Plastic-eating bacteria and the race to engineer more

In 2016, scientists discovered plastic-eating bacteria in a Japanese waste dump (1). These bacteria (Ideonella sakaiensis 201-F6) contain enzymes that utilize PET (polyethylene terphatele), a polymer typically used to make plastic bottles as an energy source. The plastic-eating bacteria discovery has enormous potential for recycling plastic and may spark innovative business ideas and processes.

In the past 70 years, plastic waste increased from 2 million metric tons to 380 million metric tons per year. It appears this was enough time for bacteria to mutate and use plastic as an energy source.

Tiny plastic pieces everywhere

In the Arctic, the deepest oceans, and the highest mountains, scientists have discovered plastic (2; 3; 4). We unknowingly inhale and eat these minuscule plastic particles, or microplastics, while we go about our regular lives. Although the health dangers are unknown, they may be similar to breathing asbestos, which causes cancer.

Plastic bottles break down into small pieces when weathered and degraded in water. These minute particles, according to The Guardian, are devoured by marine species and enter our food chain (5).

Plastic recycling is challenging, according to AaIPOL, because of the variety of chemical components. Up until recently, only fungi were capable of degrading PET, although slowly (6). However, an impressive scientific discovery for digesting microplastic better than fungi sparks hope.

A race to engineer super-enzymes inspired by plastic-eating bacteria

In 2018, a team co-led by Prof. McGeehan, University of Portsmouth, engineered an enzyme found in a Japanese waste dump and further improved plastic-eating activities (7). Enzymes are catalysts that speed up chemical reactions in living cells, including bacteria.

Prof. McGeehan’s laboratory created a super-enzyme called MHETase. Compared to the original discoveries in the Japanese dump, the super-enzyme displays a sixfold increase in breaking down plastic. A patent followed, and the team is continuing its pursuit of making even faster enzymes. 

In line with this trajectory, a French company, Carbios, revealed new data on a different plastic-eating enzyme (Deonella sakaiensis strain 201-F6). This new enzyme was discovered in a compost heap of leaves and degraded 90% of plastic bottles within 10 hours. The only limitation of the new enzyme was the need for high temperatures of 70 oC (9). 

Consequently, McGeehan’s team partnered up with Carbios. Their shared vision was to engineer a mutant enzyme from Thermobifida fusca, Fusarium solani pisi cutinase (FsC), Ideonella sakaiensis PETase (Is-PETase) and leaf-branch compost cutinase (LCC). LCC outperformed all other enzymes. 

Collaborations between science and industry giants

Henceforth, McGeehan and Carbios have partnered with giants such as Pepsi and L’Oréal to accelerate the development of this significant scientific achievement. The race to develop plastic-degrading enzymes is at full speed.

In April 2020, Carbios, a pioneer in the design and development of enzymatic processes, announced the first industrial-scale plastic-eating enzyme plant in Lyon (8). This bio-solution plant aims to redefine and benchmark plastic recycling processes.   

Plastic-degrading enzymes AI database

The creation of the world’s first and most extensive Artificial Intelligence (AI) enzyme database started with ocean water and soil bacteria sample analyses.

These samples came from rubbish dumps and similar places rife with plastic. Led by the Department of Biology and Biological Engineering at Chalmers University of Technology in Gothenburg, Sweden, the extensive enzyme database was driven by scientists studying the explosion and impact of plastic production. 

European scientists looked for similar enzymes in samples collected by other researchers from 236 locations worldwide. The study found 30,000 descendant enzymes that essentially inherited the plastic-eating potential (10).

Most remarkable is that these newly discovered enzymes degrade not one but ten different plastic types.

Plastic-degrading enzymes found on ocean floors appear to differ from those in our soils. Soil samples collected from 169 locations in 38 countries from 11 habitats revealed 18,000 plastic-degrading enzymes. Soils are known to have more plastics with phthalate additives than the oceans. 

Upon reflection, the research reveals how microbial ecology responds to plastic pollution.  Further, the study shows how much we are altering bacteria or microbes worldwide. We should, however, remember that we do not control the direction of these mutations.

