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Western Ghats are one of the biodiversity hotspots in the world. The present study was undertaken to investigate biological activities viz., antibacterial, insecticidal, anthelmintic and antioxidant activities of a Streptomyces species SRDP-07 isolated from a soil sample collected in Thirthahalli, Karnataka (state), India. Isolation of actinomycetes was carried out by plating the serially diluted soil sample on Starch casein agar. Primary screening of the actinomycete isolates for antibacterial activity was done by Cross streak method. Isolate SRDP-07, showing prominent inhibition of test bacteria in cross streak technique, was selected for further characterization and for determining biological activities. The isolate was grown in starch casein broth for 10 days and the culture filtrate was extracted with ethyl acetate. Antibacterial activity of ethyl acetate extract was tested against a panel of 6 bacteria by Agar well diffusion assay. Insecticidal activity of the extract was evaluated in terms of larvicidal effect against 2nd instar larvae of Aedes aegypti. Anthelmintic activity of the extract was performed by determining time taken for paralysis and death of adult Indian earthworms. Antioxidant activity of the extract was determined by DPPH free radical scavenging and Ferric reducing assay. A total of 9 actinomycetes were recovered on Starch casein agar by serial dilution-plating technique. The isolate SRDP-07 was identified as a species of Streptomyces by cultural and microscopic characteristics. Gram positive bacteria were more susceptible to extract than Gram negative bacteria. The extract showed dose dependent mortality of larvae of A. aegypti. Anthelmintic effect of extract was lesser and the time taken for paralysis and death of worms were considerably higher than that of reference anthelmintic. The radical scavenging and reducing potential of extract was also weaker when compared with reference standard. The results of the present study indicate that the soils of Thirthahalli are known to contain actinomycetes with potent biological activities. Isolation of active principles present in the ethyl acetate extract of Streptomyces species SRDP-07 is under progress. Further screening programmes in soils of Western Ghats of Karnataka can be fruitful in isolation of bioactive actinomycetes which can be exploited for production of novel metabolites.
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Author(s): Prashith Kekuda T R Dileep N Syed Junaid Rakesh K N Sunita C Mesta Onkarappa R
Western Ghats, Thirthahalli, Actinomycetes, Streptomyces, Biological activities