THE PROTOZOAN CILIATE Tetrahymena thermophila AS BIOSENSOR OF SUBLETHAL LEVELS OF TOXICANTS IN THE SOIL

This report describes the use of recombinant cell lines of the eukaryotic microorganism Tetrahymena thermophila as whole cell biosensors (WCB) of sublethal levels of environmental toxicity. In order to obtain the WBSs, cells of T. thermophila, a worldwide distributed, freshwater, protozoan ciliate were transfected with the expression vector pD5H8, containing the coding sequence of the reporter gene for the "Green Fluorescent Protein" (GFP), under the control of a homologous, stress inducible hsp70 promoter. By this method, a fluorescent reporter cell line that is able to detect general toxicity was obtained. The toxicity assay using the recombinant Tetrahymena cells is simply performed by exposing them to various dilutions of environmentally relevant pure compounds or more complex environmental (field) samples (effluent discharges, soil elutriates etc.) and measuring the resulting fluorescent emission by means of fluorescence microscopy. Thus, in this assay the GFP fluorescence emission represents the toxicity endpoint. In this study, the Tetrahymena biosensors were used in the frame of the BIO-BIO project (sponsored from the "Provincia di Pavia") in order to assess the potential toxicity of soil elutriates coming from three farms managed using different agricultural systems (conventional and organic). In parallel with the Tetrahymena bioreporter assay, classic lethality assays were also performed. The obtained results clearly showed a better performance of the bioreporter assay over the classical lethality in unveiling sublethal levels of environmental toxicity.