8. Bacterial–protozoan interactions
Ingestion of bacteria by protozoa is a major process controlling survival of bacteria in the environment. Eberl et al. (1997) observed green fluorescent cells within various ciliate protozoa such as Vorticella and free-swimming protozoa Aspidisca sp.and Bodo sp. within 2 min of addition of GFP-marked Pseudomonas putida Green3I cells to activated sludge. They suggested that the use of GFP-tagged bacteria may be valuable for following bacterial fate on-line, and estimating instantaneous rates of in situ protozoan grazing on bacteria. Similarly, Olofsson et al. (1998) observed ingested GFP-marked bacterial cells within predators during their study of flocs in activated sludge. In our laboratory, we visualized ingestion of GFP-marked Moraxella sp. G21 cells by a ciliate strain ( Tetrahymena sp.) in an aqueous microcosm using epifluorescence microscopy (Fig. 1c).