ABSTRACT
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 [ADMAdda
5
]microcystin-LR, which accounted for ca. 80% of the total microcystins. We assigned a structure of [DMAdda
5
]microcystin-LR and [
d
-Asp
3
,ADMAdda
5
]microcystin-LR and a partial structure of three new [ADMAdda
5
]-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.