The promise – and limits – of plastic guzzling bacteria
Microbes work wonders for us. Without their metabolic powers, traditional fermented foods like beer and cheese would be absent from our tables.
Today, we obtain many more complex byproducts from bacteria: lab-grown proteins that carefully replicate animal meat or fuels for jets and cars.
Our cultural, technological, and economic landscape would look very different if we had never harnessed these invisible workhorses. Yet one emerging microbe function may be the most important yet in the long history of human-microbe co-dependence: the ability of some strains to decompose plastic waste.
How do microbes eat plastic?
All the economically useful functions of microbes boil down to one of two substances they produce: either the enzymes they make to break down food or the chemicals they emit as waste at the end of their metabolic process. The chemical makeup of these two products, enzymes and waste, varies by species and strains, determined by their genetics.
All microbe species use enzymes to make materials chemically simpler and easier to absorb as energy. While our digestive juices reside in our stomachs, microbial digestion happens outside the organism, with the microbe secreting decomposing substances onto target foods. Some microbes can get their energy from plastics because of the special nature of their enzymes.
A moment’s pause is due to appreciate how special this ability is. An organism around tenth the size of a typical human cell can render industrial products like polyethylene and polyester – materials that would otherwise remain stable in the environment for 500 to 1000 years – into non-toxic compounds. This is an astonishing biochemical feat. Where most wildlife is harmed by plastics ingestion even at tiny concentrations, these creatures use them to survive.
While the plastic-combatting potential might be old news among researchers, commercial versions are only just starting to emerge as venture capital warms to the niche.
Epoch Biodesign: a new era of bioremediation?
Epoch Biodesign is one of very few startups developing custom plastic-chomping microbes for the market. It was founded by a scientific duo, Professor Douglas Kell, researcher into systems biology at the University of Oxford, and Jacob Nathan, then a student and still only in his early twenties.
Kell’s academic research is focused on the bioengineering of enzymes. His line of work is perfectly attuned to solving the central problem of commercial microbial bioremediation: how to manipulate microbes in the lab to develop variants that break down waste in as little time and with the fewest inputs as possible.
Setting microbes to work on breaking down microplastics is similar to the steps involved in other microbe-based biotechnologies, from the very simple traditional fermentation food techniques to the relatively recent microbial biofuels.
Epoch Biodesign tweaks strains genetically in the laboratory, then cultivates these in great vats containing microbe-friendly nutrients plus oxygen. They grow and as they feed on the nutrient soup, they excrete not beer or lipids for biofuels but an enzyme that tears apart plastics into their simple chemical components.
EpochBiodesign does not tweak their microbes through manual trial and error: they use datasets and learning models to predict the kinds of proteins microbes could output that would make easy work of the most recalcitrant plastics.
So far, Epoch Designs offers microbial strains targeted to break down detergents, agrochemicals, plastics and textiles, industrial chemicals, paints and coatings, and cosmetics products. Its products are now well on the way to scaling, after raising an $11 million seed round in June 2022 that will be pumped into expanding their protein design software, constructing new R&D facilities, and scaling their products.
Nature-based chemical recycling
In Europe, 85% of plastic waste collected every year is exported, incinerated, or landfilled. Lack of political will, technical hurdles with recycling certain plastic types, and the high costs and low returns on collecting, processing and resale are some of the factors at work.
At the moment, many plastics cannot be recycled more than once or twice. The most common recycling method – mechanical recycling – is a crude technique that involves shredding and melting down waste. This distorts the chemical bonds inside the material, degrading its quality each time. At each turn, the potential market value of the material also diminishes, turning the cost-benefit calculus in favour of simply dumping it.
Chemical recycling is the holy grail of many in the waste management industry. Chemical methods like pyrolysis and gasification are an advance on simple mechanical methods because it returns a waste plastic to original monomers that resemble virgin raw materials for plastic. Scaling chemical recycling would mean more types of plastics could be re-used without a loss in function – these include film and multi-layered and laminated plastics which are easily damaged by the mechanical process.
