Molecular and genetic ecotoxicologic approaches to aquatic environmental bioreporting.

Abstract

Molecular and population genetic ecotoxicologic approaches are being developed for the utilization of arthropods as bioreporters of heavy metal mixtures in the environment. The explosion of knowledge in molecular biology, molecular genetics, and biotechnology provides an unparalleled opportunity to use arthropods as bioreporter organisms. Interspecific differences in aquatic arthropod populations have been previously demonstrated in response to heavy metal insult in the Arkansas River (AR) California Gulch Superfund site (CGSS). Population genetic analyses were conducted on the mayfly Baetis tricaudatus. Genetic polymorphisms were detected in polymerase chain reaction amplified 16S mitochondrial rDNA (a selectively neutral gene) of B. tricaudatus using single-strand conformation polymorphism analysis. Genetic differences may have resulted from impediments to gene flow in the population caused by mortality arising from exposure to heavy metal mixture pollution. In laboratory studies a candidate metal-responsive mucinlike gene, which is metal and dose specific, has been identified in Chironomus tentans and other potential AR-CGSS bioreporter species. Population genetic analyses using the mucinlike gene may provide insight into the role of this selectable gene in determining the breeding structure of B. tricaudatus in the AR-CGSS and may provide mechanistic insight into determinants of aquatic arthropod response to heavy metal insult. Metal-responsive (MR) genes and regulatory sequences are being isolated, characterized, and assayed for differential gene expression in response to heavy metal mixture pollution in the AR-CGSS. Identified promoter sequences can then be engineered into previously developed MR constructs to provide sensitive in vitro assays for environmental bioreporting of heavy metal mixtures. The results of the population genetic studies are being entered into an AR geographic information system that contains substantial biological, chemical, and geophysical information. Integrated spatial, structural, and temporal analyses of these parameters will provide invaluable information concerning environmental determinants that restrict or promote gene flow in bioreporter populations.

The midgut epithelium of aquatic arthropods: a critical target organ in environmental toxicology.

“…Interspecific differences in aquatic arthropod populations, including reduced diversity and shifts in benthic community composition at sites located downstream from mining sites, occur in response to heavy-metal pollution (1,4,11). In addition, we previously demonstrated that the population genetic structure of Baetis tricaudatus was also perturbed in the Arkansas River in Colorado, presumably in response to impediments to gene flow in the population caused by mortality arising from exposure to pollution from heavymetal mixtures from mining sites (2). In the latter study, intraspecific differences in population structure were demonstrated using a mitochondrial 16S ribosomal DNA gene of B. tricaudatus as a measure of genetic diversity in the species in the Arkansas River.…”

“…In Colorado it is estimated that heavy metals from over 5,000 abandoned waste dumps or tailing pipes impact over 2,600 km of streams (1). These hazardous waste sites expose aquatic organisms and other wildlife to multiple heavy metals as well as to other pollutants, which can exert impacts on aquatic ecosystems at different levels of organization (1)(2)(3)(4)(5)(6)(7)(8)(9)(10). Theoretically, organisms such as aquatic arthropods that experience long-term exposure to the mixtures would be most impacted by such heavy-metal pollution.…”

“…Unfortunately, the use of such a selectively neutral gene provided no insight into the molecular mechanisms that conditioned arthropod survivorship. Delineating potential metal-responsive genes (MRGs) or other genes that impact gene flow and condition the population genetic structure of aquatic arthropods could provide a mechanistic understanding of fundamental responses to ecotoxicological insults and could be exploited to develop new molecular bioreporter systems (2,5,(12)(13)(14)(15)(16). RNA or protein products of a given MRG could be exploited as specific biomarkers of the presence or absence of heavy metals (2,5,(12)(13)(14)(15)(16).…”

“…Insects exposed to heavy metals at sublethal doses exhibit pathological effects on many biological activities (1)(2)(3)5,7,11,17). Concentrations and toxic effects of metals depend on the bioavailability of the metal and the size, age, sex, and developmental stage of the arthropod (2,6,8,10,11,18).…”

“…Concentrations and toxic effects of metals depend on the bioavailability of the metal and the size, age, sex, and developmental stage of the arthropod (2,6,8,10,11,18). Resistance to heavy metals varies with different genotypes and strains within a species (2,5-7).…”