Isolation and Characterization of Aerobic Actinomycetes from Soil in Northern Iran and Evaluation of their Antimicrobial Potential

Aerobic actinomycetes can be detected in soil, worldwide. But, their diversity can differ depending on ecological and environmental factors including, temperature, humidity and vegetation, etc. The aim of this study was antimicrobial activities of aerobic actinomycetes Isolated from soil in Northern Iran.
Fifty soil samples throughout Northern Iran provinces, including Guilan, Mazandran and Golestan, have been collected and cultured in selective medium, Starch Casein Agar (SCA). In the first step, isolates were assayed by pointing inoculation in solid medium, agar spot, for antimicrobial activity. Then, for antibiotic production, International Streptomyces Projects 2 (ISP2) and Glucose Yeast Extract Malt extract (GYM) media by submerge technique were used. Well diffusion agar method was used for detection of antimicrobial activity and antibiotic sensitivity, and finally metabolites of most active specious detected by GC/MS and GC techniques.
In this study eighty strains were isolated from soil samples. In primary screening, 12 strains (15%) recognized as active actinomycetes, among them strain SA3 showed the highest antimicrobial potential. In the secondary screening in the liquid ISP2 medium, 3 (25%) isolates (SA7, SA3, SA16) and in GYM medium 7 (58.33%) isolates (SA28, SA27, SA7, SA26, SA16, SA2, SA3) have shown the highest antimicrobial potentials; also it was found that there is a significant relation between humidity and pH of soil with the number of isolated colonies. According to results of primary and secondary screening, strains SA3 and SA7 were selected as active actinomycetes and biochemical test revealed that these two active strains isolates belong to the genus Streptomyces. Finally, produced metabolites by strain SA3 were analyzed by GC/MS and GC methods and Oleic acid was revealed as the highest peak.
The findings of the present research show that actinomycetes from Northern Iran soils have considerable antimicrobial activities against different microbial pathogens.