Iron-stimulated growth and microcystin production of Microcystis novacekii UAM 250

The impact of iron on growth and microcystin production was studied using the cyanobacterium Microcystis novacekii UAM 250. Four different iron concentrations, ranging from 0 to 5 μM, were used, while other nutrients remained constant. Growth of the cyanobacterium and the production of intracellular microcystin were maximal at the highest iron concentration. Three types of microcystins were identified: MCYST-LR, -YR, and -RR. The concentrations of microcystins in the medium (extracellular microcystins) were lowest at the initial growth phase of the cyanobacterium and increased subsequently as the cells began to decay, releasing their microcystin content to the water phase.Most cyanobacteria blooms occur in eutrophic water bodies. In most sewage treatment plants more iron is used than is required for optimal phosphorus removal. However, iron is a particularly important micronutrient for cyanobacteria. This research is relevant to understanding the potential effects of excess iron discharge from sewage treatment plants on toxin production by cyanobacteria.