Common plastics can be broken down by enzymes found in cow stomachs

By Krista Charles

Cows have stomachs with four compartments and the bacteria in one of them – the rumen – produce enzymes which can break down certain common plastics. The discovery could lead to new technology for processing the plastics after use.

Georg Guebitz at the University of Natural Resources and Life Sciences in Austria and his colleagues visited a local slaughterhouse and collected samples of the liquid from the rumen of a young Alpine pasture-fed ox. They found that the liquid contained many types of enzymes, including cutinases.

The team demonstrated that these enzymes could break down three types of widely used polyesters – namely polyethylene terephthalate (PET), polybutylene adipate terephthalate (PBAT), and polyethylene furanoate (PEF), which are often used to make products including bottles, textiles and bags. The enzymes did so within one to three days when kept at a temperature of about 40 °C to match the temperature of a cow’s stomach.

“We found that the diet of cows contains foods that have a ‘shell’ that is similar to polyesters,” says Guebitz: this explains why the microbes within the rumen produce enzymes that can also degrade synthetic polyesters.

In future, the enzymes in the rumen liquid could be used to break down polyesters on a larger, commercial scale, says Guebitz. This may, at least potentially, prove to be cheaper than the technologies currently used to process the plastics, he says – but other researchers are cautious about this.

“It has to be proven that the enzymatic activity is the same or better than what is commercially being implemented today,” says Ramani Narayan at Michigan State University in the US. “If they were to fast track to an engineering process, then there is a lot of work that needs to be done in terms of what is the yield of the product, what is the productivity, and so on to compare with existing enzyme technology.”

Journal reference: Frontiers in Bioengineering and Biotechnology, DOI: 10.3389/fbioe.2021.684459/full