Growth and microcystin production by Microcystis aeruginosa in batch cultures at different iron concentrations

In this study growth and toxin (microcystin) production by Microcystis aeruginosa at various iron (Fe) concentrations in the O2 medium, was examined. Microcystis aeruginosa PCC 7806 and MCYB¯ non-toxic mutant were grown, in 2 l batch cultures. Low Fe concentrations (250 μg Fe/l ) resulted in a decrease of growth for the PCC 7806 cultures, compared to growth in ordinary Fe concentrations (500 μg Fe/l). While adding 5000 μg Fe/l resulted in faster growth of both the MCYB¯ and PCC 7806 cultures. This also resulted in a six-fold increase of microcystin content, compared to the medium containing 250 μg Fe/l. The MCYB¯ cultures was almost not affected by the amount of Fe in the media. With only 50 μg Fe/l added to the medium, both the PCC 7806 and the MCYB¯ cultures were unable to grow. Cell density and microcystin production increased as a result of increasing Fe concentration in the medium from the start of the experiment. Microcystin content increased as the Fe concentration decreased during the experiment under all treatments. This study found M. aeruginosa PCC 7806 to adapt slower under limiting conditions. While at higher Fe concentrations both cell density and microcystin content increased. Which shows that Fe concentration is an important factor for growth of M. aeruginosa, and that the trace metal has a high influence on microcystin production.