Isolation, Molecular Characterization and Identification of Antibiotic Producing Actinomycetes from Soil Samples

A total of 9 actinomycetes (FA1-FA9) isolates were isolated from soil and water samples using starch casein agar and actinomycetes isolation agar. Except FA4, all the isolates showed antimicrobal activity against one or more of the bacteria (Escherichia coli, Enterococcus faecalis, Klebisella pneumonia and Micrococcus luteus) tested by cross-streak method. The actinomycete isolate FA9 exhibited better antimicrobial efficacy for Gram-negative (E. coli) than Gram-positive organism (E. faecalis) did. Antimicrobial activity of the crude extracts obtained from solid state fermentation showed a better zone of inhibition than those obtained by submerged state fermentation. Minimum inhibitory concentration of the crude extract was 0.51µg/ml for E. Coli and K. pneumonia whereas it was 1.02µg/ml for E. faecalis and M. luteus. The free radical scavenging ability (DPPH) of the ethanolic crude extract recorded IC50 value of 24.384. The FT-IR spectral analyses of extracts showed functional groups such as alcohol (O-H), alkanes (C-H), alkene (C = C) and alkyl halide (C-F). The isolate FA9 was Gram positive and the spore chain morphology was simple rectus with a smooth spore surface. The 16S rRNA gene sequence was closely related to Nocardia alba. The RNA secondary structure predictive of 16SrRNA gene of Nocardia alba showed a free energy of −152.4 kcal/mol, threshold energy of -4.0 with Cluster factor 2, Conserved factor 2 and Compensated factor 4. The 16SrRNA gene of Nocardia alba showed restriction sites Alu I, Hae III, Bst UI, etc. A GC content of 58% and AT content of42% was obtained based on restriction site analysis.