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  • At this very moment, almost everything around you is being eaten.

  • Invisible to the naked eye, organisms called microbes swarm every surface.

  • Hordes of bacteria, archaea, and fungi have evolved to produce powerful enzymes that break down tough organic material into digestible nutrients.

  • But there's one particularly widespread type of material that almost no microbes can biodegrade: plastics.

  • To make most plastics, molecules from oil, gas and coal are refined

  • and turned into long, repeating chains called polymers.

  • This process often requires temperatures above 100˚C, incredibly high pressure,

  • and various chemical modifications.

  • The resulting man-made polymers are quite different

  • from the polymers found in nature.

  • And since they've only been around since the 1950s,

  • most microbes haven't had time to evolve enzymes to digest them.

  • Making matters even more difficult,

  • breaking most plastics' chemical bonds requires high temperatures

  • comparable to those used to create them

  • and such heat is deadly to most microbes.

  • This means that most plastics never biologically degrade

  • they just turn into countless, tiny, indigestible pieces.

  • And pieces from the most common plastics like Polyethylene, Polypropylene,

  • and Polyester-terephthalate have been piling up for decades.

  • Each year humanity produces roughly 400 million more tons of plastic,

  • 80% of which is discarded as trash.

  • Of that plastic waste, only 10% is recycled.

  • 60% gets incinerated or goes into the landfills,

  • and 30% leaks out into the environment

  • where it will pollute natural ecosystems for centuries.

  • An estimated 10 million tons of plastic waste end up in the ocean each year,

  • mostly in the form of microplastic fragments that pollute the food chain.

  • Fortunately, there are microbes that may be able

  • to take a bite out of this growing problem.

  • In 2016, a team of Japanese researchers sampling sludge

  • at a plastic-bottle recycling plant discovered

  • Ideonella sakaiensis 201-F6.

  • This never-before-identified bacterium contained two enzymes

  • capable of slowly breaking down PET polymers

  • at relatively low temperatures.

  • Researchers isolated the genes coding for these plastic-digesting enzymes,

  • allowing other bioengineers to combine and improve the pair

  • creating super-enzymes that could break down PET up to 6 times faster.

  • Even with this boost,

  • these lab-grown enzymes still took weeks to degrade a thin film of PET,

  • and they operated best at temperatures below 40˚C.

  • However, another group of scientists in Japan had been researching

  • bacterial enzymes adapted to high temperature environments

  • like compost piles.

  • And within one particularly warm pile of rotting leaves and branches,

  • they found gene sequences for powerful degrading enzymes

  • known as Leaf Branch Compost Cutinases.

  • Using fast-growing microorganisms,

  • other researchers were able to genetically engineer

  • high quantities of these enzymes.

  • They then enhanced and selected special variants of the Cutinases

  • that could degrade PET plastic in environments reaching 70˚C—

  • a high temperature that can weaken PET polymers and make them digestible.

  • With the help of these and other tiny diehards,

  • the future of PET recycling looks promising.

  • But PET is just one type of plastic.

  • We still need ways to biologically degrade all the other types,

  • including abundant PEs and PPs

  • which only begin breaking down at temperatures well above 130˚C.

  • Researchers don't currently know of any microbes or enzymes

  • tough enough to tolerate such temperatures.

  • So for now, the main way we deal with these plastics

  • is through energy-intensive physical and chemical processes.

  • Today only a small fraction of plasticwaste

  • can be biologically degraded by microbes.

  • Researchers are looking for more heat-tolerant plastivores

  • in the planet's most hostile environments

  • and engineering better plastivorous enzymes in the lab.

  • But we can't rely solely on these tiny helpers to clean up our enormous mess.

  • We need to completely rethink our relationship with plastics,

  • make better use of existing plastics,

  • and stopproducing more of the same.

  • And we urgently need to design more environmentally friendly types of polymers

  • that our growing entourage of plastivores can easily break down.

At this very moment, almost everything around you is being eaten.

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B2 US TED-Ed plastic waste chemical compost breaking recycling

Meet the microbes that could eat your trash - Tierney Thys and Christian Sardet

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    たらこ posted on 2022/06/23
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