Effects of Caffeine Exposure and Withdrawal on TTHERM_00013550 Expression, Feeding, and Growth of Tetrahymena thermophila

Abstract

The purpose of our experiment was to determine the effects of caffeine addiction on Tetrahymena thermophila. In more complex organisms, such as humans, caffeine has stimulating effects and is addictive. We hypothesized that long-term caffeine exposure, followed by a period of withdrawal and reintroduction, would increase both expression of the TTHERM_00013550 gene and feeding behavior in Tetrahymena. The protein encoded by TTHERM_00013550 is thought to play a critical role in the molecular stress response in Tetrahymena. To test our hypothesis, a 0.1 mM solution of caffeine was added to the experimental culture medium and both the control and the experimental groups were cultured under ideal conditions for six days. Following the 6-day exposure, the cells in the experimental group were transferred to a control medium for an additional 23hrs, to allow for caffeine withdrawal to take place, after which they were placed back in the caffeine supplemented medium for the final hour of the experimental period. At the end of the week-long treatment, expression of the TTHERM_00013550 gene was measured by Reverse Transcription-quantitative Polymerase Chain Reaction (RT-qPCR) and feeding behavior was measured using an India ink-based feeding assay. It was predicted that Tetrahymena that underwent caffeine withdrawal would show increased expression of the TTHERM_00013550 gene, due to upregulation of the stress response, and increased feeding behavior.