A novel two-component signal transduction system in propionibacterium acnes and its association with a putative extracellular signalling peptide

Propionibacterium acnes, a resident micro-organism of human skin, is thought to be involved in the development of inflammatory acne, which is an exclusive human disease affecting more than 80% of the whole population. Quorum sensing is the regulation of gene expression in response to cell density. As it is often involved in pathogenecity of bacteria, its signal transduction pathway has been suggested as potential target for new drug development. This project identified a putative unique quorum sensing system of P. acnes, consisting of a putative signalling peptide, and divergently transcribed histidine kinase and response regulator. The aim of this project is to investigate the relationship among these three components as being elements of a putative quorum sensing system. Using purified proteins and in vitro phosphorylation assays, the histidine kinase was demonstrated to phosphorylate the response regulator indicating they may constitute a legitimate pair of a two-component system, despite being encoded by divergently transcribed genes. By mapping transcriptional start site, it was found that the signalling peptide and histidine kinase were co-transcribed from the same start site, suggesting that the signalling peptide was associated with the two-component system. Gene expression analysis also revealed these three genes were co-regulated during the growth of P.acnes, which is consistent with these three genes functioning together as a part of quorum sensing system. The results of this project suggested that the signalling peptide, histidine kinase and response regulator are associated with each other and may constitute a quorum sensing system.