Since 1964, plastics production has increased 20-fold, reaching 311 million tonnes in 2014, the equivalent of more than 900 Empire State Buildings. Plastics production is expected to double again in 20 years and almost quadruple by 2050. 1
Poly(ethylene terephthalate) (PET) is one of the most widely used plastic worldwide. However, the durability of PET results in its difficulty to be degraded which leads to a global accumulation of plastic waste.
Many solutions have been brought up in dealing with the plastic waste. Compared to the traditional chemical recycling processes, enzymatic hydrolysis of PET is presently evaluated as an environmentally friendly strategy for recycling post-consumer PET wastes. And during the last 15 years, many natural enzymes extracted from microorganisms have been found to be capable of decomposing PET.
In recent decades, many labs around the world have proposed a variety of ways to degrade PET biologically. The most inspiring one is the biodegradation ability of a recently found bacterial, called Ideonella sakaiensis 201-F6, by Shosuke Yoshida and his colleagues from Japan, which has been studied and published in Science this March2. They analyzed the degrading pathways and isolated two kinds of enzymes, PETase and MHETase. The PETase degrades PET into MHET (mono(2-hydroxyethyl) terephthalic acid) and MHETase degrades MHET into TPA (terephthalic acid) and EG (ethylene glycol).
We synthetize the two genes according to the sequences from NCBI, and our project aims to improve the degrading abilities of the two enzymes, especially the key enzyme, PETase, which degrades macromolecule PET with significantly low rate (60mg PET film (20 × 15 × 0.2 mm) was degraded totally by PETase after 60 days according to the Supplementary Materials3). We applied Protein Engineering stategy to rationally design the enzyme. We designed a Microbial Consortia to degrade PET and its products TPA and EG completely, as well as a Reporting and Regulation system, R-R System to make the expression visible and controllable. When we assay the enzyme activities, we use unconventional method, Cell-Free Protein Synthesis.