Introduction and objectives: Quorum-sensing (QS) is a communication mechanism used by bacteria to control various functions such as bioluminescence, competence for transformation or virulence factor production. QS regulates the expression of genes in a coordinated way when the concentration of secreted signaling molecules overcome a given threshold during the bacterial growth. In Gram-positive bacteria, these molecules called auto-inducers or pheromones are mainly oligopeptides. Pheromones’ life-cycle is divided into four steps: intracellular production, maturation and secretion, which remain poorly known, followed by detection and regulation of the expression of target genes. Streptococcus thermophilus used in dairy industry for fermentation is known to have QS systems with pheromones called SHP (Short Hydrophobic Peptides) associated to transcriptional regulators of Rgg family(1). In S. thermophilus, we want to dissect the role of PptAB, an ATP Binding Cassette transporter, known to export SHP pheromones in Streptococcus agalactiae (2) and Streptococcus pyogenes (3). Material and methods: To identify if the transporter PptAB is necessary for the activation of the SHP/Rgg mechanisms found in S. thermophilus, we used a genetic approach with transcriptional reporters composed of promoter regions of target genes of three different QS systems fused with reporter genes luxAB. These fusions were introduced by natural transformation in the chromosome of a wild-type (WT) strain and a mutant strain (ΔpptAB). To study the role of PptAB in the secretion of the mature pheromones, we used mass spectrometry (MS) to research mature forms of SHP pheromones in supernatants of WT and ΔpptAB strains. Results, discussion and conclusion: With the genetic approach, we observed that only promoter regions of targets genes from WT reporter strains were activated compared to ΔpptAB reporter strains by measuring the relative amount of light emitted by the reporter gene. Hence, we confirmed the involvement of PptAB in the activation of the studied QS systems. By MS, spectra corresponding to mature forms of two studied SHP pheromones were detected only in the supernatant of the WT strain compared to ΔpptAB strain. This showed the involvement of PptAB in secretion of the studied pheromones. Bibliographic references: 1-Fleuchot B, Gitton C, Guillot A, Vidic J, Nicolas P, Besset C et al. 2011. Rgg proteins associated with internalized small hydrophobic peptides: a new quorum‐sensing mechanism in streptococci. Mol Microbiol. 80(4), 1102-1119. 2-Pérez-Pascual D, Gaudu P, Fleuchot B, Besset C, Rosinski-Chupin I, Guillot A et al. 2015. RovS and its associated signaling peptide form a cell-to-cell communication system required for Streptococcus agalactiae pathogenesis. MBio. 6(1), e02306-14. 3-Chang JC, Federle MJ. 2016. PptAB exports Rgg quorum-sensing peptides in Streptococcus. PLoS One. 11(12), e0168461.