Xanthomonas citri

Xanthomonas citri is a Gram-negative, rod-shaped bacterium. Although it is harmless for humans, it is a phytopathogen, known for being the causing agent of citrus canker.

Xanthomonas citri
Scientific classification
Domain:	Bacteria
Phylum:	Pseudomonadota
Class:	Gammaproteobacteria
Order:	Xanthomonadales
Family:	Xanthomonadaceae
Genus:	Xanthomonas
Species:	X. citri
Binomial name
Xanthomonas citri (Hasse 1915) Gabriel et al. 1989

Bacterial X. citri black spot on a mango, note that each black lesion has “cracks”

Bacterial killing via a secretion system

Xanthomonas 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.^[1][2]

Defense against predators

Xanthomonas citri also uses type VI secretion system in defense against the predatory amoeba Dictyostelium discoideum.^[3]

References

1. Souza DP, Oka GU, Alvarez-Martinez CE, Bisson-Filho AW, Dunger G, Hobeika L, Cavalcante NS, Alegria MC, Barbosa LR, Salinas RK, Guzzo CR, Farah CS (2015). "Bacterial killing via a type IV secretion system". Nature Communications. 6: 6453. Bibcode:2015NatCo...6.6453S. doi:10.1038/ncomms7453. PMID 25743609.
2. Sgro GG, Costa TR, Cenens W, Souza DP, Cassago A, Coutinho de Oliveira L, Salinas RK, Portugal RV, Farah CS, Waksman G (2018). "Cryo-EM structure of the bacteria-killing type IV secretion system core complex from Xanthomonas citri". Nature Microbiology. 3 (12): 1429–1440. doi:10.1038/s41564-018-0262-z. PMC 6264810. PMID 30349081.
3. Bayer-Santos, Ethel; Lima, Lídia dos Passos; Ceseti, Lucas de Moraes; Ratagami, Camila Yuri; de Santana, Eliane Silva; da Silva, Aline Maria; Farah, Chuck Shaker; Alvarez-Martinez, Cristina Elisa (2018). "Xanthomonas citri T6SS mediates resistance to Dictyostelium predation and is regulated by an ECF σ factor and cognate Ser/Thr kinase". Environmental Microbiology. 20 (4): 1562–1575. doi:10.1111/1462-2920.14085. ISSN 1462-2912. PMID 29488354. S2CID 3579518.