Appetite for trash
Appetite for trash
With microorganisms and enzymes against the plastic flood: Nick Wierckx and his team want to use bacteria to decompose plastic waste. New raw materials are to be generated in the process.
Plastic litters our earth up to every nook and cranny. Tiny creatures could eliminate this problem: bacteria. In the future, they are not only to break down this waste, but also to extract valuable components for environmentally friendly products. They could also use plant waste to produce useful raw materials. Jülich biotechnologists want to establish a biobased recycling economy in this way.
When Japanese researchers discovered bacteria that nibble at plastic bottles in 2016, even the experts were astonished. After all, the smooth artificial surfaces had been considered indigestible until then. For the time being, however, the microorganisms from Japan will not solve the worldwide plastic waste apocalypse, from the Great Pacific Garbage Patch to the omnipresent microplastics. They simply work too slowly. Jülich biotechnologists are now approaching the topic from two sides. For one thing, they cultivate bacteria that decompose plastic waste more quickly and produce residual materials from which bioplastics can be made. For another thing, they train microorganisms to produce building blocks for recyclable bioplastics and other products from plant waste. The goal of Jülich biotechnology: a biobased recycling economy that produces valuable raw materials from supposedly worthless residual materials.
Picture above: With microorganisms and enzymes against the plastic flood: Nick Wierckx and his team want to use bacteria to decompose plastic waste. New raw materials are to be generated in the process.
359 million tonnes of petroleum-based plastics are currently produced worldwide each year, and counting. Around 80 percent of these are nondurable products such as bags, bottles, films or packaging. “Only 14 per cent of this waste, in turn, is collected worldwide and only 12 per cent of this small proportion is recycled at all, which is only 5 million tonnes,” explains Prof. Nick Wierckx from the Jülich Institute of Biotechnology (IBG-1). Germany, for example, had a recycling rate of only 15.6 per cent according to the Plastic Atlas 2019. “The rest usually ends up in waste-to-energy incineration plants, while in other regions of the world, it often ends up in badly managed landfills or, in the worst case, simply in wild dumps in nature,” says the biotechnologist.
Even though drinking straws and other disposable plastic tableware will be banned in the EU from mid-2021, the plastic waste of the past decades has long since accumulated everywhere: not only in the form of clearly visible rubbish in ditches and on the beach or in huge plastic patches in the oceans, but also in the form of fibres and microparticles invisible to the naked eye. These stem from the abrasion of clothing and car tyres, disintegrated packaging or cosmetic products. Some of them are so tiny that they are blown away by wind and washed down from the sky by rain.
Researchers find the finely ground plastics in snow from the Alps to the Arctic, in rivers and lakes just the same, even in the spray of seawater, in groundwater and tap water, as well as in the topsoil of arable land. They even found it in German beer. It therefore comes as no surprise that the plastic residues also reach the air we breathe and the food chain. They are associated with cancer, inflammatory processes and hormonal disorders.0.00
of plastic have been produced worldwide over the past 70 years.
Prof. Wierckx and his colleagues have two plans: first of all, they want to tackle the mountain of plastic waste with the help of enzymes and bacteria and break it down in an eco-friendly way. They then want to produce new, biobased plastics from the individual components that are created during decomposition. They were inspired, among other things, by the bacterium that Japanese scientists discovered four years ago. Ideonella sakaiensis was found on half-rotten PET bottles not far from a recycling plant. The bacterium first attaches itself to the plastic and secretes enzymes. These enzymes separate the long chain molecules of PET into their individual links. The bacterium then continues to metabolise these fragments until only water and carbon are left.
Faster and more effective
“Unfortunately, these bacteria found in Japan work extremely slowly. A thin strip of plastic only a few centimetres in size took the bacteria over 60 days to decompose,” says Nick Wierckx. Their performance fluctuates in the process: sometimes the bacteria are very busy, sometimes they are not. Moreover Ideonella reproduces very slowly. Wierckx and his team are therefore focusing on the bacterium Pseudomonas putida. Using optimised enzymes, the plastic is first decomposed within a few days at high temperatures. The bacteria then continue to convert the plastic broth.
“In our broth, the bacteria decompose plastics like PET, but also biodegradable plastic such as PLA.“
Prof. Nick Wierckx,
Institute of Bio- and Geosciences (IBG-1)
“Pseudomonas putida is very robust and an old acquaintance when it comes to cleaning contaminated soil. It even survives in an environment with high levels of pollutants and toxins,” explains the expert. It is precisely this property that is important, as the researchers have developed a decomposition method that makes things uncomfortable for microorganisms: the researchers do not apply the bacterium to individual plastic bottles, but let it work in a broth of different plastics.
