Universiteit Leiden

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Students work on bacterium that makes sustainable plastic

Rather than go on holiday this summer, a group of biology students shut themselves away in a windowless lab. They were working on a solution to the world’s plastics problem by getting bacteria to make biodegradable plastic.

The team of 13 bachelor’s and master’s students were shocked to read an article saying that microplastics have been found in human blood. ‘We wanted to do something about it’, says Jasper Smits. ‘Some of the microplastics were found to have come from agriculture. Farmers use layers of foil to help their plants grow, for example. And fertiliser pellets have a plastic coating to ensure that the fertiliser is released gradually into the soil. These plastics often do not decompose well and end up in our food or being blown into the environment. So we decided to focus on agriculture.’

International competition

The students are taking part in the International Genetically Engineered Machine (iGEM) competition. Here student teams use synthetic biology to tackle issues facing the world. This year 400 teams have entered. The winners will be announced at the Grand Jamboree in Paris at the beginning of November.

The bacterium that the students are using is pink.

The students have been working since April on their PHAse Out project, which aims to develop a biodegradable plastic for agriculture. The first months were devoted to literature research and meetings with experts, but they have been working in the lab since July. ‘We are trying to produce a biodegradable plastic known as PHA (polyhydroxyalkanoate, ed.)’, says Smits. ‘Bacteria can break down this plastic, which means it’s gone after three months. It’s a carbon-neutral process.’

Producing cheaper plastic

PHA is currently very expensive to produce, so it is not interesting for companies to use. To produce the plastic in a cheaper, more efficient way, the students are making genetic modifications to the Methylobacterium extorquens bacterium, which produces PHA naturally. ‘We are causing overexpression of the gene that produces PHA. This makes the bacterium produce more PHA than it normally would’, says Smits. ‘And we are improving the extraction – the collection of PHA from the cells. This is the biggest expense. We are trying to make genetic modifications that get the cells to lyse (when the cell membrane breaks down, releasing PHA, ed.) of their own accord. We are also working on an extraction method with chemicals.’

Not competing for human food

That M. extorquens produces PHA is not the only reason why the team has chosen this bacterium. According to Smits, it is ‘quite a special bacterium’. It eats methanol whereas most other bacteria use sugars as food. The downside of sugars as food is that it is expensive and you then can’t use these sugars for human food.’ Methanol does not compete for food and can be produced in a carbon-neutral fashion with the aid of a chemical reaction between green hydrogen and CO2. This makes it possible to produce climate-neutral plastic.

Conduct experiments in time

The students have to vacate their lab in September because it is needed for other studies. They will be able to use other labs now and then for their experiments. ‘It’s quite stressful trying to complete all the experiments in time because you hope that not too much will go wrong’, says Smits. ‘But all being well, we’ll be getting all the results soon.’


One aspect of iGEM is that students fund their projects themselves. The team has therefore started crowdfunding. They hope to raise 9,800 euros to pay for lab materials. How much money they raise will determine how many experiments they can do for their project. In return, donors can receive a biology comic strip book, for example, or a personalised lab tour with a VR game.

Text: Dagmar Aarts
Photos: iGEM Leiden 2023

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