Competence-associated peptide BriC alters fatty acid biosynthesis in Streptococcus pneumoniae

Abstract

Membrane lipid homeostasis is required for bacteria to survive in a spectrum of host environments. This homeostasis is achieved by regulation of fatty acid chain length and of the ratio of saturated to unsaturated fatty acids. In the pathogen Streptococcus pneumoniae, fatty acid biosynthesis is encoded by a cluster of fatty acid biosynthesis (fab) genes (FASII locus) whose expression is controlled by the FabT repressor. Encoded immediately downstream of the FASII locus is BriC, a competence-induced, cell-cell communication peptide that promotes biofilm development as well as nasopharyngeal colonization in a murine model of pneumococcal carriage. Here, we demonstrate that briC is co-transcribed with genes of the fab gene cluster and that a reduction of briC levels, caused by decoupling its transcription from fab gene cluster, negatively impacts biofilm development. BriC elevates fabT transcription, which is predicted to alter the balance of saturated and unsaturated fatty acids produced by the pathway. We find that briC inactivation results in a decreased production of unsaturated fatty acids that impact the membrane properties by decreasing the abundance of di-unsaturated phosphatidylglycerol molecular species. We propose that the link between BriC, FabT and phospholipid composition contributes to the ability of S. pneumoniae to alter membrane homeostasis in response to the production of a quorum-sensing peptide. IMPORTANCEAdaptation of bacteria to their host environment is a key component of colonization and pathogenesis. As an essential component of bacterial membranes, fatty acid composition contributes to host adaptation. Similarly, so does cell-cell communication, which serves as a mechanism for population levels responses. While much is known about the pathways that control the biosynthesis of fatty acids, many questions remain regarding regulation of these pathways and consequently the factors that impacts the balance between saturated and unsaturated fatty acids. We find that BriC, a cell-cell communication peptide implicated in biofilm regulation and colonization, is both influenced by a fatty acid biosynthesis pathway and impacts this same pathway. This study identified a link between cell-cell communication, fatty acid composition, and biofilms and, in doing so, suggests that these pathways are integrated into the networks that control pneumococcal colonization and host adaptation.