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Energy state and toxin content – experiments on Microcystis aeruginosa (Chroococcales, Cyanophyta)

Abstract The correlation between the ratio of microcystin to protein and the energy state of Microcystis aeruginosa NIVA-CYA 228/1 (Chroococcales, Cyanophyta) was examined at three levels of phosphorus and iron in continuous cultures. Phosphorus- and iron-depleted conditions resulted in an increased transparency of the cultures, and together this caused significant changes in adenylate energy charge (EC) and microcystin content of M. aeruginosa. The EC ranged between 0.47 and 0.63. The microcystin content of the cells increased from 3 to 23 ng microcystin μg−1 protein in phosphorus-depleted cultures and from 2 to 12 ng microcystin μg−1 protein in iron-depleted cultures. A positive correlation between EC and microcystin content of the cells in both phosphorus- and iron-depleted cultures indicates that factors that affect EC influence microcystin production. Phosphorus and iron depletion modulated the cellular composition of M. aeruginosa. Carbohydrate constituted 5–8% of dry weight when the organisms were grown in complete O2 medium. During prolonged phosphorus and iron depletion, the carbohydrate content increased to 35–60% of dry weight. The protein content of the cells was on average 65% of dry weight when grown in complete O2 medium and decreased during phosphorus and iron depletion to an average of 35% of dry weight.