Exploring Mediterranean and Arctic Environments as a Novel Source of Bacteria Producing Antibacterial Compounds to be Applied in Aquaculture

The need to discover new natural compounds has become urgent as a possible alternativesolution to contrast the spread of antibiotic resistance, also in the aquaculture field. Bacterium-bacterium inhibitory activity against bacterial pathogens relevant in aquaculture was evaluated onagar plates for bacteria isolated from cold Arctic (Kongsfjorden, Svalbard Islands; i.e., seawater andsediment samples) and temperate Mediterranean (Lake Faro in Messina and the Straits of Messina,Italy; i.e., brackish water and benthic filter-feeding organisms) environments. Cell-free supernatants(both pure and concentrated 10-fold) were further assayed and, in the case of a positive response,crude extracts were obtained and tested. After the pre-screening procedures, about 30% of thebacterial isolates inhibited the growth of at least one pathogen used as a target. The 10-foldconcentrated supernatants of two Arctic Salinibacterium spp. strains and the Mediterranean Bacillussp. PS62 (associated with the pennatulacean Pteroeides spinosum Ellis, 1764) resulted in being activeagainst P. damselae subsp. piscicida. The crude extracts obtained from Bacillus sp. PS62 also showedinhibitory activity against the same pathogen. Our findings suggest that tested bacteria couldrepresent a novel source of compounds to be applied to overcome pathogenesis in the aquaculturefield.