The
alkaloid cylindrospermopsin is the most recently discovered cyanotoxin and has caused epidemic outbreaks of human
poisoning.
Cylindrospermopsin producing cyanobacteria have in recent times appeared in countries all over the world where they had not been observed previously and, thus, represent a global public health concern. Three putative
cylindrospermopsin biosynthesis genes, encoding an amidinotransferase (aoaA), a
nonribosomal peptide synthetase (aoaB), and a
polyketide synthase (aoaC), have been described. Most
cyanotoxins are the product of nonribosomal
peptide and
polyketide synthesis, but the involvement of an amidinotransferase is novel. In the present study, functional modeling was carried out to gain insight into the mechanism of precursor recruitment in
cylindrospermopsin biosynthesis. In addition, the molecular phylogenies of putative
cylindrospermopsin biosynthesis genes and producer organisms were determined. The model indicated that AoaA may catalyze the formation of guanidino
acetate from
glycine and
arginine. The catalytic site of the AoaB adenylation domain provided two
aspartate residues, instead of the usual one, which may be involved in the binding of the guanidino moiety of guanidino
acetate. Molecular phylogenetic analysis grouped
cylindrospermopsin producing cyanobacteria into two divergent groups. Although the phylogeny of the
cylindrospermopsin biosynthesis genes followed that of the producer organisms, they were less divergent, which may indicate the recent horizontal transfer of these genes.