Team:Pasteur Paris/Description
The Problem
Every year, more and more plastics are produced. In 2000, the world plastic production was about 190 million tons per year whereas today, it is roughly 300 million tons per year (Fig.1). The most common plastics are polyethylene (PE), polyethylene terephthalate (PET) and polypropylene (PP).
Fig.1 - Evolution of the world plastic production, in million of tons, from 1950 to 2020.1
However, the treatment of plastic is not yet suited to the exponential growth of plastic production. In 2012, Europe produced 25.2 million tons of plastic waste2, among which only 26% were recycled. The remaining 74% were either burned in order to produce energy (36%) or dumped and buried (38%). This leads to an increase in plastic in nature which pollutes our ecosystem, especially the oceans.
Fig.2 - Treatment of post-consumer plastics waste in 2012, in the European Union.3
The problem is worsened by the size of the plastic particles: they are mostly microparticles. Indeed, over 90% of the ocean’s plastic particles measure less than 5mm. This makes it difficult to clean the plastic out of the ocean. The greatest danger comes from invisible plastic since the particles are becoming small enough to be accidentally ingested by zooplankton.4 Indeed, oxidation and UV radiation can break the plastic into small fragments which can attain a minimum size of 20µm. The plastic then works its way up our food chain and ends up on our plates.5
Our solution
PlastiCure is a biological system designed to degrade PET and use the degradation products to synthesize bio-active compounds. The idea is to create a new way to treat plastic waste by degrading it into a novel profitable transformation product and then increase efforts in plastic recycling.
The challenge of the project is to combine in one system a PET degradation pathway with an optimized biosynthetic pathway: we aim to transform plastic waste into a profitable life-saving drug, erythromycin A. This constitutes a revalorisation of plastic waste into drug. E. coli will be used as a heterologous host to integrate exogenous DNA sequences in multiple operons (82 % of our designed operons will be composed of heterologous genes). This will allow E. coli to express all of the necessary biodegradation and biosynthesis genes.
Fig.3 - Our E. coli system is able to synthesize biologically active products and at the same time degrade plastic waste.
Erythromycin is an antibiotic used to treat bacterial infections in cases of allergy to penicillin. It is hence a frequently prescribed drug. Erythromycin also has an important role in the hemi synthesis of new active ingredients. Despite a very important demand, the total synthesis of erythromycin A remains a very long and complex process of about 50 stages. It is therefore an expensive process.6
Recent advances in synthetic biology enabled erythromycin production in E. coli. B. Pfeifer and H. Zhang designed a system of 4 plasmids working in the E. coli BAP 1 strain and leading to erythromycin A production with a yield of 10 mg per liter of culture media.7
Fig.4 - The very complex molecule of erythromycin A.8
PlastiCure is a well-designed biological system composed of 2 parts: degradation and synthesis. The PET degradation part is composed of 2 pathways: terephthalic acid (green arrows) and ethylene glycol (blue arrows). In total, the two pathways are composed of 15 genes (~22 kb), that will be integrated in an operon into one plasmid.
Erythromycin A is synthesized by a modular Polyketide Synthase (type 1). The products of degradation, propionyl-CoA and (S)-Methylmalonyl-CoA, are used to synthesize 6-deoxyerythronolide B (6deB). Ery operon enzymes will make erythromycin A using 6deB as a precursor.
Fig.6 - Propionate metabolism in E. coli BAP 1.
We imagined creating interchangeable versions of each module. This would enable us to degrade a different plastic and still synthesize Erythromycin A or to degrade PET but synthesize a different molecule. Therefore, PlastiCure has been thought to be derived so we can use the plastic degradation module of our system to produce a broad diversity of products. This makes PlastiCure a very flexible and innovative project.
References
1 - Plastics – the Facts 2014. An analysis of European plastics production, demand and waste data
2 - http://www.planetoscope.com/petrole/989-production-mondiale-de-plastique
3 - Plastics – the Facts 2014. An analysis of European plastics production, demand and waste data
4 - http://app.dumpark.com/seas-of-plastic-2/#oceans
5 - https://www.youtube.com/Plankton-eating-plastic
6 - http://erythromycin.org/erythromycin
7 - Haoran Zhang, Yong Wang, Jiequn Wu, Karin Skalina, and Blaine A. Pfeifer (2010). Complete Biosynthesis of Erythromycin A and Designed Analogs Using E. coli as a Heterologous Host. Chemistry & Biology 17, 1232–1240.
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