By YAN Fusheng
Modern industrialization and chemical engineering rely heavily on synthetic high-polymer materials and complex chemical processes. While these innovations are essential to modern life, they have also led to the accumulation of recalcitrant pollutants, such as persistent plastics and toxic, high-salinity refinery wastes. Because many of these synthetic compounds feature novel chemical structures and complex bonds—such as specific urethane linkages—they often resist natural degradation, causing them to accumulate in landfills and oceans.
To address this growing ecological burden, scientists are retooling nature’s machinery. By deliberately engineering and optimizing microorganisms, researchers are transforming them into specialized bio-catalysts capable of degrading these stubborn pollutants. To drive this effort forward, researchers from the Institute of Microbiology (IMB) and the Shenzhen Institutes of Advanced Technology (SIAT), both under the Chinese Academy of Sciences (CAS), are developing targeted biological platforms to tackle these molecular challenges.
The Resurrection of the Foam
The first chapter of this effort concerns a material so ubiquitous that it is often neglected: polyurethane (PU). It cushions our sleep, insulates our homes, and quiets our cars. Yet, its chemical structure makes it a nightmare for recycling. Unlike thermoplastics such as PET bottles, which can be melted down and remolded like wax, commercial polyurethanes are thermoset. They are more like “cured concrete”—once the chemical reaction “sets” the material, its internal scaffolding is locked in place. You can crush it, but you can never make it flow again. The polymer chains are cross-linked into a three-dimensional net that resists heat and solvents, locking the material into a permanent state.
Current industrial methods to break this “concrete” down, such as glycolysis, are brutal. They require high temperatures and result in a biphasic mess: a top layer of reusable polyols and a bottom layer of toxic sludge containing aromatic amines and carbamates. This bottom layer is the industry’s dirty secret—usually incinerated as hazardous waste because it is too chemically complex to separate and too viscous to process.
Addressing this bottleneck, a research team led by Drs. WU Bian and CUI Yinglu at the IMB realized that biology might hold a latent key. While natural evolution never engineered enzymes specifically for synthetic plastics, certain microbial proteins possess a “promiscuous” ability to attack urethane bonds by accident—a byproduct of their role in breaking down natural polymers.
However, these natural enzymes, known as urethanases, are far from being industrial solutions. They are fragile; when placed in the harsh, solvent-heavy soup of industrial glycolysis, they quickly unravel and lose their activity. It was a classic needle-in-a-haystack problem—finding a way to re-engineer these proteins so they are robust enough to survive the chemical furnace, yet active enough to “resurrect” the plastic foam by recycling its monomers.
To solve this, the researchers did not rely on traditional screening. Instead, they turned to deep learning, developing a Graph Neural Network (GNN) framework named GRASE (GNN-based Recommendation of Active and Stable Enzymes). The brilliance of GRASE lies in its ability to look beyond the mere sequence of amino acids. Much like a master locksmith who studies the internal geometry of a lock rather than just the key number, GRASE abstracts protein structures as graphs, encoding the spatial relationships and atomic distances of the enzyme’s “pockets”—the active sites where chemical reactions occur.
The artificial intelligence (AI) navigated through the vast, chaotic data of protein structures and pinpointed a candidate from a marine bacterium, Agarivorans albus, which they named AbPURase. This enzyme was an anomaly. While traditional enzymes withered in the breakdown solvent (diethylene glycol), AbPURase thrived, exhibiting activity 465 times greater than the previous benchmark enzyme at 50°C.
When the team zoomed in to understand this miraculous stability, they found that nature—guided by AI—had engineered a microscopic fortress. AbPURase possesses a “lid” domain, a structural loop stabilized by proline residues that sits over the active site. In the chaotic environment of the solvent, where other enzymes would flap open and disintegrate, AbPURase’s lid stays remarkably rigid, protecting the hydrophobic core while allowing the substrate to enter.
Locking the Active Site: How “Lid” stability dictates enzyme performance. This comparison shows how the stability of an engineered “lid” domain (dark outlines) determines the efficiency of polyurethane-degrading enzymes. While rigid lids in highly active variants of AbPURase (GB6, GB7) protect the catalytic pocket, unstable or misaligned structures in other candidates lead to a dramatic loss of function. (Graphic: Chen et al., 2025)
The implications are staggering. Using this enzyme, the team successfully depolymerized commercial polyurethane foam at kilogram scale with 95% conversion efficiency after 8 hours at an enzyme loading of 8 mg/g, recovering valuable monomers with near purity. In other words, they essentially melt the cured concrete, turning a dead-end waste product back into raw ingredients ready for a second life.
The Ferrari of the Microcosm
While the researchers at the IMB were using AI to tackle solid wastes, a different group at the SIAT, led by Drs. TANG Hongzhi and DAI Junbiao, was waging war on liquid pollution. Industrial wastewater is hardly a simple poison; it is a complex, saline goulash of multiple toxins—phenols, toluenes, naphthalenes—that overwhelms standard bacteria.
