FIG. 9.

Size class distribution of C. acidovorans PX54 cells cultured in chemostats at different growth rates (0.5, 1.0, 2.0, 3.0, 3.5, 4.0, and 4.5 day⁻¹) and in batch culture at the maximum growth rate (bar on the right). The same medium with the same substrate concentration was used for chemostat and batch cultures. The bacterial populations were divided into size classes with different sensitivities to grazing by bacterivorous flagellates (28). Because no C. acidovorans PX54 cells were smaller than 0.4 μm, all cells smaller than 1.2 μm were considered edible bacteria. In chemostat cultures the percentage of short filaments (length, 5 to 10 μm) increased with growth rate from 0% (growth rate, 0.5 day⁻¹) to 1% (growth rate, 4.5 day⁻¹) and was thus much smaller than the percentage observed in samples obtained from the exponential stage of batch cultures. d, day.