Plastic pollution is one of the defining environmental challenges of our time - and some of nature's tiniest organisms may offer a surprising way out.
Authors
- Ronan McCarthy
Professor in Biomedical Sciences, Brunel University of London
- Rubén de Dios
Postdoctoral Research Fellow, Biotechnology, Brunel University of London
In recent years, microbiologists have discovered bacteria capable of breaking down various types of plastic, hinting at a more sustainable path forward.
These "plastic-eating" microbes could one day help shrink the mountains of waste clogging landfills and oceans. But they are not always a perfect fix. In the wrong environment, they could cause serious problems.
Plastics are widely used in hospitals in things such as sutures (especially the dissolving type), wound dressings and implants. So might the bacteria found in hospitals break down and feed on plastic?
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To find out, we studied the genomes of known hospital pathogens (harmful bacteria) to see if they had the same plastic-degrading enzymes found in some bacteria in the environment.
We were surprised to find that some hospital germs, such as Pseudomonas aeruginosa, might be able to break down plastic.
P aeruginosa is associated with about 559,000 deaths globally each year. And many of the infections are picked up in hospitals.
Patients on ventilators or with open wounds from surgery or burns are at particular risk of a P aeruginosa infection. As are those who have catheters.
We decided to move forward from our computational search of bacterial databases to test the plastic-eating ability of P aeruginosa in the laboratory.
We focused on one specific strain of this bacterium that had a gene for making a plastic-eating enzyme. It had been isolated from a patient with a wound infection. We discovered that not only could it break down plastic, it could use the plastic as food to grow. This ability comes from an enzyme we named Pap1.
Biofilms
P aeruginosa is considered a high-priority pathogen by the World Health Organization. It can form tough layers called biofilms that protect it from the immune system and antibiotics, which makes it very hard to treat.
Our group has previously shown that when environmental bacteria form biofilms, they can break down plastic faster . So we wondered whether having a plastic-degrading enzyme might help P aeruginosa to be a pathogen. Strikingly, it does. This enzyme made the strain more harmful and helped it build bigger biofilms.
To understand how P aeruginosa was building a bigger biofilm when it was on plastic, we broke the biofilm apart. Then we analysed what the biofilm was made of and found that this pathogen was producing bigger biofilms by including the degraded plastic in this slimy shield - or "matrix", as it is formally known. P aeruginosa was using the plastic as cement to build a stronger bacterial community.
Pathogens like P aeruginosa can survive for a long time in hospitals, where plastics are everywhere. Could this persistence in hospitals be due to the pathogens' ability to eat plastics? We think this is a real possibility.
Many medical treatments involve plastics, such as orthopaedic implants, catheters, dental implants and hydrogel pads for treating burns. Our study suggests that a pathogen that can degrade the plastic in these devices could become a serious issue. This can make the treatment fail or make the patient's condition worse.
Thankfully, scientists are working on solutions, such as adding antimicrobial substances to medical plastics to stop germs from feeding on them. But now that we know that some germs can break down plastic, we'll need to consider that when choosing materials for future medical use.
Ronan McCarthy receives funding from the BBSRC, NC3Rs, Academy of Medical Sciences, Horizon 2020, British Society for Antimicrobial Chemotherapy, Innovate UK, NERC and the Medical Research Council. He is also Director of the Antimicrobial Innovations Centre at Brunel University of London.
Rubén de Dios receives funding from the BBSRC and the Medical Research Council.
