Low environmental pH inhibits phagosome formation and motility of Tetrahymena pyriformis

Abstract

Tetrahymena pyriformis, single-celled protozoans, populate ponds, lakes, and streams. As 2.57 million tons of carbon dioxide enter the atmosphere every second, Earth’s bodies of water acidify rapidly, creating harmful habitats for organisms such as ciliates at the bottom of the food chain, like T. pyriformis. Investigating the ability of T. pyriformis to feed in acidic pHs presents a deeper understanding of the short-term ramifications of carbon dioxide emissions on freshwater ecological communities. In this experiment, we varied pH from 4.5 to 7.0 by diluting carbonated water. To observe T. pyriformis food vesicle formation, we counted the number of phagosomes located in iodine-fixed T. pyriformis after a 10-minute feeding period. We hypothesized that increased suspension acidity would reduce T. pyriformis’ consumption of food vesicles due to inhibited motility functions and phagosome formation during phagocytosis. Our data suggests T. pyriformis best generate phagosomes within a pH range of 6.0 to 7.0. Data displayed a low average vesicle count of 0.60 ± 0.16 at a pH of 4.5 and a high average vesicle count of 3.73 ± 0.18 at a pH of 7.0. At a pH of 6.0, average vesicle count plateaued as its rate of increase slowed. We posit that as pH levels decrease, T. pyriformis lose feeding competence due to three probable mechanisms: increased membrane density, weakened myosin necessary for vesicle transport, and inhibition of ciliary movement –– all components necessary to initiate and complete phagocytosis.