TOXIC AND NONTOXIC STRAINS OF THE CYANOBACTERIUM MICROCYSTIS-AERUGINOSA CONTAIN SEQUENCES HOMOLOGOUS TO PEPTIDE SYNTHETASE GENES

Toxic strains of. Microcystis aeruginosa produce cyclic heptatoxins (m icrocystins) that are believed to be synthesized non-ribosomally by pe ptide synthetases. We analysed toxin-producing and non-toxic strains o f M. aeruginosa with respect to the presence of DNA sequences potentia lly encoding peptide synthetases. Hybridizations of genomic DNA of var ious M. aeruginosa strains with PCR-amplificated fragments possessing homologies to adenylate-forming domains of peptide synthetase genes pr ovided first evidence for the existence of corresponding genes in cyan obacteria. Furthermore we isolated and sequenced from genomic librarie s overlapping fragments of M. aeruginosa DNA with a total length of 29 82 bp showing significant homology to genes encoding peptide synthetas es and hybridizing exclusively with DNA from toxic strains. Our result s indicate that both toxic and non-toxic strains of M. aeruginosa poss ess genes coding for peptide synthetases and that hepatotoxin-producin g and non-toxic strains differ in their content of genes for specific peptide synthetases.