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ISSE Seed Project: Toxicity Profiling of Dioxin-like Pollutants and Other Arly Hydrocarbon Receptor Agonists Using a High-Throughput Yeast Bioassay

Team: Gary Sayler and Tingting Xu, Center for Environmental Biotechnology; Joe Zhuang, Biosystems Engineering and Soil Science, UTIA; Terry Hazen, Civil and Environmental Engineering; Jiangang Chen, Public Health

2015-2016 Funded Proposal

Project description: Dioxin and dioxin-like compounds (DLCs), a group of structurally related halogenated aromatic hydrocarbons, account for a quarter of the “dirty dozen” persistent organic pollutants internationally recognized as chemical pollutants with a high priority for environmental cleanup, reduction of release, and restricted production. While the commercial production and use of some DLCs is banned in the United States, other DLCs continue to be generated as unintentional by-products of municipal, medical, and industrial waste incinerations, forest fires, cremations, oil spills, and many industrial manufacturing processes. This is especially troublesome because these compounds are extremely stable, highly resistant to degradation and metabolism, and persistent in the global environment. They are also prone to accumulation in animals, and therefore biomagnify along the food chain towards human consumption. Despite their structural variations, DLCs are of toxicological concern to human health because they induce a common pattern of biological and toxicological responses via their interaction with a crucial signaling protein. Perturbations of this signaling protein have been linked to a variety of adverse health effects, including deficiencies in reproduction and development, disruption of the endocrine system, neurotoxicity, immunotoxicity, cancer, and metabolic diseases.

diagram of autonomous dioxin bioassay
Diagram of the autonomous dioxin bioassay. The objective of this project is to develop a yeast-ased bioassay for high-throughput, rapid, and cost-effective toxicity profiling of dioxin-like compounds (DLCSs). The yeast cells will be engineered to express light-producing reporter genes under the regulation of a DLC-responsive gene switch. Exposure to DLCs will activate the gene switch and turn on the reporter genes to product an autonomous optical signal without any external stimulation. In addition to simply detecting the presence of DLCs, the whole-cell bioassay also provides valuable information on their bioavailability and biological impact.

Due to their stability in the environment, ability to bioaccumulate, and substantial toxicological effects, it is critical to monitor and quickly detect DLCs in the environment and provide a rapid tier 1 toxicity evaluation for environmental security and public health risk assessment. The current gold standard for DLC detection is an analytical chemical approach which offers superior sensitivity but with significant cost and complexity. Meanwhile, although the analytical chemical method can identify individual compounds based on their structures, it is complicated and often difficult to determine the overall biological impacts. To facilitate faster, easier, more economical, and higher-throughput tier 1 sample analysis for safeguarding environmental security and public health, the goal of this project is to develop an improved low cost tier 1 bioassay for reagent-free DLC detection using humanized yeast bioreporters that autonomously generate a high resolution optical signal in response to bioavailable DLCs. Using the robust yeast as the host organism also offers a convenient and rapid assay format while still maintaining the toxicological relationships with human exposure endpoints. This new assay, by virtue of its autonomous reporting capabilities, will also be amenable to automation and high-throughput sample analysis, making it a vastly improved candidate for large-scale use for not only environmental monitoring and risk assessment but also food supply biosurveillance and high-throughput toxicological screening of DLCs for protection of human and animal health. This autobioluminescent reporter system will also serve as a proof-of-concept “plug-and-play” platform that can be expanded to a suite of high-throughput bioassays using both yeast and human cells as hosts to profile the impact of a wide range of environment pollutants.