Long-term Studies of Ciliate-Bacterial Interactions: Use of a Chemostat Fed with Bacteria Grown in a Separate Chemostat

Summary: Two-stage chemostat cascades have been used to study growth of the ciliate Tetrahymena pyriformis on Escherichia coli over extended periods of time. Upward drifts (continuous, slow, uni-directional changes) of ciliate number density and downward drifts of ciliate mean cell size and density of residual bacteria occurred for many generations of ciliates before steady states were obtained. Ciliate chemostats were operated at two different dilution rates. Rates of drift were slower, and drifts persisted longer, both in terms of time and in terms of numbers of generations, in the chemostats operated at the higher dilution rate. Some speculations on the origins of the drifts are presented.