Isolation, Characterization and Selection of Avermectin-Producing Streptomyces avermitilis Strains From Soil Samples

Streptomyces avermitilis, belonging to Actinomycetes, is specialized for production of avermectin, used as an anthelmintic and insecticidal agent. It is mostly found in soil and its isolation is very crucial for medically important avermectin production. In the present study, 10 bacterial isolates lacking antimicrobial activities were isolated from the soil samples collected from different areas of Lahore, Pakistan. Three distinctive localities of Lahore were opted for soil assortment to isolate S. avermitilis. About 50 isolates of Streptomyces species were attained through selective prescreening procedures. All of these isolates were studied for production of the secondary metabolite, avermectin. Different test like soluble pigment color and melanin formation were used for identification. Biochemical characterizations of those isolates closely resembling the control in morphological characteristics, soluble pigment color and melanin formation tests were performed. The 10 selected isolates were identified as the avermectin-producing strain by fermentation and characterized on ISP2 medium for aerial and reverse side mycelia color, soluble pigment color and melanin formation, in comparison with S. avermitilis DSM 41445. The best avermectin-producing isolate S1-C (10.15 mg/L) showed similar result as S. avermitilis DSM 41445, when subjected for culture characteristics analysis in different media along with biochemical characterization. From the results, it was concluded that agricultural lands around Pakistan Council of Scientific and Industrial Research (PCSIR) Campus Lahore were rich sources of industrially important Streptomyces, especially S. avermitilis.