Changing situation relevant to the taxonomy of phytopathogenic Rhizobium species and their re-identification in NIAS Genebank

Abstract

In the case of the genus Agrobacterium, which comprises crown gall bacteria and hairy root bacteria, the genus and species have been artificially defined based on pathogenic characters. For some species of the genus, several biovars, equivalent to the rank of variety level, have been established. Recently, based on the results of polyphasic taxonomic approaches, it was proposed that each biovar should be elevated to the species level (Sawada et al., IJSB 43: 694-702, 1993; Ophel & Kerr, IJSB 40: 236-241, 1990), and that the genera Agrobacterium and Rhizobium should be amalgamated into one single genus Rhizobium (Young et al., IJSEM 51: 89-103, 2001). Taking these changes in the taxonomic situation into consideration, strains belonging to the phytopathogenic Rhizobium species (formerly Agrobacterium species) preserved in the NIAS Genebank were re-identified based on phylogenetic analyses using 16S rDNA, atpD, glnA and recA, inoculation tests, PCR assays and so on, and some of them with typical characters for each species/pathogenic state/genomovar were selected as approved strains (reference strains for taxonomic studies). In addition, for every host plant, we chose pathogenic strains that were proved to harbor Ti or Ri plasmids, as approved strains (reference strains for inoculation tests). The DNA sequence data of the strains are provided by the NIAS Genebank database (http://www.gene.affrc.go.jp/databases-micro_search_en.php).