Marine biofilms as reservoirs of antimicrobial bacteria: molecular identification and functional characterization of epibiotic culturable communities from biofouling invertebrates in northern Tunisia

Marine biofouling communities constitute a rich reservoir of microbial diversity and represent a promising source of bioactive metabolites. In this study, we investigated culturable epibiotic bacteria associated with fouling invertebrates from the Marina in northern Tunisia, with a focus on their enzymatic activities, antimicrobial potential, and antibiotic resistance profiles. A total of 52 bacterial isolates were recovered from 23 fouling invertebrate hosts and characterized using DNA barcoding and molecular identification. The epibiotic culturable bacterial community was dominated by members of the genera Vibrio , Photobacterium , Halomonas , and Pseudomonas . Enzymatic screening revealed a high hydrolytic potential, with DNase (71.2%), lipase (65.4%), and gelatinase (59.6%) being the most prevalent activities. Antimicrobial assays showed that a substantial proportion of isolates exhibited inhibitory activity against at least one pathogenic indicator strain, whereas antibiotic susceptibility testing revealed frequent resistance, particularly to fosfomycin and cefoxitin. Together, these findings highlight the dual nature of epibiotic culturable bacteria in the Marina in northern Tunisia, acting both as a reservoir of biotechnologically valuable antimicrobial producers and as potential carriers of antibiotic resistance, underscoring their ecological relevance and public health significance in Mediterranean coastal ecosystems.