Fungal infections are an evolving public health challenge due to their antimicrobial resistance and the growth of immunocompromised populations. Aquatic environments, the largest ecosystem on earth, are recently considered as a source for the production of bioactive compounds. Marine actinomycetes are considered for their potential to produce novel bioactive metabolites like antifungal compounds. In this study, strain ADR10 was obtained from the sediment sample of the Caspian Sea and its 16S rDNA gene sequence analysis suggested that the isolate belongs to Streptomyces albidoflavus. The preliminary cross-streak and double-layer agar screening revealed that the isolate has potent activity against pathogenic fungi, i.e. Aspergillus niger, Candida albicans, Fusarium oxysporum, and Penicillium crustosum. One-factor-at-a-time and Response surface methodology (RSM) was employed to evaluate the effects of six parameters (carbon source, initial pH, inoculation volume, NaCl concentration, nitrogen source, and temperature) on the production of antibiotics in the basal starch casein broth medium. The maximum antibiotic activity was achieved at the initial pH 7.05, sucrose 1.17 g l-1, malt 0.2 g l-1, temperature 30 ºC, inoculation size 5.0% v/v, and NaCl 1% w/v after 121.1 hours. Through the optimization experiments, antifungal activity was enhanced 2.7-fold. Ethyl acetate showed the highest antibiotic extraction capacity from the fermentation media compared with dichloromethane, hexane, and chloroform. The preliminary purified antibiotic by thin layer chromatography (ethyl acetate/ mobile petroleum phase) showed a more significant growth inhibition zone than nystatin (100 μg mL-1) against Candida albicans. This study underlines the potential of the marine actinomycete for the identification of novel antifungal agents.

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