Let’s go back to the early 21th century, more precisely to 2001 in Japan. A group of scientists, led by Kohei Oda, professor at the Kyoto Institute of Technology (KIT), found a little bacterium that was breaking down plastic to make energy to survive. Oda used to study bacteria given that his research philosophy says that when humans try to find a solution, the bacteria probably already have one.
This amazing finding was put apart. The reason that the plastic global issue wasn’t that critical at that time is that (the term microplastic wasn’t used yet). In 2016, scientists “re-opened” the research program based on plastic-vore bacteria. The discovered bacterium was Ideonella sakaiensis (fun fact: the name comes from the recycling plant based in Sakai, Japan). Ideonella sakaiensis is capable to “eat” one of the most common types of plastic used for the production of water bottles and of packages: polyethylene terephthalate, the so-called PET.
Earlier I used the term “eat” plastic. You will probably understand it’s not scientifically
accurate. Ideonella sakaiensis breaks down PET.

PET is formed by chains of C10H8O4 molecules (ten atoms of carbon, 8 atoms of hydrogen and 4 atoms of oxygen). The polyethylene terephthalate is a so-called monomer. A monomer is a simple based molecule which has the capability of combining itself with other molecules with the objective of creating a macromolecule (A molecule of a high relative molecular mass). A monomer chain forms a polymer. All plastics are polymers (but not all polymers are plastics).

Monomer of polyethylene terephthalate (PET)

Polymers are useful as the links of the monomer are so strong that at human scale that it’s
nearly impossible to tear apart a plastic-made container. Polymer’s strength is due to the high relative molecular mass. The more a polymer is “heavy” the more its strength will be important.
When you see that plastic remains intact for quite a long period of time, it’s not due to the fact that “plastic is a bad material” but that it’s obviously the polymer’s strength. So, when we talk about biodegradability as the physician P. Goswami said, we talk about “the ability of a material to decompose after interactions with biological elements” right after he affirms that “many plastics are highly stable and are slower to biodegrade”.

Now let’s go back to Ideonella sakaiensis, because we have to understand how it breaks
down the monomer’s links and so split and divide polymers.
Bacteria, like humans and living beings use enzymes to help and accelerate the cell’s work. For example, humans have plenty of different enzymes to help their body during the digestion (enzymes are specific to molecules, so an enzyme that divide complex carbohydrates (amylase), cannot break-down fats (lipase)). Ideonella sakaiensis has an enzyme (PETase) capable of breaking down PET polymers to take the carbon molecules and receive energy.

Ideonella sakaiensis on the left and degraded remains of plastic broken down by PETase and his host (Ideonella sakaiensis)

There are some issues with PETvore to; the main disadvantage with the use of PETase is that these enzymes (there isn’t just one enzyme as other bacteria, with obviously other enzymes, were found) work very slowly. Scientists are working to accelerate these digestion times drastically to try global applications. In fact, Prof John McGeehan, at the University of Portsmouth and his team have created a super-enzyme that works 6 times faster than the others. Secondly, like living beings, Ideonella sakaiensis produces waste after digestion: what before digestion was a polymer, becomes plastic a monomer. Luckily this waste can be recycled and transformed into new plastic. The temperature issue is also being solved.

In conclusion, scientists have found a complete natural way to break-down plastic polymers and in certain cases recycle them. As they are a brand-new research and development fields, scale, temperature, speed, economical and logistical issues have to be worked out by scientists and economists. The global community looks forward to see if with these microscale living beings, planet-scale climate crisis can be stopped or slowed.