Effects of Xenobiotic Compounds on Cell Activities in Euplotes crassus

Abstract

It is now widely accepted that Protists are relevant bioassays to be exploited for the study of environmental modifications due to the presence of xenobiotic compounds. In this work, we evaluated the possibility of utilizing Euplotes crassus, an interstitial marine ciliate, for the pre‐chemical screening of environmental sites, such as estuarine and coastal sediments. With this aim, we tested the sensitivity of E. crassus to exposure to three classes of pollutants: an organophosphate neurotoxic drug, basudin, largely used for pest control in agricultural sites, a toxic heavy metal, mercury (HgCl2), and an aromatic polycyclic hydrocarbon, benzopyrene (BP). We found a dose‐dependent effect of these compounds on cell viability at concentrations ranging from 1/102 v/v to 1/107 v/v for basudin, from 5 μM to 0.1 μM for HgCl2, and from 50 μM to 1 μM for BP. In particular, 100% mortality was caused by a 1‐h exposure to 1/105 v/v basudin, or 2 μM HgCl2, or 25 μM BP, and by a 24‐h exposure to 1/106 v/v basudin, 0.5 μM HgCl2, or 5 μM BP. A significant decrease in the daily mean fission rate (P<0.001) was found after exposure to 1/107 v/v basudin, or 0.25 μM HgCl2, or 1 μM BP. Moreover, as it is well known that the inhibition of acetylcholinesterase (AChE) activity represents a specific biomarker for neurotoxic drugs, we first detected this enzyme activity in E. crassus, using cytochemical, spectrophotometric, and electrophoretic methods; then, AChE activity was characterized by its sensitivity to specific AChE inhibitors and to variations in pH and temperature. Like AChE present in higher organisms, the AChE activity detected in E. crassus was inhibited by exposure to basudin. Conversely, exposure to HgCl2, or PB did not inhibit AChE activity, but caused a significant reduction in lysosomal membrane stability.