Toxin production in cyanobacterial mats from ponds on the McMurdo Ice Shelf, Antarctica

Cyanobacteria are known to produce hepatotoxic substances, the functional a nd ecological role of these toxins, however, remains largely unclear. Toxic properties of cyanobacteria collected in Antarctica were investigated to d etermine whether toxin-producing species can also be found under these envi ronmental conditions. Samples were collected from meltwater ponds on the Mc Murdo Ice Shelf, Antarctica in the summers of 1997 to 1999. These ponds are colonized by benthic algae and cyanobacterial mats. Oscillatoriales, Nodul aria sp., and Nostoc sp. constituted the major taxa in freshwater ponds, wh ile Nostoc sp. was missing from brackish and saline ponds. Samples were tak en from either floating, submerged or benthic mats, and extracted for in vi tro toxicity testing. The presence of toxins was determined by the phosphat ase-inhibition assay and by high performance liquid chromatography. The cyt otoxic properties of the extracts were investigated in hepatocytes determin ing 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide metabolis m and trypan blue dye exclusion. The results show that all cyanobacterial e xtracts display phosphatase-inhibiting activity, of which approximately hal f had significantly greater than 50% inhibiting activity. The presence of n odularin and microcystin-LR was established by high performance liquid chro matography. Cytotoxic properties, independent of the phosphatase inhibiting activity,were also detected. Toxic strains of cyanobacteria can therefore also be found in Antarctica and this finding may lead to further insight in to potential ecological roles of cyanobacterial phosphatase inhibiting toxi ns. (C) 2000 Elsevier Science Ltd. All rights reserved.