The bacteria Azospirillum brasilense, used as biofertilizers, have a signifi cant positive eff ect on the growth and development of plants. The genome of the strain A. brasilense Sp7 is represented by a chromosome and numerous plasmids with molecular weight of 90, 115, and over 300 MDa. Genomic rearrangements that cause changes in the “plasmid profi le” can contribute to the formation of subpopulations or phenotypic variants in a bacterial population. There is little data on the role of such rearrangements in the adaptation of A. brasilenseto dynamic environmental conditions. The ability of azospirilla to form biofi lms also has a determined signifi cance for the successful functioning of the plant-microbial association and the resistance of bacteria and plants to various abiotic stresses. The purpose of this work consisted of the analysis of the genomic rearrangements in spontaneous derivatives of A. brasilense Sp7 and the assessment of the resistance of their biofi lms to drying, water stress and oxidative stress. PCR analysis to detect changes in the structure of genomic DNA was performed using primers corresponding to known conservative motifs in repetitive bacterial nucleotide sequences. The relative amount of the biofi lm biomass was assessed by measuring the crystal violet A540 desorbed after staining. The level of relative respiratory activity of cells in biofi lms was determined by the fl uorometric resazurin test. The non-penetrating osmotic agent PEG 6000 was used to create the osmotic/water stress model. It was shown that rearrangements in genomic DNA contribute to the formation of stable phenotypic variants of the Sp7 strain, which form biofi lms in diff erent ways under water stress conditions. A derived strain of A. brasilense Sp7.8, the biofi lm population of which is more resistant to water stress compared to the parent strain was selected.