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 expo sure to heavy metals in aqueous solution. This stress response can be quantified, using enzymatic assays for the reporter gene-product (Esch erichia coil beta-galactosidase), or estimated approximately by in sit u staining for beta-galactosidase in exposed worms. Stress responses t o heavy metals have been demonstrated both in laboratory tests using C d2+ or Hg2+, and also in water samples taken from a metal-polluted riv er system in southwest England. The River Carnon flows through an area with an ancient mining history, principally for Sn, but also for Cu a nd other metals; As, Cd, Al, Mn, and Zn, as well as large amounts of F e, 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 w ater 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 le ss so for the least polluted of the sites (which also supported a rich er macroinvertebrate fauna). Two different transgenic strains were tes ted in this study; strain PC72 (using a homologous hsp16 promoter) is slightly more sensitive to most metal-containing water samples than st rain CB4027 (using a heterologous Drosophila hsp70 promoter). Both tra nsgenic strains and two different assay methods gave essentially simil ar results. These findings demonstrate that transgenic nematodes could provide a rapid and simple assessment of aquatic pollution, in that t he transgene response is inducible by mixtures of dissolved metals at concentrations actually encountered in metal-polluted watercourses.