An extensive repetoire of type III secretion effectors in Escherichia coli O157 and the role of lambdoid phages in their dissemination

Toru Tobe, Scott A. Beatson, Hisaaki Taniguchi, Hiroyuki Abe, Christopher M. Bailey, Amanda Fivian, Rasha Younis, Sophie Matthews, Olivier Marches, Gad Frankel, Tetsuya Hayashi, Mark J. Pallen

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Abstract

Several pathogenic strains of Escherichia coli exploit type III secretion to inject "effector proteins" into human cells, which then subvert eukaryotic cell biology to the bacterium's advantage. We have exploited bioinformatics and experimental approaches to establish that the effector repertoire in the Sakai strain of enterohemorrhagic E. coli (EHEC) O157:H7 is much larger than previously thought. Homology searches led to the identification of >60 putative effector genes. Thirteen of these were judged to be likely pseudogenes, whereas 49 were judged to be potentially functional. In total, 39 proteins were confirmed experimentally as effectors: 31 through proteomics and 28 through translocation assays. At the protein level, the EHEC effector sequences fall into >20 families. The largest family, the NIeG family, contains 14 members in the Sakai strain alone. EHEC also harbors functional homologs of effectors from plant pathogens (HopPtoH, HopW, AvrA) and from Shigella (OspD, OspE, OspG), and two additional members of the Map/IpgB family. Genes encoding proven or predicted effectors occur in >20 exchangeable effector loci scattered throughout the chromosome. Crucially, the majority of functional effector genes are encoded by nine exchangeable effector loci that lie within lambdoid prophages. Thus, type III secretion in E. coli is linked to a vast phage "metagenome," acting as a crucible for the evolution of pathogenicity.

Original languageEnglish
Pages (from-to)14941-14946
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume103
Issue number40
DOIs
Publication statusPublished - Oct 3 2006
Externally publishedYes

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