Scientists find way to remove polluting microplastics with bacteria

Microbiologists have devised a sustainable way to remove polluting microplastics from the environment – and they want to use bacteria to do the job.

Bacteria naturally tend to group together and stick to surfaces, and this creates an adhesive substance called “biofilm” – we see it every morning when brushing our teeth and getting rid of dental plaque, for example. Researchers at the Hong Kong Polytechnic University (PolyU) want to use this sticky bacteria property and create tape-like microbe nets that can capture microplastics in polluted water to form an easily disposable and recyclable blob.

Although these findings, presented on Wednesday at the Microbiology Society’s annual conference, are still preliminary, this invention could pave the way for sustainably lowering plastic pollution levels in the long run by simply using something found in nature.

“It is imperative to develop effective solutions that trap, collect, and even recycle these microplastics to stop the ‘plastification’ of our natural environments,” said Sylvia Lang Liu, microbiology researcher at PolyU.

Microplastics are the plastic fragments, usually smaller than 5mm, which are accidentally released into the environment during production and breakdown of, for example, grocery bags or water bottles – or during everyday activities such as washing synthetic clothes such as nylon or using personal care products with scrubbing microbeads in them.

Although they are tiny, the risk they post to the environment is huge. Microplastics are not easily biodegradable, so they stick around for long periods of time and they also absorb and accumulate toxic chemicals. They disperse into wastewater and into the oceans, endangering marine animals who end up eating them and eventually trickling into the food chain and harming human health too. Microplastics had been found in more than 114 aquatic species in 2018, according to the International Maritime Organization, and they have been found in salt, lettuce, apples, and more.

Yet, there are not any sustainable, one-size-fit-all ways to eliminate microplastics.

With this research, Liu and the team led by Professor Song Lin Chua and James Kar-Hei Fang have engineered a bacterial biofilm, from a bacteria called Pseudomonas aeruginosa, able to immobilise and incorporate rogue microplastics floating around in the water. These microbe nets trap and group the microplastics and make them sink to the bottom of the water. Then, thanks to a “capture-release mechanism” using a biofilm-dispersal gene, the researchers can unlatch the microplastics from the bacteria traps and find themselves with bulks of collected microplastics ready to recycle.

“This is a really innovative and exciting application of biofilm engineering to address the plastic pollution crisis,” said Dr Joanna Sadler, researcher at University of Edinburgh, who was not involved in this study. “One of the biggest challenges in dealing with microplastics is capturing such small particles so they can be degraded and removed from the environment. Liu and co-workers have demonstrated an elegant solution to this problem, which holds great potential to be further developed into a real-world wastewater treatment technology.”

However, the experiment is still preliminary: it has been carried out as a proof-of-concept test in a controlled lab environment and not in the ocean or the sewers; and it was done using the “aeruginosa” bacteria strain, which is a disease-carrying bacteria for humans and probably could not be used in large-scale projects. But the researchers are confident that the method can be replicated to find natural biofilm-forming bacteria directly in sewage or other watery environments and go from there.

“In terms of the capture of microplastics, it’s an interesting development,” said Dr Nicholas Tucker, senior lecturer in molecular microbiology at the University of Strathclyde, who was not involved in the study. “Whether it’s scalable is going to be interesting to see.” According to Tucker, there will need to be more research on what types of surfaces to grow the biofilm on.

However, research like this provides a good example of the many uses for microbial biotechnology and what big feats tiny bacteria can accomplish. “In general, this shows that microbes can and will play a role in every stage of the life cycle of plastics,” Tucker said.