Benthic cyanobacteria from the Baltic Sea contain cytotoxic <i>Anabaena</i>, <i>Nodularia</i>, and <i>Nostoc</i> strains and an apoptosis‐inducing <i>Phormidium</i> strain

Abstract

Benthic cyanobacteria from aquatic environments have been reported to produce biologically active metabolites. However, the toxicity and other biological activities of benthic cyanobacteria from the Baltic Sea are not well known. We determined the biological activities of 21 Anabaena, Calothrix, Nodularia, Nostoc, and Phormidium strains isolated from benthic littoral habitats of the Baltic Sea. We studied whether benthic cyanobacterial extracts caused cytotoxicity by necrosis or induced apoptosis in two mammalian cell lines, a human leukemia cell line (HL-60) and a mouse fibroblast cell line (3T3 Swiss), and examined potential hepatotoxin (microcystin and nodularin) production. Five of the six benthic Anabaena strains, one of the two Nostoc strains, and two of the three Nodularia strains were highly cytotoxic to human leukemia cells. The Calothrix and Phormidium strains did not cause LDH leakage, but the extract of Phormidium strain BECID15 induced apoptosis in the HL-60 cells. Neither the microcystin synthetase E (mcyE) nor the nodularin synthetase F (ndaF) gene was amplified by PCR, and no microcystins or nodularins were detected by the protein phosphatase inhibition assay from the cyanobacterial strains included in this study. This indicates that benthic Baltic cyanobacteria contain potentially harmful cytotoxic compounds even though they do not produce microcystins or nodularins. These cytotoxic compounds remain to be characterized, and the mechanisms of cytotoxicity need to be studied further.