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The taxonomic structure of the microbiomes colonizing the rapeseed rhizosphere soil was investigated using high-throughput sequencing of the 16S rRNA gene amplicon libraries. Effect of introduction of bacteria with ACC deaminase activity into the rapeseed rhizosphere community on rapeseed yeild was studied. In the prokaryotic complex, Proteobacteria, Actinobacteria, Gemmatimonadetes, and Acidobacteria predominated. An inverse correlation was found between abundance of the taxa Crenarchaeota and Proteobacteria (r = ‒0.71, P < 0.01). All detected archaeal sequences belonged to the family Nitrososphaeraceae, which is directly involved in intensification of plant nitrogen nutrition. Independent of the mineral nutrition, addition of ACC-utilizing strain resulted in a significant decrease in the shares of Crenarchaeota (63‒72%), Verrucomicrobia (42‒53%), and Bacteroidetes (50‒56%) and an increase in the share of the Proteobacteria (38%). Introduced bacteria were shown to have a positive effect on the relative abundance of the metabolically significant Proteobacteria classes in the rapeseed rhizosphere due to improved condition of the plants. A reliable correlation was found between relative abundance of the Proteobacteria and production of the plant‒microbial system (r = 0.85, P < 0.01) on addition of the strains Pseudomonas oryzihabitans Ep4 and Variovorax paradoxus 3-P4, which possess an ACC deaminase complex. Observed differences in the composition of microbial populations were primarily associated with the effect of introduced strains, rather than with addition of mineral fertilizers. [ABSTRACT FROM AUTHOR]

Compared to free-living relatives, bacterial symbionts of plants exhibit higher rates of population diversification (microevolution), as well as of speciation and formation of super-species taxa (macroevolution). Analysis of rhizobia, the N2-fixing symbionts of leguminous plants, suggests that both evolutionary modes are determined by the hosts, which have mutagenic and recombinogenic effects on their microsymbionts, apart from activating the selective processes that determine the fate of newly emerged genotypes in their populations. Migration induced by leguminous plants plays a key role in the evolution of rhizobia, including: (1) joint movement of the symbionts and their hosts into new ecological zones and (2) local circulation of the symbionts in plant‒soil systems. In the first case, allopatric speciation occurs in rhizobia due to transfer of the symbiotically specialized (sym) genes from the introduced strains into local bacteria, which are transformed into novel symbionts. In the second case, a sympatric divergence of Rhizobium populations occurs, resulting in formation of intraspecies taxa (biovars and symbiovars) contrasting in their host ranges. In the evolutionarily advanced rhizobia, Rhizobium leguminosarum and Neorhizobium galegae interacting with galegoid legumes (tribes Fabeae, Galegae, and Trifolieae), these processes are associated with diversification of the sym genes representing the accessory genome parts due to the interaction between bacteria and the hosts differing in their symbiotic affinities. In parallel, formation of new cryptic (genomic) species was revealed in local rhizobia populations, which is associated with divergence of the core genome parts. It may be caused either by genetic drift or by selection for resistance against local edaphic stresses, which in combination with disruptive selection can sufficiently enhance the rhizobia diversity and change the structures of their pangenomes. [ABSTRACT FROM AUTHOR]

The composition of rhizosphere microbial communities was studied for different species and varieties of agricultural gramineous plants (rye and wheat) grown in the soils contrasting in a number of agrochemical parameters. The data on analysis of the rhizosphere microbial communities obtained by sequencing of the V4 variable region of the 16S rRNA gene and on the ion and mass spectral composition of soil extracts are presented. Alpha diversity indices of the rhizosphere and control communities were almost the same. Analysis of beta diversity revealed higher variability of the rhizosphere microbial communities for chernozem-grown plants. Rhizosphere communities of the plants grown on sod-podzol soil were more similar and formed separate clusters. The taxa reliably involved in formation of specific rye and wheat rhizosphere microbiomes were established. Both common rhizosphere taxa (Sphingobacteriia, Betaproteobacteria) and species- or variety-specific ones (Oxalobacteraceae, Sphingobacteriaceae) were determined. Ion concentrations in soil extracts varied significantly depending on the soil type, while the similarity of mass spectral profiles depended more on the plant species than on the soil type. [ABSTRACT FROM AUTHOR]

Two hundred forty-three isolates of alfalfa root-nodule bacteria ( Sinorhizobium meliloti) were obtained from nodules and soils sampled in the northern Aral region, experiencing secondary salinization. Isolates obtained from nodules (N isolates) were significantly more salt-tolerant than those from soils (T isolates) when grown in a liquid medium with 3.5% NaCl. It was found that wild species of alfalfa, melilot, and trigonella preferably formed symbioses with salt-tolerant root-nodule bacteria in both salinized and nonsalinized soils. Only two alfalfa species, Medicago falcata and M. trautvetteri, formed efficient symbioses in soils contrasting in salinity. The formation of efficient symbiosis with alfalfa in the presence of 0.6% NaCl was studied in 36 isolates (N and T) differing in salt tolerance and symbiotic efficiency. Fifteen isolates formed efficient symbioses in the presence of salt. The increase in the dry weight of the plants was 25–68% higher than in the control group. The efficiency of symbiotic interaction under salinization conditions depended on the symbiotic efficiency of the isolates under standard conditions but did not correlate with the source of root-nodule bacteria (soil or nodule) or their salt tolerance. The results indicate that the strains of root-nodule bacteria forming efficient symbioses under salinization conditions can be found. [ABSTRACT FROM AUTHOR]

A correction to the article "Symbiosis Between the Root-Nodule Bacterium Sinorhizobium meliloti and alfalfa ( Medicago sativa) Under Salinization Conditions" that was published in the previous issue is presented.