At an elevated copper content, the viability of Azospirillum baldaniorum on wheat seedling roots and the number of cells colonizing the roots and forming biofilms depended on the physicochemical properties of the lipopolysaccharides (LPSs) synthesized by these bacteria. Compared to the strain Cal+ LpsI LpsII A. baldaniorum strain Sp245, its mutants Cal– LpsI– KM252, Lps II– KM139, and Cal– LpsII– Mot– KM018 colonized the roots less efficiently and formed thinner biofilms. Changes in the polysaccharide synthesis in KM252, KM139, and KM018 mediated increased copper accumulation by the cells and decreased the resistance of bacterial cultures to the negative effect of copper ions. Copper excess in planta and/or on the model polystyrene surface resulted in higher levels of the polysaccharide antigens in the biofilms of strain Sp245 and of its mutants with altered glycopolymer composition. Inoculation with strain Sp245 had a positive effect on the growth of wheat stems and leaves both at copper concentrations which had no noticeable effect on the growth of any of the partners (0.001 mM) and at elevated concentrations of copper ions (up to 0.5 mM). Strains КМ018, КМ139, and КМ252 had a positive effect on the seedlings only at high copper concentrations in the medium. [ABSTRACT FROM AUTHOR]