This project focuses on the molecular study of small plasmids (circular and linear), insertion sequences and conjugative plasmids isolated from Bacillus cereus and Bacillus thuringiensis in order to 1) gather new insights into the transposition and transfer mechanisms among gram-positive bacteria, 2) evaluate the contribution of these elements to the genomic flexibility of these bacteria, 3) to assess the distribution and diversity of these genetic elements inside the Bacillus cereus sensu lato group.