Prokaryotic Community Structure in the Rapeseed (Brassica napus L.) Rhizosphere Depending on Addition of 1-Aminocyclopropane-1-Carboxylate-Utilizing Bacteria

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.