Team:Exeter/Description
Project Inspiration and Description
Inspiration
Microplastics are polluting natural ecosystems. 35% of all microplastic waste is produced by small fibres and particles breaking off synthetic clothing during the washing process. 1. This accounts for 1 million tons of microplastic waste every year 2, 3. The current methods for filtering microplastics do not actually tackle the problem fully, as they only collect the microplastics and do not degrade them. This results in them eventually ending up in landfill, which does not completely eliminate the chance of them being washed by the rain back into rivers and soils. Most microplastics produced from washing eventually finding their way into the oceans 4, ultimately being ingested by marine organisms, and therefore ending up in our food chain. We propose to degrade the microplastics at the source of the problem in our household washing machines using enzymes, thus removing a huge amount of microplastics from circulation.
Decision Making Process
We started researching potential projects by having several brainstorming sessions. We reached out to various stakeholders and academics to gain a better understanding of the issues and feasibilities of each concept. After this we were able to narrow our selections down to three initial project ideas: clean meat, sustainable clothing dyes and degradation of plastic microfibres. We then presented these ideas to a panel of academics who advised us on what would make a good iGEM project and which parts of our ideas showed promise and were worth developing, as well as warning us of any potential difficulties they could foresee with each of them. After taking their feedback into consideration and having a vote amongst team members, we chose to focus our project on the degradation of plastic microfibres.
Description
Exeter iGEM 2019 is removing microplastic waste at its source by utilising plastic degrading enzymes, PETase and MHETase, originally found in Ideonella sakaiensis (I. sakaiensis)5. We are aiming to identify the most efficient combination of PETase and MHETase mutants that would be integrated into a filtering system for capturing and degrading microplastic fibres released from synthetic clothing during washing cycles. We also had to take the BHETase enzyme into consideration as this is sometimes the intermediate result of PETase breaking down PET as shown in the flow chart below in Figure 1.
Explanation
We aim to tackle this issue by using PETase and MHETase, which are naturally-occuring
enzymes found to degrade plastic6. A synthetic biology approach to this problem
would ensure plastics do not just end up in landfill, where they could still pose a threat to
the environment, which is the case for waste from most conventional filtration systems. Taking the genes from
I. sakaiensis which code for the PETase and MHETase enzymes and
expressing them in E. coli, enables a very well characterised bacterium
to reproduce these extremely useful plastic degrading properties7.
We have two main approaches towards achieving the degradation of PET captured by the microplastic
filter. The first approach makes use of existing literature to identify the most efficient
rationally designed enzymes, which will then be used to carry out enzymatic assays. This will help us identify which
mutant is the most efficient. We have also combined the changes that have resulted in an increased
efficiency in a novel mutant that we will then be able to test.
The second approach makes use of the method of ancestral reconstruction in order to engineer
a more stable PETase that will be able to survive for a longer time in the filter. This consists of
large sequence analysis that aims to identify useful ancentral traits that may have been lost during evolution.
Project Goals
Following the project selection we reached out to additional stakeholders in
order to develop clear objectives that would have real world impacts. From this
process we concluded that the overall aim of our project should be
to create a filtration system that is capable of capturing and degrading
microfibres that detach from synthetic clothing.
There are several objectives we aim to meet in order to achieve this goal:
E. coli to include the PETase and MHETase mutant genes in their genome.
[2] B. Henry, K. Laitala, I. G. Klepp (2019) Microfibres from apparel and home textiles: Prospects for including microplastics in environmental sustainability assessment. Sci. Total Environ. 652, pp483-494.
[3] Orb Media, 2017.
[4] Rubymoon.org, 2019.
[5] S. Yoshida et al (2016) A bacterium that degrades and assimilates poly(ethylene terephthalate) . Science, 351(6278), pp.1196-1199.
[6] Y. Ma et al (2018) Enhanced Poly(ethylene terephthalate) Hydrolase Activity by Protein Engineering . Engineering, 4(6), pp.888-893.
[7] I. Taniguchi et al (2019) Biodegradation of PET: Current Status and Application Aspects . ACS Catalysis, 9(5), pp.4089-4105.
