Inactivation of the Rgg2 transcriptional regulator ablates the virulence of Streptococcus pyogenes

Streptococcus pyogenes adapts to different niches encountered in the human host via the activity of numerous regulatory proteins including the Rgg family of transcriptional regulators. The S. pyogenes chromosome encodes four Rgg paralogues designated Rgg1 (RopB), Rgg2 (MutR), Rgg3, and Rgg4 (ComR). In order to understand the role of the Rgg2 protein in the regulation of metabolic and virulence-associated properties of S. pyogenes, the rgg2 gene was inactivated in the M1 serotype strain SF370. Inactivation of rgg2 increased the growth yield of S. pyogenes in THY broth, increased biofilm formation, and increased production of SIC, which is an important virulence factor that inhibits complement mediated lysis. To identify Rgg2-regulated genes, the transcriptomes of SF370 and the rgg2 mutant strains were compared in the middle-exponential and post-exponential phases of growth. Rgg2 was found to control the expression of dozens of genes primarily in the exponential phase of growth, including genes associated with virulence (sse, scpA, slo, nga, mf-3), DNA transformation, and nucleotide metabolism. Inactivation of rgg2 decreased the ability of S. pyogenes to adhere to epithelial cells. In addition, the mutant strain was more sensitive to killing when incubated with human blood and avirulent in a murine bacteremia model. Finally, inoculation of mice with the avirulent rgg2 mutant of S. pyogenes SF370 conferred complete protection to mice subsequently challenged with the wild-type strain. Restoration of an intact rgg2 gene in mutant strain restored the wild-type phenotypes. Overall, the results demonstrate that Rgg2 is an important regulatory protein in S. pyogenes involved in controlling genes associated with both metabolism and virulence.