Immunoelectron microscopy investigation of the cell surface of Azospirillum brasilense strains

Abstract

The genus-specific surface protein antigens of Azospirillum brasilense strains were visualized immunochemically. The procedure used for cell sample preparation was optimized to ensure that the surface protein structures were detected on cells in situ. Gold and gold-silver nanoparticles were conjugated to antibodies raised against the flagellin of A. brasilense type strain Sp7, against the lipopolysaccharide of A. brasilense Sp245, and against the genus-specific protein determinants of A. brasilense Sp7. Electron microscopic analysis using nanoparticle-labeled antibodies revealed antigenic determinants of the polar flagellum on the A. brasilense Sp245 cell surface, which in these bacteria are normally screened from the surroundings by a lipopolysaccharide sheath. Pili-like structures were detected on the Sp245 wild-type strain and on its Fla^– Swa^– Omegon-Km mutant SK048, which are presumably involved in microcolonial spreading in these bacteria.