Electron microscopic studies of aggregation and pellicle formation in Azospirillum spp.

Microscopic studies on aggregation of Azospirillum brasilense Cd and the local isolate Cd-1 revealed the presence of an extracellular layer (ECL) on the outer surface of cells taken from the early exponential phase. Incubation of the bacteria with cationized ferritin (CF) was followed by labelling of the ECL of both Cd and Cd-1 taken from the stationary phase. Concanavalin-A-ferritin (Con-A-F), a lectin conjugated with ferritin, was bound to the ECL which was developed during the stationary phase, but not the exponential phase, in both isolates. In static liquid cultures, Azospirillum brasilense Cd formed lateral flagella and fimbriae-like structures which were not observed in shaking liquid cultures. It is suggested that these filaments may play a role in cell-to-cell adhesion of Azospirillum that results in pellicle formation observed in static cultures.