Cultural, Microscopic, and Genetic Identification of a Natamycin-Producing Streptomyces Isolate

Abstract

Soil samples were collected from six different fields, including those at the University of Baghdad/Al-Jadriya, Abu Ghraib, Zakho, Sulaimaniyah, Kirkuk, and Duhok, and were assigned the following codes: G, B, Z, S, K, and D, respectively. The samples were divided into two groups. One group was treated with calcium bicarbonate (10 g soil / 1 g calcium carbonate), while the other group was heated (56°C / 30 minutes). After performing decimal dilutions, the samples were cultured on three selective solid culture media for Streptomyces bacteria: Starch casein agar (SCA), glycerol asparagine agar (GAA), and tyrosine agar (TA), in addition to the general culture medium, Nutrient agar. The soil samples collected from the Abu Ghraib field performed better than the other samples tested from the five fields. The second treatment method for the soil samples was superior to the first, and the selective culture medium, SCA, outperformed the other three in obtaining a higher number of colonies. Nineteen colonies were collected with culture characteristics similar to those of Streptomyces: seven colonies designated B, four G, three D, two K, two S, and one Z. Based on culture characteristics such as the slightly grayish-white color, height, and characteristic earthy odor (gusmine) of Streptomyces, initial screening was completed by culturing the collected colonies on glass slides using slide culture. Six isolates were selected from among the nineteen that exhibited clear branching filaments under the microscope and a positive Gram stain (violet). These six were then selected for the second screening stage, which involved testing the isolates' ability to produce natamycin in Three liquid culture media, SCB, GAB, and NB, were tested. Isolate B4 exhibited the highest natamycin yield when cultured on SCB liquid medium, surpassing both tested media and the other tested isolates, with a yield of 557.50 mg/ml. isolate B4 was selected and subjected to genetic diagnosis based on 16S rRNA , It was found to belong to Streptomyces grisues with a percentage match.