Effect of caffeine addition on population growth of Tetrahymena thermophila

Tetrahymena thermophila is a unicellular eukaryote commonly used as a model organism in biological research. While there have been several studies on the effect of various substances on the population growth of T. thermophila, the effects of caffeine have not been widely studied. The purpose of this study was to characterize the effects of different concentrations of caffeine on the population growth of T. thermophila therefore determining if an increased concentration decreases the population growth. After exposing T. thermophila to 0 M, 10-1 M, 10-2 M, 10-3 M, and 10-4 M caffeine solutions, the population growth was monitored with a haemocytometer-based counting method at time intervals over a 24 hour period. From 4 hours onwards, our results suggest that caffeine concentrations of 10-3 M or higher significantly decrease population growth (all P-values<0.05) when compared to the control which had no caffeine. The long-term investigation of the population sizes (after 24 hours) also suggests a mechanism of adaptation or resistance to caffeine as the populations exposed to the highest caffeine concentration (10-1 M) partially recovered after initially decreasing.