DNA Supercoiling Regulates the Motility of Campylobacter jejuni and Is Altered by Growth in the Presence of Chicken Mucus.

Claire Shortt,Eoin Scanlan,Amber Hilliard,Billy Bourke,Tadhg Ó Cróinín,Chiara E Cotroneo,Martin J Blaser

doi:10.1128/mbio.01227-16

Abstract

ABSTRACTCampylobacter jejuni is the leading cause of bacterial gastroenteritis in humans, but relatively little is known about the global regulation of virulence factors during infection of chickens or humans. This study identified DNA supercoiling as playing a key role in regulating motility and flagellar protein production and found that this supercoiling-controlled regulon is induced by growth in chicken mucus. A direct correlation was observed between motility and resting DNA supercoiling levels in different strains of C. jejuni, and relaxation of DNA supercoiling resulted in decreased motility. Transcriptional analysis and Western immunoblotting revealed that a reduction in motility and DNA supercoiling affected the two-component regulatory system FlgRS and was associated with reduced FlgR expression, increased FlgS expression, and aberrant expression of flagellin subunits. Electron microscopy revealed that the flagellar structure remained intact. Growth in the presence of porcine mucin resulted in increased negative supercoiling, increased motility, increased FlgR expression, and reduced FlgS expression. Finally, this supercoiling-dependent regulon was shown to be induced by growth in chicken mucus, and the level of activation was dependent on the source of the mucus from within the chicken intestinal tract. In conclusion, this study reports for the first time the key role played by DNA supercoiling in regulating motility in C. jejuni and indicates that the induction of this supercoiling-induced regulon in response to mucus from different sources could play a critical role in regulating motility in vivo.

Highlights

Campylobacter jejuni is the most common cause of bacterial gastroenteritis worldwide
We reveal a direct correlation between DNA supercoiling and motility, report that changes in DNA supercoiling lead to divergent expression of the FlgRS two-component regulatory system, and reveal for the first time that chicken mucus from different sites in the chicken intestine can have different effects on DNA supercoiling levels and, dictate flagellar gene expression and the functionality of the flagella
Many virulence and colonization factors have been identified for C. jejuni, relatively little is known about how the organism regulates the expression of these factors during survival in different ecological niches

Summary

Introduction

Campylobacter jejuni is the most common cause of bacterial gastroenteritis worldwide. The complex flagellar structure of C. jejuni plays a role in motility but has been reported to function as a protein export apparatus for the secretion of factors involved in invasion of host epithelial cells [5, 6]. Phase variation has been identified as playing a role in flagellar regulation, and recent studies have characterized phase variation in FlgS, FlgR, and other genes involved in motility [14,15,16]. Further exploration of the role and regulation of the flagellar apparatus in protein export and motility will be key to understanding how C. jejuni colonizes chicken and human intestines. DNA supercoiling is sensitive to various environmental conditions, and pathogenic bacteria can exploit this system by using supercoiling-sensitive promoters to regulate virulence genes in response to these changes in the environment [29,30,31]

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Results

Conclusion