Project description:The type III secretion system (T3SS) is an important virulence factor of Gram-negative bacteria, including the genus Aeromonas, a group of aquatic bacteria capable of both mutualistic and pathogenic interactions. Aeromonas species are increasingly recognized as opportunistic human pathogens. The type strain A. schubertii ATCC 43700 encodes two distinct T3SSs located in the Aeromonas pathogenicity islands 1 and 2, hereby designated as API1 and API2, respectively. This work investigates the role of API1 and API2 in A. schubertii-induced cytotoxicity and identifies novel type III secretion effectors. HeLa cell infections showed that API1, but not API2, is essential for cellular cytotoxicity resulting in both apoptotic and necrotic cell death. The ΔAPI1 mutant failed to induce cytotoxicity, whereas the wild-type (WT) and ΔAPI2 strains induced comparable cytotoxic effects. Proteomic analysis identified 7 candidate effectors secreted by the API1 injectisome under low-calcium conditions. These included two previously characterized effectors, AopH and AopO of A. salmonicida, and five novel effectors hereby named AopI, AopJ, AopL, AopT, and AopU, whose injection into host cells via API1 was validated using a split luciferase reporter system. Functional analysis revealed distinct roles for these effectors. AopL, homologous to the VopQ effector of Vibrio cholerae, accelerated caspase 3-independent necrosis, while AopI, homologous to ExoY of Pseudomonas aeruginosa, suppressed caspase activation and necrosis, indicating a pro-survival function. These results show the role of API1 injectisome in the cytotoxicity of A. schubertii and expand our understanding of T3SS-mediated host-pathogen interactions in Aeromonas species.
Project description:We sequenced the complete genome of the type strain of Aeromonas schubertii, ATCC 43700. The full genome sequence of A. schubertii ATCC 43700 is 4,356,858 bp, which encodes 3,842 proteins and contains 110 predicted RNA genes.
Project description:Aeromonas caviae has been associated with human gastrointestinal disease. Strains of this species typically lack virulence factors (VFs) such as enterotoxins and hemolysins that are produced by other human pathogens of the Aeromonas genus. Microarray profiling of murine small intestinal extracts, 24 hours after oral infection with an A. caviae strain, provides evidence of a Th1 type immune response. A large number of gamma-interferon (γ-IFN) induced genes are up-regulated as well as several tumor necrosis factor-alpha (TNF-α) transcripts. A. caviae has always been considered an opportunistic pathogen because it lacks obvious virulence factors. This current effort suggests A. caviae colonizes murine intestinal tract and causes what has been described by others as a dysregulatory cytokine response leading to an irritable bowel-like syndrome. This response would explain why a number of diarrheal waterborne outbreaks have been attributed to A. caviae even though it lacks obvious enteropathogenic properties. Keywords: Aeromonas caviae, infection, disease mechanism, TH1 resposne
