MOLECULAR SCREENING OF MANGROVE DERIVED ACTINOBACTERIA ALONG THE COASTAL BELT OF COCHIN AS A SOURCE OF AROMATIC POLYKETIDES

Actinobacteria is found to have a potent metabolic activity against pathogens. The present study explores the biosynthetic potential of actinobacteria from the mangrove sediments of Cochin. Samples were collected from five different mangrove areas of Cochin, Vallarpadam Island, Panambukadu, Kovilakathumkadavu, Bolgatty and Cherai. A collection of 22 different actinobacteria was obtained which differ in their colony morphological appearance. The antibacterial effects of these strains were screened qualitatively and quantitatively. In qualitative screening, 22 different strains were assessed for their antibacterial activity against different human pathogens, namely Escherichia coli, Klebsiella sp. Staphylococcus aureus and Proteus sp. by cross streak method. It could be seen that 50 % isolates were active against at least one of the test organisms and 21.31 % strains exhibited a broad spectrum activity against almost all of the test bacteria except Klebsiella sp. The activities of the isolates were quantified by agar well diffusion method. Solvent extraction with ethyl acetate was done to obtain the crude extracts which were further tested for zone of inhibition. The isolates, S1-1, S1-2, S1-3, S1-4, S1-5, S2-2, S2-3, S2-5, S3-2, S3-3, and S5-2 were found to show significant antibacterial activity. 10 potent isolates were selected and subjected to molecular screening for their ability to synthesize aromatic polyketides based on amplification of Ketosynthase α domain of type II PKS. Among the 10 isolates only one isolate (S1-1) had shown positive amplification. The positive isolate was characterized based on partial 16s rRNA gene analysis. The result revealed that it belongs to the Streptomyces sp. BLAST and phylogenetic analysis showed 97.22 % identity to Streptomyces violascens but the identity could be established only on characterization of the full gene. Thus the molecular data highlights the importance of Streptomyces isolates in antibiotic production. The antibacterial activity and the PKS gene based approach can be applied together for efficient screening of isolated strains for pharmaceutical value and related compounds.