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Microcystis aeruginosa has quickly risen in infamy as one of the most universal and toxic bloom-forming cyanobacteria. Here we presented a species of golden alga (Poterioochromonas sp. strain ZX1), which can feed on toxic M. aeruginosa without any adverse effects from the cyanotoxins. Using flow cytometry, the ingestion and maximal digestion rates were estimated to be 0.2 approximately 1.2 and 0.2 M. aeruginosa cells (ZX1 cell)(-1)h(-1), respectively. M. aeruginosa in densities below 10(7)cells mL(-1) could be grazed down by ZX1, but no significant decrease was observed when the initial density was 3.2 x 10(7)cells mL(-1). ZX1 grazing was a little influenced by the light intensity (0.5 approximately 2500l x) and initial pH of the medium (pH=5.0 approximately 9.5). ZX1 could not survive in continuous darkness for longer than 10 days. The pH value was adjusted to 8 by ZX1 while to 10 by M. aeruginosa. This study may shed light on understanding the ecological interactions between M. aeruginosa and mixotrophic Poterioochromonas sp. in aquatic ecosystems.