Background: The ever-increasing resistance of microorganisms to pathogens and our inability to control infectious diseases indicate the importance of conducting research to find new antibiotics. Objectives: The aim of the present research was to isolate, identify, and optimize a cold and pH resistant strain of Streptomyces with high antibiotic production capability. Methods: Soil samples were taken from the Telar forests of northern Iran, and the ACS52 strain was identified as a Streptomyces strain based on the morphological, biochemical, and 16S rRNA gene analysis. Antibacterial features of the obtained strain were studied against a wide range of Gram-positive and Gram-negative bacteria using the cross-culture method. In order to evaluate the antibacterial activity of culture product, two seed cultures and three fermentation media were examined. Finally, the effects of various factors such as the type of carbon and nitrogen sources, temperature, pH, and inoculation rate were investigated. Results: Streptomyces sp. ACS52 is a cold-resistant alkalophilic bacterium strain with antibacterial activity against a broad spectrum of pathogenic bacteria. The fermentation medium containing glycerol and ethyl acetate was suitable for the production and extraction of antibacterial compound, respectively. Glycerol and starch as the carbon source, soybean extract as the nitrogen source, temperature of 25°C, pH of 7, and inoculation rate of 10% were found to provide the optimal conditions for the antibacterial activity. Conclusions: The crude extract of Streptomyces sp. ACS52 had high antibacterial activity against a wide spectrum of bacteria and could be of interest due to its features such as ability to grow at low temperatures and alkaline pH levels.

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