The Metabolism of Escherichia coli and other Bacteria by Entodinium caudatum

SUMMARY: 14C-labelled Escherichia coli and other bacteria were used to measure their uptake by washed suspensions of Entodinium caudatum. All the bacteria tested were engulfed by the protozoa with a maximum uptake of 1·1 x 104 E. coli/protozoon at an initial rate of over 200 bacteria/protozoon/min. After 30 min. only 12% of the engulfed bacteria were still viable. 50% of the bacterial carbon was retained by the protozoa and, after breakage of the protozoa and centrifugation of the homogenate, 40% of this carbon was present in the supernatant fluid, principally as protein. Competition experiments where the protozoa were offered two different species of bacteria showed that the protozoa engulfed bacteria in the proportion in which they were present in the medium. The growth of E. caudatum in the presence of rice starch, autoclaved rumen fluid and penicillin was stimulated by several species of bacteria, including E. coli, Clostridium welchii, Lactobacillus casei.