CONICET | Buscador de Institutos y Recursos Humanos

Xanthomonas axonopodis pv. citri (Xac) is the causative agent of citrus canker, an important threat to the citrus industry worldwide. Previous work from our laboratory demonstrated that Xac is able to form biofilm communities in biotic and abiotic surfaces where the extracellular polysaccharide xanthan (EPS) plays a key role in the biofilm maturation. Biofilm formation in other bacteria is a flagellar-dependent process. Xac has a single polar flagellum. To evaluate its participation in biofilm development we generated two deletion mutants: Xac ΔfliC (flagellin gene) and Xac ΔflgE (hook gene), both involved in the flagellar structure. Using the crystal violet technique we observed that flagellar mutants were impaired in the first steps of biofilm development, however, their ability to stick to the bottom of the Polystyrene-well was partially recovered after 72 h. By confocal microscopy we observed that these mutants were able to adhere but not to form a mature structure as wild type Xac did. We also show in this work that Xac has the ability to swim and to perform another type of movement that shows to be flagellar-independent but EPS and quorum sensing-dependent. All mutants affected in the flagellar-independent motility described here exhibit dispersal growth without any cell-cell architecture in biofilms growth conditions. We propose that this type of surface translocation is important for Xac at the adhesion step of biofilm development and that the lack of flagellum was responsible for the impairment of the mutants to develop a mature biofilm.