Genetic, morphological, and toxicological variation among globally distributed strains of Nodularia (cyanobacteria)

Morphological, toxicological, and genetic variation was examined among 19 s trains of Nodularia. The strains examined could be morphologically discrimi nated into four groups corresponding to N. spumigena Mertens, N, sphaerocar pa Bornet et Flahault, and two strains that did not clearly correspond to c urrently accepted Nodularia species. Genetic variation was examined using n ucleotide sequencing of the phycocyanin intergenic spacer region (cpcBA-IGS ) and RAPD-PCR, The PCR-RFLP of the cpcBA-IGS differentiated four genotypes corresponding to the four morphological groups, However, nucleotide sequen cing of 598 bp of the 690-bp fragment showed that one of the three strains corresponding to N. sphaerocarpa (PCC 7804) was genetically divergent from the other two, suggesting that it constitutes a distinct species. Nucleotid e variation within the morphospecies groups was Limited (<1%), and all 14 A ustralian strains of N, spumigena possessed identical cpcBA-IGS sequences. The RAPD-PCR differentiated the same groups as the cpcBA sequencing and dis criminated each of the seven different Australian populations of N. spumige na. Strains from within a bloom appeared genetically identical; however, st rains isolated from different blooms could be separated into either a weste rn or a southeastern Australian cluster, with one strain from western Austr alia showing considerable genetic divergence, The pattern of variation sugg ests that individual blooms of N. spumigena are clonal but also that Austra lian N. spumigena populations are genetically distinct from each other. Exa mination of genetic distance within and between blooms and within and betwe en morphological groups showed clear genetic dicontinuities that, in combin ation with the cpcBA-IGS data, suggest that Nodularia contains genetically distinct morphospecies rather than a continuous dine of genetic variation, Furthermore, these morphospecies are genetically variable, exhibiting hiera rchical patterns of genetic variation on regional and global scales. Produc tion of the hepatotoxin nodularin was not restricted to one genetic lineage but was distributed across three of the five genotypic groups. A strain of N. spumigena from a nontoxic Australian population was found to fall withi n the range of genetic variation for other toxic Australian strains and app ears to be a unique nontoxic strain that might have arisen by loss of toxin production capacity.