Geographical segregation of the neurotoxin-producing cyanobacterium Anabaena circinalis

Blooms of the cyanobacterium Anabaena circinalis are a major worldwide prob lem due to their production of a range of toxins, in particular the neuroto xins anatoxin-a and paralytic shellfish poisons (PSPs). Although there is a worldwide distribution of A. circinalis, there is a geographical segregati on of neurotoxin production. American and European isolates of A. circinali s produce only anatoxin-a, while Australian isolates exclusively produce PS Ps, The reason for this geographical segregation of neurotoxin production b y A. circinalis is unknown. The phylogenetic structure of A. circinalis was determined by analyzing 16S rRNA gene sequences. A. circinalis was found t o form a monophyletic group of international distribution. However, the PSP - and non-PSP-producing A. circinalis formed two distinct 16S rRNA gene clu sters. A molecular probe was designed, allowing the identification of A. ci rcinalis from cultured and uncultured environmental samples. In addition, p robes targeting the predominantly PSP-producing or non-PSP-producing cluste rs were designed for the characterization of A. circinalis isolates as pote ntial PSP producers.