Topic Selection
At the beginning of the project, our goal was to degrade and recycle the microplastics in the water and we aimed to achieve this by using engineered E. coli. However, as the project progressed, we realisedthat the presence and propagation of engineered bacteria in water bodies will present an inevitable safety flaw in the process. After discussions with many researchers, we came across a lab that uses the nematode – C.elegans as their model organism. The information that was interesting for us was that C.elegans feeds on E. coli. and hence had the potential to address the safety flaw in our design. So, we decided to design a two-part system using both E. coli and C.elegans to degrade and recycle microplastics safely.
Background Research
Plastic is widely used due to its chemical stability, waterproofness, lightweight, multifunctionality, and low cost. In 2021, global plastic production reached 367 million tons, with China being the world's largest plastic producer/user, accounting for nearly one-third of the world's plastic production. Although, the widespread use of plastics brings convenience to people's lives, but it also causes serious environmental pollution. Plastic entering the environment through various means may rupture and decay, leading to the formation of plastic fragments. Among them, plastic particles with a size less than 5.0 mm are defined as microplastics (MP), also known as PM 2.5 in water.
MPs can be ingested by aquatic organisms as often they cannot distinguish MPs from food or the MPs may be mixed in their food. MPs have been detected in a variety of aquatic organisms including zooplankton, benthic animals, and fish. Numerous studies have reported the toxic effects of MPs on the behavior, growth, development, reproduction, immune system, nervous system of the organisms.. In addition, MPs are carriers of pollutants such as persistent organic pollutants, antibiotics and heavy metals etc. Hence, the treatment and elimination of this kind of pollution is a matter of great concern.
Our specific goal is to degrade PET, a type of plastic that is relatively easy to biodegrade in the above-mentioned pollution. In fact, our literature review on microplastic pollution in some waters of southern China revealed that among the polymer components that make up microplastic pollutants, PA and PET account for the largest proportion, emphasizing the necessity of PET treatment.
Normally, technical degradation of PET focuses on the use of pure enzyme. In order to get the enzyme,normally the organism producing it has to be lysed and then the enzyme can be extracted. Further, one of the product generated by PET degradation - TPA has been shown to be toxic, which means that it is the recovery of the degradation product - TPA is also critical.
Our strategy
A double mediation tool degrading PET while avoiding bio-leakage
The main aim of our project is to degrade PET and enrich the degradation product TPA.
To do so, we first use engineered E. coli BL21 strain to secrete turboPETase, which is a kind of enzyme that has higher efficiency of PET degradation than normal PETase. After that, another engineered E. coli BL21 strain is responsible for enriching TPA and indicating the level of enrichment by expressing fluorescence after it transports TPA into itself.
Next, we use C. elegans, a model organism that feeds on E. coli, as our recycler and amplifier. After the two strains of E. coli have achieved the expected processing of PET and absorption of TPA, we introduce the C. elegans that feed on the engineered bacteria to avoid biological leakage and further achieve enrichment and recycling. Meanwhile, the engineering of C. elegans is ongoing-we are attempting to create a C. elegans with the ability to transport TPA into their intestinal tract, in order to further enrich TPA monomers.
Hardware
Our long-termgoal is to test the degradation of other types of plastics and molecules by modifications
to the current system. And it would be ideal to have a standard pipeline to test different experiment
conditions. For this, we designed a petri dish-based device for our experiments on solid and liquid
cultures of C. elegans to facilitate C. elegans experiments in the laboratory. It is a
modular culture system designed for C. elegans, consisting of a reusable base tray and
interchangeable 24/96-well plates. We design it to solve challenges in existing solid and liquid culture
methods, allowing separate handling of C. elegans, E. coli, and samples for more precise molecular
detection. It can facilitate both solid and liquid cultures within the same setup, enabling easy sample exchange
and partitioned detection to enhance experimental flexibility and safety.
We also designed a modular fermenter system for the co-culture of E. coli and C. elegans.
We designed it to support research into microplastic wastewater treatment by providing an adaptable environment
for bacterial and nematode interactions. It can ensure optimal conditions for growth and interaction through
stirring, temperature control, and oxygen supply, while maintaining ecological safety with effective containment systems.
Reference
1. Gong H, Li R, Li F, Xu L, Gan L, Li J, Huang H, Yan M, Wang J. Microplastic pollution in water environment of typical nature reserves and scenery districts in southern China. Sci Total Environ. 2023 Dec 10;903:166628. doi: 10.1016/j.scitotenv.2023.166628. Epub 2023 Aug 26. PMID: 37640084.