Brucella deploys multiple type IV effectors that simultaneously control bacterial survival and host inflammatory cell death

Abstract

ABSTRACT The type IV secretion system (T4SS) acts as the central virulence determinant of Brucella, facilitating intracellular survival via the secretion of effector proteins. In this study, we combined bioinformatic prediction with translocation assays to identify seven novel VirB-dependent effectors. Functional characterization revealed distinct roles for these proteins in both bacterial physiology and host-pathogen interactions. We identified BT4E19 and BT4E43 as critical determinants of cell envelope integrity: BT4E19 is required for core oligosaccharide maintenance and nitrosative stress tolerance, whereas BT4E43 is essential for O-antigen biosynthesis and oxidative stress resistance. Furthermore, BT4E43 is required for the efficient avoidance of lysosomal trafficking during intracellular infection. Notably, BT4E4 displays dual functions under tested conditions, being essential for oxidative stress resistance while simultaneously functioning to inhibit Caspase-5-mediated pyroptosis. In vivo assays further demonstrated that both BT4E19 and BT4E43 are indispensable for establishing chronic infection in mice. Collectively, these findings expand the Brucella effector repertoire and uncover the dual functions of specific effectors in maintaining bacterial structural integrity and orchestrating immune evasion, highlighting them as potential targets for anti-virulence therapies.