Growth responses of ciliate protozoa to the abundance of their bacterial prey.

The growth rate or numerical response of five species of bactivorous ciliates to the abundance ofEnterobacter aerogenes was examined in monoxenic culture. The ciliatesColpidium campylum, C. colpoda, Glaucoma scintillons, G. frontata, andCyclidium glaucoma were isolated from a small pond. Four were grown in shaken cultures, while three were grown in cultures in which the bacteria were allowed to settle on the bottom of the culture vessel. Of the seven response curves generated, four had distinct thresholds, so that the Michaelis-Menten model usually fitted to ciliate numerical response curves was not appropriate. In shaken cultures, half-saturation prey densities ranged from 5.5 × 10(6) to 42.9 × 10(6) bacteria/ml. In unshaken cultures, half-saturation densities ranged from 0.057 × 10(6) to 14.6 × 10(6) bacteria/cm(2). Two species grown on both suspended and settled bacteria attained higher growth rates and had lower half-saturation prey densities feeding on settled bacteria.