Filogenia de Rizóbios do feijoeiro com base no sequenciamento do gene 16S rRNA e na análise de sequenciamento multilocus

Abstract

The genotypic characterization of rhizobia is fundamental for their taxonomic definition and to improving knowledge about their biodiversity. In this context, the present work aimed to characterize a collection of 139 rhizobium strains isolated from common bean nodules and to make phylogenetic inferences based on multilocus sequencing analysis in order to define their taxonomic positioning. These strains were isolated from different locations in Brazil and worldwide, and deposited in the Culture Collection of Diazotrophic Bacteria (CCBD) of EMBRAPA Agrobiologia. Those strains were examined with BOX-PCR analysis and phylogenetic inference based on 16S rRNA, recA, dnaK and glnII gene sequences. BOX-PCR analysis showed that there is a great genotypic diversity among the strains, with 63 groups formed at the level of 85% similarity. Sequencing of the 16S rRNA gene revealed that 87% belong to the genus Rhizobium, mainly to the species R. phaseoli, R. laguerrae, and R. tropici. Phylogenetic trees revealed the existence of two major clades: one of them was formed by the group R. phaseoli-R. Etli-R. leguminosarum and the other by R. tropici and related species. The groups formed in the individual trees of each gene were shown to be cohesive, but the results were incogruent for some of the strains. The recA presented the highest number of conflicting phylogenetic signs, indicating a possible recombination event among species, especially within the clade R. phaseoli-R. etli-R. leguminosarum.