Mickaël Maziero will present their research on the competence induction pathways caracterisation for Streptococcus pneumoniae transformation.
Abstract :
Streptococcus pneumoniae is a pathogenic bacterium commensal of human nasopharynx. This bacterium is involved in multiple pathologies such as pneumonia, otitis media and meningitis. According to the world health organisation, it is responsible for several million deaths per year. This bacterium poses many problems due to its adaptability skill based on its ability to perform natural genetic transformation. Natural transformation allows cells to capture exogenous DNA in the external environment, internalize it into the cytoplasm and recombine it into the chromosome by homologous recombination. By this way, pneumococcus is able to easy acquire new genetic traits. This ability is transient and only takes place during a stress-induced physiological state called competence. The comCDE operon is the central element in triggering the competence state. The secreted peptide encoded by the comC gene is capable of activating the two-component regulatory system ComD/E. Sequentially at this activation, ComD/E which will auto-activate its own transcription, generating an positive autocatalytic loop and resulting in a rapid populational switch to competence. Due to its exponential propagating nature, competence must be tightly regulated. However, the external stimuli and molecular signalling pathways controlling competence development remain poorly characterized. The work of this thesis aims to address this issue. We have demonstrated that fever-level temperatures induce competence. We have characterized the molecular pathway linking this stress to the comCDE operon. We have also shown that this induction pathway is not the only one for competence stimulation and that at least one independent second exists and involves a toxin/antitoxin system cibling the cellular DNA replication machinery. The fact that there is an existence of multiple pathways converging on the comCDE operon strongly suggests that competence is a general stress regulon and that is highly linked to the pneumococcal cell cycle.