Active substances such as antimicrobial peptides (AMPs) defined as antibiotics naturally produced by
all living species, have already been characterized and identified from various marine organisms (fish, sponges,
annelids, echinoderms, crustaceans, molluscs and tunicates) except from nematodes. In this study, we
investigated the biochemical isolation of antibacterial substances from three free-living marine nematodes
belonging to the Oncholaimidae family that dominated meiofauna of two coastal environments characterized by
reduced and hypoxic sediments with high concentration of sulfides (Roscoff Harbour in France and Secca delle
Fumose in Italy). There are no consensus sequences for AMPs which are even more diversified in the marine
environment compared to the terrestrial one. A bioassay guided purification protocol was used since it
constitutes the only method to find novel active peptides. Data showed the potential of two of the three
nematodes species as interesting sources of small sized antibiotics. The third species showed an occasional
epi-symbiotic association with filamentous bacteria, but singularly lacked antimicrobial activity. The lack of
biological material did not allow the identification of the antimicrobial molecules