Microbiological and molecular characterization of thermophilic Streptomycesvariabilis with antimicrobial activity
Ramy Fikry* ,Ahmed G. Abdelhamid*, Heba S. Essawy*, Dina M. Baraka* and Mahmoud M. Hazaa*†
The rise of antibiotic resistance phenomena increased the interest for finding effective antimicrobial alternatives to control microbial pathogens. Actinomycetes represent a great reservoir for isolation and identification of antimicrobial compounds. In this study, various samples were randomly collected from the soil of different places in south Delta in Egypt. Two isolates of thermophilic Streptomyces spp were isolated on starch nitrate agar under thermophilic conditions, and were identified according to their morphological characteristics. Only, one isolate showed antifungal and antibacterial activity against various fungal and bacterial pathogens including Staphylococcus aureus, Escherichia coli and Streptococcus. Maximum antimicrobial activity was detected against Aspergillus niger. This isolate was identified as Streptomyces variabilisEG1on the base of the morphological characteristics and 16s rRNA gene sequencing. Optimization of some culture conditions was studied for attaining maximum antimicrobial agent production. This was achieved via adjusting carbon, nitrogen sources including starch and potassium nitrate, pH, time and temperature. Antimicrobial agent production by S.variabilis EG1 was observed on the 5th day of growth on the starch nitrate culture media (incubation at 50° C and pH 7.0) and was efficiently extracted by many solvents. This work confirmed the ability of thermophilic actinomycetes, S. variabilisEG1 to produce unpurified antimicrobial agents for pharmaceutical applications.