The WHO has identified antibiotic resistance as one of the major threats to human health. According to predictions, the number of deaths related to antibiotic resistance is estimated at 10 million a year by 2050. This situation is prompting scientists to find new molecules, ideally natural ones, whose structures and mode of action differ from those of conventional antibiotics, to overcome the phenomena of resistance. One promising alternative concerns antimicrobial peptides of the RiPPs family (ribosomally synthesized and post-translationally modified peptides) produced by bacteria. Numerous studies show that the intestinal microbiome plays a very important role in the health of the host. Among the mechanisms involved, the production of antimicrobial peptides appears to be of particular importance. Part of our collaborative work aims to identify new antimicrobial peptides from complex biological ecosystems using metagenomic methods. To date, we have identified ten potentially interesting sequences. In this project, we will focus on the biosynthesis as well as the biochemical and structural characterizations of the antimicrobial peptides. An important part of the project will be devoted to the biological activity of these compounds on resistant and multi-resistant pathogens to conventional antibiotics. Moreover, the mode of action and the toxicity of the most effective peptides will be addressed.