Stomach that: Liquid from cow stomachs digests plastic

Bacteria from the stomach of a cow can digest some plastic, removing it from the environment, according to a team of Austrian researchers.

The polymers that plastics are made of usually aren’t digestible by ordinary organisms – be they animal, plant or bacteria – meaning the molecules accumulate in the environment very easily. While there has been some success in recent years finding microbes that can digest plastic polymers, the idea has so far been focussed on individual organisms, usually breaking down individual plastics.

This new research, published in Frontiers in Bioengineering and Biotechnology, has found a combination of bacteria from cow stomachs to be more effective at digesting three different polyesters, including the common and long-lasting polyethylene terephthalate, or PET.

The researchers, who are based at the University of Natural Resources and Life Sciences in Vienna, collected liquid from rumens (one of the four components of a cow’s stomach) from a slaughterhouse.

“A huge microbial community lives in the rumen reticulum and is responsible for the digestion of food in the animals,” says Doris Ribitsch, corresponding author on the study.

“We suspected that some biological activities could also be used for polyester hydrolysis.”

Hydrolysis – using water to break down molecules – is an effective method of dealing with polymers, because it divides the long, difficult-to-digest molecules into smaller pieces.

The researchers incubated three different polyester plastics – PET, and two biodegradable plastics, PBAT (polybutylene adipate terephthalate) and PEF (polyethylene furanoate) – in the rumen liquid.

All three plastics could be digested, with the authors noting that plastic powder could be digested faster than plastic film within the cow stomach fluid.

The method is unlikely to work for other types of plastic, such as polyethylene, because they’re not chemically similar enough to the molecules that cow stomachs are meant to digest. But it could be an important discovery for the way we deal with polyesters.

“Due to the large amount of rumen that accumulates every day in slaughterhouses, upscaling would be easy to imagine,” says Ribitsch. She points out that the lab equipment used in this study is very expensive, though, and more research is required before it could be rolled out industrially.