Identification of a novel prophage regulator in Escherichia coli controlling the expression of type III secretion

Allen F Flockhart,Sean P Mcateer,Chad Laing,Maryia Karpiyevich,Kenan C Murphy,Thamarai Schneiders,Jai J Tree,Darren J Shaw,Victor Gannon,David L Gally,Angus Best,Ronen Rosenblum,John M Leong,Xuefang Xu,Roberto La Ragione,Christopher J Low

doi:10.1111/j.1365-2958.2011.07927.x

Abstract

This study has identified horizontally acquired genomic regions of enterohaemorrhagic Escherichia coli O157:H7 that regulate expression of the type III secretion (T3S) system encoded by the locus of enterocyte effacement (LEE). Deletion of O-island 51, a 14.93 kb cryptic prophage (CP-933C), resulted in a reduction in LEE expression and T3S. The deletion also had a reduced capacity to attach to epithelial cells and significantly reduced E. coli O157 excretion levels from sheep. Further characterization of O-island 51 identified a novel positive regulator of the LEE, encoded by ecs1581 in the E. coli O157:H7 strain Sakai genome and present but not annotated in the E. coli strain EDL933 sequence. Functionally important residues of ECs1581 were identified based on phenotypic variants present in sequenced E. coli strains and the regulator was termed RgdR based on a motif demonstrated to be important for stimulation of gene expression. While RgdR activated expression from the LEE1 promoter in the presence or absence of the LEE-encoded regulator (Ler), RgdR stimulation of T3S required ler and Ler autoregulation. RgdR also controlled the expression of other phenotypes, including motility, indicating that this new family of regulators may have a more global role in E. coli gene expression.

Highlights

Escherichia coli strains are usually present in the flora of mammalian gastrointestinal (GI) tracts and many are considered non-pathogenic
The deletion had a reduced capacity to attach to epithelial cells and significantly reduced E. coli O157 excretion levels from sheep
Important residues of ECs1581 were identified based on phenotypic variants present in sequenced E. coli strains and the regulator was termed RgdR based on a motif demonstrated to be important for stimulation of gene expression

Summary

Introduction

Escherichia coli strains are usually present in the flora of mammalian gastrointestinal (GI) tracts and many are considered non-pathogenic. Some strains are associated with serious intestinal and extra-intestinal infections. The main differences among strains of these different pathotypes can be attributed to the acquisition of genetic information from mobile genetic elements, in particular bacteriophage (Kaper et al, 2004). Bacteriophage integration and recombination leads to phage evolution, but is a key driver in the acquisition of virulence attributes in enteric bacteria, and of the complex regulatory networks that control their expression. Enterohaemorrhagic E. coli (EHEC) contain prophage-encoded Shiga toxins and are associated with severe GI and systemic disease in humans (Nataro and Kaper, 1998; Karmali, 2004). The predominant pathogenic serotype in North America, parts of Asia and the UK is O157:H7 (Armstrong et al, 1996; Besser et al, 1999; Caprioli et al, 2005)

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