| Research Abstract |
To elucidate the actual state of diversity of bacterial species belonging to the family Rhizobiaceae, including Agrobacterium and Rhizobium species, phylogenetic analysis was conducted for a total of 69 strains of bacterial species belonging to or closely related to the family Rhizobiaceae using dnaK, eno, pyrG, recA, and rpoD as markers. Specifically, the optimum evolutionary model and parameters were searched by conducting a likelihood ratio test, and phylogenetic trees were constructed using the distance method, parsimony, maximum likelihood, and Bayesian analysis, respectively, based on the selected optimum condition (GTR + G + I). Then, an intercomparison of these phylogenetic trees was performed for evaluating their reliability by conducting likelihood-based statistical tests, which led to a conclusion that the phylogenetic tree constructed based on the Bayesian analysis was most reliable. In this Bayesian tree, the members of the genera Agrobacterium and Rhizobium formed one extremely monophyletic cluster together with Sinorhizobium and other species belonging to the family Rhizobiaceae, Blastobacter species, and pesticide-degrading bacteria. Within this cluster, no tendency was observed that the species were grouped for each genus which they belong to. Thus, the bacterial species constituting the family Rhizobiaceae were shown to be extremely closely related to one another, which therefore suggests that subclassification of these species into multiple genera within this family is inappropr
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