The study of the pheromone exporter PptAB reveals crosstalk between different quorum sensing systems in Streptococcus thermophilus

International audience ; In Gram-positive bacteria, oligopeptides are the signaling molecules of quorum sensing (QS) mechanisms whose life cycles follow four steps: intracellular production, maturation and secretion followed by detection and regulation of the expression of target genes. Streptococcus thermophilus strain LMD-9 possesses 5 QS systems. Their functioning rely on pheromones called SHP (Short Hydrophobic Peptides) associated to transcriptional regulators of the Rgg family whose encoding genes are colocated on the chromosome. In this bacterium, we have established the role of PptAB, an ATP Binding Cassette transporter, known to export SHP in other streptococci.By comparing the transcriptomes of a ΔpptAB mutant with that of a wild-type background, we showed that the transcription of genes located downstream of each of the 5 rgg genes (target genes) requires the expression of pptAB. This suggests that the expression of these target genes is controlled by SHP pheromones exported by PptAB. However, only three shp genes were expressed and their corresponding peptides detected by mass-spectrometry in our experimental condition. Thus, these results highlighted the complex interconnected network that exists between SHP/Rgg systems. We confirmed this interconnection by the study of one locus and we showed that the target genes of this locus are controlled by at least two other distant SHPs.