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The legume–rhizobia symbiosis is a unique natural phenomenon, which supplies the plant with the necessary mineral nitrogen via fixation of atmospheric dinitrogen. This interaction involves two partners: the legume plant and root nodule bacteria (rhizobia). In the wild, members of the Fabaceae family enter into symbiosis with a polymorphic group of rhizobia specific to them; the mechanism and reasons for the formation of heterogeneity of rhizobia are currently the subject of active research. In the present work, a Rhizobium leguminosarum strain strictly specific to Phaseolus vulgaris L. was used to show that within 30 days upon its introduction into soil, genetic rearrangements occurred in the cells, as was revealed by changes in the pattern of its genetic profile. It was also found that recombination activity of the cells was also affected by the root exudates produced during seed germination, which may indicate involvement of the plant in the formation of polymorphism of its microsymbionts. These findings suggest interpretation of this process not as a spontaneous event, but rather as an event controlled by the plant. [ABSTRACT FROM AUTHOR]

The legume-Rhizobium symbiosis is a unique natural phenomenon responsible for providing a legume plant with mineral nitrogen fixed from the atmosphere. In the temperate climatic zone, due to seasonal cycles, plants have to form new interactions with rhizobia at the beginning of each round of vegetation with the formation of specialized structures on the roots, called root nodules, where molecular nitrogen is actually fixed. Nitrogen requirements of the host vary depending on the period of plant growth and development, which may affect its trophic relationships with the microsymbionts. In the present work, using the perennial leguminous plant Lotus corniculatus L. as an example, we assessed the influence of the macrosymbiont vegetation stage on the composition of its root nodule bacteria and carried out the characterization of these microbial communities. The highest microbial genetic diversity was found in the communities developing at the beginning of L. corniculatus vegetation. At the medium stage of plant development, the diversity decreased, while by the end of vegetation it increased again. Analysis of the nitrogen-fixing activity revealed the highest values for microbial strains isolated from the root nodules collected at the early stages of the macrosymbiont development, while it was lower in the strains isolated at the end of vegetation. At different stages of their development legumes may probably use different strategies for selection of microsymbionts. [ABSTRACT FROM AUTHOR]

The functional activity of different phylogenetic variants of the transcriptional activator of nitrogen fixation genes in the cells of root nodule bacteria (rhizobia) of different taxa was analyzed. For this purpose, recombinant strains of root nodule bacteria of the genera Mesorhizobium, Ensifer (Sinorhizobium), and Rhizobium were created using genetic engineering constructs based on the plasmid pJN105. This plasmid contains different phylogenetic variants of the nifA gene typical for bacteria of the genera Mesorhizobium, Ensifer, and Rhizobium under the control of the ParaBAD bacterial promoter. It was shown that in free-living recombinant cells of all three bacterial genera, the introduction of an additional active copy of the nifA gene to their genome resulted in emergence of detectable nitrogenase activity. The level of nitrogenase activity was not directly related to the phylogeny of the introduced nifA gene, which is most likely explained by the universality of the product of this gene within the studied group of bacteria. The data obtained indicate the possibility of combinatorial processes in the evolution of nitrogen fixation genes. [ABSTRACT FROM AUTHOR]

In order to investigate the effect of the RapA1 protein on growth-stimulating activity, biofilm formation, and root colonization by rhizobia, strains Rhizobium leguminosarum Pvu5, VSy12, Thy2, TPr4 and R. galegae 0702 were transformed with the pJN105TurboRapA1GFP vector, providing for constitutive expression of the rapA1 and gfp genes. Constitutive expression of the rapA1 gene was shown to result in more efficient biofilm formation on inert surfaces and to promote microcolony formation on plant root surfaces. Analysis of auxin production by wild and transformed strains revealed decreased auxin synthesis in all transformed strains, except for R. leguminosarum Thy2. Growth-stimulating activity of the wild and transformed strains did not correlate with the amount of auxins produced in vitro. [ABSTRACT FROM AUTHOR]

The genetic diversity and phylogeny of root nodule bacteria entering into symbiosis with bitter peavine Lathyrus vernus (L.) Bernh. ( Fabaceae) growing in various regions of the Republic of Bashkortostan were studied. RAPD analysis revealed a high degree of polymorphism of the DNA of the isolated strains giving evidence of the heterogeneity of the microorganisms in question. The study of the phylogeny of microsymbionts based on comparative analysis of the nucleotide sequences of 16S rRNA genes showed that the bacteria isolated from the plant nodules of L. vernus growing on the territory of Ufa and Beloretsk raions belonged to the species Rhizobium leguminosarum, whereas the microsymbionts of L. vernus growing on the territory of Tatyshly raion belonged to the species Rhizobium tropici,@ except for several strains of Rhizobium leguminosarum [ABSTRACT FROM AUTHOR]

Different species of Rhizobium were successfully introduced into the extracellular slime of Nostoc paludosum (Kütz) Elenk, strain 18; cyanobacteria did not eliminate them and exhibited no specificity to the introduced species. Both partners were shown to exist in a self-sufficient manner in an artificial consortium, the stability of which is determined by the technology of growing the cultures in collections. Cyanobacteria act as carriers of introduced satellites, providing contact with the inoculated material through the slime, and increase the nitrogen-fixing ability of legume plants due to the increase of the number and activity of nodules. The fact of penetration of cyanobacterial hormogonia into the nodules has been noted. The treatment of seeds by the consortium resulted in an increase of the harvest as compared with the standard methods of nitragin treatment of legumes. [ABSTRACT FROM AUTHOR]