Development and application of whole cell biosensors based on recombinant cell lines of the ciliated protozoan Tetrahymena thermophila for ecotoxicity screening

This report describes the development and the application in ecotoxicity screening of whole cell biosensors (WCB) based on recombinant cell lines of the ciliated protozoan Tetrahymena thermophila. Cells of this worldwide distributed, freshwater, eukaryotic microorganism were transfected with the expression vector pD5H8, containing the coding sequence of the reporter genefor the “Green Fluorescent Protein” (GFP), under the control of a homologous, stress inducible hsp70 promoter. By this method a fluorescent bioreporter strain able to detect general toxicity was obtained. The toxicity assay was performed by exposing the cells to various dilutions of environmental relevant pure compounds or more complex environmental (field) samples (effluent discharges, soil elutriates etc..) and the fluorescent emission was easily detected by means of fluorescence microscopy. In this study, the Tetrahymena whole cell 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, organic and threaded with sewage sludge). In parallel to the Tetrahymena bioreporter assay, also classic lethality assays were performed. The results showed that the bioreporter assay allows a better evaluation of the toxicity displayed by the elutriate samples with respect to the lethality, assay in the presence of low levels of toxicity.