EFFECTS OF METAL-IONS IN COMBINATION WITH A NONIONIC SURFACTANT ON STRESS RESPONSES IN A TRANSGENIC NEMATODE

Exposure to metal ions induces a stress response by activating beta-ga lactosidase expression in a strain of transgenic nematode (Caenorhabdi tis elegans strain PC72) carrying an E. coli lacZ gene under the contr ol of an hsp16 heat-shock promoter sequence. This system can also be a ctivated by several organic toxicants, and low beta-galactosidase acti vities are induced in worms exposed to non-ionic Pluronic surfactants. These surfactants have been shown to stimulate worm growth, possibly through enhanced nutrient uptake via membrane pores created by surfact ant action. This paper demonstrates that, in the presence of one such surfactant (Pluronic F-127 at 10 ppm throughout), the stress response of transgenic worms to several metal ions (Cd2+, Hg2+, Cu2+, Mn2+ and Zn2+) is markedly enhanced (by 1.5- to four-fold). This enhancement di minishes at high concentrations of Cd2+, possibly due to increased mor tality. A three-way ANOVA confirms that both metal concentration and t he presence of surfactant have extremely significant effects on beta-g alactosidase induction, and that there are significant interactions be tween these factors (generally, the surfactant effect is more pronounc ed at higher metal concentrations). However, the ANOVA also reveals hi ghly significant variations between repeat runs under the same test co nditions,although the trends attributable to metal dose or to surfacta nt are present consistently in all runs. In situ histochemical stainin g shows that beta-galactosidase is expressed throughout worms treated with metal plus surfactant, in contrast to the localised pharyngeal st aining characteristic of worms treated with metal alone. This suggests that Pluronic F-127 may facilitate metal entry into tissues which do not normally display a strong stress response. Tentative support for t his is provided by the observation that worms treated with Pluronic F- 127 (10 ppm) accumulate slightly (ca. 10%) more Cu2+ or Zn2+ during th e standard exposure period than do control worms exposed to metal only . Thus metal ions are significantly more toxic to C. elegans when comb ined with a non-ionic surfactant, itself present at sub-toxic (indeed, growth promoting) concentrations. (C) 1997 Elsevier Science B.V.