Superfund Research Program
Identification of Metal Responsive Genes in Aquatic Arthropods
When gold and other valuable metals were first discovered in the western United States during the mid-1800's, the country wasn't aware of the impact that mining and metallurgical operations would have on watersheds in this region. We now know that the extraction and processing of metallic rich ores have resulted in substantial metal contamination of the surface and groundwater near many former mining operations. This knowledge has sparked concern over the effects of metals on the health of aquatic life, and created a need for methods that can detect metal stress in aquatic systems.
Measuring the molecular and genetic responses of organisms to metals provides direct evidence of metal exposures, as well as a means to assess metal contamination in the environment. For example, some metals produce measurable changes in the expression of genes. With recent advances in molecular genetic technology, it is possible to trace the subtle genetic changes that accompany metal exposures. In many cases, these molecular changes occur at very low exposures; thus, they can serve as early warning signs of contamination in the environment.
Researchers at Colorado State University are developing a novel approach to measure the presence and effects of metals in aquatic systems. They are assessing the molecular genetic responses of aquatic insects to metals in an effort to develop molecular approaches for biomonitoring metal pollution in aquatic ecosystems. Aquatic insects are favorable monitors of metal pollution because they are ubiquitous, easy to collect and identify, and they accumulate metals in a manner directly proportional to environmental conditions. Although some conventional methodologies already use aquatic insects as biomonitors, little is known about their potential for biomonitoring at a molecular genetic level. In these studies, the researchers are identifying and characterizing metal responsive genes in benthic arthropod populations (bottom dwelling insects) collected from the Arkansas River-California Gulch Superfund Site in Leadville, Colorado.
The scientists have isolated and are characterizing several metal responsive genes from a variety of common aquatic insects. Because these genes are induced in a metal- and dose-dependent manner, they may be useful as indicators of metal contamination in aquatic systems. For example, a metal responsive gene termed B6u from mosquito (Aedes aegypti) was found to code for a midgut protein with similarities to human and moth mucins. B6u was most strongly induced by the binary combination of copper and mercury. Although the exact role played by this protein during metal exposure is unknown, the insect mucin has been shown to facilitate digestion and to protect the digestive track from microbial infections.
In addition, metal responsive homologs of the mucin gene have been isolated from other insects. A metal responsive gene termed C610B was isolated from midges (Chironomus tentans) and found to be induced by cadmium and copper. Expression of a metal responsive gene from mayflies (Baetis tricaudatus) is apparently higher in individuals collected from a metal exposed section of the Arkansas River than in those from a less polluted site in the river suggesting the usefulness of this gene as a biomarker.
These findings have far reaching implications in terms of biomonitoring heavy metal contamination. With available molecular genetic techniques, analysis of metal responsive gene expression is exquisitely sensitive. In fact, the researchers have already demonstrated that metal responsive gene induction was a more sensitive indicator of metal pollution than traditional biological assays. These metal responsive genes are important not only for their potential in biomonitoring metal pollution in aquatic systems, but also because they provide fundamental knowledge and tools for understanding the mechanisms of genetic response to metals.
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To learn more about this research, please refer to the following sources:
- Klimowski LK, Rayms-Keller A, Olson KE, Yang RH, Carlson JE, Beaty BJ. 1996. Inducibility of a molecular bioreporter system by heavy metals. Environ Toxicol Chem 15:85-91.
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