Évaluation du potentiel antimicrobien de métabolites d’actinobactéries provenant de l’environnement marin.

Abstract

The increasing resistance of microorganisms to antibiotics has become a major public health concern, highlighting the urgent need to discover new antimicrobial agents. Marine actinobacteria, particularly those belonging to the genus Streptomyces, represent a promising source of bioactive secondary metabolites. This study aimed to isolate and characterize marine actinobacteria, evaluate their antimicrobial and biotechnological potential, and identify strains capable of producing novel compounds of primary pharmaceutical interest. Marine actinobacteria were isolated from algae and marine sediments collected along the coast of Mostaganem, Algeria. The isolates were purified and characterized using morphological, physiological, and biochemical approaches. Their biotechnological potential was assessed through enzymatic activities, plant growth-promoting rhizobacteria traits, and antimicrobial activities. The most promising strains were subsequently cultivated for the production, extraction, and concentration of secondary metabolites, whose antimicrobial activity was evaluated using the disk diffusion method against several pathogenic bacteria and fungi. Eight marine actinobacterial isolates were obtained, including two from algae and six from marine sediments, belonging mainly to the genera Streptomyces, Nocardiopsis, Micromonospora, Microellobosporia, and Streptosporangium. All isolates grew at 3% NaCl, whereas only isolate I₃ maintained abundant growth at 10% NaCl, demonstrating high halotolerance. Among the isolates, strains I₁ and I₃ exhibited the strongest antimicrobial activity. Using the central streak method, they produced complete inhibition (30 mm) against several pathogenic bacteria, including Staphylococcus aureus, Escherichia coli, and Klebsiella pneumoniae. The cross-streak method confirmed the superior performance of isolate I₃, with inhibition zones ranging from 45 to 61 mm, compared with 3 to 21 mm for I₁, indicating broad-spectrum activity against Gram-positive bacteria, Gram-negative bacteria, and Candida albicans. Crude extracts tested by the disk diffusion method produced inhibition zones ranging from 7 to 13.5 mm, with isolate I₃ remaining the most active, although less effective than ciprofloxacin (29–37 mm). Regarding phytopathogenic fungi, extracts from isolates I₁ and I₃ showed activity against the tested strains Alternaria alternata and Alternaria sp. For Alternaria alternata, inhibition diameters were 19 mm for I₁ and 33 mm for I₃, compared to 30 mm for econazole. For Alternaria sp., they were 32 mm for I₁ and 50 mm for I₃, compared to 28 mm for econazole. Furthermore, the isolates showed variable enzymatic activities, including amylolytic, pectinolytic, cellulolytic, proteolytic, and lipolytic activities, as well as some complementary functional traits such as nitrogen fixation and zinc or phosphate solubilization. These findings demonstrate the considerable biotechnological potential of marine actinobacteria isolated from the Mostaganem coastline, particularly isolate I₃, which represents a promising candidate for the production of novel antibacterial and antifungal secondary metabolites.