A cow farting in a feedlot isn’t just a roadside view in the midwest: for climate scientists, it’s a cause of concern. After all, cow farts and belches release significant amounts of methane into the atmosphere. Beef production currently accounts for 3.7 percent of greenhouse gas emissions in the U.S.
But while cows may be slowly killing the planet — death by millions of farts, if you will — new research says the digestive tract of cattle may have just the ingredients to save us.
According to research published Friday in the journal Frontiers in Bioengineering and Biotechnology, microbes that break down food in the cow gut could help solve the massive plastics problem engulfing planet Earth.
"A huge microbial community lives in the rumen reticulum and is responsible for the digestion of food in the animals," Doris Ribitsch, a co-author on the study from the University of Natural Resources and Life Sciences in Vienna said in a press statement.
What’s new — Cow guts, like our own, are teeming with microbes like bacteria, fungi, and other microbes. These gut florae contain enzymes that can break down and digest food.
In one particularly large chamber of the cow stomach, known as the rumen, bacteria digest plant cellulose from the grass and feed that the cow eats.
The researchers speculate that because the cow’s gut breaks down natural plant polyesters, the rumen flora could probably do the same for polyesters found in plastic materials.
The team thus tested how well cow rumen could degrade or break down three common polyester materials found in plastic:
- Polyethylene terephthalate (PET) — A lightweight plastic that is found in many common types of packaging, including water bottles
- Polybutylene adipate-co-terephthalate (PBAT) — A biodegradable plastic that has been used in compostable packaging
- Polyethylene furanoate (PEF) — A plastic made of renewable materials that serves as an alternative to PET for bottle drinks and packaging
As it turns out, cow rumen and its arsenal of bacteria are very good at breaking down plastic in a sustainable way. The researchers write that the “rumen samples were able to degrade all three tested polyesters” successfully.
However, the rumen microbes were more active when it came to digesting PEF than PET. PET is notoriously hard to break down. PET can be found in common items like plastic water bottles, which often degrade into microplastics.
How they did it — From a cattle slaughterhouse in Austria, researchers received a liquid slurry of rumen microbes. The scientists then incubated the liquid with a form of each of the plastics — either plastic powder or plastic film.
This method allowed the researchers to see how well the rumen chemistry broke down each of the plastics.
Finally, the researchers sequenced and analyzed the DNA of the liquid to understand the specific microorganisms that made up the cow rumen flora. Around 98 percent of the microbes were bacteria, with other microorganisms like archaea and viruses making up the rest.
Why it matters — The researchers are not the first to propose using microbes to break down waste in an eco-friendly way. In fact, the ancient Romans used a form of bio-leaching, which scientists have proposed to recycle metals from electronic waste using bacteria.
“What it does is to show that the mechanism of plastic digestion is more [wide]spread than we thought,” Sebastien Farnaud, a professor in bio-innovation and enterprise at Coventry University who has written about bio-leaching and was not involved in the study, tells Inverse.
According to a 2017 American Association of Science report, humans generated 9.1 billion tons of plastic since the 1950s. Only 9 percent of that plastic was successfully recycled, and much of the rest gets dumped in landfills, where it lingers for decades and even centuries.
The cow rumen chemicals may be a good way to sustainably — and efficiently — recycle plastic in a way that doesn't contribute to greenhouse gas emissions, the researchers suggest, since it’s available in large quantities at slaughterhouses across the world.
The scientists conclude that rumen fluid is a “cheap source” of plastic-degrading bacterial enzymes.
What’s next — Farnaud adds that this study, “gives us hope to find other enzymes — which is what these microbes secrete — [that] may be even more efficient” than the ones found in the cow’s rumen.
The researchers write that “future studies should aim at identification and cultivation of the microbes and enzymes” that can break down plastic.
However, Farnaud says that lack of scientific research or technology isn’t the biggest problem with implementing eco-friendly microbial recycling. The challenge lies in another factor: lack of investment in eco-recycling.
“The main issue is not technical. It is economic,” Farnaud says. “There is no money in recycling plastic, so that investment to develop these technologies [is] very difficult to find.”
However, Farnaud suggesting that biotechnology could help make these plastic-degrading enzymes a more commercially appealing product. In 2018, scientists from the University of Portsmouth bioengineered enzymes that can break down the plastic found in water bottles, paving the way for such industrial use.
With some help from the enzymes dwelling within our fellow mooing friends and bioengineers’ labs, perhaps we can save the planet from being drowned in plastic detritus.
Abstract: Microorganisms, like bacteria and fungi, are becoming an emerging resource for the development of eco sustainable plastic degradation and recycling processes. In this study, the rumen content from cattle (Bos taurus) was investigated regarding synthetic polyester hydrolyzing enzymes based on the fact that the diet of ruminants may contain natural plant polyesters. A screening with model substrates demonstrated hydrolytic activities of rumen fluid on p-NP-esters with 4 to 8 carbon atoms. Rumen fluid hydrolyzed synthetic aromatic polyesters with higher amounts of terephthalic acid released from poly(butylene adipate-co-terephthalate (PBAT) (0.75 and 0.5 mM for polymer powder and film, respectively) and thus exceeded when compared to the hydrolysis of the second terephthalic acid-based polymer- poly(ethylene terephthalate) (PET) (0.6 and 0.15 mM, for powder and film, reciprocally). Additionally, rumen fluid hydrolyzed the bio-based polyester poly(ethylene furanoate) (PEF) according to HPLC and SEM analysis. Environmental metagenomic analysis of the rumen microbial community revealed a composition of bacteria (98%), followed by Eukaryota (1%) and finally Archaea. Among the most abundant genera encountered in this study, polyester hydrolysis activity has already been proved (e.g. Pseudomonas).