Mediterranean grey mullets intestinal microbiota: isolation and identification of bacteria with surfactant and antibacterial activities

Fish gut represents a peculiar ecological niche where bacteria can transit and reside to playvital roles by producing bio-compounds with nutritional, immunomodulatory and other functions.This complex microbial ecosystem reflects several factors (environment, feeding regimen, fish species,etc.). The objective of the present study was the identification of intestinal microbial strains able toproduce molecules called biosurfactants (BSs), which were tested for surface and antibacterial activityin order to select a group of probiotic bacteria for aquaculture use. Forty-two bacterial isolates fromthe digestive tracts of twenty Mediterranean grey mullets were screened for testing emulsifying(E-24), surface and antibiotic activities. Fifty percent of bacteria, ascribed to Pseudomonas aeruginosa,Pseudomonas sp., P. putida and P. anguilliseptica, P. stutzeri, P. protegens and Enterobacter ludwigii werefound to be surfactant producers. Of the tested strains, 26.6% exhibited an antibacterial activityagainst Staphylococcus aureus (10.0 ± 0.0-14.5 ± 0.7 mm inhibition zone), and among them, 23.3%of isolates also showed inhibitory activity vs. Proteus mirabilis (10.0 ± 0.0-18.5 ± 0.7 mm inhibitionzone) and 6.6% vs. Klebsiella pneumoniae (11.5 ± 0.7-17.5 ± 0.7 mm inhibition zone). According topreliminary chemical analysis, the bioactive compounds are suggested to be ascribed to the class ofglycolipids. This works indicated that fish gut is a source of bioactive compounds which deserves tobe explored.