A large number of used plastic bottles are discarded every day, but now microbes may hold the promise of solving the problem. Now, researchers at ACS Central Sciences report that they have developed an edible plastic E. coli that effectively converts polyethylene terephthalate (PET) waste into adipic acid, which is used in the manufacture of nylon materials, medicines and perfumes.
Previously, a group of researchers, including Stephen Wallace, engineered a strain of E. coli bacteria to convert terephthalic acid, the main ingredient in old PET bottles, into something tastier and more valuable: the vanilla-flavored compound vanillin. Meanwhile, other researchers have engineered microbes to metabolize terephthalic acid into a variety of small molecules, including short acids. So a new team at Wallace and the University of Edinburgh wanted to expand the biosynthetic pathway of E. coli to include metabolizing terephthalic acid into adipic acid, the raw material for many everyday products that are often produced from fossil fuels through energy-intensive processes.
The team developed a new strain of E. coli that produces an enzyme that converts terephthalic acid into compounds such as muconic acid and adipic acid. Then, to convert the mucous acid to adipic acid, they used a second hydrogen-producing E. coli and a palladium catalyst. In their experiments, the team found that attaching engineered microbial cells to alginate hydrogel beads improved their efficiency, with up to 79 percent of the terephthalic acid being converted to adipic acid. Using terephthalic acid samples from discarded bottles and coatings from discarded package labels, the engineered E. coli system effectively produced adipic acid. The researchers say that in the future they will look for ways to biosynthesize other high-value products.
