18. Feeding Selectivity of Tetrahymena pyriformis with the Use of Charged Latex Beads

Abstract

Tetrahymena pyriformis is a single-cellular alveolate that uses cilia to filter-feed on small particles. The fact that T. pyriformis ingests non-nutritive material, such as latex beads and carbon particles, along with nutritional ones, led to the hypothesis that the organism feeds non-selectively. One recent article, however, calls this hypothesis into question. We sought to investigate feeding preference in Tetrahymena by determining its rate of phagocytosis on three types of 3 mm polystyrene beads, each at two concentrations. Beads had either a neutral surface, one that was negatively-charged through carboxylation, or a positively-charged, aminated surface. To determine feeding rate, we mixed one type of bead with Tetrahymena and made slides from that mixture at three time points. Since beads accumulate in T. pyriformis over time, the slope of the best-fit line provides a measure of feeding rate. Thirty such measures were obtained for each type of bead and concentration. ANOVA revealed that both bead-type and concentration had significant effects on feeding rate, but there was no hint of an interaction. Tetrahymena fed 54% more rapidly on positively-charged beads than on the ones that were negatively charged. The rate of feeding on neutral beads fell in between the other two. Our study provides new evidence that Tetrahymena feeds selectively. Since surface charge plays a role, electrostatic interactions, as often occur when receptors bind ligands, appear to underlie that selectivity