Quorum sensing regulation of a major facilitator superfamily transporter affects multiple streptococcal virulence factors

Abstract

Cell-cell signaling mediated by Rgg-family transcription factors and their cognate pheromones is conserved in Firmicutes, including all streptococci. In Streptococcus pyogenes, or Group A strep, one of these systems, the Rgg2/3 quorum sensing (QS) system, has been shown to regulate phenotypes including cellular aggregation and biofilm formation, lysozyme resistance, and macrophage immunosuppression. Here, we show that the abundance of several secreted virulence factors (streptolysin O, SpyCEP, and M protein) decreases upon induction of QS. The main mechanism underlying the changes in protein levels appears to be transcriptional, occurs downstream of the QS circuit and is dysregulated by the deletion of an Rgg2/3 QS-regulated major facilitator superfamily (MFS) transporter. Additionally, we identify this MFS transporter as the factor responsible for a previously observed increase in aminoglycoside sensitivity in QS-induced cells. ImportanceThe production of virulence factors is a tightly regulated process in bacterial pathogens. Efforts to elucidate the mechanisms by which genes are regulated may advance the understanding of factors influencing pathogen behavior or cellular physiology. This work finds that expression of a major facilitator superfamily (MFS) transporter, which is governed by a quorum sensing (QS) system, impacts the expression of multiple secreted virulence factors and accounts for a documented QS-dependent antibiotic susceptibility. Although the mechanism underlying this effect is not clear, MFS orthologs with high sequence similarity from S. pneumoniae and S. porcinus were unable to substitute indicating substrate specificity of the GAS MFS gene. These findings demonstrate novel associations between the expression of a transmembrane transporter and virulence factor expression and aminoglycoside transport.