Selective isolation and antimicrobial activity of rare actinomycetes from mangrove sediment of Karwar

Abstract

The mangrove ecosystem is a largely unexplored source for actinomycetes. Various pretreatment procedures and selective media were applied to assess the optimal conditions for the isolation of rare actinomycetes from Mangrove sediment. Pretreatment of wet-heating for 15 min at 70oC and phenol treatment of soil suspension were the most effective methods for the isolation of those microorganisms. Hair hydrolysate vitamin agar (HHVA) was the most suitable medium for the recovery of rare actinomycetes. Fifty-three rare actinomycete strains were chosen using selective isolation approaches, then morphological and chemical properties of the isolates were determined. The isolates belonged to one of the following genus, Micromonospora, Microbispora, Actinoplanes, and Actinomadura. Later Micromonospora and Actinomadura were selected for antimicrobial activity. Minimum bactericidal concentration (MBC) of ethyl acetate extract against Staphylococcus aureus were 1.20 mg/ml for Micromonospora species and 5mg/ml for Actinomadura species. Thin layer chromatography (TLC) of the ethyl acetate extracts were carried out in duplicate using Chloroform: methanol (4:1) as solvent system and Tetracycline as reference antibiotic. Under UV light they gave greenish yellow spots with Rf value 0.85 for the antimicrobial from Actinomadura species and 0.88 for that from Micromonospora species. In bioautography (using Staphylococcus auras as test organism) inhibition zones were obtained and they were associated with the yellowish green spots of the chromatogram as detected under UV light. This may indicate the same compounds were responsible for the antibacterial activity of those actinomycetes isolates.