Team:UC Davis/Project

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Team:UC Davis - 2012.igem.org


Project

Polyethylene terephthalate (PET) is a commonly used plastic due to its durability and molecular stability, but its high molecular weight and hydrophobicity also make it one of the hardest plastics to degrade. PET is used in beverage containers, oven food trays, and video tapes. Although the PET recycling rate has increased from 7% to 30% in the last few years, a majority of the plastic is still dumped in landfills and continues to pollute the environment. Within the landfills, rainwater can trickle through the trash, creating toxic leachate. The leachate carries microorganisms and toxic chemicals into drinking water sources, making its impact go beyond the landfill. Plastic pollution is not isolated to landfills; plastic debris can wash up on shores and tons of plastic trash build up in the ocean. Marine animals can mistake the plastic debris as food, but since they cannot digest plastic they can starve. Plastic six pack rings can also choke animals by closing off the airway. We hope to achieve biodegradation of PET by manipulating E. coli to secrete a key enzyme called cutinase, a lipolytic and esterolytic enzyme. Degradation of PET creates two by-products, one of which is a mildly toxic compound called ethylene glycol. Ethylene glycol will be broken down by two enzymes (glycolaldehyde reductase and glycolaldehyde dehydrogenase) into glycolate, a glycolysis intermediate. Aside from ethylene glycol, another byproduct of PET degradation is terephthalic acid (TPA). It is a harmless substance that can be reused for PET production. We will not be focusing on turning TPA into a more useful material. However, we do know that a certain strain of E. coli is able to convert TPA into polyhydroxyalkanoates (PHA), a kind of biodegradable plastic. Even if the E. coli could successfully degrade a majority of the plastic, the strain would face intense competition if we were to try and implement is use in a landfill. E. coli will probably require a controlled, suitable environment to thrive in. One way to ensure this control would be to use a bioreactor.

What we did