Team:TU Darmstadt/Project

Overview

Since the discovery of Polyethylene terephthalate (PET) in the 1940s, it has become the most widely manufactured synthetic. In 2012, global annual production exceeded 100 million tons. Its popularity also creates the issue of PET waste. In Western countries today, less than 70% of PET produced are recovered by common means of recycling. Biological processes currently play no role, as its chemical properties make PET inert to biological degradation.

Recently it was discovered that the erosion of PET in a maritime environment ultimately creates nanoparticles with undesired characteristics, as these particles tend to accumulate toxic substances on their surface. This poses a growing threat to the environment and a serious health risk. Therefore, developing new methods for PET degradation became an urgent issue. We suggest the development of a bacterial recycling system, transforming PET waste into harmless, environmentally benign compounds which can be used in a wide range of applications. Thus converting PET waste into a new ressource preventing pollution by making it too useful to toss away.

How would such a bacterial recycling system look like and what features are required?

The bacterial recycling system we aim for is based on a easy to cultivate microorganism that we enhance by inserting enzymes that handle a specific task ultimately enabling it to recycle PET. This recycling will be done in fermenters preventing any release of or organism. We named it PET.er (PET terminator). First of all our genetical modified organism (GMO) would need to be able to digest the PET decomposing it into its terephtalic acid (TPA) subunits. Due to its chemical properties TPA uptake by diffusion isn't possible at pH higher than 3.0, a condition in which Escherichia coli (E. coli) the most common microogranism in genetics, can't be cultivated. This fact makes it necessary to implement a specialised TPA uptake system in order to enable E. coli for an uptake at pH 7.0. There are multiple reasons for which we decided to use E. coli as our host bacteria. It is easy to cultivate, secure to handle and tons of different strains and materials are available. Most important is the circumstance that the genome of E. coli is well known and characterised. This enables us to modify and insert proteins as we please. Furthermore even if E. coli is able to absorb TPA, it can't use it in its metabolism. Therefore we are required to insert additional enzymes to 'adjust' the metabolic pathway enabling E. coli of using the TPA as an engergy source. Information about the E. coli genome is essential for this task.

Briefly we need to insert enzymes for degradation, transport (uptake) and metabolism. This may sound easy, but it isn't. First of all E. coli is a living system. It kicks out, mutates and modifies DNA that it doesn't like or simply dies after insertion. Secondly even if the enzymes that are proven to work in other microogranism are inserted in E. coli it doesn't necessarily mean that they'll work. Therefore a whole variety of tests is required to evaluate the project. This involves material science (physical testing) and modeling.

How did you handle the task? Due to the fact, that we were able to recruit an enormous team, we split our project according to their objectives:

1. Degradation
2. Transport
3. Metabolism
4. Material Science
5. Simulation/Modeling

In addition to those sub-projects we convinced students of other departments to contribute to our project. This involves:

• Ecology
• Philosophy

The information provided in this overview is just a brief introduction. Want to learn more? Continue with 1. Degradation.