Genetic diversity of Agrobacterium species isolated from nodules of common bean and soybean in Brazil, Mexico, Ecuador and Mozambique, and description of the new species Agrobacterium fabacearum sp. nov.

Abstract

Agrobacterium strains are associated with soil, plants and animals, and known mainly by their pathogenicity. We studied 14 strains isolated from nodules of healthy soybean and common bean plants in Brazil, Mexico, Ecuador and Mozambique. Sequence analysis of the 16S rRNA gene positioned the strains as Agrobacterium, but with low phylogenetic resolution. Multilocus sequence analysis (MLSA) of three partial housekeeping genes (glnII, gyrB and recA) positioned the strains in four distinct clades, with Agrobacterium pusense, Agrobacterium deltaense, Agrobacterium radiobacter and Agrobacterium sp. genomospecies G1. Analysis by BOX-PCR revealed high intraspecies diversity. Genomic analysis of representative strains of the three clades indicated that they carry the protelomerase telA gene, and MLSA analysis with six complete housekeeping genes (atpD, glnII, gyrB, recA, rpoB and thrC), as well as average nucleotide identity (less than 90 % with closest species) and digital DNA-DNA hybridization (less than 41 % with closest species) revealed that strain CNPSo 675T and Agrobacterium sp. genomospecies G1 compose a new species. Other phenotypic and genotypic characteristics were determined for the new clade. Although not able to re-nodulate the host, we hypothesize that several strains of Agrobacterium are endophytes in legume nodules, where they might contribute to plant growth. Our data support the description of the CNPSo 675T and Agrobacterium sp. genomospecies G1 strains as a new species, for which the name Agrobacterium fabacearum is proposed. The type strain is CNPSo 675T (=UMR 1457T=LMG 31642T) and is also deposited in other culture collections.