EVALUATION OF A STRESS-INDUCIBLE TRANSGENIC NEMATODE STRAIN FOR RAPID AQUATIC TOXICITY TESTING

A transgenic strain of the nematode Caenorhabditis elegans which carries a stress-inducible lacZ reporter gene has been evaluated in terms of its response to several environmental toxicants. Optimal sensitivity is obtained by exposing these worms to toxicants at a temperature just below that required for heat induction of the transgene. Under these circumstances, several heavy metals (Cd2+, Zn2+, Hg2+, Mn2+, Sn2+, Ag+) cause dose-dependent transgene expression, which can be monitored as beta-galactosidase enzyme activity or by in situ histochemical staining. A simple assessment procedure has been developed so that staining patterns can be compared between runs. The induced enzyme activity is localised in a single band (of apparent size 170 kD) on Western blots, as shown both by histochemical staining and immunoprobing. Endogenous heat-shock proteins (hsp70) are optimally induced under the same assay conditions, but modest induction is also apparent under control conditions (sub-heat-shock temperatures alone). Our system requires relatively high concentrations (ppm) of metallic ions for clear-cut induction, but is apparently more sensitive to certain organic and organo-metallic compounds (lindane and tributyltin are effective at ppb levels). This system works well within strictly defined assay conditions, but some toxicants are more effective inducers than others (e.g. Cd2+ versus Mn2+), while some give paradoxical dose-response curves possibly due to enzyme poisoning at high toxicant concentrations (e.g. Ag+). However, similar problems are likely to be encountered with any transgenic assay system based on the heat-shock response when used to monitor environmental pollution.