When it comes to solutions for PET pollution, degradation is always a key concept. Plastic degradation refers to the process in which plastic is gradually broken down into smaller fragments or transformed into other substances under certain conditions. Common degradation modes discovered by scholars and have been implemented through industries and academia include: biodegradation, photodegradation, thermal degradation, etc. (Yousif, E., & Haddad, 2013).

Our passion on synthetic biology urged us to pay a special attention to biodegradation, as well as how synthetic biology can provide us with a creative path to address this problem. In 2016, Shosuke Yoshida and his collgues reported the discovery of the first IsPETase degradation enzyme, which can effectively degrade low-crystallinity PET plastics at the temperature of 30°C. IsPETase depolymerizes PET and releases soluble products, including mono(2-hydroxyethyl) terephthalate (MHET), which is further cleaved by the MHET enzyme (MHETase) into terephthalic acid (TPA) and ethylene glycol (EG) (Yoshida, 2016). To enhance the degradation efficiency of PET, a PETase/MHETase dual enzyme system has been developed. However, this enzyme has poor stability and cannot satisfy the practical application requirements for biodegradation.

The key enzyme for PET degradation is IsPETase. To improve its activity, American researcher Hongyuan Lu and his team have utilized machine learning to develop a modified enzyme, Fast-PETase, which can reduce the degradation time of plastics from centuries to mere hours or days (Lu, 2022). This breakthrough brings new hope for the effective degradation of PET.

Inspired by those previous work, we plan to use synthetic biological methods to recombinantly express Fast-PETase and MHETase. While prokaryotes like Escherichia coli are commonly used as vectors in relevant research, our interests and inquiry was drawn to the silkworm (bombyx mori).

China has a history of thousands of years in silkworm breeding and silk production. Silk holds a unique position in China’s cultural, artistic, and economic history, continuing to display significant commercial and artistic influence worldwide. Shanghai, where we are located, is situated in the middle and lower reaches of the Yangtze River. In ancient Chinese cultural concepts, this area is known as “Jiangnan” (the South to the Yangtze River), one of the epicenters of Chinese silk culture. This heritage gives us a natural affinity and enthusiasm for silkworms and silk, making it easier for us to connect with related stakeholders.

More importantly, the silk glands of silkworms, functioning as bioreactors, have successfully expressed various biologically active human cell growth factors (Chen et al., 2018), serum albumin (Qian et al., 2018), and lactoferrin (Xu et al., 2019), among other functional target proteins. Additionally, as natural long protein fibers, silkworm silk exhibits excellent biodegradability and biocompatibility, making it a prioritized candidate for the development of various medical biomaterials. It stands out as a natural protein raw material with significant application potential. Additionally, silk itself is an excellent high-molecular protein material. Previous researches has shown that silkworm’s advatnage in several fields: nanotechnology, syntic material and syntic biology beased on its high quality and stable gene expressing (Huang, 2018).

The goal of our research project is to construct gene expression vectors targeting Fast-PETase and MHETase genes. By utilizing techniques such as silkworm embryo microinjection and screening, we intend to create silkworm strains capable of high-level and specific expression of plastic-degrading enzymes in their glands and the silk.

Based on the successful production of this new silk material, ultimately, we aim to develop silk products with the ability to degrade plastic products, and implement them into realistic pollution-control scenarios.