Ref ID : 7011
Joanne L. Dennis, Mohammed H.A.Z. Mutwakil, Kenneth C. Lowe, and David I. de Pomerai; Effects of metal ions in combination with a non-ionic surfactant on stress responses in a transgenic nematode. Aquatic Toxicology 40:37-50, 1997
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Exposure to metal ions induces a stress response by activating beta-galactosidase expression in a strain of transgenic nematode (Caenorhabditis elegans strain PC72) carrying an E. coli lacZ gene under the control of an hsp16 heat-shock promoter sequence. This system can also be activated by several organic toxicants, and low beta-garactosidase activities 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 surfactant 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 diminishes at high concentrations of Cd2+, possibly due to increased mortality. A three-way ANOVA confirms that both metal concentration and the presence of surfactant have extremely significant effects on beta-galactosidase induction, and that there are significant interactions between these factors (generally, the surfactant effect is more pronounced at higher metal concentrations). However, the ANOVA also reveals highly significant variations between repeat runs under the same test conditions, although the trends attributable to metal dose or to surfactant are present consistently in all runs. In situ histochemical staining shows that beta-galactosidase is expressed throughout worms treated with metal plus surfactant, in contrast to the localised pharyngeal staining 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 this is provided by the observation that worms treated with Pluronic F-127 (10 ppm) accumulate slightly (ca. 10%) more Cu2+ or Zn2+ during the standard exposure period than do control worms exposed to metal only. Thus metal ions are significantly more toxic to C. elegans when combined with a non-ionic surfactant, itself present at sub-toxic (indeed, growth promoting) concentrations.