Biodiversity and screening of antimicrobial, antioxidant, and cytotoxic activity of bacteria isolated from the Persian Gulf sponge (Halicona oculata)

Screening of marine bacteria for developing new drugs is an emerging field in marine biotechnology. The purpose of this study was to investigate the diversity of sponge-associated bacteria from Kish and Larak islands (Persian Gulf) and to determine their antimicrobial, antioxidant, and cytotoxic activities. After sampling, bacteria were grown on the marine sponge agar medium. The isolated bacteria were characterized by polyphasic methods. The antimicrobial activity of the isolated bacteria was determined by the microdilution broth method. Cytotoxic activity was evaluated by MTT (3-4,5-dimethylthiazol-2yl-2,5-diphenyltetrazolium bromide) assay on human cell lines. Antioxidant activity was performed by inhibiting DPPH free radicals. Among 121 bacterial isolates, Vibrio and Bacillus genera were the dominant frequency. The minimum inhibitory concentration of the extracted metabolites was recorded in the range of 64 to 512 µg/mL. The IC50 of antioxidant activity varied from 73.42 to 670.90 µg/mL. The cytotoxic activity of the extracted metabolites ranged from 40.57 to 181.80 µg/mL against SW 480 cell line and 141.30 to 359.70 µg/mL against HepG2 cell line. The HL 15, HL 85, and HK 5 extracts showed less toxicity against human umbilical vein endothelial cells. The results of genetic identification based on the comparison of 16S rRNA gene sequence showed that the potent strains HL 15, HL 24, HL 85, HK 5, and HK 36 belonged to B. safensis, V. alginolyticus, V. rotiferianus, B. aureus and Pseudomonas paralactis, respectively. The present study provided a new understanding of the diversity pattern and biological activity of the bacteria associated with Haliclona oculata.