The Effect of Paromomycin on the Population Heath of Tetrahymena thermophila

Abstract

Tetrahymena thermophila, a fresh water ciliate, is a unicellular eukaryote that feeds by phagocytosis. Tetrahymena reproduce by asexual fission (Asia and Forney 2000). The mutant (TTHERM_00442300) is resistant to paromomycin, an aminoglycoside antibiotic. In this experiment, we observed the effects of paromomycin on the population health of both wild type and mutant Tetrahymena thermophila. Both types were placed in a growth medium to which paromomycin had been added and observed following immediate exposure to different concentrations of paromomycin. Population health was measured by counting motile cells in the sample taken immediately after cells were placed in a paromomycin medium and after an overnight incubation. Dividing cells were counted after an overnight incubation in paromomycin medium. Proportions of motile cells were calculated relative to the control for each treatment. Peptone growth medium with a 0μg/ml paromomycin concentration yielded about 70 dividing cells per slide throughout the observation time; a 10 μg/ml concentration reduced this number to 50, and later on to 30, after 15 minutes of observation. Thus, on average a reduction of 100 cells per slide at the end of 30 minutes’ observation was noted for three replicates in 10, 100 and 200 paromomycin concentrations. The wild-type cells did not undergo any cell division after prolonged exposure to paromomycin and the number of motile cells was reduced to 0-5 cells. Exposure to paromomycin had a dramatic effect on wild type T.thermophila and resulted in no dividing cells after 24 hours. Even though immediate exposure to paromomycin had no apparent effects on the mutant, it did negatively affect the population health when grown in paromomycin medium for 24 hours. Paromomycin can result in the inhibition of protein synthesis (Eustice and Wilhelm 1984) as well as the mistranslation of the polypeptide chain (Wilhelm et.al. 1978). Thus, the population health of both the wild type and the mutant was reduced as the concentration of paromomycin increased.