Group A Streptococcus (GAS), a pathogen capable of both localized and systemic infection, is known to secrete numerous virulence factors in temporal patterns during growth in vitro and in vivo, indicating the presence of intricate regulatory circuits. An inverse relationship exists between expression levels of the secreted cysteine protease, SpeB, and severity of disease [1-3]. The so-called "stand-alone" regulator Rgg (also known as RopB) is required, but is not sufficient, for expression of SpeB. An unknown growth-phase-dependent factor is additionally required, but has remained elusive [4-6]. Our preliminary data demonstrate that the unknown factor is a bacterially-produced pheromone with properties consistent with a small peptide. Additionally, analysis predicts that Rgg is a peptide-binding transcription factor with structural homology to PlcR and PrgX of other quorum sensing systems. The overall hypothesis to be tested is that a pheromone modulates the activity of Rgg for the purpose of controlling speB transcription. This is a departure from the paradigm that the Rgg-dependent pathway responds to environmental changes;instead, we provide compelling evidence that GAS produces its own impetus to induce speB. Our preliminary results demonstrate that Rgg paralogs found in GAS are indeed responsive to small peptide pheromones, providing a convincing precedent for our hypothesis and are the first examples that Rgg proteins are quorum sensing effectors. The goal of our research will be to define the signaling pheromone(s) present in culture supernatants and characterize the mechanism for its production and recognition by GAS. Genetic disruption of these systems will be tested for their contributions in localized and invasive infection models. Demonstration that GAS utilizes Rgg proteins for cell-to-cell signaling will provide a foundation for future development of therapies designed to interfere with intercellular signaling in GAS and in other Rgg-containing organisms.

Public Health Relevance

We are defining how Group A Streptococcus uses cell-to-cell communication to regulate expression of genes contributing to its virulence. We have found that a previously uncharacterized pheromone controls expression of a major virulence factor. We will conduct experiments designed to elucidate what this pheromone is, how it is made, and how it elicits its control of gene expression. Our research will provide a basis for alternative antimicrobial therapies aimed at interfering with bacterial communication to control virulence.

Agency
National Institute of Health (NIH)
Institute
National Institute of Allergy and Infectious Diseases (NIAID)
Type
Research Project (R01)
Project #
5R01AI091779-03
Application #
8487351
Study Section
Bacterial Pathogenesis Study Section (BACP)
Program Officer
GU, Xin-Xing
Project Start
2011-07-01
Project End
2016-06-30
Budget Start
2013-07-01
Budget End
2014-06-30
Support Year
3
Fiscal Year
2013
Total Cost
$368,950
Indirect Cost
$133,950
Name
University of Illinois at Chicago
Department
Microbiology/Immun/Virology
Type
Schools of Medicine
DUNS #
098987217
City
Chicago
State
IL
Country
United States
Zip Code
60612
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