Grazing and growth of the heterotrophic flagellate Diphylleia rotans on the cyanobacterium Microcystis aeruginosa

Abstract

The grazing and growth rates of the algivorous heterotrophic flagellate (HF) Diphylleia rotans were investigated on toxic (Microcystis aeruginosa NIER-10001, M. aeruginosa NIES-298, M. viridis NIES-102 and M. wesenbergii NIES-104) and non-toxic (M. aeruginosa NIES-101) Microcystis strains as well as other different algae such as the green alga Chlorella TM (Aquanet), and diatoms Cyclotella meneghiniana and Stephanodiscus hantzschii. The flagellate D. rotans showed active growth when fed M. aeruginosa and lower levels of growth when fed Chlorella TM , but no growth when fed C. meneghiniana and S. hantzschii. The flagellate grew actively at 25C and at a pH range between 6 and 9. The highest maximum specific growth rate (1.88 d -1 ) and a high ingestion rate (27.0 prey HF -1 d -1 ) by D. rotans were observed when they were fed the most toxic of the 5 Microcystis strains, M. aeruginosa NIER-10001. These results suggest that D. rotans has a high tolerance to M. aeruginosa and may undergo microcystin-mediated growth.