Molecular characterization of planktic cyanobacteria of Anabaena, Aphanizomenon, Microcystis and Planktothrix genera

Toxic and non-toxic cyanobacterial strains from Anabaena, Aphanizomenon, Ca lothrix, Cylindrospermum, Nostoc, Microcystis, Planktothrix (Oscillatoria a gardhii), Oscillatoria and Synechococcus genera were examined by RFLP of PC R-amplified 16S rRNA genes and 16S rRNA gene sequencing. With both methods, high 16S rRNA gene similarity was found among planktic, anatoxin-a-produci ng Anabaena and non-toxic Aphanizomenon, microcystin-producing and non-toxi c Microcystis, and microcystin-producing and non-toxic Planktothrix strains of different geographical origins. The respective sequence similarities we re 99.9-100 %, 94.2-99.9 % and 99.3-100 %. Thus the morphological character istics (e.g. Anabaena and Aphanizomenon), the physiological (toxicity) char acteristics or the geographical origins did not reflect the level of 16S rR NA gene relatedness of the closely related strains studied. In addition, cy anobacterial strains were fingerprinted with repetitive extragenic palindro mic (REP)- and enterobacterial repetitive intergenic consensus (ERIC)-PCR. All the strains except two identical pairs of Microcystis strains had diffe rent band profiles. The overall grouping of the trees from the 16S rRNA gen e and the REP- and ERIC-PCR analyses was similar. Based on the 16S rRNA gen e sequence analysis, four major clades were formed. (i) The clade containin g filamentous heterocystous cyanobacteria was divided into three discrete g roups of Anakaena/Aphanizomenon, Anakaena/Cylindrospermum/Nodularia/Nostoc and Calothrix strains, The three other clades contained (ii) filamentous no n-heterocystous Planktothrix, (iii) unicellular non-heterocystous Microcyst is and (iv) Synechococcus strains.