AN EXAMINATION OF SELECTIVE FEEDING AND MOLECULAR RECOGNITION IN THE CILIATE, TETRAHYMENA PYRIFORMIS Ehrenberg, 1830

In amoeboid cells, food particles are engulfed only after receptors on the phagocytic cell’s membrane bind to ligands on a particle’s surface. Ciliates also feed via phagocytosis, but instead of enveloping particles the way amoebae do, ciliates take up particles through a complex, permanent, funnel-shaped feeding apparatus. It is unclear whether receptor-ligand interactions are needed to trigger the process. If ciliates were shown to prefer certain particles over others, based on the particles’ surface properties, then receptor-ligand interactions would likely play a role in phagocytosis. The literature includes few reports of such selectivity in ciliates. To further investigate this issue, we chose to study feeding selectivity in the ciliate Tetrahymena pyriformis Ehrenberg, 1830. We fed Tetrahymena mixtures of orange and green fluorescent, 3 μm, latex beads at two concentrations in which one type of bead was coated with bovine serum albumin through passive adsorption (BSA; 8–13 μg protein/mg beads). Authors were unaware of which beads were coated while collecting data. Treatment groups included the results of 12–16 trials. We found no evidence of a preference for either coated or uncoated beads at either concentration (coated vs. not coated, P = 0.131; bead concentration, P = 0.866; interaction, P = 0.294). In contrast, others have reported that T. pyriformis feeds more rapidly on BSA-coated beads than uncoated ones. We also found no trend toward the development of a preference as cells acquired more beads over time. The literature indicates that two species of nanoflagellates develop such a preference. Although we cannot rule out the possibility that Tetrahymena feeds selectively, we did not find convincing evidence of such selectivity when T. pyriformis is given a choice between uncoated beads and those coated with BSA. Our results failed to demonstrate a role for molecular recognition when Tetrahymena engages in phagocytosis