“In this plastic broth, special enzymes have predigested the various plastics, which makes our bacteria’s work easier. We developed the process together with colleagues from RWTH Aachen University and Leipzig University,” explains Nick Wierckx. The advantage of the mixture of different plastics: the plastic waste does not have to be presorted. “In the broth, the bacteria decompose exactly those plastics for which their new enzyme equipment is suitable – in our specific case, the plastic type PET, but also biodegradable plastic such as PLA. What remains will be chemically processed,” says the biotechnologist. In this way, the Jülich laboratory bacteria decompose plastic fragments in four days that, in nature, would still not have finished decomposing after 400 years.0
is how long it takes for a package, bottle, curd cheese cup or plastic bag to decompose in nature.
The researchers’ aim is to get their bacteria to digest as many different types of plastic as possible so that the recycling process will be as efficient as possible. In addition, the Jülich researchers are also getting Pseudomonas to synthesize valuable chemicals such as aromatic compounds from the colourful plastic broth. These aromatics can then be used to produce new, more environmentally compatible plastics. The circle is thus complete: from plastic waste to new, environmentally friendly materials.
Finding new ways
Together with research groups from Heinrich Heine University Düsseldorf, the Jülich biotechnologists are pursuing a number of paths to achieve this. One path leads through point mutations – tiny, targeted changes in genetic information that cause the bacteria to also produce other, more helpful enzymes. Another path is to replicate already known enzymes on the computer in order to understand their interaction with the plastic molecules in detail. Computer simulations are then used to find a better – that is, more effective – variant that, for example, degrades plastics even faster. The third path is to find previously unknown enzymes in bacteria that, for example, work at lower temperatures so that they could also be used in sewage treatment plants. “In collaboration with our partners in the PlastiSea project, we want to find such candidates, such as in the Atlantic garbage patch,” says doctoral researcher Rebecka Molitor from the Düsseldorf Institute for Molecular Enzyme Technology. “We have already discovered that marine bacteria of the species Pseudomonas aestusnigiri also process plastics,” she adds.
Such brine bacteria are difficult to keep in the laboratory because their requirements in terms of temperature and environment are too complex – but the researchers at Jülich and Düsseldorf are nevertheless examining their enzymes closely. For example, they have transferred the genetic information of the enzymes into comparatively undemanding bacteria. In the laboratory, the modified bacteria can be used to break down polyester from textile coatings or PET components. Such plastics wrap synthetic fibres of waterproof or windproof clothing, for example. After each wash, residues are found in the waste water and finally in the environment.
Added value with bacteria
“The potential use of such microorganisms is of particular importance in sewage treatment plants,” says Wierckx, “because up until now, the filters in the plants have not been sufficient enough to completely remove the artificial substances, fibres and microparticles from the wastewater.” It would be even better if the textile fibres were directly biologically produced and biodegradable.
“The project is a prime example for completely new types of value chains that we are working on at Jülich.”
Prof. Michael Bott,
head of “Systemic Microbiology” at IBG-1
This is the aim of a new project in which Jülich researchers are involved. In the Glaukos project, named after a Greek sea god, they aim to develop biobased and biorecycled textile fibres suitable for both fishing nets and clothing: it is not only the abrasion of functional clothing that ends up in the water and finally in the sea, but also fishing nets made of synthetic fibres. After all, such fibres and nets account for 27 per cent of plastic waste in European waters.
The novel nets and textiles are environmentally friendly in two ways: they do not consume fossil resources, and they rot naturally without releasing microplastics. “This project is a prime example for completely new types of value chains that are only possible with the help of microbiology and one which we are working on at Jülich,” summarises institute director Prof. Michael Bott.
Brewing beer, baking bread, making cheese, yoghurt or kimchi, delivering medicines and pesticides, boosting digestion – microorganisms are ubiquitous helpers in and around us. Yes, some make us ill, but others help us to stay healthy or get healthy again. Bacteria, microalgae and yeasts also play a central role when it comes to healing our earth: leaving fossil raids and brutal exploitation of nature behind, towards a biobased recycling economy. In order to exploit the full potential of nature without bleeding it, there is no getting around these tiny jack-of-all-trades. After all, their ability to decompose even the most persistent materials – from massive logs to plastic bottles or oil residues – and convert them into energy or recyclable raw materials is the linchpin of an environmentally friendly economy.
Enzymes are complex proteins. They build up, break down or convert molecules such as nutrients or pollutants in living organisms without themselves being consumed or changed. Generally, a multi-layered cascade of enzyme reactions allows for a successful metabolic process sequence. This is why, for complicated processes such as the degradation and conversion of plastics, biotechnology uses bacteria that have the desired enzyme cascades, either naturally or through gene transfer. The process then usually takes place within the bacteria. Individual, isolated enzymes are sometimes sufficient in simple processes, for example in washing laundry. The enzymes are contained in the detergent and help to remove stains even at low temperatures.
Images: Forschungszentrum Jülich/Sascha Kreklau, MICHAL CIHLÁŘ, Jens Neubert, MOHAMED ABDULRAHEEM/Shutterstock.com