Wheat root colonization by Azospirillum brasilense strains with different motility

Migration of associative bacteria Azospirillum brasilense in semisolid media is performed mainly by swarming (Swa(+) phenotype), which depends on the flagellar functioning and intercellular contacts. Non-swarming mutants of A. brasilense Sp245 lacking a polar flagellum migrate in semisolid media with microcolony formation using a unrevealed mechanism (Gri(+) phenotype). The study of wheat root colonization dynamics demonstrated that A. brasilense Sp245 Gri(+) mutants exhibited lower capacity for wheat root adsorption. However, after anchoring has occurred, both A. brasilense Sp245 and its Swa-Gri(+) mutants colonized the growing roots with virtually the same efficiency. All strains under study formed microcolonies on the surface of roots, stimulated root branching, and exhibited changes in the composition of protein antigens exposed on the bacterial cell surface. Indirect evidence was obtained for enhanced production of genus-specific protein antigens in the process of A. brasilense Sp245 adaptation to growth on plant roots.