However vaunted chemical recycling might be, the tech is not mature and remains much more expensive than mechanical methods. It is also questionable whether it offers a genuinely ecological alternative. It involves large amounts of energy – the process works only in temperatures of between 250 and 400 celsius – and the synthetic chemicals themselves post an environmental waste problem at the end of their lives.
The key attraction of microbial recycling is that it combines the functionality-preserving quality of chemical recycling with eco-friendly enzymes. Microbial enzymes deployed by companies like Epoch Biodesign break down plastics in the same way that conventional chemical recycling does, resulting in a material that is almost as good as new. However, microbial enzymes are nowhere near as eco-toxic. Since they are produced by living organisms, they resemble other substances found throughout natural ecosystems. At the end of their lives, they easily fade away into the chemical soup of the surrounding soil or water.
What’s more, just like in industrial synthetic chemicals, microbial enzymes can be precisely engineered to work on different forms of plastic at different scales.
Even though many plastic degrading microbes are now approaching the market, researchers are still hard at work on the area. Microbiologist Aatikah Tareen published research in 2022 relating to fieldwork where scientists hunted for new candidate strains in a dumping site. Of the microbes recovered, two species showed particularly high rates of plastic degradation activity: Alcaligenes faecalis and Bacillus cereus.
It is likely that we will discover more wild strains naturally adapted to consuming a high rate of plastic, giving commercial enterprises new stock from which to cultivate hyper-efficient recyclers.
An international startup scene
Apart from Epoch BioDesign, other startups are jostling to become the first major names in the plastic-eating microbes business.
Carbios is a French biotech startup working on microbial enzymatic recycling. Although it only just set up an industrial demonstration plant in 2021, it has already partnered with some of the biggest producers of plastic consumer goods packaging, PepsiCo, Nestle Waters, and L’Oreal. Its microbial strains can recycle any kind of PET, which make up 20 to 25 percent of plastics, without quality loss.
Their goal is to create a product that can enable endless recycling without a loss in quality. The startup, like many others in the biobased space, are waiting for the tipping point where petroleum prices rise and the cost-benefit calculus shifts in favour of the recycling process they have pioneered.
Another PET-focused microbial startup is Turkey’s PETman. It follows the same model as Epoch BioDesign and Carbios: selecting and then genetically reprogramming bacteria to enhance their waste devouring capacities.
Most startups in this space focus on tackling PET waste but one startup is using microbes to turn a range of plastics into a gloopy soup of soil nutrients. Hungary’s Poliloop strains can target a wide range of plastics: polypropylene, LDPE, HDPE, PS, CPE, EVA, composite, and multilayer packaging.
Poliloop’s end products are not virgin-like monomers that can be remade into new plastic goods. Instead, their microbes specialise in turning the plastics into a non-toxic brown sludge that can be used as soil improvers. Thanks to bacteria, it turns out that plastic waste could feed us.
The limits of microbial solutions
Bioengineered microbes offer one of the most promising methods for tackling plastic waste before it reaches the environment.
Yet even Carbios’ impressive biotech is not a panacea to the quality degradation problem in recycling: it can recycle PET 30 to 50 times – a huge leap compared to mechanical methods but still no justification for endless growth in resource extraction.
Even though microbial recycling is far less carbon intensive than mechanical or chemical recycling, there is always an amount of energy that is lost in any recovery process. Even biological resources do not escape the fundamental laws of thermodynamics, which guarantee that no resource loop will ever be perfectly circular.
Microbes work wonders for us but offer no magical solution. Innovations like this run the risk, with all their promise, of sidelining efforts to reduce waste at its root: an economic model that depends on extracting ever-increasing amounts of energy and materials. Even with scaling in plastic-eating microbes, advances in both recycling and demand reduction will still be necessary to reign in waste dumping.