Packaging is necessary, especially in the food industry. Most packaging has traditionally been manufactured from non-degradable fossil-fuel plastic. Today, awareness of the growing waste mountain, and of all the plastic in our oceans, has led to the gradual replacement of plastic with more eco-friendly paper alternatives where possible.

But using paper alone does not work. A package that needs to hold liquids, such as a juice or yoghurt packet, cannot consist entirely of paper, for example. In that case the package needs to be ‘lined’ with a plastic barrier material.

Yeast to produce plastic

Thomas Andlid, Associate Professor of Food and Nutrition Science in the Department of Biology and Biological Engineering at Chalmers, explains that it is actually possible to manufacture degradable and environmentally friendly plastic.

“The polymer PHB is produced naturally in certain bacteria and is an excellent component. PHB plastic is said to break down and disappear after only a few months in the soil – depending of course to some extent on the composition of the soil – and it leaves no toxic residues behind.”

But the production of PHB from bacteria is too slow and too expensive. Now a research team headed by Andlid is seeking to make yeast produce the polymer they seek and he thinks that they are well placed to succeed:

“Researchers have tried to get normal bakers’ yeast to do this, but it’s difficult to obtain more than small amounts because of the bakers’ yeast resistance. Instead, we use an oleaginous yeasts. They have characteristics which are much closer to what we are looking for,” explains Andlid, who has isolated yeast strains from exotic plants in previous studies.

“At the outset we were looking for a yeast that can produce oil and store it in large oil droplets – and these strains can do that. Many people want to make oil using yeast, but one day I thought about it from the opposite point of view: What would happen if you stopped the production of oil instead? At least in principle you would then have a strain ideally suited to the production of biodegradable plastic. The step towards the production of PHB is therefore not so far away.”

Genetic paths redirected

Very simply, this is how it works: When the yeast produces oil, it creates a special molecule – acetyl coenzyme A – that is required to produce the oil. The same molecule is also needed to produce PHB. So far we have a match; this indicates that the oil-producing yeast may be suitable for the production of PHB. The researchers now have to shut off the production stage that results in oil, and instead steer onto a genetically modified path towards PHB. Andlid compares it with breaking up a new trail to the sea instead of to the pool in the grove just next to it.

“We already know that our yeast produces large quantities of oil; this proves that it produces plenty of the right molecule. Now we are going to redirect the process so that it produces plastic instead. If we are successful, we believe the yeast can also produce large quantities of the new plastic. We’re on to something, and we believe that it’s going to be economically viable,” he says.

“But to get the production to be economically viable, it must also be possible to convert cheap waste products into PHB. That’s why we’ve chosen an oleaginous yeast with characteristics that are suitable for growing on forestry and agricultural waste products. This is a prerequisite for the bio-based production of degradable plastic.”

High level of commitment to the project

The large grants awarded to the researchers in early 2019 confirm that the field of research has potential. A number of industrial partners are involved – including Stora Enso – and the project is shared between Chalmers University of Technology and Lund University. At Chalmers, researchers from both Food and Nutrition Science and Systems Biology are involved.

“We want to get further down the road, create production strains and study the production of PHB in the lab, and then others can follow on behind and work on the plastic itself. Perhaps it can be used as part of composites, making it sufficiently durable for use in cars, for example,” says Andlid and adds:

“Many industries are currently pushing for better and more environmentally friendly alternatives. There’s quite clearly a demand.”