Allison Cartwright is our ECS Publications Officer. Here she ponders the downsides of plastic and whether microbes can help us.
When I moved to Northern Ireland in 2001, my family lived beside the Bann. This tidal river mouth revealed one of man’s greatest impacts on the planet – plastic waste.
No matter how often we collected litter from these river banks, more was back the next day. Having studied marine science, I’ve been surrounded by plastic pollution discussions for years, but since BBC’s Planet Earth II, more people are aware of the problem.
Death by plastic
Animals become entangled in plastic and die. Animals eat plastic, and if this doesn’t kill them, they can die from starvation as the plastic offers no nutritional value. In addition to this, we are also now eating this plastic.
If you’ve ever eaten a mussel, you’ll have ingested microplastics. It takes over 48 days to remove this pollution from their body.
Mussels are left to filter pure water for around 42 hours before they are tested for human consumption- a process known as depuration. The testing of mussels involves bacteria analysis, rather than testing for Lidl carrier bag fragments. Eat a mussel and you’re swallowing plastic waste.
Bin at the deep end
But what can we do, and can microbes help us? It’s easy to use the advice of ‘reduce, reuse and recycle’, but it’s hard not to be cynical. Try doing a weekly shop where you buy nothing contained in plastic. It’s nearly impossible.
I try my best to recycle – proud in the knowledge that my plastic will be reused. But is it? Did you know that if you recycle a plastic bottle, it won’t become another plastic bottle?
Once it’s been melted down, it will be a lower grade of plastic, used for something else. Regardless of the efforts we make, some of it could still end up in landfill.
Microbial mop up
If the ‘reduce, reuse and recycle’ concept is flawed, how can microbes to fix this mess? As microbes rapidly reproduce, they have a quick evolution. This means we have provided a unique food source (plastic) in such abundance that something was bound to evolve to use it.
The bacteria Ideonella sakaiensis has evolved to break up the plastic PET (polyethylene terephthalate) which makes up plastic bottles. This plastic is estimated to take 450 years to break down naturally, but as Leo Baekeland made the first plastic bakelite 111 years ago and PET was developed later, none produced to date has degraded naturally.
I. sakaiensis breaks up plastic using an enzyme which is thought to have originally broken up cellulose (the woody material in plants). Over time, this enzyme has shifted its specificity to match that of plastic, a readily available food source with no competition. It has even inspired a song by a chorus of grad students!
Suck it up
These bacteria are found in wastewater so will help to reduce the amount of plastic entering the oceans. So far I. sakaiensis is alone on the list of bacteria which purely use plastic for their food, but there are other bacteria which help to degrade bacteria. It is also possible other bacteria are waiting discovery.
Plastic pollutants are colonised by bacterial species that are not usually found in the surrounding water.[iii] High numbers of bacteria can accumulate on plastic pollution, which may negatively alter marine microbiomes. For example, plastic waste can introduce harmful bacteria to coral reefs, increasing the likelihood of coral disease from 4% to 89%.[iv]
Waxworm caterpillars can also break down plastic, thanks to special microbes that live in their gut. The waxworms break off chunks of PE (polyethylene) found in straws and cleaning product bottles. This plastic is then broken down by Enterobacter asburiae YT1 and Bacillus sp. YP1. Although the combined effort degrades this hard plastic, the process is slow, with around 100 mg of the plastic degraded in 60 days.
Just stop it
It is estimated that 99.6 million tons of this plastic will be made this year alone and so we would need a massive amount of waxworm caterpillars to degrade this plastic. I estimated we would need 1,000,000,000,000 caterpillars at the very least.
Ocean plastic pollution is an increasingly devastating crisis, however bacteria-based solutions may be around the corner. Bacteria that grow and feed on plastics may be used on a large scale to break down and remove this harmful ocean pollution.[i]
Researchers are also investigating marine microbes as a source of new sustainable bioplastics.[ii] The idea of ’microbial upcycling’ is an emerging vision, where bacteria may be engineered to convert non-biodegradable plastics into biodegradable products.
If the costs associated with these processes can be reduced, marine microbes may be part of a sustainable solution to future plastic use and recycling.
Shout about it
There’s potential for microbes to start to fix our mess, but the best option is still to try and stop using plastic. More and more commercial groups are pledging to reduce use of plastic, based on requests from consumers.
Hopefully this will cause a reduction in the plastic entering our environment, harming fellow animals and entering our food chain. But with so much plastic already in the system, it will be a long time before we can detect the changes being made today.
Browne, M.A., Dissanayake, A., Galloway, T.S., Lowe, D.M., Thompson, R.C. (2008). Ingested microscopic plastic translocates to the circulatory system of the mussel, Mytilus edulis (L.). Environment, Science and Technology, 42: 5026-5031.
Patel, N.V. (2018) Scientists stumbled upon a plastic-eating bacterium then accidently made it stronger [Online]. Available from: https://www.popsci.com/bacteria-enzyme-plastic-waste
Yang, J., Yang, Y., Wu, W.-M., Zhao, J., Jiang, L. (2014). Evidence of polyethylene biodegradation by bacterial strains from the guts of plastic-eating waxworms. Environment, Science and Technology, 48: 13776-13784.
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