Genetic Diversity and Phylogeny of Root Nodule Bacteria Isolated from Nodules of Plants of the Lupinaster Genus Inhabiting the Southern Urals

The genetic diversity and phylogeny of root nodule bacteria, microsymbionts of plants of the genus Lupinaster Adans. (L. albus Link and L. pentaphyllus Moench), were studied, and also their symbiotic genes were analyzed. The bacterial strains studied were shown to be phylogenetically different; however, all of them are related to the Mezorhizobium genus with the exception of the single strain which is related to the Rhizobium genus. Analysis of the symbiotic genes nifH and nodC revealed their high homology among all strains independently of strain phylogeny, as well as the phylogenetic relation of these genes to those of Mezorhizobium. Mezorhizobium bacteria are likely specific microsymbionts of these plants, while the Rhizobium strain acquired its symbiotic genes and became capable of nodule formation in Lupinaster plants through horizontal gene transfer. Thus, the genetic composition of nodule bacteria inhabiting Lupinaster plants represents additional support for the idea that they do not belong to the Trifolium genus.