RESUMEN

Multilocus enzyme electrophoresis (MLEE) of 99 Brucella isolates, including the type strains from all recognized species, revealed a very limited genetic diversity and supports the proposal of a monospecific genus. In MLEE-derived dendrograms, Brucella abortus and a marine Brucella sp. grouped into a single electrophoretic type related to Brucella neotomae and Brucella ovis. Brucella suis and Brucella canis formed another cluster linked to Brucella melitensis and related to Rhizobium tropici. The Brucella strains tested that were representatives of the six electrophoretic types had the same rRNA gene restriction fragment length polymorphism patterns and identical ribotypes. All 99 isolates had similar chromosome profiles as revealed by the Eckhardt procedure.

Asunto(s)

Brucella/clasificación , Brucelosis/microbiología , Productos Lácteos/microbiología , Variación Genética , Animales , Brucella/enzimología , Brucella/genética , Brucella/aislamiento & purificación , Bovinos , ADN Bacteriano/análisis , ADN Bacteriano/genética , ADN Ribosómico/análisis , ADN Ribosómico/genética , Perros , Electroforesis en Gel de Almidón/métodos , Enzimas/análisis , Humanos , Hibridación de Ácido Nucleico , Polimorfismo de Longitud del Fragmento de Restricción , ARN Ribosómico 16S/genética , Ribotipificación

RESUMEN

Fifty rhizobial isolates from root nodules of Mimosa affinis, a small leguminous plant native to Mexico, were identified as Rhizobium etli on the basis of the results of PCR-RFLP and RFLP analyses of small-subunit rRNA genes, multilocus enzyme electrophoresis and DNA-DNA homology. They are, however, a restricted group of lineages with low genetic diversity within the species. The isolates from M. affinis differed-from the R. etli strains that orginated from bean plants (Phaseolus vulgaris) in the size and replicator region of the symbiotic plasmid and in symbiotic-plasmid-borne traits such as nifH gene sequence and organization, melanin production and host specificity. A new biovar, bv. mimosae, is proposed within R. etli to encompass Rhizobium isolates obtained from M. affinis. The strains from common bean plants have been designated previously as R. etli bv. phaseoli. Strains of both R. etli biovars could nodulate P. vulgaris, but only those of bv. mimosae could form nitrogen-fixing nodules on Leucaena leucocephala.

Asunto(s)

Fabaceae/microbiología , Oxidorreductasas , Plantas Medicinales , Rhizobium/clasificación , Rhizobium/genética , Conjugación Genética , Dermatoglifia del ADN , ADN Bacteriano/genética , Electroforesis/métodos , Enzimas/análisis , Genes de ARNr , Variación Genética , Datos de Secuencia Molecular , Nitrogenasa/genética , Raíces de Plantas/microbiología , Plásmidos/genética , Reacción en Cadena de la Polimerasa , Polimorfismo de Longitud del Fragmento de Restricción , Rhizobium/aislamiento & purificación , Simbiosis