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Infect Immun. 2014 Aug;82(8):3446-56. doi: 10.1128/IAI.01824-14. Epub 2014 Jun 2.

A specific polymorphism in Mycobacterium tuberculosis H37Rv causes differential ESAT-6 expression and identifies WhiB6 as a novel ESX-1 component.

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  • 1Grupo de Genética de Micobacterias, Departamento de Microbiología, Medicina Preventiva y Salud Pública, Facultad de Medicina, Universidad de Zaragoza, Zaragoza, Spain CIBER Enfermedades Respiratorias, Instituto de Salud Carlos III, Madrid, Spain.
  • 2Grupo de Genética de Micobacterias, Departamento de Microbiología, Medicina Preventiva y Salud Pública, Facultad de Medicina, Universidad de Zaragoza, Zaragoza, Spain CIBER Enfermedades Respiratorias, Instituto de Salud Carlos III, Madrid, Spain Servicio de Microbiología, Hospital Universitario Miguel Servet, ISS Aragón, Zaragoza, Spain.
  • 3Institut Pasteur, Unit for Integrated Mycobacterial Pathogenomics, Paris, France.
  • 4Grupo de Genética de Micobacterias, Departamento de Microbiología, Medicina Preventiva y Salud Pública, Facultad de Medicina, Universidad de Zaragoza, Zaragoza, Spain CIBER Enfermedades Respiratorias, Instituto de Salud Carlos III, Madrid, Spain jagonzal@unizar.es.

Abstract

The ESX-1 secreted virulence factor ESAT-6 is one of the major and most well-studied virulence factors of Mycobacterium tuberculosis, given that its inactivation severely attenuates virulent mycobacteria. In this work, we show that clinical isolates of M. tuberculosis produce and secrete larger amounts of ESAT-6 than the widely used M. tuberculosis H37Rv laboratory strain. A search for the genetic polymorphisms underlying this observation showed that whiB6 (rv3862c), a gene upstream of the ESX-1 genetic locus that has not previously been found to be implicated in the regulation of the ESX-1 secretory apparatus, presents a unique single nucleotide insertion in its promoter region in strains H37Rv and H37Ra. This polymorphism is not present in any of the other publicly available M. tuberculosis complex genomes or in any of the 76 clinical M. tuberculosis isolates analyzed in our laboratory. We demonstrate that in consequence, the virulence master regulator PhoP downregulates whiB6 expression in H37Rv, while it upregulates its expression in clinical strains. Importantly, reintroduction of the wild-type (WT) copy of whiB6 in H37Rv restored ESAT-6 production and secretion to the level of clinical strains. Hence, we provide clear evidence that in M. tuberculosis--with the exception of the H37Rv strain--ESX-1 expression is regulated by WhiB6 as part of the PhoP regulon, which adds another level of complexity to the regulation of ESAT-6 secretion with a potential role in virulence adaptation.

Copyright © 2014, American Society for Microbiology. All Rights Reserved.

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