Science for all: New research opens doors to upcycling plastic waste into paracetamol 

(This article forms a part of the Science for All newsletter that takes the jargon out of science and puts the fun in! Subscribe now!)

Scientists at the University of Edinburgh have found a way to make a classic lab reaction, called the Lossen rearrangement, happen safely inside living Escherichia coli cells — thus opening a potential new path to recycling plastic waste into valuable products.

The team started with a bacterium that couldn’t make para-aminobenzoic acid (PABA), a small molecule every cell needs to build DNA. When the mutant strain was given PABA, it grew. Without it, the strain was stalled. Researchers fed the cells a synthetic compound, simply called 1, that would release PABA only if a Lossen rearrangement reaction took place.

After 72 hours at 37 degrees C, the bacteria cultures turned cloudy, proving the reaction, and therefore PABA production, had taken place inside the flask.

The cloudiness test allowed the authors to track chemistry and cell health at the same time.

The reaction worked even when the researchers added no metal catalyst. They were able to figure out with more tests that ordinary phosphate ions, which are present in most cell media and inside cells themselves, quietly catalysed the rearrangement reaction.

High-performance liquid-chromatography measurements revealed that active, growing cells sped up the reaction up even more. The team also found that none of the tested substrates harmed cell growth at realistic concentrations, meaning they were not toxic to the bacteria.

Compound 1 was easy to make from terephthalic acid, which is the basic unit of polyethylene terephthalate (PET) soda bottles. This means the Lossen rearrangement reaction happening inside the bacteria could consume (a form of) plastic to produce a different, newly useful compound.

The researchers shredded a used bottle, hydrolysed it to terephthalic acid, and converted that into PET-1. The mutant E. coli strain grew just as well on PET-1 as on the lab-grade material, directly linking plastic-waste upcycling to biomass production and hinting at future bioremediation strategies.

Because the rescued cells stayed healthy, the team next checked whether they could perform additional tasks while the Lossen rearrangement reaction ticked on in the background. Indeed, cultures containing Compound 1 smoothly reduced dimethyl maleate and keto-acrylates to their saturated products using native bacterial enzymes — proof that abiotic and biotic chemistries could cooperate in one setting.

Finally, the authors built a two-enzyme genetic pathway: a fungal hydroxylase turned PABA into 4-aminophenol while a bacterial N-acetyl-transferase capped it with an acetyl group to yield paracetamol, the highly popular pain-relieving drug.

In fact, the researchers were able to convert up to 92% of PET-1 into paracetamol in one simple brew.

From the Science pages

Question Corner

Flora and fauna