Bacterial secretion systems are versatile structures that can secrete proteins and DNA into the extracellular medium or into target cells. Type IV secretion systems (T4SS) are protein complexes formed by 12 proteins (VirB1-VirB11 and VirD4) that play a fundamental role in the virulence of several bacterial species. In the last ten years, our laboratory has been studying interactions involving subunits of the T4SS of Xanthomonas citri, the causative agent of canker citrus, and identified 12 protein substrates secreted by this system. Recently, we demonstrated that T4SS of X. citri is capable of killing other bacterial species, thus working in an analogous manner to the type VI secretion system (T6SS). Once the T4SS of X. citri operates analogously to the T6SS of a variety of bacterial species, such as Vibrio cholerae and Pseudomonas aeruginosa, which are able to inject toxins in both prokaryotic and eukaryotic cells; this project aims to study the role of X. citri T4SS in interactions with a phagocytic eukaryotic cell, such as the social amoeba Dictyostelium discoideum. In addition, this project aims to study the T4SS of the opportunistic pathogen Stenotrophomonas maltophilia to determine whether this secretion system could play a similar role in other species phylogenetically related to Xanthomonas spp. The characterization of the S. maltophilia T4SS and its secreted toxins will be of great value to increase our knowledge about the biology and virulence mechanisms of this emerging pathogen. The knowledge generated at the end of this project will increase our understanding of the ecology of free-living bacteria and the mechanisms by which they survive their environmental predators.
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