Microcystin production by Microcystis aeruginosa: Direct regulation by multiple environmental factors

Effects of environmental variations on microcystin (MCYST) production were tested by evaluating results obtained from batch culture experiments with Microcystis aeruginosa MASH-01A19. Time series of cell and MCYST concentrations were evaluated independently with two models, a static linear and a dynamic non-linear model. Significant influences of irradiance, sulphur and phosphorus (P_i) supply on MCYST production were identified and notably, these effects occurred independently of influences on growth rate. Specifically, effects on the two main parameters intrinsic growth rate and MCYST production coefficient were inversely correlated. With increasing irradiance and P_i supply MCYST production was reduced. By contrast, MCYST production was lowered when sulphur was depleted. Since MCYST production was influenced by more than one environmental variable it is suggested that MCYST is under multiple regulation. A well-distinguishable control of MCYST production by one environmental factor can be excluded. All the observed effects on MCYST production do not disagree with earlier findings that MCYST may be involved in processes linked to photosynthesis.