Previous work has indicated that the ubiquitous freshwater ciliate Tetrahymena pyriformis acclimates to the presence of hydrophobic chemicals acting by nonpolar narcosis. Four explanations have been identified to explain this apparent acclimation: (1) genetic adaptation occurs resulting in a resistant population, (2) T. pyriformis quickly biodegrades hydrophobic chemicals resulting in a perceived acclimation response, (3) hydrophobic chemicals are not bioavailable, and (4) T. pyriformis contain an endogenous biochemical adaptation system which can quickly cause cellular changes resulting in acclimation. Results of biodegradation experiments indicated that the total extractable 1-octanol did not change over the duration of the experiments. Bioavailability experiments were performed using the solid-phase microextraction technique. Although there is a decrease in freely available concentrations of 1-octanol over a 2.5 log unit range of Tetrahymena population density, the freely available concentration is constant for the population densities used for population growth experiments. Genetic change is highly unlikely since acclimation occurs in less than the time required for one population division. It is hypothesized that the acclimation response seen in Tetrahymena results from partitioning of the chemical into the membrane followed by active changes in the membrane structure to restore homeostasis. Copyright 1999 Academic Press.
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