Role of type III secretion in Edwardsiella tarda virulence.
Edwardsiella tarda is a Gram-negative enteric bacterium affecting both animals and humans. Recently, a type III secretion system (TTSS) was found in Ed. tarda. Such systems are generally used by bacterial pathogens to deliver virulence factors into host cells to subvert normal cell functions. Genome-walking was performed from the eseB and esrB genes (homologues of Salmonella sseB and ssrB, respectively) identified in previous studies, to determine the sequences of the TTSS. Thirty-five ORFs were identified which encode the TTSS apparatus, chaperones, effectors and regulators. Mutants affected in genes representing each category were generated and found to have decreased survival and growth in fish phagocytes. LD(50) values of the mutants were increased by at least 10-fold in comparison to those of the wild-type strain. The adherence and invasion rates of the esrA and esrB mutants were enhanced while those of the other mutants remained similar to the wild-type. The eseC and eseD mutants showed slight autoaggregation in Dulbecco's Modified Eagle Medium, whereas the rest of the mutants failed to autoaggregate. Regulation of the TTSS was found to involve the two-component regulatory system esrA-esrB. This study showed that the TTSS is important for Ed. tarda pathogenesis. An understanding of this system will provide greater insight into the virulence mechanisms of this bacterial pathogen.
Department of Biological Sciences, Faculty of Science, National University of Singapore, Science Drive 4, Singapore 117543.
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Tan
Department of Biological Sciences, Faculty of Science, National University of Singapore, Science Drive 4, Singapore 117543.
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Zheng
Department of Biological Sciences, Faculty of Science, National University of Singapore, Science Drive 4, Singapore 117543.
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Tung
Department of Molecular Genetics and Biotechnology, Faculty of Medicine, The Hebrew University, PO Box 12272, Jerusalem 91120, Israel.
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Rosenshine
Department of Biological Sciences, Faculty of Science, National University of Singapore, Science Drive 4, Singapore 117543.
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Leung
D001426:Bacterial Proteins / Q000378:metabolism*; D020609:Edwardsiella tarda / Q000235:genetics / Q000378:metabolism* / Q000472:pathogenicity*; D004925:Escherichia / Q000235:genetics; D005393:Fish Diseases / Q000382:microbiology; D008969:Molecular Sequence Data; D010586:Phagocytes / Q000382:microbiology; D021381:Protein Transport; D014774:Virulence
D001426:Bacterial Proteins