A molecular and phenotypic analysis of Nodularia (cyanobacteria) from the Baltic Sea

The filamentous diazotrophic cyanobacterium Nodularia forms water blooms ea ch year in the Baltic Sea. Filaments isolated from such water blooms vary i n their trichome width, degree of coiling, and properties of their gas vesi cles; previously, these characters have been used to classify individuals t o species level. To test the validity of such a phenotypic classification, we determined the nucleotide sequences for a region of the phycocyanin locu s that includes a noncoding intergenic spacer (PC-IGS), the IGS between two adjacent copies of the gvpA gene (which encodes the main structural gas ve sicle protein) and the rDNA internal transcribed spacer (rDNA-ITS), for 13 clonal Nodularia isolates from the Baltic Sea during August 1994. The compl ete 16S-rDNA sequence was determined for three isolates and was found to be identical in each of them, Molecular sequences for noncoding regions of th e genome were used to assign isolates to three groups on the basis of PC-IG S, two groups on the basis of gvpA-IGS, and three groups on the basis of rD NA-ITS. No consistent correlation was found between genotype and any of the phenotypic features examined, and no link was found between any of these f eatures themselves, indicating that these characters are not useful for pla cing Nodularia isolates into meaningful taxonomic groups. The PC-IGS, gvpA- IGS, and rDNA-ITS genotypic groupings were not congruent. This might indica te that gene flow occurs between individuals in Nodularia populations.