Austrian scientists have discovered that bacteria present in cows’ digestive systems can break down plastic and it has the potential to become a powerful way to help reduce plastic pollution. These early findings were reported in the journal Frontiers in Bioengineering and Biotechnology.
A cow's diet already contains natural plant polyesters, so the team was confident that there is some mechanism within their stomach that is able to conduct polyester hydrolysis, a chemical reaction that breaks down such materials. The line of thought was: if they can tear these biological polyesters apart, can they do the same for artificial ones?
"A huge microbial community lives in the rumen reticulum and is responsible for the digestion of food in the animals," corresponding author Dr Doris Ribitsch, of the University of Natural Resources and Life Sciences in Vienna, said in a statement. "So we suspected that some biological activities could also be used for polyester hydrolysis."
Once the team identified these bacteria in the rumen (one of the four compartments of a cow’s stomach) they tested their ability to break down polyethylene terephthalate, or PET, the most common thermoplastic in the polyester family. They also tested two other types of plastic. One was polybutylene adipate terephthalate or PBAT, commonly used in compostable plastic bags. The other was Polyethylene furanoate, PEF, which is made from sugars derived from plants.
Samples of these three plastics were placed in an incubated rumen liquid. The plastic was either turned into a powder or into a plastic film. The results are certainly exciting – all three plastics were broken down with no problem. Powders were broken down faster than films, which is hardly surprising given that chemical reactions tend to happen faster as the surface area of the reactant increases.
The team noticed that the reactions with the rumen liquid were more effective compared to research that looked at a single microorganism to break plastics apart. The team believes that the environment of the rumen liquid might be more conducive to the task. The degradation of the plastic might be down to the work of multiple enzymes working at peak conditions thanks to the rumen liquid properties.
"Due to the large amount of rumen that accumulates every day in slaughterhouses, upscaling would be easy to imagine," Dr Ribitsch explained.
But the team warns that this discovery is a first step, not a full-scale approach to the problem of plastic pollution. While the liquid can break down plastic, recycling might be an easier option, or there could be a different method that might be cheaper in the long term.
The team will continue to investigate this approach, as well as looking for how microbial communities can be employed for more eco-friendly industrial processes.