Characterization of novel marine bacteria isolated from deep Atlantic Ocean in Morocco as a source of natural bioactive compounds to control infections in aquaculture

With the rapid expansion of aquaculture production, there has been a concomitant increase in fish diseases, generally combatted by the utilization of chemicals and antibiotics. However, their overuse leads to the emergence of drug-resistant microorganisms and the appearance of oxidative stress. Consequently, antibiotics contribute to a reduction in fish immune defense. In this work, eight marine bacteria were characterized using physiological, biochemical and microbiological tests, and were evaluated for their safety by studying their haemolytic and gelatinase activities. Then, we evaluated their ability to produce active biomolecules and tested their in vitro antibacterial activities against five bacterial pathogens that are highly prevalent in aquaculture. Moreover, we evaluated their antioxidant potential using DPPH, ABTS and ferric reducing power tests. The obtained results revealed that cell-free supernatants were effective, they exhibited good antioxidant and antibacterial activities. Their biomolecules showed good stability under different temperatures ranging from 60 to 121 °C and were found to be chemically composed of peptides, exopolysaccharides and polyphenols. Therefore, the secreted bioactive substances are of great biotechnological interest and constitute a promising eco-friendly alternative to antibiotics and chemical agents in the context of sustainable aquaculture.