Abstract

A Gram positive, filamentous, spore forming antagonistic Streptomyces speibonae ERI-01derived from Western Ghats of Tamil Nadu, India, was studied for its antagonistic activities. Preliminary screening revealed that 38% of Streptomyces strains showed activity against Bacillus subtilis (34%), Staphylococcus aureus (32.4%), Staphylococcus epidermidis (27%), Escherichia coli (27%) Enterococcus faecalis (25%), Pseudomonas aeruginosa (22%) (Klebsiella pneumonia) and 18% (Xanthomonas sp), respectively. However, Streptomyces sp. ERI-01 exhibited significant antimicrobial activity against all the tested bacteria compared to other Streptomyces strains. The 16S rDNA gene based phylogenetic affiliation was determined by using bioinformatic tools identifiedStreptomyces sp. ERI-01 with 99% sequence similarity to Streptomyces speibonae.Fermentation conditions for antibacterial compound production were optimized. The antibacterial substances were extracted using chloroform, ethyl acetate and methanolfrom modified nutrient glucose medium (MNGA) in which ERI-01 had grown for 8 days at 28°C. Antimicrobial activity was assessed using the broth microdilution technique. The lowest minimum inhibitory concentration (MIC) of crude extracts and column purifiedfractions of ERI-01 against Gram positive and Gram negative bacterial pathogens were determined. The lowest MIC of the extract for B. subtilis, S. aureus, S. epidermidis and P. aeruginosa were 0.25 mg/ml. respectively. Extracts were evaluated for their typical polyene-like property.

Key words: Streptomyces, Antibacterial activity, minimum inhibitory concentration (MIC), polyene.

Abbreviation

MNGA, Modified nutrient glucose agar medium; ISP, International Streptomyces Project; MIC, minimum inhibitory concentrations; MBC, minimum bactericidal concentrations; BLAST, Basic Local Alignment Search Tool; SCA, starch casein agar.