CHARACTERIZING CELL-CELL AND CELL-SURFACE INTERACTIONS IN THE RHIZOBACTERIUM AZOSPIRILLUM BRASILENSE

Microaerophilic and chemotaxic diazotrophs, azospirilla are found in close association with certain cereals such as durum wheat and maize and are active in enriching these ecological niches with the macronutrient nitrogen as ammonia. Regarded as highly pleomorphic, Azospirillum spp. are highly motile, using either a single polar flagellum when grown in liquid environments or peritrichous lateral flagella in viscous environments. Additionally, azospirilla are able to adhere onto surfaces as a biological film or aggregate cell-to-cell as nonproliferating flocculi, and these two processes having been suggested as positively affecting the survival and dispersal of the bacteria in the soil. Even though both biofilm formation and flocculation have been characterized via the presence of bacterial extracellular polysaccharides, the nature of the observed exopolysaccharides is still obscure, as are the underlying molecular mechanisms facilitating their organization. Here, we identified the optimal conditions for biofilm formation as a high C:N ratio under conditions of low aeration. Cells showed an increased preference for hydrophobic plastic rather than hydrophilic glass when the bacteria were first grown in a rich medium, TY, then were subcultured in a minimal media under these conditions. Using transposon mutagenesis, we also identified metabolic and cell-surface functions perhaps involved in the flocculation potential of these bacteria and we present an initial characterization of their contribution to this cellular differentiation process.