Quorum sensing and transcriptional regulation in Gram-positive bacteria.

The bacteriocin production in Lactobacillus plantarum is regulated by the pln regulatory unit which is a quorum-sensing based signal transducing pathway. Such quorum-sensing based regulatory systems are of crucial importance in regulating gene expression in bacteria in response to environmental changes. Processes applying this regulatory mechanism are quite diverse, including virulence in Staphylococcus aureus, competence for DNA uptake in Bacillus subtilis and Streptococcus pneumoniae, sporulation in B. subtilis, conjugal plasmid transfer in Enterococcus faecalis, and bacteriocin production in lactic acid bacteria. The pln regulatory circuit represents hitherto one of the best-studied models of peptide-pheromone based signal transducing pathway in G+ bac teria, and it was also the first peptide-pheromone quorum sensing-based system identified (that later led to the identification of the peptide pheromone involved competence in S. pneumonia!). There exists experimental proof for all steps in the pln signal ling pathway in our working model. However several crucial issues remain to be addressed in order to understand in depth the signalling pathway. (1) The interaction between the induction peptide IP-PlnA and the histidine protein kinase PlnB is poorly unde rstood. (2) The roles of each of the two response regulators PlnC and PlnD have not been fully clarified. Although it is conclusively shown that PlnC up-regulates gene expression, the function of PlnD varies when it is expressed alone and when it is expre ssed in the presence of PlnC. In addition, we have shown that two N-terminally truncated forms of PlnC can be produced by bacteria however; we do not know the biological significance of these findings. These preliminary results will be followed up in this project. (3) Binding constants/affinity of the regulators on DNA regulatory elements need to be determined in order to understand differential regulation of the five operons in the pln regulon.