Use of Stress-Inducible Transgenic Nematodes as Biomarkers of Heavy Metal Pollution in Water Samples from an English River System

Transgenic strains of the nematode Caenorhabditis elegans, which carry stress-inducible lacZ reporter genes, are measurably stressed by exposure to heavy metals in aqueous solution. This stress response can be quantified, using enzymatic assays for the reporter gene-product (Escherichia coliβ-galactosidase), or estimated approximately by in situ staining for β-galactosidase in exposed worms. Stress responses to heavy metals have been demonstrated both in laboratory tests using Cd2+ or Hg2+, and also in water samples taken from a metal-polluted river system in southwest England. The River Carnon flows through an area with an ancient mining history, principally for Sn, but also for Cu and other metals; As, Cd, Al, Mn, and Zn, as well as large amounts of Fe, are all present in these ore bodies. Four sites in the Carnon river basin were compared with respect to their macroinvertebrate diversity, physical and chemical characteristics (including the concentrations of As, Cd, Al, Cu, Mn, Zn, and Fe). Transgenic worms were exposed to water samples from these four sites, and also to a 0.33% (v/v) dilution of metal-laden minewater from the principal local mine (Wheal Jane). Transgene expression was induced in all five cases, though markedly less so for the least polluted of the sites (which also supported a richer macroinvertebrate fauna). Two different transgenic strains were tested in this study; strain PC72 (using a homologous hsp16 promoter) is slightly more sensitive to most metal-containing water samples than strain CB4027 (using a heterologous Drosophila hsp70 promoter). Both transgenic strains and two different assay methods gave essentially similar results. These findings demonstrate that transgenic nematodes could provide a rapid and simple assessment of aquatic pollution, in that the transgene response is inducible by mixtures of dissolved metals at concentrations actually encountered in metal-polluted watercourses.