Isolation of Extremely Heavy Metal Resistant Strains of Rare Actinomycetes from High Metal Content Soils in Iran

Using of microorganisms to remove industrial pollutions of environment is an efficient method that mimics natural process and decrease remediation cost. In this study, 450 actinomycete strains were isolated from high metal content soils in Iran. Heavy metal salt solutions in different concentrations were used to isolate the resistant strains. 40 resistant actinomycetes which they showed highly resistance to the most applied heavy metals were selected. After examination of these strains in broth media with high levels of metals, 13 resistant isolates were selected as high resistant actinomycetes. Some strains showed resistance to 140 mM ZnCl2, 7 mM CuSO4, 9.2 mM CdCl2, and 60 mM NiCl2. Molecular identification revealed that resistant strains belonged to different actinomycetes genera including Streptomyces,Nonomuraea, Saccharothrix, Streptosporangium and Promicromonospora which was the first report on occurrence of highly metal resistant strains in Nonomuraea, Streptosporangium and Promicromonospora genera. Cadmium removal studies by Promicromonospora sp. UTMC 2243 indicated 96.5% reduction in cadmium residual concentration, reflecting cadmium removal capacity in Promicromonospora sp. UTMC 2243.