Isolation and Characterization of Cyanobacteria Possessing Antimicrobial Activity From the Sundarbans, the World’s Largest Tidal Mangrove Forest1

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.

Antibacterial and Antifungal Activities of Cyanobacterial Strains Isolated from Hot Springs in Oman

“…Phormidium spp. have been previously reported to produce compounds that inhibit growth of different Gram-positive and Gram-negative bacterial strains, yeasts, and fungi [40][41][42]. Butanol extracts of Lyngbya sp.…”

Effects of flask configuration on biofilm growth and metabolites of intertidal Cyanobacteria isolated from a mangrove forest

“…Pramanik et al . () reported the antimicrobial activity of the extracts of Cyanobacteria isolated from the intertidal soil of Sundarbans mangrove forest, which showed positive results against Bacillus subtilis and multiple drug‐resistant clinical isolates. Cyanobacterial strains isolated from microbial mats developed on the soil surface and mangrove pneumatophores were reported to produce toxins (microcystins and saxitoxins) and exhibited toxicity to brine shrimp (Mohamed and Al‐Shehri ).…”

“…Thus, biofilm-forming Cyanobacteria in particular could be harnessed for exploiting novel low volume yet high value specialized chemicals of immense industrial applications especially pharmaceuticals, nutraceutical and cosmeceuticals. Pramanik et al (2011) reported the antimicrobial activity of the extracts of Cyanobacteria isolated from the intertidal soil of Sundarbans mangrove forest, which showed positive results against Bacillus subtilis and multiple drug-resistant clinical isolates. Cyanobacterial strains isolated from microbial mats developed on the soil surface and mangrove pneumatophores were reported to produce toxins (microcystins and saxitoxins) and exhibited toxicity to brine shrimp (Mohamed and Al-Shehri 2015).…”

A Study on Heavy Metal Load in Two Different Freshwater Systems, Tiruchirappalli, Tamil Nadu, India

“…Cyanobacteria are emerging as an exciting resource for the discovery of new classes of therapeutics (Pramanik and Mukherjee, 2011). The current increase in scientific and commercial interest in the use of genetic resources is also of significance to international policy makers.…”