Anatoxin-a-concentration in cells of Anabaena- and Aphanizomenon-strains and in their growth media. were studied in the laboratory in batch cultures at different temperatures, light fluxes, orthophosphate and nitrate concentrations and with different nitrogen sources for growth. Toxin concentrations were detected by HPLC. Also, the growth of the toxic Anabaena-strains was compared to that of a non-toxic one. The non-toxic Anabaena was never found to produce anatoxin-a. The amount of toxin in the cells of the toxic strains was high, often exceeding 1% of their dry weight. High temperature decreased the amount of the toxin regardless of growth. Growth limiting low and growth inhibiting high light decreased the amount of the toxin in the cells of Anabaena-strains. The highest light flux studied did not limit the growth or decrease the level of the toxin in the cells of Aphanizomenon. Growth in N-free medium (i.e. N-2 fixation) showed that the cells contained more toxin than growth in N-rich medium. Orthophosphate concentration had no effect on toxin levels, although the lowest concentrations limited the growth of ah strains studied. The toxic strains tolerated higher temperatures than the non-toxic one, but the non-toxic strain seemed to be more adjustable to high irradiance than the toxic ones. The yields (dry weight) of non-toxic and toxic strains differed significantly in different phosphate concentrations.
