IHF stabilizes pathogenicity island I of uropathogenic Escherichia coli strain 536 by attenuating integrase I promoter activity

Marco Chittò,Luisa Klotz,Petya Berger,Ulrich Dobrindt,Michael Berger,Peter Dröge

doi:10.1038/s41598-020-66215-2

Abstract

Pathogenicity islands (PAIs) represent horizontally acquired chromosomal regions and encode their cognate integrase, which mediates chromosomal integration and excision of the island. These site-specific recombination reactions have to be tightly controlled to maintain genomic stability, and their directionality depends on accessory proteins. The integration host factor (IHF) and the factor for inversion stimulation (Fis) are often involved in recombinogenic complex formation and controlling the directionality of the recombination reaction. We investigated the role of the accessory host factors IHF and Fis in controlling the stability of six PAIs in uropathogenic Escherichia coli strain 536. By comparing the loss of individual PAIs in the presence or absence of IHF or Fis, we showed that IHF specifically stabilized PAI I536 and that in particular the IHFB subunit seems to be important for this function. We employed complex genetic studies to address the role of IHF in PAI I536-encoded integrase (IntI) expression. Based on different YFP-reporter constructs and electrophoretic mobility shift assays we demonstrated that IntI acts a strong repressor of its own synthesis, and that IHF binding to the intI promoter region reduces the probability of intI promoter activation. Our results extend the current knowledge of the role of IHF in controlling directionality of site specific recombination reactions and thus PAI stability.

Highlights

Urinary tract infection is the most frequent type of nosocomial, and community-acquired bacterial infection and in general the most frequent type of bacterial infections in women[1]
In order to address the question whether Fis and/or integration host factor (IHF) play a role in stabilizing Pathogenicity islands (PAIs) I536-VI536 of E. coli strain 536, we constructed isogenic fis and ihfA/B mutants in our previously described reporter strains that allow for the measurement of the stability of PAI I536-VI53637
We found that almost 40% of the bacteria had lost PAI I536 in the ihfA/B mutant as judged by the absence of YFP signal in a large part of the population

Summary

Introduction

Urinary tract infection is the most frequent type of nosocomial, and community-acquired bacterial infection and in general the most frequent type of bacterial infections in women[1]. In addition to the integrase itself, bacteriophages such as ʎ, P2 and P4 require accessory host proteins, such as the integration host factor (IHF) and the factor for inversion stimulation (Fis) for integrative recombination These accessory DNA bending proteins bridge between distinct DNA sites, thereby implementing integrative or excisive recombination[26,27,28]. It is generally involved in a variety of DNA-depended processes including site-specific DNA recombination, transposition, transcriptional regulation and DNA replication[32,33,34]. The stability of PAI I536 was severely compromised in cells lacking IHF

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Conclusion