Microbes eating plastics

                              

Breaking down the microbiology world one bite at a time


Microbes eating plastics

As carefully we try to live a plastic-free life, there’s still a big chance that you use plastic every day. It is just everywhere! An estimated 2.4 to 12.7 million tons of plastic end up in the ocean every single year [1]! Because, unfortunately, only a small portion of the plastic we use is recycled. And as we all know, plastics are tough to degrade, some can take thousands of years before breaking down, and their presence in the environment releases chemicals into our soil and oceans. 

However, guess what is also found everywhere? Microbes of course! And they are able to adapt and survive in the most extreme and unusual places! If you are not convinced, read other articles on MicroBites to discover how diverse they are. 

But let’s go back to plastics. The most produced plastic types are polyethylene (PE) (36%), polypropylene (PP) (21%), and polyvinyl chloride (PVC) (12%), in addition to polyethylene terephthalate (PET), polyurethane (PU), and polystyrene (PS), with <10% each.

Image = polyethylene terephthalate polymer, also known as PET, a polyester used in most plastic bottles.
Source: Wikicommons

Research has shown, as far as 30 years ago, that some bacteria were able to degrade plastics. However, before the study of Gambarini and colleagues, the overview of the number and type of microbes able to break down plastics were still understudied. In their study, the authors compiled all the information known about microbial species able to degrade plastics. They looked at the type of plastics they were able to degrade, as well as their genetic capabilities to be successful. 

They found that most microbes able to degrade plastics were bacteria (65% of identified species) belonging to 5 different phyla, and the rest were fungal degraders (34.4%) from 3 phyla. By combining many studies, they were able to find trends in the microbial families. They found many plastic degraders within the Pseudonocardiaceae family, and the Bacillales order, suggesting a conserved feature among these microbes.

So, can we just feed all our plastic waste to bacteria? Well, it’s not that easy… Most plastics are complex polymers, and many of our microbial friends showed degradation for their monomers, but not their complex form. So what do we do now? The authors highlight that many microbes are able to degrade naturally derived plastics such as PHB (polymer polyhydroxybutyrate), or PLA (polymer polylactic acid). You know, these compostable plastics we get now in the shops! So that is a start. These naturally derived plastics are made by other microbes during fermentation and are biodegradable (Figure below).

Cycle of biodegradable plastics such as PHB. Created in biorender.com

By referencing the available data about plastics eaters, the authors laid a foundation for future research in this field. Further studies will hopefully bring us towards a better understanding of the origin and evolution of plastic degradation in microbes and potentially help us find new plastic-degrading microorganisms from species that are not yet cultured or screened for such superpowers. 

From the Ocean Conservancy

Link to the original post: Gambarini V, Pantos O, Kingsbury JM, Weaver L, Handley KM, Lear G. 2021. Phylogenetic distribution of plastic-degrading microorganisms. mSystems 6:e01112-20.

Other reference:
[1] Ilaria Conti, Carolina Simioni, Gabriele Varano, Cinzia Brenna, Eva Costanzi, Luca Maria Neri,
Legislation to limit the environmental plastic and microplastic pollution and their influence on human exposure, Environmental Pollution, 2021,

Featured image: https://ndla.no/subject:1:c8d6ed8b-d376-4c7b-b73a-3a1d48c3a357/topic:9e6c9f83-32a1-4cb4-977a-7a780c4948a3/topic:80fc34c3-f197-4e05-a2a8-49fea7278a32/resource:f721bdda-545f-48fa-adc9-290e05b571d4