Designer bugs for creating greener plastics
Plastics are desirable because they are very durable and resistant to degradation. Plastic waste is undesirable because of these very properties. EU-funded researchers are designing bacteria to efficiently consume plastic waste and turn it into novel destructible plastic - good for the environment and health.
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Europe generates over 55 million tonnes of plastic waste every year. These petroleum-derived plastics are very resistant to natural microbial decay and can persist in the environment for a very long time. They can release hazardous chemicals into groundwater reservoirs and cause severe damage to marine environments and life thus endangering food chains.
To combat this environmental and health threat, the EU has set 50% to 70% recycling targets for waste, including plastic waste, in all member countries by 2020. All plastic packaging should be recyclable by 2030.
However, plastic waste poses particular problems. There are limits to how many times plastics can be recycled before they are no longer fit-for-purpose. At that point they must be burned or go to landfill. And once there, they are not easily biodegradable lasting hundreds of years in some cases.
The EU-funded P4SB project is developing an innovative solution to the indestructability of plastics. Project coordinator Nick Wierckx of RWTH Aachen University in Germany explains: With our partners we have modified natural bacterial, producing new designs that can live off plastics and break them down into useful end products that can be used to make new, biodegradable plastics. This effectively removes the damaging effects of plastic waste from the environment at the same time as producing economically attractive raw materials.
Leveraging synthetic biology
The project is developing these solutions in one package. Using the tools of synthetic biology it is designing customised bacteria as the core of a cell factory that digests commonly used packaging plastics and turns them into new formulations of biodegradable plastics.
In nature, bacterial decomposition is universal, all organic matter such as trees, vegetation and animal remains can be broken down, says Wierckx. However, man-made plastics are totally new to nature. Bacteria have never come across them and cannot process them. So we are designing and creating new bacteria to do this in contained bioreactors.
The implications for policymakers of the P4SB partners work are clear. Using the tools of synthetic biology, plastics and plastic waste can be incorporated into new life cycles for a sustainable circular economy maintaining their many technological benefits while avoiding their current environmental drawbacks.
From designer drugs to designer bugs
As medical researchers use genetic engineering to modify molecules for effective therapies, as in the case of insulin, so the P4SB partners are using similar synthetic biology tools to design a four stage process for treating plastic waste in particular polyethylene plastics (PET) used for food and liquid packaging; and polyurethane (PU) used in foams and hard plastics.
In the first stage the project successfully designed enzymes to break down the massive polymer molecules in PET and PU, resulting in much smaller monomer molecules. These enzymes are specifically engineered to do this with high efficiency.
In parallel the partners reengineered a naturally occurring bacterium, Pseudomonas putida, such that it can consume these monomer molecules essentially living off of them as a food source.
In the third stage the partners identified the conditions under which the Pseudomonas bacteria most effectively consume the monomers to produce and store PHA molecules. PHA is a source material for biodegradable plastics, and the bacteria store it inside themselves, much as humans store fat in their bodies.
We have successfully shown how the first three steps can be turned into an innovative process at a laboratory scale, says Wierckx. We are now investigating the fourth step, which is to recover these valuable PHA molecules from the bacteria in the most effective manner. While these individual steps have been observed before, this is the first time they have been designed as part of a process.
With its combination of academic and industrial partners P4SB aims to demonstrate a novel, scalable value chain that will take undesirable and unsustainable plastic waste and turn it into a source of high-value sustainable plastics. By demonstrating clear environmental and economic benefits they then expect their innovative technology to move to a pilot manufacturing phase.