The RepliChroms project aims at decrypting plasmid adaptation mechanisms in their bacterial host. Bacterial genomes are composed of two types of replicons: chromosomes and plasmids. Bacteria commonly have a unique circular chromosome, and current models of genome dynamics are based on this assumption. However, 5-10% of bacteria also have secondary chromosomes which originate from megaplasmids. Secondary chromosomes and megaplasmids also called “chromids” confer specific traits to their host (e.g. pathogenicity, resistance). Incoming plasmids are often poorly adapted to their new hosts and their stabilization requires integration with the host’s cellular mechanisms in a process termed domestication. RepliChroms project focuses on the identification of the fundamental mechanisms driving chromid domestication in bacteria with a detailed description of their replication process.