Population Growth Kinetics of Tetrahymena pyriformis Exposed to Selected Nonpolar Narcotics

Abstract.

This study describes effects of selected nonpolar narcotics of varying hydrophobicity (quantified by the 1-octanol-water partition coefficient, log K_ow) and molecular structure on the population growth kinetics of the freshwater ciliate Tetrahymena pyriformis. The response of Tetrahymena exposed to different nonpolar narcotics varied from a change in generation time to a change in lag phase with similar generation time compared to control. Two narcotics with high (>3.00), intermediate (>0.00 and <3.00), and low log K_ow (<0.00) values were tested. Growth of Tetrahymena inhibited up to 85% by the high log K_ow toxicants (2-decanone and butylbenzene) grew with similar rates as the control, but exhibited increased lag time, suggesting that the protozoan became acclimated to toxicant stress. Results from growth of Tetrahymena in the low log K_ow toxicants (ethanol and acetone) indicate an increased generation time with increasing concentration. Cells inhibited by the intermediate log K_ow chemicals, 1-pentanol and anisole, exhibited a response that was a combination of the previously mentioned two contrary responses. Cells inhibited <35% with 1-pentanol and <50% with anisole grew with similar generation times as control flasks, whereas in cells inhibited >35% or >50%, respectively, the doubling times were longer than control growth.