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Applied and Environmental Microbiology, October 2004, p. 5756-5763, Vol. 70, No. 10
0099-2240/04/$08.00+0     DOI: 10.1128/AEM.70.10.5756-5763.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Discovery of Rare and Highly Toxic Microcystins from Lichen-Associated Cyanobacterium Nostoc sp. Strain IO-102-I

Ilona Oksanen,1 Jouni Jokela,1 David P. Fewer,1 Matti Wahlsten,1 Jouko Rikkinen,2 and Kaarina Sivonen1*

Department of Applied Chemistry and Microbiology,1 Department of Biological and Environmental Sciences University of Helsinki, Helsinki, Finland2

Received 12 March 2004/ Accepted 1 June 2004

The production of hepatotoxic cyclic heptapeptides, microcystins, is almost exclusively reported from planktonic cyanobacteria. Here we show that a terrestrial cyanobacterium Nostoc sp. strain IO-102-I isolated from a lichen association produces six different microcystins. Microcystins were identified with liquid chromatography-UV mass spectrometry by their retention times, UV spectra, mass fragmentation, and comparison to microcystins from the aquatic Nostoc sp. strain 152. The dominant microcystin produced by Nostoc sp. strain IO-102-I was the highly toxic [ADMAdda5]microcystin-LR, which accounted for ca. 80% of the total microcystins. We assigned a structure of [DMAdda5]microcystin-LR and [D-Asp3,ADMAdda5]microcystin-LR and a partial structure of three new [ADMAdda5]-XR type of microcystin variants. Interestingly, Nostoc spp. strains IO-102-I and 152 synthesized only the rare ADMAdda and DMAdda subfamilies of microcystin variants. Phylogenetic analyses demonstrated congruence between genes involved directly in microcystin biosynthesis and the 16S rRNA and rpoC1 genes of Nostoc sp. strain IO-102-I. Nostoc sp. strain 152 and the Nostoc sp. strain IO-102-I are distantly related, revealing a sporadic distribution of toxin production in the genus Nostoc. Nostoc sp. strain IO-102-I is closely related to Nostoc punctiforme PCC 73102 and other symbiotic Nostoc strains and most likely belongs to this species. Together, this suggests that other terrestrial and aquatic strains of the genus Nostoc may have retained the genes necessary for microcystin biosynthesis.

* Corresponding author. Mailing address: Department of Applied Chemistry and Microbiology, Viikki Biocenter 1, Viikinkaari 9, P.O. Box 56, University of Helsinki, 00014 University of Helsinki, Finland. Phone: 358-9-19159270. Fax: 358-9-19159322. E-mail: kaarina.sivonen{at}helsinki.fi.

Applied and Environmental Microbiology, October 2004, p. 5756-5763, Vol. 70, No. 10
0099-2240/04/$08.00+0     DOI: 10.1128/AEM.70.10.5756-5763.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.



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