Functional Analysis of the Quorum-Sensing Streptococcal Invasion Locus (sil)

Ilia Belotserkovsky,Eran Dov,Yoav Smith,Emanuel Hanski,Asaf Peer,Merav Persky,Inbal Mishalian,Moshe Baruch,Miriam Ravins,Michael S Gilmore

doi:10.1371/journal.ppat.1000651

Ilia Belotserkovsky, Eran Dov + Show 8 more

Open Access

https://doi.org/10.1371/journal.ppat.1000651

Copy DOI

Journal: PLoS Pathogens	Publication Date: Nov 6, 2009
Citations: 57	License type: CC BY 4.0

Affiliation: Hebrew University of Jerusalem

Abstract

Group A streptococcus (GAS) causes a wide variety of human diseases, and at the same time, GAS can also circulate without producing symptoms, similar to its close commensal relative, group G streptococcus (GGS). We previously identified, by transposon-tagged mutagenesis, the streptococcal invasion locus (sil). sil is a quorum-sensing regulated locus which is activated by the autoinducer peptide SilCR through the two-component system SilA-SilB. Here we characterize the DNA promoter region necessary for SilA-mediated activation. This site is composed of two direct repeats of 10 bp, separated by a spacer of 11 bp. Fusion of this site to gfp allowed us to systematically introduce single-base substitutions in the repeats region and to assess the relative contribution of various positions to promoter strength. We then developed an algorithm giving different weights to these positions, and performed a chromosome-wide bioinformatics search which was validated by transcriptome analysis. We identified 13 genes, mostly bacteriocin related, that are directly under the control of SilA. Having developed the ability to quantify SilCR signaling via GFP accumulation prompted us to search for GAS and GGS strains that sense and produce SilCR. While the majority of GAS strains lost sil, all GGS strains examined still possess the locus and ∼63% are able to respond to exogenously added SilCR. By triggering the autoinduction circle using a minute concentration of synthetic SilCR, we identified GAS and GGS strains that are capable of sensing and naturally producing SilCR, and showed that SilCR can be sensed across these streptococci species. These findings suggest that sil may be involved in colonization and establishment of commensal host-bacterial relationships.

Highlights

Group A streptococcus (GAS) is a common human pathogen that has major healthcare and economic impacts
By applying transposon-tagged mutagenesis (STM) on a strain isolated from a necrotizing fasciitis (NF) patient (M14 type strain JS95) and using a murine model of human soft-tissue infections, we identified the streptococcal invasion locus [11]
We discovered that GAS and group G streptococcus (GGS) strains naturally produce SilCR and demonstrate, for the first time, that the peptide can be sensed across these streptococci species

Summary

Introduction

Group A streptococcus (GAS) is a common human pathogen that has major healthcare and economic impacts. It causes a variety of human diseases ranging from superficial skin and throat infections to severe life-threatening diseases such as necrotizing fasciitis (NF). The distinction between commensals and pathogenic bacteria in general is blurred This is mainly because both categories of bacteria use common modes of interaction with their hosts [3]. Bacteria communicate by secreting and subsequently sensing signal molecules [4,5] These molecules are termed autoinducers because when their concentration exceeds a given threshold, their own expression, as well as that of other genes, is abruptly activated [4,5]. This activation usually occurs at high bacterial cell densities, which ensures that the increased gene expression only takes place in the presence of a sufficient number (a quorum) of cells, giving this mechanism the name quorum-sensing (QS.)

Methods

Results

Conclusion