Bacterial preferences and growth kinetic variation inUronema marinum andUronema nigricans (Ciliophora: Scuticociliatida).

The growth kinetics of two species of the genus Uronema, the marine U. marinum and the freshwater U. nigricans, have been studied under equivalent culture conditions. Ciliates were fed on three bacterial strains at three different concentrations (10(6), 10(7), and 10(8) bacteria ml(-1)). Growth rates in U. marinum were between 10 and 70% higher than those observed for the freshwater clone of U. nigricans, while net stationary phase populations were 1-60 times higher in U. marinum than in U. nigricans. The half-saturation constants (KS) for each bacterial strain showed that U. nigricans reached its [Formula: see text] μmax at one to three times lower concentration than that observed for U. marinum. Despite the close morphological similarity of these species, U. marinum and U. nigricans exhibited sustained distinct growth behavior that might reflect the survival strategies followed in their specific environments.