The chrysophyte Poterioochromonas malhamensis has potential for controlling algal blooms through rapid grazing of toxic Microcystis cells and efficient degradation of microcystin. However, this method has not been used in practice because a high-cell-density method for cultivating P. malhamensis has not yet been established and the actual effect of the chrysophyte in controlling Microcystis blooms in the field is still unknown. To achieve the application of this method, high-cell-density heterotrophic cultivation of P. malhamensis was established through optimizing the carbon/glucose concentration, C:N ratio, temperature, pH, and dissolved oxygen concentration. Under optimized conditions, the cell concentration of P. malhamensis reached more than 3 x 10(8) cells mL(-1), which exceeds that reported in other studies by more than an order of magnitude. The ability of the chemoheterotrophic P. malhamensis to graze unicellular Microcystis cells was comparable to that of autotrophic and phagotrophic P. malhamensis. A controlled field experiment showed that chemoheterotrophic P. malhamensis could live in the aquatic environment with a Microcystis bloom and decrease the Microcystis biomass on the surface of the water by promoting the sedimentation of colonial Microcystis cells. This study offers an opportunity to drive the development of methods to control Microcystis blooms using predatory P. malhamensis.