Xanthomonas citri T6SS mediates resistance to Dictyostelium predation and is regulated by an ECF sigma factor and cognate Ser/Thr kinase

Author(s)

Bayer-Santos, Ethel ; Lima, Lidia dos Passos ; Ceseti, Lucas de Moraes ; Ratagami, Camila Yuri ; de Santana, Eliane Silva ; da Silva, Aline Maria ; Farah, Chuck Shaker ; Alvarez-Martinez, Cristina Elisa

• Document type: Journal article
• Source: ENVIRONMENTAL MICROBIOLOGY; v. 20, n. 4, p. 14-pg., 2018-04-01.

Abstract

Plant-associated bacteria of the genus Xanthomonas cause disease in a wide range of economically important crops. However, their ability to persist in the environment is still poorly understood. Predation by amoebas represents a major selective pressure to bacterial populations in the environment. In this study, we show that the X. citri type 6 secretion system (T6SS) promotes resistance to predation by the soil amoeba Dictyostelium discoideum. We found that an extracytoplasmic function (ECF) sigma factor (EcfK) is required for induction of T6SS genes during interaction with Dictyostelium. EcfK homologues are found in several environmental bacteria in association with a gene encoding a eukaryotic-like Ser/Thr kinase (pknS). Deletion of pknS causes sensitivity to amoeba predation and abolishes induction of T6SS genes. Phosphomimetic mutagenesis of EcfK identified a threonine residue (T51) that renders EcfK constitutively active in standard culture conditions. Moreover, susceptibility of Delta pknS to Dictyostelium predation can be overcome by expression of the constitutively active version EcfK(T51E) from a multicopy plasmid. Together, these results describe a new regulatory cascade in which PknS functions through activation of EcfK to promote T6SS expression. Our work reveals an important aspect of Xanthomonas physiology that affects its ability to persist in the environment. (AU)

• FAPESP's process: 15/25381-2 - Study of the role of type IV secretion system of Xanthomonas citri and Stenotrophomonas maltophilia in the interaction with Dictyostelium discoideum.
• Grantee: Ethel Bayer Santos
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• FAPESP's process: 16/08400-6 - The effects of host plant extracts in Xanthomonas citri subsp citri physiology and protein secretion
• Grantee: Camila Yuri Ratagami
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• FAPESP's process: 11/07777-5 - Cyclic di-GMP signaling and the Type IV macromolecule secretion system in Xanthomonas citri
• Grantee: Shaker Chuck Farah
• Support Opportunities: Research Projects - Thematic Grants
• FAPESP's process: 14/19720-6 - The Xanthomonas citri pv. citri type vi secretion system: function, gene regulation and secreted substrates
• Grantee: Cristina Elisa Alvarez Martinez
• Support Opportunities: Regular Research Grants
• FAPESP's process: 14/25261-4 - Gene expression analysis of the Xanthomonas citri subsp citri type VI secretion system
• Grantee: Lucas de Moraes Ceseti
• Support Opportunities: Scholarships in Brazil - Scientific Initiation