analysis and cross-nodulation with selected legume species. From the results generated using these approaches, it was concluded that Lespedeza spp. were promiscuous hosts for rhizobia. Four main clusters of bacteria, which included 35 of the strains isolated from Lespedeza spp., were defined upon numerical taxonomic analysis; these groups corresponded to those determined from analyses of protein electrophoretic and DNA-DNA hybridization data. The four clusters were found to define strains belonging to one of four species, Sinorhizobium saheli, Bradyrhizobium japonicum, Bradyrhizobium elkanii or a novel species of the genus Bradyrhizobium. The strains of B. japonicum and B. elkanii were all from the USA soil samples, and their representative strains could not nodulate soybean. The seven strains found to represent the novel Bradyrhizobium sp. were from China. These were differentiated from recognized species of the genus Bradyrhizobium by all of the taxonomic methods used here; hence, it is proposed that the novel strains isolated from Lespedeza spp. represent a novel species of the genus Bradyrhizobium, Bradyrhizobium yuanmingense. The type strain of the novel species, CCBAU 10071(T) (= CFNEB 101(T)), formed ineffective nodules on Medicago sativa and Melilotus albus but did not nodulate soybean. The other 23 bacterial strains isolated from Lespedeza spp. were found to form single branches or small groups (two to three strains) that were related to Bradyrhizobium, Mesorhizobium, Rhizobium and Sinorhizobium spp. on the basis of numerical taxonomic analysis, indicating the possibility that other rhizobial species are also associated with Lespedeza spp.