Toxicity studies of Trichodesmium erythraeum (Ehrenberg, 1830) bloom extracts, from Phoenix Bay, Port Blair, Andamans

Occurrence of toxic cyanobacterial blooms has become a worldwide problem, increasing the risk of human poisoning due to consumption of seafood contaminated with cyanotoxins. Though no such cases of human intoxication due to toxic blooms have been reported so far from India, most of the studies related to blooms have been restricted to reporting of a bloom and/or antimicrobial activity of its extract. Detailed toxicity study of cyanobacterial blooms are lacking. A study on the toxicity of a dense bloom (14.56 × 106 trichomes L−1) of the marine diazotrophic cyanobacteria, Trichodesmium erythraeum, observed in the coastal waters of Phoenix Bay, Port Blair, Andamans was undertaken. The significance of this bloom is that it was a single species and had conspicuously inhibited the growth of other phytoplankton and complete exclusion of zooplankton from the bloom region, intimating the involvement of toxins in the bloom. The cyanobacterial extracts showed prominent antimicrobial activity against certain human pathogenic bacteria and fungi. Studies on the toxicity of the cyanobacterial extracts was carried out using brine shrimp bioassay, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and comet assay. The cyanobacterial extract exhibited toxic effect to Artemia salina causing mortality of up to 40% after 48 h at a concentration of 1 mg mL−1, while it induced cytotoxicity in cell lines (HepG2 and HaCat) and caused DNA damage in human lymphocytes in vitro.