Polyethylene terephthalate (PET) is a type of plastic that is one of the most widely used plastics in the world. It is used in things such as running shirts, carpet fibers, curtains, solar panels, tennis balls, microwavable containers, and plastic bottles. The PET Resin Association says, “Virtually all single-serving and 2-liter bottles of carbonated soft drinks and water sold in the U.S. are made from PET.” The plastic is very popular amongst manufacturers and with good reason! It is an extremely durable, lightweight, safe, and is 100% recyclable. However, the recycling rate for PET in the United States has been on a decline in 2019, residing at a low 27.9%. The un-recycled PET plastics that remain in the landfills are extremely problematic for the same reasons that make PET a preferred material. According to the World Wildlife Fund, those plastic bottles listed earlier could take about 450 years to decompose. These plastics are in turn, killing wildlife and polluting the world ecosystem.
Researchers at Reed College, located
in Oregon, are working on ways to break down PET using certain combinations of
bacteria. However, “[PET’s] long tough strands of ethylene glycol
and terephthalic acid monomers, all tangled up together. These strands lend PET
its durability; they also make it virtually impervious to biological reaction.”
Professor Jay Mellies had previously examined bacteria, using only plastics as
their source of nutrition, with some bacterial species remaining alive at the
end of his experiments. He assumed that because plastic was their only
nutritional source, they must be able to break down plastic in some way. He was
then given a grant to further explore the use of bacteria to break down these
PET’s. The students looked at numerous colonies and after 8 weeks of trials,
one sample was found to be working quite well. The sample of 5 different strains
of bacteria had consumed 3 percent of the plastic’s mass. Under further inspection
of the sample, tiny holes where the bacteria had ate the plastic could be seen
under a microscope. The bacteria had formed a symbiotic relationship where some
were breaking down the plastics into new forms that each other could digest. 
This is the chemical structure of PET.
Looking at how the bacteria do this; they naturally produce hydrolases. These are enzymes that the bacteria produce and use to digest their food. These hydrolases work like scissors that cut the bacteria’s food into smaller counterparts that they can eat. Even though PET is much larger and more complex than anything the bacteria would normally consume, the theory is that the bacteria would be able to adapt and produce more efficient enzymes to break down the PET.
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| Above is the reaction of an esterase (a type of hydrolase) and how it breaks down into smaller components. |
Further
experimentation is still going on where they are looking to boost and speed of
the generation of these hydrolases that can break down PET. The genetic
pathways are not fully understood in this situation, but Professor Mellies is
confident that new genetic techniques can solve their problems. This research
will be extremely beneficial in the case of pollution, as well as furthering
the use of symbiotic bacteria.
Read the article here.
Sources:
https://www.reed.edu/reed-magazine/articles/2021/reed-biologists-plastic-eating-bacteria.html
http://www.petresin.org/news_introtoPET.asp
https://www.wwf.org.au/news/blogs/the-lifecycle-of-plastics#gs.xnq6tn
Good title. You might have looked for a graphic that featured the plastic material itself rather than a molecular structure. Your explanation of the search for appropriate bacterial digesters is very good and easy to follow. It seems like this idea, while interesting, is a long way from scaling up treating whole landfills. Might have noted that and put in a word for more vigorous recycling efforts. PET is really very recyclable.
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