Ubiquitous waste plastics like discarded mineral water bottles and marine plastic trash are hard to degrade, and therefore seriously threaten the Earth’s environment. Traditional plastic waste is treated using concentrated high temperature, which leads to high energy consumption, low efficiency and also secondary pollution. A better way to deal with the problem is to use bacteria. An undergraduate team from the School of Chemical Engineering and Technology of Tianjin University has researched and developed a high-efficiency plastic biodegradation system based on a mixed bacteria system. Recently, this achievement obtained the Gold award in the 2016 International Genetically Engineered Machine Competition (iGEM) held by the American Massachusetts Institute of Technology, and was nominated for the Best Environment Project.
A mixed bacteria system is an artificial way of organizing bacteria. It is much like a “small society” of bacteria, where various kinds of bacterium perform their own functions. Some bacterium in this system degrade macromolecules of plastic into micromolecules, while others absorb the micromolecules or turn them into beneficial substances.
This team eventually developed a mixed bacteria system which allows different kinds of bacterium to peacefully coexist by means of exploring bacteria culture conditions through more than one hundred mixed bacteria experiments. They intelligently designed a particular kind of metabolic pathway within the mixed bacteria system, which lessens competition for nutrients between different bacterium and realizes the stability of the mixed bacteria system.
In order to degrade plastics more quickly, this team employed a genome-editing technique to transform the PETase enzyme, the key for plastic degradation, which successfully improved the enzyme’s efficiency for decomposing plastics. Furthermore, students also creatively utilized the technique of 'CELL-FREE' to set up an “enzyme production factory” by putting cell substances into test tubes. In this way, the steps required to sift the PETase enzyme were simplified and its production rate increased.
This mixed bacteria system can completely degrade a common plastic, which is PET. On condition the mixed bacteria system can be released into the natural world, this system can efficiently decompose polyester plastics which would otherwise last unchanged for centuries. This research can potentially realize on-site decomposition of plastic waste in the future.