en ميکروبيولوژي Microbiology پژوهشي Research <p style="text-align: justify;"><strong>Background: </strong>The appearance of <a name="OLE_LINK11"></a><a name="OLE_LINK10">multi-drug resistant microorganisms </a>is becoming a global problem. Already several strategies have been employed to overcome antibiotic resistance issue. <a name="OLE_LINK13"></a><a name="OLE_LINK12">Developing new antimicrobial compounds from microbial sources could be a beneficial solution</a>. Hence screening programs in order to discover new antibiotics from microbial entities are interesting. <a name="OLE_LINK15"></a><a name="OLE_LINK14">Because of high capabilities of extremophiles for adaptation to harsh environmental conditions</a>, the microbial communities of the extreme environments could be regarded as rich resources for new antibacterial metabolites.</p> <p style="text-align: justify;"><strong>Materials and Methods: </strong>In this research different saline environments of Iran have been subjected to screening of antibiotic producing actinomycetes using overlaid method after the ingredient optimization of culture media. <a name="OLE_LINK17"></a><a name="OLE_LINK16">The strain which was shown pronounce inhibition zone in the screening step, </a>has been phylogenetically analyzed followed by studying the effect of agar concentration and cultivation time on the production of antibacterial agent(s).</p> <p style="text-align: justify;"><strong>Results: </strong><a name="OLE_LINK19"></a><a name="OLE_LINK18">The strain RS1</a>, a rare actinomycete, had antibacterial activity against <em>Escherichia coli</em> (PTCC 1330) and <em>Bacillus subtilis</em> (PTCC 1023) and taxonomically belongs to the genus <em>Amycolatopsis </em><a name="OLE_LINK22"></a><a name="OLE_LINK21"></a><a name="OLE_LINK20">with high similarity of 99.6% to </a><em>Amycolatopsis coloradensis</em> IMSNU 22096^Tbased on sequencing of 16S rRNA gene nucleotide. The <a name="OLE_LINK24"></a><a name="OLE_LINK23">zone of growth inhibition of <em>E.coli</em> was the widest </a>when the base layer had contained 1.2% agar, while no significant differences were observed on <a name="OLE_LINK26"></a><a name="OLE_LINK25">anti-gram-positive bacterial </a>assay. This strain produced the antibacterial agent at the highest level after 5 days when <em>B. subtilis</em> was used as an indicator, but the production of antibacterial agent active against <em>E.Coli</em> was reached to its highest level <a name="OLE_LINK28"></a><a name="OLE_LINK27">on the 3^rd days </a>of cultivation and then was decreased significantly.</p> <p style="text-align: justify;"><strong>Conclusion: </strong>Due to the results of agar concentration and time course study as well as possessing activity against both Gram-positive and Gram-negative indicators, it could be concluded that the previously discovered active agent, avaporcin, produced by <em>Amycolatopsis coloradensis </em>which is active only against Gram-negative bacteria, is not the same bioactive compound or , at least, the only bioactive compound produced by RS1 strain and it is worth further investigation in order to purify and identify the active agent.&nbsp;</p> Rare actinomycete, Halophiles, Antimicrobial activity, Iran 10 16 http://rmm.mazums.ac.ir/browse.php?a_code=A-10-771-2&slc_lang=en&sid=1 Samaneh Mashhadi 10031947532846005354 10031947532846005354 No 2. School of Pharmacy, Mashhad University of Medical Sciences, Mashhad, Iran. Mahdi Moshtaghi Nikou 10031947532846005355 10031947532846005355 No 3. Microorganisms Bank, Iranian Biological Resource Centre (IBRC), ACECR Tehran-Iran Mohammad Ali Amoozegar 10031947532846005356 10031947532846005356 No 4. Extremophiles Laboratory, Department of Microbiology, Faculty of Biology and Center of Excellence in Phylogeny of Living Organisms, College of Science, University of Tehran, Tehran, Iran. Abolghasem Danesh DaneshA@mums.ac.ir 10031947532846005357 10031947532846005357 Yes Biotechnology Research Center, School of pharmacy, Mashhad University of Medical Sciences, Mashhad, Iran