isolation and identification of a rare actinomycete with antibacterial activity from saline region of iran

background: the appearance of multi-drug resistant microorganisms is becoming a global problem. already several strategies have been employed for overcoming antibiotic resistance issue. developing new antimicrobial compounds from microbial source could be a beneficial solution. hence screening programs in order to discover new antibiotics from microbial entities is interesting. because of high capabilities of extremophiles for adaption with harsh environmental conditions, the microbial communities of the extreme environments could be regarded as rich resources for new antibacterial metabolites. materials and methods: 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. then, the strain shown pronounce inhibition zone, has been phylogenetically analyzed followed by studying the effect of agar concentration and cultivation time on production of antibacterial agent(s). results: the strain rs1, a rare actinomycete, had antibacterial activity against escherichia coli (ptcc 1330) and bacillus subtilis (ptcc 1023) taxonomically belongs to the genus amycolatopsis with 99.6% high similarity to amycolatopsis coloradensis imsnu 22096t based on sequencing of 16s rrna gene nucleotide. the zone of growth inhibition of e.coli was widest when the base layer had contained 1.2% agar, while no significant differences were observed on anti gram-positive bacterial assay. this strain produced the antibacterial agent at the most level after 5 days when b. subtilis was used as an indicator, but the production of antibacterial agent active against e.coli was reached to its highest level on 3th days of cultivation and then was decreased significantly. conclusion: 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 amycolatopsis coloradensis 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 worth further investigation in order to purify and identify the active agent.