Polycyclic aromatic hydrocarbons (PAHs) enter our rivers through anthropogenic pollution and poison the environment. PAHs are chemically stable products of incomplete combustion reactions, occurring wherever something carbon-based is burned (for example cigarettes, car fuel, etc). Additionally, they are a part of crude oil, and most products made from it. After an oil spill cleanup or by being washed into rivers by rain, these PAH molecules are emulsified in the water, forming tiny micelles, invisible to the human eye and thereby almost impossible to clean up [1], [2].

PAHs are a hazard to humans and other animals, causing diverse health issues. The most significant ones are their carcinogenic and teratogenic effects. The reason for these effects is, when trying to break them down, our bodies convert the PAHs to very reactive epoxides, which easily bind to our DNA and thereby alter our genetic code, sometimes defunctionalizing important genes [3].

To clean up the water, we decided to use bacteria with the ability to digest complex PAHs. Our choice landed on Pseudomonas vancouverensis DSM8368, because it is adjusted to riverine conditions and can already digest naphthalene and phenanthrene [4]. These two are of the most common dangerous PAHs and their digestion pathway offers great stepstones for our work.

As P. vancouverensis can degrade PAHs consisting of two and three benzene rings, the natural next step would be, enabling it to break down the four ring system pyrene. And that’s exactly what we did. To get there, we assembled a plasmid coding enzymes to create a complete pyrene degradation pathway.

Our genetically modified organisms can produce enzymes which break down pyrene until a product is reached that can be degraded further by its native phenanthrene degrading enzymes. We merged this existing metabolic way with our new pathway. Therefore, our modified P. vancouverensis can not only degrade and thereby detoxify pyrene, but it can feed of it.

With this approach toxic chemical are removed from the environment and serve as nutrients on the way. To keep the GMOs contained, they will be deployed into the environment using a specialized device which can be placed in rivers permanently. The GMOs immobilized inside reduce PAH-levels autonomously, saving riverine and marine ecosystems. Visit our project description to learn more.

[1] Yan, J., Liu, J., Shi, X., You, X., & Cao, Z. (2016). Polycyclic aromatic hydrocarbons (PAHs) in water from three estuaries of China: Distribution, seasonal variations and ecological risk assessment. Marine Pollution Bulletin, 109(1), 471–479. https://doi.org/10.1016/J.MARPOLBUL.2016.05.025 [2] Sarria-Villa, R., Ocampo-Duque, W., Páez, M., & Schuhmacher, M. (2016). Presence of PAHs in water and sediments of the Colombian Cauca River during heavy rain episodes, and implications for risk assessment. Science of The Total Environment, 540, 455–465. https://doi.org/10.1016/J.SCITOTENV.2015.07.020 [3] Sun, K., Song, Y., He, F., Jing, M., Tang, J., & Liu, R. (2021). A review of human and animals exposure to polycyclic aromatic hydrocarbons: Health risk and adverse effects, photo-induced toxicity and regulating effect of microplastics. Science of The Total Environment, 773, 145403. https://doi.org/10.1016/J.SCITOTENV.2021.145403 [4] W. W. Mohn, A. E. Wilson, P. Bicho, and E. R. B. Moore, “Physiological and phylogenetic diversity of bacteria growing on resin acids,” Syst Appl Microbiol, vol. 22, no. 1, 1999, doi: 10.1016/S0723-2020(99)80029-0.