ISOLATION AND CHARACTERIZATION OF CYANOBACTERIA POSSESSING ANTIMICROBIAL ACTIVITY FROM THE SUNDARBANS,THE WORLD’S LARGEST TIDAL MANGROVE FOREST1 |
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| Authors: | Arnab Pramanik Muthuraman Sundararaman Satadal Das Uma Ghosh Joydeep Mukherjee |
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| Institution: | 1. School of Environmental Studies, Jadavpur University, Kolkata 700032, India;2. National Facility for Marine Cyanobacteria, Bharathidasan University, Tiruchirappalli 620024, India;3. Peerless Hospital and B.K. Roy Research Centre, Kolkata 700094, India;4. Department of Food Technology and Biochemical Engineering, Jadavpur University, Kolkata 700032, India |
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| Abstract: | Eight obligately halophilic, euryhaline cyanobacteria from intertidal soil were isolated in artificial seawater nutrients III (ASN‐III) medium. Antimicrobial activity, 16S rRNA gene sequences, phenotypic characters as well as growth and antibiosis in response to variable salinity, temperature, phosphate concentration, and pH were studied. Minimum inhibitory concentrations (MIC) of the extracts against Staphylococcus aureus, Escherichia coli, Bacillus subtilis, Pseudomonas aeruginosa, and multiple drug‐resistant clinical isolates ranged between 0.25 and 0.5 mg · mL−1. Cytotoxicity tests showed 73%–84% human colon adenocarcinoma (HT‐29/C1) cell survival at MIC values, indicating that the extracts were nontoxic. Morphologically, six cyanobacteria were assigned to the Lyngbya‐Phormidium‐Plectonema (LPP) group B, and one each was assigned to Oscillatoria and Synechocystis genera. Glycerol, mannitol, and starch supported better photoheterotrophic growth than simpler mono‐ and disaccharides. No heterocyst formation was observed when grown under nitrogen‐starved conditions. All isolates survived 7‰ salinity, grew at minimum 32‰ salinity, and showed sustained growth throughout 32‰–82‰ salinity but matured poorly in freshwater medium supplemented with 30.0 g · L−1 NaCl. Antimicrobial production occurred only at 32‰ salinity. While four of the eight isolates demonstrated sustained growth at 37°C, maximum antimicrobial activity was obtained at 25°C. All strains showed maximum growth and antimicrobial elaboration at 0.04 g · L−1 phosphate. All isolates thrived at pH 9.5; six grew at pH 4.5, though antimicrobial production occurred only at pH 7.5. Molecular phylogenetic analysis based on 16S rRNA gene sequences of the filamentous isolates validated the previous taxonomic affiliations established on morphological characteristics. This is the first study of antimicrobial‐producing halophilic cyanobacteria from the mangroves. |
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| Keywords: | antimicrobial cyanobacteria estuarine mangroves Sundarbans |
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