A Quorum Sensing-Regulated Protein Involved in Biofilm Formation and Lysozyme Resistance in S pyogenes

Cell-to-cell communictation events in bacteria coordinate collective behaviours in a process known as quorum sensing (QS). QS systems are based on the basic mechanism of production, accumulation, and detection of chemical signal termed autoinducing peptides or pheromones. Recently, a novel QS pathway in the human pathogen Streptococcus pyogenes has been characterized, the Rgg2/3 pathway. While the molecular events involved in the signaling through the Rgg2/3 pathway are well understood, the behaviours regulated and their effect over the physiology of S. pyogenes are unknown. In this work we show how the activation of Rgg2/3 signaling by the use of QS pheromones triggers the processes of cellular aggregation and biofilm formation in the NZ131 isolate of S. pyogenes. In order to understand the molecular mechanisms at work, we generated deletions in several target genes of Rgg2/3 and followed biofilm formation. Results showed that a small secreted protein, 0414c, was required and sufficient to trigger biofilm increase. Additionally, lysozyme resistance, a novel phenotype related with Rgg2/3 activation, was also dependent on 0414c. Bioinformatic analysis has led us to hypothesize that 0414c works as a cysteine protease inhibitor protein. Our initial characterization of 0414c inhibition-targets point towards a role for 0414c in modulating the activity of cysteine proteases that may have roles in tailoring the components cellular envelope of S. pyogenes.