A new role for Zinc limitation in bacterial pathogenicity: modulation of \u03b1-hemolysin from uropathogenic Escherichia coli

Elsa Velasco,Marianna Sanet,Jorge Fernández-Vázquez,Thomas V O’Halloran,Annabel F Valledor,Suning Wang,Daniel Jové,Estibaliz Glaría,Carlos Balsalobre

doi:10.1038/s41598-018-24964-1

Elsa Velasco, Marianna Sanet + Show 7 more

Open Access

https://doi.org/10.1038/s41598-018-24964-1

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Abstract

Metal limitation is a common situation during infection and can have profound effects on the pathogen’s success. In this report, we examine the role of zinc limitation in the expression of a virulence factor in uropathogenic Escherichia coli. The pyelonephritis isolate J96 carries two hlyCABD operons that encode the RTX toxin α-hemolysin. While the coding regions of both operons are largely conserved, the upstream sequences, including the promoters, are unrelated. We show here that the two hlyCABD operons are differently regulated. The hlyII operon is efficiently silenced in the presence of zinc and highly expressed when zinc is limited. In contrast, the hlyI operon does not respond to zinc limitation. Genetic studies reveal that zinc-responsive regulation of the hlyII operon is controlled by the Zur metalloregulatory protein. A Zur binding site was identified in the promoter sequence of the hlyII operon, and we observe direct binding of Zur to this promoter region. Moreover, we find that Zur regulation of the hlyII operon modulates the ability of E. coli J96 to induce a cytotoxic response in host cell lines in culture. Our report constitutes the first description of the involvement of the zinc-sensing protein Zur in directly modulating the expression of a virulence factor in bacteria.

Highlights

Metal limitation is a common situation during infection and can have profound effects on the pathogen’s success
The hlyCABDII operon (hlyII)-J96 operon was the first hlyCABD operon cloned from human isolates and used to substantiate the contribution of HlyA to Uropathogenic Escherichia coli (UPEC) virulence[25,26]
The presence of two hlyCABD operons in the UPEC isolates J96 and 536, with more than 7 Kb DNA sequence sharing 99% identity, is intriguing considering that the presence of large homologous DNA sequences in a chromosome may cause genome instability and result in detrimental effects on bacterial fitness

Summary

Introduction

Metal limitation is a common situation during infection and can have profound effects on the pathogen’s success. Zinc concentration in host fluids can rise in response to bacterial infection and inflammation by its release from damaged or apoptotic cells, and from sequestering proteins such as metallothionein[7]. Studies in both E. coli and B. subtilis have shown that, in response to variations in zinc concentration, cells regulate gene expression using the metalloregulatory protein Zur (zinc uptake regulator) as a sensor. In hemolytic UPEC isolates from humans, the hlyCABD operon is present in the chromosome within pathogenicity islands, together with genes coding for other virulence factors[22,23]. Most hemolytic UPEC strains carry a single copy of the operon, the presence of two functional copies of the hlyCABD operon has been detected in two pyelonephritis isolates, J96 and 53623

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