Biodegradation Breakthroughs: Innovative Approaches to Tackle Plastic Waste

By Jian Hong, GRC 2024 Global Essay Competition Top 5

Plastic pollution touches every part of our lives, harming ecosystems and infiltrating everything from the food we eat to the air we breathe. Plastic production has increased 20-fold in the past five decades, driving unsustainable disposal practices (Walker & Fequet 2023). With only 9% of plastic waste ever actually being recycled, and incineration leading to the release of even worse

chemicals, many solutions for plastic disposal have been attempted, yet all have proven lackluster over the years (OECD 2022). This has driven us toward a general conclusion that we must simply decrease plastic use. While lessening the amount of waste is certainly a net good, it fails to actually solve the problem—without adequate action, 33 billion tonnes of plastic are expected to accumulate on the planet by 2050, dumped into our environment or piled up in toxic landfills (Geneva Network 2024).

A potential solution to this worldwide calamity may just be underneath our feet, in the form of small, disregarded organisms such as soil bacteria and insects. With the earliest discoveries made a few years back, biodegrading plastic using nature itself has already begun to look promising.

Bacteria

In an experiment published in the Communications Biology journal, researchers found that 44% of randomly selected stains of Streptomyces, a genus of soil bacteria, were able to degrade BHET, an organic compound that acts as a crucial intermediate in breaking down PET plastic (Verschoor et al 2024). A separate study in the Journal of Coastal Life Medicine focused on polyethylene, the most common type of plastic, and showed that Streptomyces could successfully biodegrade HDPE (high density polyethylene) samples with a high efficiency and without any significant toxic material being produced in the process. 18.26% of one sample was degraded in 18 days with a small sample of (Farzi et al 2017). Two other independent research papers supported this notion, showing soil bacteria are capable of degrading polyethylene, polyurethane, and impranil (Pantelic et al, 2024, Pometto et al, 1992).

Scientists at the Qingdao National Laboratory for Marine Science and Technology also discovered marine bacteria that can degrade plastics like polyethylene terephthalate and polyethylene using enzymatic hydrolysis (Gao & Sun 2021). The scientists also revealed the mechanistic pathways for

such processing to occur, with plastic being integrated into the normative fatty acid degradation cycle to generate ATP.

Carbios, a French biochemistry corporation, has begun applying the technology to develop a recycling plant focusing on enzymatic processing of “all types of PET waste” using Cutinase, known mainly for its role in breaking down β bonds in glucose, which converts 90% of PET back to its starting materials within hours (Carbios, 2024, Tournier et al, 2020). Leaf-branch Compost Cutinase (LCC) was found to be most effective in research; however, bacterial cutinase was also reported to be found in strains of soil bacterium like Streptomyces scabies and Pseudomonas putida, as well as eleven classes in the fungal bacteria phyla Ascomycota (Sulaiman 2012, Chen et al 2008, Ekanayaka et al 2022).

What should be drawn from the results of such studies is not that abandoning plastic waste in soil will solve the plastic problem; methodical systems for processing such plastic must be developed.

Effective recycling of plastic requires the depolymerization of stronger plastic bonds, which can be achieved through the secreted enzymes from bacteria. Similar to how enzymes are used in wastewater management, a microbe-based solution could be released into containerized waste, or the activated enzymes could be extracted from the bacteria themselves (Orlando et al, 2023). Research already conducted by Dr. Elizabeth Bell on the targeted evolution of enzymes like PETase, produced by aerobic bacteria named Ideonella sakaiensis, could be key to expanding the efficiency of bacterial degradation methods (Bell 2022, Yoshida 2016).

Insects

Insects have also featured in discussions on the biodegradation of plastic ever since researchers stumbled across insect larvae eating away at styrofoam in 2022 (BBC 2022). At the Research Center for Industries of the Future (RCIF), the larvae of the fall armyworm moth, Spodoptera frugiperda, were found to degrade PVC, the third-most widely produced plastic (Zhang 2022). The results showed that a Klebsiella strain in their intestinal microbiota was driving the breakdown and identified S. frugiperda originating from soil, landfills, and marine environments as having the greatest ability to process PVC internally. Waxworms, Galleria mellonella, can also process plastic. Researchers found that polyethylene-fed waxworms retained intestinal functions comparable to honeycomb-fed caterpillars, even while eating plastic (Grove 2021).

Similarly, researchers and professors at Texas Tech examined the larvae of Tenebrio molitor, the yellow mealworm beetle, and its effects on different kinds of plastic. They showed that polystyrene was most easily consumed by mealworms, with the average consumption rate of 8.70% being the highest of any plastic (Pham 2023). The study also examined efficiency, revealing that 100 mealworms could consume 9.11 mg of polystyrene in a day. Researchers at Tongji University found similar PVC degradation capabilities in the same species of mealworms (Peng 2020).

Compared to bacterial biodegradation, the viability of insect-based biodegradation is likely contingent on continuous discoveries, as insects take up more area and are harder to release on larger scales than bacterial cultures. However, feeding co-diets to insect larvae or administering pretreatments like plasma exposure can improve breakdown rates across a variety of plastic types (Siddiqui 2024), potentially making them more versatile. A focus on ways to optimize the biodegradation speed of insects and ways to integrate them into current waste management solutions may provide further promising results. In particular, the fact that plastic-fed insects could potentially be used for animal feed (Siddiqui 2024) opens numerous new possibilities.

Conclusion

While the expense of developing and implementing a new plastic biodegradation system is impossible to ignore, the costs of neglecting the environment will be far worse. Principles of circular economies and societies center on utilizing what we already have; the widespread

application of naturally-occurring fungal, bacterial, and marine enzymes or plastic-consuming insects, could be the key to our continued use of plastic without irreversibly destroying our environment.

Figure 1:

Time lapse images from study by Verschoor et al, 2024.

Figure 2:

Graphic abstract from Pham et al, 2023.

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