Plastic waste on beach

Plastic-degrading enzymes on the rise in pollution hotspots

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The number of microbial enzymes with the ability to degrade plastic is growing in correlation with local levels of plastic pollution, a new study has found.

Researchers from Chalmers University of Technology in Sweden measured samples of environmental DNA from around the globe and used computer modelling to search for microbial enzymes with plastic-degrading potential.

This was then cross-referenced with the official numbers for plastic waste pollution across countries and oceans.

The results illustrate the impact plastic pollution is having on the environment and hint at potential new solutions for managing the problem.

“Using our models, we found multiple lines of evidence supporting the fact that the global microbiome’s plastic-degrading potential correlates strongly with measurements of environmental plastic pollution – a significant demonstration of how the environment is responding to the pressures we are placing on it,” said associate professor Aleksej Zelezniak.

Global plastic pollution has been growing exponentially in the last 70 years: from around two million tonnes per year to around 380 million tonnes.

The researchers believe this has given sufficient evolutionary time for various microbes present in the environment to respond to these compounds and many different enzymes have been discovered in previous studies with the ability to degrade different plastics.

In total, over 30,000 enzyme ‘homologues’ were found with the potential to degrade 10 different types of commonly used plastic.

Homologues are members of protein sequences sharing similar properties. Some of the locations that contained the highest amounts were notoriously highly polluted areas, for example samples from the Mediterranean Sea and South Pacific Ocean.

“Currently, very little is known about these plastic-degrading enzymes and we did not expect to find such a large number of them across so many different microbes and environmental habitats. This is a surprising discovery that really illustrates the scale of the issue,” explained Jan Zrimec, first author of the study.

Every year, around eight million tonnes of plastic escapes into the world’s oceans. Plastic typically degrades very slowly with natural processes – the lifetime of a PET-bottle, for example, can be hundreds of years.

The growth and accumulation of plastic waste in the oceans and on land is a truly global problem and there is an increasing need for solutions to manage this waste. The researchers believe that their results could potentially be used to discover and adapt enzymes for novel recycling processes.

“The next step would be to test the most promising enzyme candidates in the lab to closely investigate their properties and the rate of plastic degradation they can achieve. From there you could engineer microbial communities with targeted degrading functions for specific polymer types,” Zelezniak said.

Last month, a team demonstrated a prototype speaker system that can efficiently separate out microplastics from polluted water using acoustic waves.

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