CONICET | Buscador de Institutos y Recursos Humanos

Adherence to eukaryotic cells is an important early step during the infection of host cells by many bacterial pathogens. Adherent pathogens typically have one or more extracellular molecules or structures that interact with various types of surfaces. One of the most widespread adherence structures among Gram negative bacteria are the filamentous appendages called pili or fimbriae. Type IV pili (Tfp) is among the most common and best studied. In addition to their role in adherence, Tfp mediate a form of flagella-independent surface translocation called twitching and this structure can be important for autoaggregation, biofilm formation, natural transformation competence and muticellular development. Twitching motility also is required for host colonization and pathogenesis, including the activation of host cell responses. Xanthomonas axonopodis pv. citri (Xac) is the phytopathogen responsible for citrus canker. Adhesins have an important function in Xac attachment to host cell surface. The objective of this work is to determine if Tfp of Xac participates in the virulence process during citrus canker. A Xac mutant strain defective in Tfp was constructed by conjugation with the mobilizable suicide vector pKmob. No differences were observed in the growth curves in liquid medium between Xac wild-type (wt) and the mutant strain. Differences were observed in twitching motility on agar plates. Xac wt formed colonies with a characteristic rough appearance in the peripheral twitching zone consisting of a thin layer of cells. On the other hand, mutant strain produced smooth colonies on agar plates. Also, adhesion and biofilm assays showed differences between Xac wt and the mutant strain. These results indicate that bacterial growth was not affected in the Tfp mutant of Xac but others features related to cell adhesion and motility that are important in the virulence process were altered in the mutant bacteria, suggesting a possible role of Tfp of Xac in citrus canker.