Microbes that are ingested from cows' stomachs can eat certain types of plastics, such as the polyethylene Terephthalate (PET), used in food packaging, synthetic fabrics, and soda bottles.Scientists discovered these microbes in liquid taken from the rumen of ruminants. Ruminants are hooved animals such as sheep and cattle that rely on microorganisms for their diet of coarse vegetation. According to the University of Minnesota, the rumen is an incubator for these microbes that either ferment or digest foods eaten by cows or other ruminants. Researchers suspected that microbes in cow's rumen could be capable of degrading polyesters, which are substances whose components are linked by so called ester groups.Cutin, a natural plant-based polyester, is what cows eat. PET is a synthetic polyester with a similar chemical structure as the natural material. Cutin, which is the outer layer of plant cells, makes up the majority of the cuticle. It can be found in large quantities in the skins of tomatoes and apples.Related: How much plastic can be recycled?Ribitsch explained to Live Science that bacteria and fungi can penetrate fruits by producing enzymes capable of cleaving the cutin. This is a way to break down chemical bonds in the substance. Cutinases, a group of enzymes, can hydrolyze cutin. This is a chemical reaction that causes water molecules to break down the substance into pieces.Ribitsch and her collaborators have previously isolated these enzymes from microbes and discovered that cows could be a source for similar polyester-munching insects. She said that these animals are eating a lot of plant material and it is highly likely that such microbes could be found in cows' stomachs.In fact, their latest study was published in Frontiers in Bioengineering and Biotechnology on Friday, July 2. The researchers discovered that microbes in the cow's rumen could not only degrade PET, but also two other plastics, polybutylene-adipate-terephthalate(PBAT) used in compostable plastic bags and polyethylene furanoate, made from renewable, plant derived materials.The team incubated each plastic type in rumen liquid for a minimum of one to three days in order to determine how well the microbes could consume it. The team could then measure the amount of byproducts released from the plastics to find out how much the bugs actually broke down the components. According to the team, PEF was broken down most efficiently by rumen liquid, but all three types of plastic were affected.To determine which microbes may be responsible for plastic degrading, the team took DNA from the rumen fluid. According to reports in the Journal of Hazardous Materials and Applied Microbiology, 98% of DNA was from the bacteria kingdom.The liquid also contained high levels of bacteria from the genus Acinetobacter. A 2017 Journal of Agricultural and Food Chemistry report revealed that synthetic polyesters were also broken down by several species in the genus.Ribitsch and her group want to characterize the plastic-eating bacteria found in rumen fluid and identify the specific enzymes they use to breakdown the plastics. They can genetically engineer microbes to produce the enzymes they are looking for, and they will not need to take them from cow stomachs. Ribitsch stated that enzymes can be easily produced at low cost and used on industrial scales.Ribitsch and her colleagues have already patented a method for recycling textile materials that exposes them to different enzymes in a sequence. This is similar to Ribitsch's previous work. The first batch of enzymes destroys the cloth fibers, while the second batch targets specific polyesters. Each enzyme has a very specific chemical structure and won't be able to break down any material that it comes across. Ribitsch explained that textiles made up of multiple materials can be recycled by separating them into their individual parts.According to the new study, cows rumens could be another environment for discovering these helpful enzymes. However, such enzymes can also crop up in many other places in nature according to David Levin, a molecular biologist, biotechnologist, and professor at the University of Manitoba Department of Biosystems Engineering. He was not involved with the research.Levin stated that Ideonella sakaiensis was the first bacterium to be able to consume PET. This is a species used in sake fermentation. He noted that certain marine organisms have cutinases, which can be used to break down plastic, and that there are fungi that can infect land plants.Scientists have so far succeeded in discovering plastic-eating enzymes capable of breaking down PET and biodegradable materials like PBAT, PEF. But now Levin says the real challenge lies with finding enzymes that can break down more problematic plastic products.Ribitsch stated that plastics such as polyethylene and propylene are made up of strong bonds among carbon atoms. This structure hinders enzymes' ability to grab the molecules and start hydrolysis. Levin stated that while scientists have developed, characterized, and sold enzymes to break down PET, microbes are still needed to handle the polyethylene and polypropylene. While Levin's lab has identified some promising candidates, they are still trying to figure out how to maximize their plastic-eating abilities.Ribitsch stated that her team is also looking for microbes capable of consuming polyethylene. She wonders if these bugs could be hiding in the cows' stomachs. She said that she hoped to find enzymes that could also be used to degrade polypropylene or polyethylene in large communities like those found in the rumen fluid.Original publication on Live Science
