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Cornell iGEM

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Project Lead it Go

Heavy metal pollution in water is one of the most significant public health risks around the world. Pollutants including lead, mercury, and nickel can enter water supplies through a number of methods including improper disposal of waste, industrial manufacturing, and mining. When solubilized, they have the ability to cause environmental and health problems. These heavy metals are acutely toxic at high concentrations and carcinogenic with long-term exposure even at low concentrations. Methods exist to remove heavy metals from water supplies, but these methods create other hazardous wastes and are much more effective in waters with high concentrations of metals. Due to the high affinity of binding proteins, a biological based filtration system can be more effective at treating water contaminated with lower concentrations of heavy metals without generating large volumes of toxic waste. Our team plans to combat heavy metal pollution problems by improving existing biological filtration methods and developing a novel system for lead remediation. To this end, we are engineering bacterial strains that will simultaneously express heavy metal transport proteins and metallothioneins, a class of low-molecular weight, cysteine-rich proteins with high binding affinities for various heavy metals. The heavy metal transport proteins are specific to certain metals and will cause rapid intake of these ions. The metallothioneins will then bind to these ions intracellularly and permanently sequester them. After filtration, the respective heavy metals can be isolated by recollecting the cells from the filter. In addition to developing these strains, our dry lab team has designed a hollow fiber reactor with several chambers, each designed to collect a specific metal. The filter system was then assembled into a compact and transportable prototype. We plan to test the efficacy of different combinations of filters in series using samples of contaminated waters near a local brownfield site. Previously, research groups have developed such filtration systems for some of the most harmful heavy metals: nickel, mercury, and lead. One of our faculty advisors at Cornell, Dr. David Wilson, has developed such systems for mercury and nickel. We propose to improve the efficiency and lifespan of these filtration systems. Additionally, we are developing a novel sequestration system for lead by utilizing a putative lead transport protein from Nicotiana tabacum. To this end, we have successfully synthesized four BioBricks: (1) a nickel BioBrick consisting of the Anderson promoter, the nixA gene, and a terminator, (2) a mercury BioBrick consisting of the Anderson promoter, the merT gene, merP gene, and a terminator, (3) a metallothionein BioBrick consisting of a T7 promoter, the GST gene, the CRS5 gene, and a terminator, and (4) a metallothionein BioBrick consisting of the GST gene, the CRS5 gene, and a terminator. We began a series of growth assays and metal sequestration experiments to determine the effectiveness of these constructs.