Team:Hong Kong HKU/Description


The Plastics Problem

Plastic waste is a global problem. While they are inexpensive, durable, and malleable, making them a popular material in a variety of industries; they can take up to thousands of years to decompose. This means that the ubiquitous material has persisted in the natural environment, polluting water bodies, land, and coasts. In Hong Kong, the plastics problem is also a waste management problem, where landfills are filling up at an alarming rate. The Hong Kong Government estimates that at the current rate, landfills in Hong Kong will be full in the 2030s.

The influx of plastics into the environment is problematic not only because it impacts economies, where tourism wanes with poor waste management, but also because it has a direct impact on human health. As organisms consume plastic, plastics make their way through the food chain, and eventually into us.

Our Solution

We are engineering E. coli (Strain BL21-DE3) to express two enzymes found to degrade PET: PETase and MHETase. PETase will digest PET into its monomer, MHET, with trace amounts of BHET. MHETase will digest MHET into TPA and EG, which can be resynthesized into new bioplastics in the future.

Our E. coli will be placed in a co-culture system with S. elongatus (Strain PCC7942), a cyanobacteria. E. coli will also be engineered to take up sucrose, which will be produced by S. elongatus. This is achieved by using three systems: cscB for sucrose permease, cscA as an invertase for hydrolysis, and cscK for metabolism. The systems are incorporated into the genome using the Lambda Red system to ensure they persist throughout generations.

S. elongatus will use the lacI system to produce sucrose, which will be turned on by IPTG. The inducible system ensures S. elongatus will not be exhausted by the extreme sucrose production. cscB will also be used to transport sucrose out of the cell.

The Co-culture System

Co-culture systems in synthetic biology allow for more complex interactions between engineered organisms. As outlined by Imperial College London’s 2016 iGEM team, much research remains to be done on co-culture systems, as determining and maintaining optimal conditions for all organisms in the co-culture is difficult. Our co-culture system was inspired by Liu et al. (2021) and Hays et al. (2017), which demonstrated the possibility of a co-culture with E. coli and S. elongatus. Having a co-culture system allows for our system to be self-sustaining, with no additional inputs for maintenance outside of the culture medium.


1. Hays, S. G., Yan, L. L. W., Silver, P. A., & Ducat, D. C. (2017). Synthetic photosynthetic consortia define interactions leading to robustness and photoproduction. Journal of Biological Engineering, 11, 4. PMC.

2. Liu, H., Cao, Y., Guo, J., Xu, X., Long, Q., Song, L., & Xian, M. (2021). Study on the isoprene-producing co-culture system of Synechococcus elongates–Escherichia coli through omics analysis. Microbial Cell Factories, 20(1).

3. Tournier, V., Topham, C. M., Gilles, A., David, B., Folgoas, C., Moya-Leclair, E., Kamionka, E., Desrousseaux, M.-L. ., Texier, H., Gavalda, S., Cot, M., Guémard, E., Dalibey, M., Nomme, J., Cioci, G., Barbe, S., Chateau, M., André, I., Duquesne, S., & Marty, A. (2020). An engineered PET depolymerase to break down and recycle plastic bottles. Nature, 580(7802), 216–219. nature.