en Biotechnology Biotechnology پژوهشي Orginal research papers <span style="font-size:11pt"><span style="line-height:120%"><span style="text-autospace:none"><span style="font-family:Calibri,sans-serif"><span lang="TR" style="font-size:12.0pt"><span style="line-height:120%"><span new="" roman="" style="font-family:" times=""><span style="color:black">There are several studies on biological activities of echinoderms&rsquo; secondary metabolites. Sea cucumbers are known to contain natural products with biological activities. Different sea cucumber species exist in Iranian waters of Oman Sea. We investigated cytotoxic and anti- bacterial activities of <i>Holothuria </i>(<i>Mertensiothuria</i>)<i> leucospilota </i>form Chabahar Bay. We derived four methanolic, chloroformic, n<i>-</i>hexane and aqueous<i> </i>extracts of sea cucumber, <i>H. </i>(<i>Mertensiothuria</i>)<i> leucospilota</i>. The cytotoxic activity of these extracts were evaluated by MTT and brine shrimp lethality assays. Disc diffusion method was used to evaluate antibacterial effect of <i>H</i>. (<i>Mertensiothuria</i>)<i> leucospilota</i></span></span></span></span><span lang="TR" style="font-size:12.0pt"><span style="line-height:120%"><span new="" roman="" style="font-family:" times=""><span style="color:black"> extracts against two gram negative pathogenic bacteria: </span></span></span></span><i><span lang="TR" style="font-size:12.0pt"><span style="line-height:120%"><span new="" roman="" style="font-family:" times=""><span style="color:black">Escherichia coli </span></span></span></span></i><span lang="TR" style="font-size:12.0pt"><span style="line-height:120%"><span new="" roman="" style="font-family:" times=""><span style="color:black">(PTCC 1399)<i> </i>and<i> E. coli K 12</i>(ATCC 23716)<i>, </i>and two gram positive</span></span></span></span><span lang="TR" style="font-size:12.0pt"><span style="line-height:120%"><span new="" roman="" style="font-family:" times=""><span style="color:black"> pathogenic bacteria</span></span></span></span><span lang="TR" style="font-size:12.0pt"><span style="line-height:120%"><span new="" roman="" style="font-family:" times=""><span style="color:black">:<i> Staphylococcus aureus</i> (ATCC 25923) and <i>Listeria monocytogenes </i>(ATCC 19117). Methanolic extract (100 mg/mL) was effective on <i>S. aureus </i>and <i>L. monocytogenes </i>while aqueous extract of <i>H</i>. (<i>Mertensiothuria</i>)<i> leucospilota</i> (100 mg/mL) demonstrated antibacterial effect against all tested strain. Chloroformic extract (100 mg/mL) was effective on both <i>E. coli K 12</i> and <i>S. aureus, </i>while<i> </i>n<i>-</i>hexane extract (100 mg/mL) was just effective on <i>E. coli</i>. Studying brine shrimp lethality assay indicated that all experimented extracts had strong cytotoxic activity with LC₅₀= 1.2&ndash;2.3 &micro;g/mL. MEHL, ChEHL and n-hEHL showed cytotoxic effect on Caco-2with 0/6, 0/8 and 1 mg/mL LC_50, respectively. Due to our results, it can be said that <i>Holothuria (Mertensiothuria</i>)<i> leucospilota</i> extracts are potential antibacterial and cytotoxic agents.</span></span></span></span></span></span></span></span> Sea cucumber, Cytotoxic, Antibacterial, Oman Sea 138 155 http://jifro.ir/browse.php?a_code=A-10-3572-1&slc_lang=en&sid=1 S. Keipour sepideh.keypour530@gmail.com 100319475328460047122 100319475328460047122 No Islamic Azad University North Branch M. Emtyazjoo moz_emtyazjoo@yahoo.com 100319475328460047123 100319475328460047123 Yes Islamic Azad University North Branch S.M.H. Ghaderian sghaderian@sbmu.ac.ir 100319475328460047124 100319475328460047124 No Shahid Beheshti University of medical sciences.Tehran, Iran. P. Eghtesadi Araghi Eghtesadi@inio.ac.ir 100319475328460047125 100319475328460047125 No Iranian National Institute for Oceanography and Atmospheric