Biol. Mar. Mediterr. (2014), 21 (1): 341-342 R. FLORIS, G. SCANU, N. FOIS, J. KUEGLER 1 , R. MALAVENDA 2 AGRIS-Sardegna Agenzia per la Ricerca in Agricoltura, Dip. Ricerca Produzioni Animali, Loc. Bonassai, S.S. 291 km 18.600 - 07040 Olmedo (SS), Italy. rfloris@agrisricerca.it 1 Inst. Proc. Engineering Life Science, Sect. Tech. Biol., Karlsruhe Inst. of Technol., Karlsruhe, Germany. 2 Dip. Scienze Biologiche ed Ambientali, Università di Messina, Messina, Italy. BIOACTIVE COMPOUNDS PRODUCTION BY BACTERIA ISOLATED FROM THE INTESTINAL TRACT OF GILTHEAD SEA BREAM ( SPARUS AURATA LINNAEUS, 1758) FROM COASTAL MARINE ENVIRONMENTS OF SARDINIA ISLAND (ITALY) PRODUZIONE DI COMPOSTI BIOATTIVI DA PARTE DI BATTERI ISOLATI DAL TRATTO INTESTINALE DI ORATE (SPARUS AURATA LINNAEUS, 1758) PROVENIENTI DA AMBIENTI MARINO-COSTIERI DELLA SARDEGNA (ITALIA) Abstract - The aim of the present study was to detect biosurfactant-producing bacteria isolated from the intestine of gilthead sea bream from Sardinian aquatic environments. A total of 100 microbial strains from three groups of fish were screened by different tests: emulsification index (E24), microplate and drop-collapse tests and CTAB assay. Thin-layer chromatography (TLC) was performed for characterising the presumptive biosurfactant-producers bacterial products. The most interesting strains belong to Pseudomonas spp. and Psychrobacter spp. which showed a stable emulsion and a good surface tension activity. Key-words: biosurfactants, gut microflora, natural emulsifier, bioremediation. Introduction - Biosurfactants are biodegradable surface-active compounds produced by a wide variety of microorganisms. They play several important functions such as bioremediation of hydrocarbon, organic pollutants and heavy-metal-contaminated sites, and a potential role in stimulating plant and animal defence responses against microbes has been reported. Previous researches on the microbial ecology of the intestinal tract of Sparus aurata from Sardinian coastal lagoons showed the presence of a complex bacterial community which provide information about the origin of the aquatic environment (Floris et al., 2013). The aim of the present work was to screen these intestinal bacteria for the ability of producing natural biosurfactants in order to select candidate strains of fish origin to be investigated as beneficial microbes for biotechnological applications in aquaculture. Materials and methods - A total of 100 strains was isolated from the gut of gilthead sea bream from three different aquatic environments along Sardinian coast (Alghero Bay, north western Sardinia; Tortoli lagoon, eastern Sardinia and Porto Pino lagoon, southern Sardinia). The strains were tested for biosurfactant production in two or three independent experiments after incubation with shaking (200 rpm) in Bushnell-Hass medium (BH-Himedia) with sunflower oil (2% v/v) at 25-27 °C for 48-72h. Bacterial growth was monitored by measuring the optical density at OD 600 and the pH values. Microbial culture were screened for biosurfactant production in duplicate during all growth phases by the following tests: emulsification index (E24) (Tuleva et al. , 2002), qualitative microplate (Chen et al. , 2007) and drop collapse assays (Bodour et al., 2003) for testing surface activity and CTAB assay. The bacterial cultures which showed positive results in the performed tests were further investigated by extracting the presumptive biosurfactants and characterizing them by thin-layer chromatography (TLC) according to Samadi et al. (2007). Bacterial strains