Anchoring of Azospirillum brasilense to hydrophobic polystyrene and wheat roots

The anchoring (irreversible attachment) of Azospirillium brasilense Cd to hydrophobic polystyrene and to root surfaces was compared. Live A. brasilense Cd cells attached in significantly greater numbers to roots than to polystyrene, regardless of treatments made to the surfaces or to the bacterial cells. Triton X-100, Na2EDTA and several bacterial -inhibitory substances reduced bacterial attachment to both surfaces, although this effect was greater with attachment to polystyrene than to roots. Pre-coating with root exudates, bovine serum albumin or gelatin significantly increased anchoring to both surfaces. Manganese-limited cells showed increased anchoring to roots, whereas dead cells adsorbed better to polystyrene. Although the anchoring of A. brasilense Cd to a nonbiological surface can be significantly altered by using several promoting or inhibiting substances to affect the properties of both the surface and the bacterial cell, anchoring to root surfaces is less affected by these substances. It is proposed that at least two different quantitative types of anchoring exist in this bacterium: a sparse attachment to a non-biological surface and a prolific attachment to roots.