en Biotechnology Biotechnology پژوهشي Orginal research papers <span lang="TR" style="font-size:11.0pt"><span calibri="" style="font-family:"><span style="color:black">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, <i>Vibrio</i> and <i>Bacillus</i> genera were the dominant frequency. The minimum inhibitory concentration of the extracted metabolites was recorded in the range of 64 to 512 &micro;g/mL. The IC₅₀ of antioxidant activity varied from 73.42 to 670.90 &micro;g/mL. The cytotoxic activity of the extracted metabolites ranged from 40.57 to 181.80 &micro;g/mL against SW 480 cell line and 141.30 to 359.70 &micro;g/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 <i>B. safensis</i>,<i> V. alginolyticus</i>, <i>V. rotiferianus</i>, <i>B. aureus</i> and <i>Pseudomonas</i> <i>paralactis</i>, respectively. The present study provided a new understanding of the diversity pattern and biological activity of the bacteria associated with <i>Haliclona</i> <i>oculata</i>.</span></span></span><span style="font-size:11pt"><span style="line-height:200%"><span style="font-family:Calibri,sans-serif"><span style="font-size:12.0pt"><span style="line-height:200%"><span new="" roman="" style="font-family:" times=""> </span></span></span></span></span></span> Antimicrobial activity, Antioxidant activity, Bacterial metabolites, Cytotoxic activity, Marine sponge, Persian Gulf 739 755 http://jifro.ir/browse.php?a_code=A-10-673-4&slc_lang=en&sid=1 N. Nasiri n.nasiri1389@gmail.com 100319475328460052600 100319475328460052600 Yes Department of Marine Biology, Faculty of Marine Science and Technology, University of Hormozgan, Bandar Abbas, Iran M.R. Taherizadeh taheri.1965@gmail.com 100319475328460052601 100319475328460052601 No Department of Marine Biology, Faculty of Marine Science and Technology, University of Hormozgan, Bandar Abbas, Iran M. Gozari m_gozari@yahoo.com 100319475328460052602 100319475328460052602 No Persian Gulf and Sea of Oman Ecology Research Institute, Fisheries Research Institute, Agricultural Research, Education and Extension Organization, Bandar Abbas, Iran S. Tamadoni jahromi Stamadoni@gmail.com 100319475328460052603 100319475328460052603 No Persian Gulf and Sea of Oman Ecology Research Institute, Fisheries Research Institute, Agricultural Research, Education and Extension Organization, Bandar Abbas, Iran