Rhizobium ecuadorense sp. nov., an indigenous N2-fixing symbiont of the Ecuadorian common bean (Phaseolus vulgaris L.) genetic pool.

Abstract

There are two major centres of genetic diversification of common bean (Phaseolus vilgaris L.), the Mesoamerican and the Andean, and the legume is capable of establishing nitrogen-fixing symbioses with several rhizobia; Rhizobium etli seems to be the dominant species in both centres. Another genetic pool of common bean, in Peru and Ecuador, is receiving increasing attention, and studies of microsymbionts from the region can help to increase our knowledge about coevolution of this symbiosis. We have previously reported several putative new lineages from this region and here present data indicating that strains belonging to one of them, PEL4, represent a novel species. Based on 16S rRNA gene sequence phylogeny, PEL4 strains are positioned in the Rhizobium phaseoli/R. etli/Rhizobium leguminosarum clade, but show unique properties in several morphological, physiological and biochemical analyses, as well as in BOX-PCR profiles ( < 75% similarity with related species). PEL4 strains also differed from related species based on multilocus sequence analysis of three housekeeping genes (glnII, gyrB and recA). Nucleotide identities of the three concatenated genes between PEL4 strains and related species ranged from 91.8 to 94.2%, being highest with Rhizobium fabae. DNA-DNA hybridization ( < 47% DNA relatedness) and average nucleotide identity values of the whole genomes ( < 90.2%) also supported the novel species status. The PEL4 strains were effective in nodulating and fixing N2 with common beans. The data supported the view that PEL4 strains represent a novel species, Rhizobium ecuadorense sp. nov. The type strain is CNPSo 671(T) ( = UMR 1450(T) = PIMAMPIRS I 5(T) = LMG 27578(T)).