Reversal of phenol and naphthalene effects on ciliate chemoattraction

Reversibility of the inhibition of protozoan attraction to yeast by phenol and naphthalene was tested using 2 freshwater ciliates (Tetrahymena sp. and Tetrahymena pyriformis) and 2 marine ciliates (Paranophryus sp. and Miamiensis avidus). Capillary tubes containing 0.15 per cent yeast extract solutions and different concentrations of toxicant were placed in ciliate suspensions, and the number of cells in each capillary after 15 minutes was counted by direct microscopic examination to determine inhibition. Analysis of variance tests showed that washing ciliates by repeated centrifugation after exposure to the toxicant for 15 minutes nullified the inhibitory effects of 100-200 mg phenol per litre on Tetrahymena sp. and Miamiensis and 25 per cent naphthalene on Tetrahymena sp. Movement tests showed that random movement of T. pyriformis was not affected by phenol or by naphthalene at concentrations lower than 25 per cent, indicating that inhibition was not due to interference with chemosensory responses. The reversal of inhibition demonstrated protozoan adaptation to the test toxicants, and further studies would investigate longer-term exposures.