Xanthomonas citri

Xanthomonas citri is a Gram-negative, rod-shaped proteobacteria. Although it is harmless for humans, it is a phytopathogen, known for being the causing agent of citrus canker. X. citri uses its type IV secretion system to kill other Gram-negative bacterial species in a contact-dependent manner. The secretion of the effector proteins requires a conserved C-terminal domain, and its bacteriolytic activity is neutralized by a cognate immunity protein. X. citri uses type VI secretion system in defense against predatory amoeba Dictyostelium discoideum.