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Applied and Environmental Microbiology, October 2007, p. 6543-6550, Vol. 73, No. 20
0099-2240/07/$08.00+0     doi:10.1128/AEM.01377-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Direct Evidence for Production of Microcystins by Anabaena Strains from the Baltic Sea

Department of Applied Chemistry and Microbiology, University of Helsinki, Viikki Biocenter, P.O. Box 56, 00014 University of Helsinki, Finland

Received 21 June 2007/ Accepted 20 August 2007

Anabaena is a filamentous, N₂-fixing, and morphologically diverse genus of cyanobacteria found in freshwater and brackish water environments worldwide. It contributes to the formation of toxic blooms in freshwater bodies through the production of a range of hepatotoxins or neurotoxins. In the Baltic Sea, Anabaena spp. form late summer blooms, together with Nodularia spumigena and Aphanizomenon flos-aquae. It has been long suspected that Baltic Sea Anabaena may produce microcystins. The presence of microcystins has been reported for the coastal regions of the Baltic proper, and a recent report also indicated the presence of the toxin in the open Gulf of Finland. However, at present there is no direct evidence linking Baltic Sea Anabaena spp. to microcystin production. Here we report on the isolation of microcystin-producing strains of the genus Anabaena in the open Gulf of Finland. The dominant microcystin variants produced by these strains included the highly toxic MCYST-LR as well as [D-Asp³]MCYST-LR, [D-Asp³]MCYST-HtyR, MCYST-HtyR, [D-Asp³,Dha⁷]MCYST-HtyR, and [Dha⁷]MCYST-HtyR variants. Toxic strains were isolated from the coastal Gulf of Finland as well as from the easternmost open-sea sampling station, where there were lower salinities than at other stations. This result suggests that lower salinity may favor microcystin-producing Anabaena strains. Furthermore, we sequenced 16S rRNA genes and found evidence for pronounced genetic heterogeneity of the microcystin-producing Anabaena strains. Future studies should take into account the potential presence of microcystin-producing Anabaena sp. in the Gulf of Finland.

Published ahead of print on 31 August 2007.

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