Published on 14 September 2018

A group of students from Université Paris-Saclay is taking part in the 2018 international Genetically Engineered Machine competition (iGEM) through their project for the development of a bacterial bioreactor for hospital wastewater depollution.

Created by MIT in 2004, iGEM is an international student competition focused on promoting the emerging field of synthetic biology. This year, the GO team from Paris-Saclay is supervised by researchers from I2BC and consists of 12 students, including mathematicians, biologists and pharmacists. Their goal is to break down the anti-cancer drugs found in hospital wastewater in just 3 steps: (1) the effective entry of these molecules into bacterial cells, through specific channels and transporters; (2) the appropriate degradation of these compounds by enzymes (e.g. carboxypeptidase G2, cytochrome P450, etc.) and (3) the long-term operation of the bioreactor through a heterogeneous population of bacteria with bi-modal, "stem cell" behavior, thus reducing the need for regular reseeding.


Water contamination by anti-cancer drugs: a major issue

As cancer remains the leading cause of death worldwide, the consumption of cytotoxic (anti-cancer) drugs is on the rise. Although these pharmaceuticals are capable of interacting with DNA and blocking the proliferation of cancer cells, they lack selectivity and may also affect healthy cells. Unfortunately, these compounds have been detected in surface water. In fact, current wastewater treatment plants are not able to eliminate cytotoxic compounds due to their low concentrations and high hydrophilicity. With this in mind, it is essential to develop new techniques for their elimination.

Fig : Summary of the 2018 iGEM GO Paris-Saclay team project

The solution proposed by the GO Paris-Saclay team

As proof of concept, the GO team from Paris-Saclay chose to focus on the most dangerous and abundant anti-cancer drugs in wastewater, including methotrexate.

Methotrexate (MTX) is a folate analog that inhibits the activity of dihydrofolate reductase (DHFR), an enzyme which catalyzes the NADPH-dependent reduction of dihydrofolate to tetrahydrofolate. The inhibition of the activity of DHFR causes the inhibition of DNA synthesis, and ultimately, cell death.

To achieve the partial degradation of MTX and therefore the bioprocessing into a non-toxic product, the essential genes were cloned into E. coli, a naturally resistant bacterium expressing the MTX transporter.

Combined with the FolC gene, carboxypeptidase G2 (CPDG2) allows for the rapid hydrolysis of MTX to inactive metabolite DAMPA (4-[[2,4-diamino-6-(pteridinyl)methyl]-methylamino]-benzoic acid) and glutamate.

The team's preliminary results reveal the transformation of MTX by bacteria after only 20 hours, leading to DAMPA which, in turn, can be reprocessed by the pharmaceutical industry.

One of the applications of this project is to upgrade the degradation systems to turn them into flexible toolboxes that respond to a broad spectrum of anti-cancer molecules.

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