Phylogenetic analysis of rhizobium strains, isolated from nodules of Vavilovia formosa (Stev.) Fed

Among the 5 genera of tribe Fabeae the least studied is Vavilovia Fed., consisting of the only species Vavilovia formosa (Stev.) Fed. Vavilovia’s area of growth is limited by the highlands of Central and Eastern Caucasus, with only several known populations on the territories of Armenia, Dagestan, Norht Ossetia, Azerbaijan, Iran, Iraq, Siria, Turkey, and by the environmental conditions. The only phylogenetic research of rhizobia isolated from the nodules of vavilovia from the Nortn Ossetian population demonstrated significance of both slow-growing and fast-growing microsymbionts’ specific and genetic diversity. It was shown that all of the fast-growing isolates, belonging to Rhizobium leguminosarum species, carry nodX gene in their genomes. Three expeditions to the regions of Armenia, Dagestan and North Ossetia succeeded in finding and collecting plants of Vavilovia formosa (Stev.) Fed. with its nodules, from which later rhizobia isolates were obtained. We have chosen nineteen fast-growing isolates, derived from ten plants’ nodules, to identify their species affiliation, to trace geographical isolation and also to try to track down its genetic differences from rhizobia, which nodulate other plants of tribe Fabeae. To make this we sequenced ITS (internally transcribed spacer) fragment and nodA gene, and made screening of the isolates for the presence of nodX gene, which controls rhizobia host specificity. Obtained sequences were used to calculate genetic distances between groups of rhizobia, i.e. different regions isolates (Armenia, Dagestan, North Ossetia) and isolates from different plant hosts (vavilovia, pea, clover). Results of ITS sequencing showed that all strains involved in the analysis belong to R. leguminosarum (bv. viciae ) species. ITS-dendrogram shows relatively high heterogeneity of isolates, but on nodA -dendrogram they form a very compact group. Difference in the structure of these dendrograms allows to assume that nodA gene, chained with the genes of host specificity, can be easily transferred within the populations of R. leguminosarum, providing unlimited combinations of specificity to vavilovia with different variants of bacterial chromosome. Comparison of genetic distances based on ITS-sequences for the isolates in this study shows tendency to geographic isolation between them. Data on nodA -based genetic distances along with the presence of nodX gene in the genomes of all R. leguminosarum strains in this study point out the presence of its host specificity within biovar viciae. It seems that correlation between strain origin and the genetic structure of nodA reflects presence of highly specific interactions among each group of R. leguminosarum strains with their plant-hosts, whereas correlations with the structure of ITS-loci reflect rhizobia adaptation to soil environment.