Consequences of the variability of the CovRS and RopB regulators among Streptococcus pyogenes causing human infections.

Ana Friães,Mario Ramirez,Catarina Pato,José Melo-Cristino

doi:10.1038/srep12057

Abstract

To evaluate the importance of covRS and ropB mutations in invasive disease caused by Group A Streptococci (GAS), we determined the sequence of the covRS and ropB genes of 191 isolates from invasive infections and pharyngitis, comprising a diverse set of emm types and multilocus sequence types. The production of SpeB and the activity of NAD glycohydrolase (NADase) and streptolysin S (SLS) were evaluated. The results support the acquisition of null covS alleles (predicted to eliminate protein function), resulting in downregulation of SpeB and upregulation of NADase and SLS, as a mechanism possibly contributing to higher invasiveness. Among the isolates tested, this mechanism was found to be uncommon (10% of invasive isolates) and was not more prevalent among clones with enhanced invasiveness (including M1T1) but occurred in diverse genetic backgrounds. In lineages such as emm64, these changes did not result in upregulation of NADase and SLS, highlighting the diversity of regulatory pathways in GAS. Despite abrogating SpeB production, null alleles in ropB were not associated with invasive infection. The covRS and ropB genes are under stabilising selection and no expansion of isolates carrying null alleles has been observed, suggesting that the presence of these regulators is important for overall fitness.

Highlights

Nucleotide diversity in the downregulation of proteins like the extracellular cysteine protease SpeB and the protein-G-related α 2-macroglobulin-binding protein GRAB7,8
Contrasting results have been reported regarding the effect of covRS mutations in some of those virulence factors, which may be partly explained by the interaction of CovRS with other transcriptional regulators, resulting in complex regulation patterns that can vary between different strains[8,9]
The sequence of the covR, covS, and ropB genes was determined for a collection of 191 isolates (Supplementary Table S1) comprising one third of the isolates of each emm type present in a larger collection of strains recovered from pharyngitis and invasive infections in Portugal, which has been characterized elsewhere[21]

Summary

Introduction

Nucleotide diversity in the downregulation of proteins like the extracellular cysteine protease SpeB and the protein-G-related α 2-macroglobulin-binding protein GRAB7,8. RopB ( known as Rgg) is encoded by the ropB (rgg) gene, which is located 940 bp away from speB, in the opposite DNA strand, and directly binds the promoter of the latter gene to activate its transcription[13] In some strains, this regulator has been reported to affect the transcription of other virulence factors, including DNases, the hyaluronic acid capsule, NADase, streptokinase, streptolysins, and phage-encoded superantigens, among others[10,11]. The genetic diversity of the genes was evaluated, and the respective alleles were correlated with the activity of SpeB and of two other virulence factors whose expression has been suggested to be under the influence of CovRS and RopB, at least in some strains, namely the NADase and the streptolysin S (SLS)[7,11,18,24]

Methods

Results

Conclusion