Microbes that are ingested from cows' stomachs can eat certain types of plastics, such as the polyethylene Terephthalate (PET), used in food packaging and synthetic fabrics.Scientists discovered these microbes in liquid drawn from the Rumen, the largest part of ruminant stomachs. Ruminants are hooved animals such as sheep and cattle that rely on microorganisms for their coarse vegetation diet.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 cows' rumens could be capable of digesting polyesters. These substances are linked by so called ester groups.Because cows eat cutin, a natural polyester made from plants, this is why. PET is a synthetic polyester with a similar chemical structure as the natural material.Cutin, which is the outer layer of plant cell wall cells, makes up the majority of the cuticle. It can also be found in large quantities in the skins of tomatoes and apples. Doris Ribitsch (corresponding author), is a senior scientist at University of Natural Resources and Life Sciences, Vienna.Related: How much plastic can be recycled?Ribitsch explained to Live Science that bacteria and fungi want to enter such fruits by producing enzymes. These enzymes can cleave the cutin, or break the chemical bonds in the substance.Cutinases, a group of enzymes, can hydrolyze cutin. This means they can jump-start a chemical process in which water molecules are broken down 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 bugs.She said that these animals are eating a lot of plant material and it is highly likely that such microbes will 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 byproducts produced by the plastics to determine how much the bugs dissolved the material into its components.According to the team, PEF was broken down most efficiently by rumen liquid, but all three types of plastic were affected.To find out which microbes may be responsible for plastic degrading, the team took DNA from the rumen. According to reports in the Journal of Hazardous Materials and Applied Microbiology, 98 percent of DNA was from the bacteria kingdom.According to a 2017 Journal of Agricultural and Food Chemistry report, bacteria from the genus Acinetobacter were also found in large quantities in the liquid.Ribitsch and her colleagues are looking forward to determining which enzymes bacteria uses to breakdown plastics.They can genetically engineer microbes to produce enzymes in large amounts without having to take the microbes from cow stomachs.Ribitsch stated that enzymes can now be easily produced at low cost and used on industrial scales.Ribitsch and her colleagues have already patented a method for recycling textiles that exposes them to different enzymes in sequence. The team has previously identified these enzymes.The first batch of enzymes targets the fabric's 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 reused without having to separate 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 largely of strong bonds between carbonatoms. This structure restricts enzymes' ability to grab hold of molecules and start hydrolysis.Levin stated that while PET degrading enzymes have been commercialized and characterized by scientists, microbes are still being sought out by researchers to handle polypropylene and polyethylene.Levin and his laboratory have identified some promising candidates, but they are still trying to figure out how to maximize the plastic-eating abilities of the bugs.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, "Maybe, we can find in such large communities like in the Rumen Liquid, enzymes that also can degrade polypropylene or polyethylene."Similar content:How can we make oil into plastic?Informationgraphic: Plastic bag waste litters the landscapeFive ways your gut bacteria can impact your healthLive Science originally published this article. You can read the original article here.
