Active Attachment of Azospirillum brasilense Cd to Quartz Sand and to a Light-textured Soil by Protein Bridging

SUMMARY: Inoculation and incubation of Azospirillurn brasilense Cd in pure quartz sand resulted in their attachment to sand particles by fibrillar material. Addition of low concentrations of nutrients, such as fructose or malate together with NH4C1 or root extract, enhanced bacterial multiplication and attachment. This attachment was relatively weak, grid depended on the presence of living bacterial cells and on growth conditions. Sequential washing after bacterial attachment decreased the number of bacterial cells in the sand. The killing of A. brasilense Cd, either before or after attachment, resulted in elimination of most of the applied cells from the sand. By comparison, light-textured soil adsorbed both dead and live bacteria. Addition of protease or EDTA to attached bacteria in sand significantly reduced the number of bacteria. The addition of various inhibitors or exposure to high temperatures yielded a reduced attachment of bacteria, proportionate to their relative inhibitory effect on growth of A. brasilense Cd. Agitating A. brasilense Cd cells immediately after addition to sand reduced bacterial attachment, but increased bacterial multiplication proportionate to the increase in agitation. Attachment of A. brasilense Cd under microaerophilic conditions was lower than under aerobic conditions, and depended on the amount, quality and composition of the available nutrients. The richer the mixture, the greater the attachment and multiplication of bacteria. Similar trends, but at a lower magnitude, were observed in light-textured soil.