A common form of gene transfer is the vertical gene transfer between one organism and its offspring during sexual reproduction. However, some organisms, such as bacteria, are able to acquire genetic material independently of sexual reproduction by horizontal gene transfer (HGT). Three mechanisms mediate HGT in bacteria: conjugation, transduction and natural transformation. HGT and the selective pressure exerted by the widespread use antibiotics (in medicine, veterinary medicine, agriculture, animal feeding, etc) are responsible for the rapid spread of antibiotic resistance genes among pathogenic bacteria.In this proposal, we focus on bacterial transformation systems, also named competence systems. Natural transformation is the acquisition of naked DNA from the extracellular milieu. It is the only programmed process for generalized genetic exchange found in bacteria. This highly efficient and regulated process promotes bacterial genome plasticity and adaptive response of bacteria to changes in their environment. It is essential for bacterial survival and/or virulence and greatly limits efficiency of treatments or vaccine against some pathogenic bacteria.The architecture and functioning of the membrane protein complexes mediating DNA transfer through the cell envelope during bacterial transformation remain elusive. We want to decipher the molecular mechanism of this transfer. To attain this goal, we will carry out structural biology studies (X-ray crystallography and high resolution electron microscopy) as well as functional and structure-function in vivo studies. We have the ambition to make major contributions to the understanding of bacterial transformation. Ultimately, we hope that our results will also help to find compounds that could block natural transformation in bacterial pathogens.