An O Island 172 Encoded RNA Helicase Regulates the Motility of Escherichia coli O157:H7

Yanmei Xu,Ailan Zhao,Zhihong Ren,Changyun Ye,Li Liu,Yanwen Xiong,Ruiting Lan,Jianguo Xu,Xuefang Xu,Long-Fei Wu,A Mark Ibekwe

doi:10.1371/journal.pone.0064211

Abstract

Enterohaemorrhagic Escherichia coli (EHEC) O157:H7 is a major cause of zoonotic food- and water-borne intestinal infections worldwide with clinical consequences ranging from mild diarrhoea to hemolytic uraemic syndrome. The genome of EHEC O157:H7 contains many regions of unique DNA that are referred to as O islands including the Shiga toxin prophages and pathogenicity islands encoding key virulence factors. However many of these O islands are of unknown function. In this study, genetic analysis was conducted on OI-172 which is a 44,434 bp genomic island with 27 open reading frames. Comparative genome analysis showed that O1-72 is a composite island with progressive gain of genes since O157:H7 evolved from its ancestral O55:H7. A partial OI-172 island was also found in 2 unrelated E. coli strains and 2 Salmonella strains. OI-172 encodes several putative helicases, one of which (Z5898) is a putative DEAH box RNA helicase. To investigate the function of Z5898, a deletion mutant (EDL933ΔZ5898) was constructed in the O157:H7 strain EDL933. Comparative proteomic analysis of the mutant with the wild-type EDL933 found that flagellin was down-regulated in the Z5898 mutant. Motility assay showed that EDL933ΔZ5898 migrated slower than the wild-type EDL933 and electron microscopy found no surface flagella. Quantitative reverse transcription PCR revealed that the fliC expression of EDL933ΔZ5898 was significantly lower while the expression of its upstream regulator gene, fliA, was not affected. Using a fliA and a fliC promoter – green fluorescent protein fusion contruct, Z5898 was found to affect only the fliC promoter activity. Therefore, Z5898 regulates the flagella based motility by exerting its effect on fliC. We conclude that OI-172 is a motility associated O island and hereby name it the MAO island.

Highlights

Enterohaemorrhagic Escherichia coli (EHEC) O157:H7 is a major cause of zoonotic food- and water-borne infections worldwide
OI-122 carries the virulence gene efa1-lifA encoding the EHEC adherence/lymphocyte inhibitory factor, which is involved in the colonization of the intestinal mucosa and in the inhibition of the host immune response [6,7,8] and has been frequently found in Shiga toxin E. coli strains associated with severe human disease [9]
Prophage island CP-933H encodes an AraC-like regulator, PatE, that activates the transcription of the hdeAB-yhiD cluster and other acid resistance operons, which greatly enhances the ability of O157:H7 to survive in different acidic environments [16]

Summary

Introduction

Enterohaemorrhagic Escherichia coli (EHEC) O157:H7 is a major cause of zoonotic food- and water-borne infections worldwide. The genome of E. coli O157:H7 strain EDL933 contains 177 Oislands (OIs) in comparison to E. coli K12 MG1655 [1] These islands encode 26% of the EDL933 genes (1,387/5,416) [1]. OI-122 carries the virulence gene efa1-lifA encoding the EHEC adherence/lymphocyte inhibitory factor, which is involved in the colonization of the intestinal mucosa and in the inhibition of the host immune response [6,7,8] and has been frequently found in Shiga toxin E. coli strains associated with severe human disease [9]. OI-48, consists of three functional gene clusters that encode urease, tellurite resistance, and adhesins Iha and AIDA-1, which may contribute to EHEC O157:H7 pathogenesis by promoting adherence of the pathogen to the host intestinal epithelium [12]. Prophage island CP-933H encodes an AraC-like regulator, PatE, that activates the transcription of the hdeAB-yhiD cluster and other acid resistance operons, which greatly enhances the ability of O157:H7 to survive in different acidic environments [16]

Methods

Results

Conclusion