Team:Yale

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Converting E. coli into a foundry for bioplastics


    Poly(lactic acid) (PLA) is a plastic that has lately become very attractive due to various excellent properties that make it a great biomaterial. It is biodegradable, having a typical lifetime of about 6 months to 2 years until microorganisms break it down into water and carbon dioxide. It is biocompatible, degrading all at once instead of starting with the outermost layer, allowing the body’s immune response to break down the pieces into water, carbon dioxide, and, of course, lactic acid, before it has the time to overreact and damage surrounding tissues. It is bioabsorbable, allowing it to be resorbed into the body for applications such as spinal implants, slowly transferring the load to the body and allowing the bone to heal in a physically supportive environment. Lastly, it is thermoplastic, allowing it to be extruded in filament form and reshaped, as in a three-dimensional (3D) printer. Unfortunately, conventional methods of synthesizing PLA chemically are quite expensive: one gram of pure PLA costs around $90. Moreover, even though it is mostly manufactured from corn, the processing and purifying steps use many chemicals that are environmentally unfriendly.


    Recently, researchers have genetically engineered E. coli to produce PLA, but at low yields and at insufficiently long chain lengths for commercial use. We propose using multiplex automated genome engineering (MAGE) to improve both the yield and chain length of biosynthesized PLA. MAGE is recombineering on steroids. Instead of introducing one type of synthetic DNA, many areas of the genome are targeted in parallel. By repeating the procedure numerous times, an incredible amount of diversity can be created. MAGE utilizes a specific strain of E. coli called EcNR2, which has the λ Red recombination proteins Exo, Beta, and Gam (Wang HH). The λ Red recombination proteins come from the lambda phage, a virus that infects E. coli. The lambda phage naturally uses these proteins to integrate its DNA into the host E. coli.
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