Xanthomonas citri T6SS mediates resistance to Dictyostelium predation and is regulated by an ECF σ factor and cognate Ser/Thr kinase. (26th March 2018)

• Record Type: Journal Article
• Authors: 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
• Is Part Of: Environmental microbiology. Volume 20:Number 4(2018)
• Page Start: 1562
• Page End: 1575
• Publication Date: 2018-03-26
• Subjects: Microbial ecology -- Periodicals; Environmental Microbiology -- Periodicals; 579.17
• DOI: 10.1111/1462-2920.14085
• Languages: English
• ISSNs: 1462-2912

Abstract

Summary: 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 Δ 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.