Toxic and non-toxic cyanobacterial strains from Anabaena, Aphanizomenon, Calothrix, Cylindrospermum, Nostoc, Microcystis, Planktothrix (Oscillatoria agardhii), Oscillatoria and Synechococcus genera were examined by RFLP of PCR-amplified 16S rRNA genes and 16S rRNA gene sequencing. With both methods, high 16S rRNA gene similarity was found among planktic, anatoxin-aproducing Anabaena and non-toxic Aphanizomenon, microcystin-producing and non-toxic Microcystis, and microcystin-producing and non-toxic Planktothrix strains of different geographical origins. The respective sequence similarities were 999-100 %, 942-999 % and 993-100 %. Thus the morphological characteristics (e.g. Anabaena and Aphanizomenon), the physiological (toxicity) characteristics or the geographical origins did not reflect the level of 16S rRNA gene relatedness of the closely related strains studied. In addition, cyanobacterial strains were fingerprinted with repetitive extragenic palindromic ( Abbreviations : ERIC, enterobacterial repetitive intergenic consensus ; LTRR, long tandemly repeated sequence ; ML, maximum-likelihood ; MP, maximum-parsimony ; NJ, neighbour-joining ; REP, repetitive extragenic palindromic ; STRR, short tandemly repeated sequence ; UPGMA, unweighted pairs group method with averages.The GenBank/EMBL accession numbers for the cyanobacterial 16S rRNA gene sequences are AJ133151-AJ133154, AJ133156, AJ133157, AJ133159-AJ133170, AJ133172-AJ133176 and AJ133185 bacteria occur in a wide range of habitats. In eutrophic fresh and brackish waters cyanobacteria form toxic water blooms which have caused human and animal poisonings (Ressom et al., 1994 ; Kuiper-Goodman et al., 1999). The most frequently found toxins in cyanobacterial blooms worldwide are hepatotoxic cyclic peptides, microcystins and nodularins (Sivonen & Jones, 1999). Mass occurrences of cyanobacteria that contain neurotoxins [anatoxin-a, anatoxin-a(S) and saxitoxins] have been found in Australia, Europe and North America (Sivonen & Jones, 1999). Cyanobacteria are a morphologically diverse group of organisms ranging from unicellular to filamentous forms. Traditionally, the classification of cyanobacteria has been based on morphological characters, Asayama et al. (1996) ; 2, Giovannoni et al. (1988) ; 3, Herdman et al. (1979a) ; 4, Herdman et al. (1979b) ; 5, Kenyon et al. (1972) ; 6, Kondo et al. (2000) ; 7, Lachance (1981) ; 8, Leeuwangh et al. (1983) ; 9, Lehtima$ ki et al. (2000) ; 10, Lu et al. (1997) ; 11, Luukkainen et al. (1993) ; 12, Luukkainen et al. (1994) ; 13, Lyra et al. (1997) ; 14, Masephol et al. (1996) ; 15, Mazel et al. (1990) ; 16, Neilan et al. (1995) ; 17, Neilan et al. (1997a) ; 18, Neilan et al. (1997b) ; 19, Neilan et al. (1999) ; 20, Otsuka et al. (1999) ; 21, Rapala et al. (1993) ; 22, Rasmussen & Svenning (1998) ; 23, Rippka & Herdman (1992) ; 24, Rippka et al. (1979) ; 25, Rouhiainen et al. (1995) ; 26, Rudi & Jakobsen (1999) ; 27, Rudi et al. (1997) ; 28, Rudi et al., 1998 ; 29, Sivonen et al. (1989) ; 30, Sivonen et al. (1990) ;...

The growth and intracellular microcystin concentration of two hepatotoxic and two nontoxic axenic Microcystis strains were measured in batch cultures with variable nitrogen (0.84-84 mg L(-1)) and phosphorus (0.05-5.5 mg L(-1)) concentrations. Growth was estimated by measuring dry weight, optical density, chlorophyll a, and cellular protein concentration. Microcystin concentrations in cells and in culture medium were measured by HPLC analysis. Both nontoxic strains needed less nutrients for their growth at low nutrient concentrations. With high nutrient concentrations the toxic strains grew better than the nontoxic strains. Growth and intracellular microcystin concentration did not correlate in the hepatotoxic strains. Multivariate regression analysis together with mathematical modeling revealed a significant interactive effect of nitrogen and phosphorus, which partly explains the controversial results obtained in previous studies. In this study we have shown that variation of nitrogen and phosphorus concentrations influence the growth and the microcystin production of Microcystis strains and that the strains differ in their response to nutrients. High levels of nitrogen and phosphorus in freshwaters may favor the growth of toxic Microcystis strains over nontoxic ones.

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