How do the bacteria that eat plastic work? A chemist explains

Scientists have recently discovered a strain of bacteria that can actually eat the plastic used to make bottles, and have even improved it to speed up the process

By Emily Fleshman, Research Fellow in Enzyology, University of Oxford

The plastic bottles we throw away today will survive for hundreds of years. This is one of the main reasons why the problem of plastic pollution, which has a deadly effect on marine life, is so serious.

However, scientists recently discovered a strain of bacteria that can actually eat the plastic used to make bottles, and even improved them to speed up the process. True, the effects are still modest - it's not a complete solution to plastic pollution - but the discovery shows how bacteria can help create more environmentally friendly recycling.

Plastics are complex polymers, i.e. long. These are repeated chains of molecules that do not dissolve in water. The strength of these molecular networks makes plastic durable and means that it takes a long time to break down naturally. If they could be broken down into their small, soluble chemical units, these building blocks could be “harvested and recycled to create new plastics in a closed system.

In 2016, scientists from Japan tested different bacteria in a bottle recycling plant and found that Ideonella sakaiensis 201-F6 could digest the plastic used to make single-use beverage bottles, polyethylene terephthalate (PET). The bacterium secretes an enzyme (a type of protein that can catalyze chemical reactions) known as PETase. This enzyme splits certain chemical bonds (esters) in PET, leaving at the end of the process smaller molecules that the bacteria can absorb, turning their carbon into food.

Although enzymes from other bacteria that know how to digest PET slowly were already known, the new enzyme was apparently developed specifically for this purpose. It may be cheaper and more efficient and therefore has the potential to be used for biological recycling of plastics.

As a result, several teams are trying to understand exactly how PETase works by studying its structure. In the last 12 months, groups from Korea, China, Great Britain, the USA and Brazil have published all their works showing the structure of the enzyme in high resolution and analyzing its mechanisms.

These documents show that part of the PETase protein that performs the chemical digestion is physically adapted to adhere to PET surfaces at a temperature of 30 degrees Celsius. Both teams also showed that by subtly changing the chemical properties of the enzyme it is able to react with PET surfaces much faster than natural PETase.

The use of bacterial enzymes in biological reactors to break down plastic for its recycling is still not simple because the physical properties of plastic make the enzyme's reactions with it difficult.

The PET used in beverage bottles has a semi-crystalline structure, meaning the plastic molecules are dense and difficult for the enzyme to penetrate. The latest research shows that the improved enzyme probably worked well because the part of the molecule involved in the reactions is very accessible, making it easy for the enzyme to attack even buried PET molecules.

modest improvements

The improvements in PETase activity have not been dramatic, and we are still far from solving our plastic crisis. But this research helps us to understand how this enzyme promises to break the PET molecules and we got hints how we can make it work faster by manipulating the active parts of the enzyme.

Engineering enzymes so that they work better than they do in nature is a rare feat. Perhaps this is because the bacteria that use PETase have only recently evolved to live off man-made plastic. The process could give scientists an exciting opportunity to bypass evolution by engineering more optimal forms of PETase.

But there is one concern. While the use of such bacteria in bioreactors is expected to be controlled, the fact that bacteria's ability to consume plastic in the first place suggests that this material on which we rely widely - plastic, is not as durable as we thought. If more bacteria start eating plastic in nature, products and structures designed to survive for many years will be in danger. . The plastics industry will face the serious challenge of preventing the contamination of its products by hungry microorganisms.

The lessons from antibiotics teach us that we have difficulty eliminating bacteria, but perhaps such studies will give us an advantage over them.

For the original article on THE CONVERSATION website

More of the topic in Hayadan:

• Can caterpillars that eat plastic save the world?
• Where does our plastic go?
• where is the plastic
• The microscopic plastic: a danger to the beaches and to life, especially in the sea