The effects of the ciliate Paramecium cf. caudatum Ehrenberg on toxin producing Cylindrospermopsis isolated from the Fitzroy River, Australia

The large ciliate Paramecium cf. caudatum Ehrenberg was found to be a succe ssful grazer of toxin producing Cylindrospermopsis in the laboratory. The f eeding rate increased with increasing cell concentration to 1367 cell anima l hr(-1) at 4.1 x 10(5) cells mL(-1) but declined slightly at cell concentr ations greater than this. Preliminary studies on the effects of this grazin g on toxin concentrations in cultures of both straight and coiled forms of Cylindrospermopsis resulted in the production of different amounts of the t oxin cylindrospermopsin in the different isolates. Differences in toxin pro duction were also found between cultured and field populations from the low er Fitzroy River indicating that toxin production may be influenced by a su ite of genetic and environmental factors. The proven ability of this ciliat e to graze toxic Cylindrospermopsis provides some insight into interactions that may be able to control some toxic blooms in semiarid Australian condi tions. (C) 2001 by John Wiley & Sons, Inc.