In the wild, no single bacterium is a jack-of-all-trades; each strain has evolved to thrive in one narrow niche. One might eat phenol but die in salt; another might tolerate salt but choke on toluene. The engineering challenge was to create a generalist—a “super-strain” capable of metabolizing a diverse cocktail of pollutants simultaneously, even in the harsh, salty conditions of ocean water or industrial brine.
The team chose a chassis that is becoming legendary in synthetic biology: Vibrio natriegens. If E. coli is the reliable workhorse of the bacterial world—the foundational tool used for everything from producing human insulin to cloning DNA—Vibrio natriegens is the Ferrari—it is the fastest-growing bacterium known, capable of doubling its population in under 10 minutes. Speed, however, was not enough. The organism needed new genetic software.
The researchers developed a method with the somewhat affectionate acronym INTIMATE (Iterative Natural Transformation based on Vmax with Amplified TfoX Effect). This technique allowed them to “download” massive chunks of genetic code into the bacterium’s genome, stacking trait upon trait like Lego bricks. They didn’t just add one gene; they chemically synthesized entire degradation pathways—massive gene clusters totaling 43,000 base pairs—and integrated them into the organism.
The result was VCOD-15, a microbial chimera designed for shattering the organic wastes specific to the Anthropocene. In testing, this engineered strain faced a “death squad” of five major pollutants: biphenyl, phenol, naphthalene, dibenzofuran, and toluene. Where natural bacteria would have perished or selectively eaten only the easiest course, VCOD-15 devoured the entire buffet.
The most dramatic proof of concept came not in a sterile flask, but in the dirty reality of the field. The team collected real wastewater from a chlor-alkali plant and a petroleum refinery—liquids thick with toxins and heavy with salt. In multi-parallel bioreactors, VCOD-15 stripped the water of nearly all organic pollutants within 48 hours, removing over 98% of the naphthalene and dibenzofuran. It thrived in the high salinity that usually shrivels freshwater bacteria, proving itself a robust warrior for marine and industrial bioremediation.
Engineered Microbes: The scheme for the development of bacterial strain Vibrio natriegens VCOD-15 that tackles five pollutants at once. (Graphic: Su, et al., 2025)
Converging Paths to a Clean Earth
These two breakthroughs, though distinct in their methods, weave together into a compelling narrative about the future of environmental science in China. The work on polyurethane demonstrates the power of mining the past—using artificial intelligence to excavate the evolutionary history of enzymes and find ancient tools that can solve modern problems. Conversely, the work on Vibrio natriegens showcases the power of building the future—using synthetic biology to write new genetic destinies that evolution has not yet had time to produce.
There is a profound elegance in the contrast: One team used a “locksmith” approach, finding the perfect key (AbPURase) for a specific chemical lock, while the other used an “architect” approach, building a factory (VCOD-15) capable of processing mixed materials.
However, moving from the lab to the ecosystem requires navigating the jagged reefs of ethics and safety. The release of genetically modified organisms—especially those as fast-growing as Vibrio natriegens—may raise public concerns regarding biocontainment. Could these super-eaters outcompete native flora? The scientists are acutely aware of this “Frankenstein” risk. The SIAT team has proposed incorporating “suicide loops” into the genome—genetic kill-switches that would cause the bacteria to self-destruct once their specific job is done or if they wander outside their designated environment. This ensures that the synthetic stomach digests only the wastes, not the ecosystem itself.
Furthermore, the economic implications are just as critical as the ecological ones. The GRASE-discovered enzyme reduces the energy burden of recycling. Process modeling suggests that using AbPURase at an optimized loading reduces operating costs significantly compared to traditional methods. Similarly, the VCOD-15 strain could offer a way to reclaim industrial water—a resource becoming as precious as oil—without energy-intensive filtration or chemical treatment.
The Alchemists of the Anthropocene
We are transitioning from an era of extraction to an era of circulation. For two centuries, industrialization has been a linear process: We dig, we burn, we build, then we discard. The physics of our planet can no longer support this linearity. The work presented by these CAS scientists represents the closing of the loop. They are the new alchemists, but instead of transmuting lead into gold, they are transmuting toxicity into neutrality, and wastes into resources.
The discovery of AbPURase and the engineering of VCOD-15 are not just isolated scientific papers; they are blueprints for sustainability. They tell us that while human technology created the burden of pollution, human ingenuity—partnered with the biological machinery of nature—can lift it.
Reference
Su, C., Cui, H., Wang, W., et al. (2025) Bioremediation of complex organic pollutants by engineered Vibrio natriegens. Nature, 642(8069), 1024–1033. doi:10.1038/s41586-025-08947-7
Chen, Y., Sun, J., Shi, K., et al. (2025) Glycolysis-compatible urethanases for polyurethane recycling. Science, 390(6772), 503–509. doi:10.1126/science.adw4487