title: Evolutionary genetics and biogeographic structure of Rhizobium gallicum sensu lato, a widely distributed bacterial symbiont of diverse legumes.
abstract: We used phylogenetic and population genetics approaches to evaluate the importance of the evolutionary forces on shaping the genetic structure of Rhizobium gallicum and related species. We analysed 54 strains from several populations distributed in the Northern Hemisphere, using nucleotide sequences of three 'core' chromosomal genes (rrs, glnII and atpD) and two 'auxiliary' symbiotic genes (nifH and nodB) to elucidate the biogeographic history of the species and symbiotic ecotypes (biovarieties) within species. The analyses revealed that strains classified as Rhizobium mongolense and Rhizobium yanglingense belong to the chromosomal evolutionary lineage of R. gallicum and harbour symbiotic genes corresponding to a new biovar; we propose their reclassification as R. gallicum bv. orientale. The comparison of the chromosomal and symbiotic genes revealed evidence of lateral transfer of symbiotic information within and across species. Genetic differentiation analyses based on the chromosomal protein-coding genes revealed a biogeographic pattern with three main populations, whereas the 16S rDNA sequences did not resolve that biogeographic pattern. Both the phylogenetic and population genetic analyses showed evidence of recombination at the rrs locus. We discuss our results in the light of the contrasting views of bacterial species expressed by microbial taxonomist and evolutionary biologists.
authors.affiliation: Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, AP 565A, Cuernavaca, Morelos, México. csilva@ccg.unam.mx
authors.forename: Claudia
authors.initials: C
authors.lastname: Silva
authors.forename: Pablo
authors.initials: P
authors.lastname: Vinuesa
authors.forename: Luis E
authors.initials: LE
authors.lastname: Eguiarte
authors.forename: Valeria
authors.initials: V
authors.lastname: Souza
authors.forename: Esperanza
authors.initials: E
authors.lastname: Martínez-Romero
mesh_terms: D001483:Base Sequence; D016000:Cluster Analysis; D003710:Demography; D007887:Fabaceae / Q000382:microbiology*; D022761:Gene Transfer, Horizontal / Q000235:genetics*; D005798:Genes, Bacterial / Q000235:genetics; D005828:Genetics, Population; D005843:Geography; D016013:Likelihood Functions; D008957:Models, Genetic; D008969:Molecular Sequence Data; D010802:Phylogeny; D012231:Rhizobium / Q000145:classification / Q000235:genetics*; D017422:Sequence Analysis, DNA; D013045:Species Specificity; D013559:Symbiosis