A combination of chemical catalysts and engineered bacteria has been used to convert a mix of common plastic rubbish into a useful product.
Gregg Beckham at the National Renewable Energy Laboratory in Colorado and his colleagues have designed a two-step process that uses readily available catalysts and a modified soil bacterium, Pseudomonas putida, to treat mixtures of some of the most common plastic waste materials.
The group transformed polystyrene, polyethylene terephthalate (PET) and high-density polyethylene (HDPE) into a family of biodegradable compounds called polyhydroxyalkanoates, which are frequently used in biomedical applications such as sutures or in repairing tendons.
The first step of the process borrows from a common industrial method to make terephthalic acid, one component of PET. This uses oxygen and chemical catalysts to break down carbon bonds in the mixed plastic waste, which makes the resultant compounds more digestible for the bacterium.
“Step one is like a big hammer: you just take oxygen and simple chemical catalysts to make oxygenated bioavailable intermediates – and then we engineer an organism to funnel those into a single product,” says Beckham.
Although Beckham and his team engineered the bacterium to produce polyhydroxyalkanoates, it should be feasible to produce other more widely used products instead, such as the building blocks for easily recyclable and environmentally friendly plastics. They also hope to extend the method to cope with a greater diversity of plastics.
“The cool thing about synthetic biology, metabolic engineering and this idea of biological funnelling… is that as long as the organism can eat or consume the oxygenated intermediates, then potentially one could make anything,” says Beckham.