Study of the genetic diversity of microsymbionts isolated from Hedysarum gmelinii subsp. Setigerum, growing in the Baikal lake region

One of the urgent problems of modern microbiology and biotechnology is the study of the mechanisms of interaction between leguminous plants and root nodule bacteria (rhizobia), which are an extensive group of microorganisms capable to form nitrogen-fixing symbiosis with a host plant. Knowledge of these mechanisms is necessary for carrying out scientifically based selection of highly effective rhizobia-legume symbiotic systems. To understand the evolution of the specificity of plant-microbe interactions, symbiotic systems with the participation of relic leguminous plants, which are an intermediate link between the extinct and modern species, are of particular importance. One of these unique objects is the pleistocene relic Hedysarum gmelinii Ledeb. subsp. setigerum (Turcz. ex Fischer et Mey.) Kurbatsky. The aim of this study was to isolate and identify the world's first collection of microsymbionts of this plant species growing in the Lake Baikal region. The study of taxonomic positions of 19 isolates from root nodules of H. gmelini subsp. setigerum plants was conducted by the methods of ITS-RFLP and 16S rRNA gene ( rrs ) sequencing. Phylogenetic analysis revealed the considerable genetic diversity among microsymbionts of the plant species studied. Fourteen rhizobial isolates belonged to 3 genera: Rhizobium (family Rhizobiaceae ), Phyllobacterium (family Phyllobacteriaceae ) and Bosea (family Bradyrhizobiaceae ). It was noted the presence in the root nodules of non-symbiotic rhizobial species that are not able to form symbiosis with leguminous plants ( Phyllobacterium endophyticum, Ph. loti and Bosea sp.). In addition, five non-rhizobial isolates belonging to the genera Acinetobacter, Stenotrophomonas, Sphingomonas и Agromyces were obtained. The obtained data may indicate that the relic rhizobia-legume symbioses, formed in particular by the H. gmelini subsp. setigerum plants, are prototypes of modern symbiotic systems and reflect the evolutionary pathways in the direction of recruiting symbiotic genes of different microorganisms and increasing the specificity of plant-microbe interactions. It is possible that strains of non-symbiotic rhizobial species are present in nodules as a source of genes that do not participate directly in the formation of symbiosis, but affect its activity. Such strains, after appropriate genetic and phenotypic study, can be used for the production of biopreparations with increased efficacy.