The future life of a plastic bottle and more

Given that the predicted lifetime of a PET bottle under ambient conditions ranges from 16 to 48 years, multienzyme systems that can degrade plastic in hours represent a promising and fruitful area for further research.

Scientists were surprised to discover such a large number of enzymes in such a diverse range of microbes and environmental habitats. The discovery highlights the magnitude of the problem, as nearly 60% of newly discovered enzymes did not fit into existing database classes (11).

Science is still learning about the degrading plastic potential. Scientists are now searching for bacteria and microbes in landfills all over the world.

Some scientists predict plastic-eating microbes might one day be sprayed on huge plastic garbage patches in our oceans and soils. 

In the hope of a greener future, we thank the bacteria that think plastic is fantastic.

References

1. Yoshida, S., Hiraga, K., Takehana, T., Taniguchi, I., Yamaji, H., Maeda, Y., Oda, K. (2016). A bacterium that degrades and assimilates poly(ethylene terephthalate). Science (New York, N.Y.), 351(6278), 1196-1199. doi:10.1126/science.aad6359
2. Bergmann, M., Collard, F., Fabres, J., Gabrielsen, G. W., Provencher, J. F., Rochman, C. M., Marine and Atmospheric Research. (2022). Plastic pollution in the arctic. Nature Reviews Earth & Environment, 3(5), 323. Retrieved from https://www.narcis.nl/publication/RecordID/oai:dspace.library.uu.nl:1874%2F420403
3. Eisenstein, M. (2021, Sep 24,). Rising tide of floating plastics spurs surge in research. Nature (London) doi:10.1038/d41586-021-02408-7 Retrieved from https://search.proquest.com/docview/2576655997
4. Napper, I. E., Davies, B. F. R., Clifford, H., Elvin, S., Koldewey, H. J., Mayewski, P. A., Thompson, R. C. (2020). Reaching new heights in plastic Pollution—Preliminary findings of microplastics on Mount Everest. One Earth (Cambridge, Mass.), 3(5), 621-630. doi:10.1016/j.oneear.2020.10.020
5. Smillie, S., (2017, Feb 14). From sea to plate: how plastic got into our fish. The Guardian, Lifestyle/Food. Retrieved from https://www.theguardian.com/lifeandstyle/2017/feb/14/sea-to-plate-plastic-got-into-fish
6. Think Tank European Parliament. (2020). The environmental impacts of plastics and micro-plastics use, waste and pollution: EU and national measures | think tank | European parliament. Retrieved from https://www.europarl.europa.eu/thinktank/en/document/IPOL_STU(2020)658279
7. Austin, H. P., Allen, M. D., Donohoe, B. S., Rorrer, N. A., Kearns, F. L., Silveira, R. L., Beckham, G. T. (2018). Characterization and engineering of a plastic-degrading aromatic polyesterase. Proceedings of the National Academy of Sciences, 115(19), E4350-E4357. doi:10.1073/pnas.1718804115
8. CARBIOS. (2020, -04-15T04:45:49+00:00). Carbios and TechnipFMC to build demonstration plant for depolymerization of waste PET plastics to monomers. Retrieved from https://www.carbios.com/en/carbios-and-technipfmc-to-build-demonstration-plant-for-depolymerization-of-waste-pet-plastics-to-monomers/
9. Palm, G. J., Reisky, L., Böttcher, D., Müller, H., Michels, E. A. P., Walczak, M. C., Weber, G. (2019). Structure of the plastic-degrading ideonella sakaiensis MHETase bound to a substrate. Nature Communications, 10(1), 1-10. doi:10.1038/s41467-019-09326-3
10. Zrimec, J., Kokina, M., Jonasson, S., Zorrilla, F., & Zelezniak, A. (2021). Plastic-degrading potential across the global microbiome correlates with recent pollution trends. mBio, doi:10.1128/mBio.02155-21
11. Ekanayaka, A. H., Tibpromma, S., Dai, D., Xu, R., Suwannarach, N., Stephenson, S. L., Karunarathna, S. C. (2022). A review of the fungi that degrade plastic. Journal of Fungi (Basel, Switzerland), 8(8) doi:10.3390/jof8080772