One of the engines of economic development in the second half of the last century was plastics. They are cheap, easy to produce, resistant, elastic and, if loose, transparent, but they have a b-side, since they are not biodegradable, since there is no living organism capable of feeding on them.
Their long durability is, without a doubt, one of the great challenges we face, since a minimum of four hundred and fifty years must pass for polymers to begin the process of disintegration at the molecular level.
It is estimated that more than 300 million tons of plastic are produced globally, of which 90% derives from oil and a small part, approximately 15%, will be recovered and recovered on a global scale.
Of that astronomical amount, an average of eight million tons end up floating every year in our oceans, where they sink, accumulate in the sediments or end up being incorporated into the human food chain.
Short-term predictions are not at all rosy, some authoritative voices estimate that by 2050 the production of plastic waste will reach thirteen billion tons. A figure that, without a doubt, forces us to take energetic and urgent measures.
Thanks in 2016 we discovered the existence of a possible ally and, as has happened so many times in the history of science, serendipity played an important role. This year a group of Japanese scientists investigated bacterial colonies at a recycling plant in the city of Sakai, Japan. During this period we analyzed the bacteria extracted from the polyethylene terephthalate (PET) residues in addition to the component (ethylene glycol and terephthalic acid).
Surprised, they discovered that a bacterium, which was named Ideonella sakaiensis, was capable of using PET as a primary carbon source. Some time later it was possible to show that the microorganism has two key genes that can 'devour' PET: a PETase and a mono(2-hiroexieethyl) terephthalate hydrolase.
A hopeful solution
The discovery of the metabolic chain made it possible to explain why Ideonella has established its residence in a recycling plant, but what remains to be unraveled is what has been the path for the bacterium to have evolved to convert a plastic, which was patented in the decade of the forties of the last century, in its food source.
The bacterium is capable of converting PET into poly(3-hydroxybutyrate) – also known as PHB – which is a type of biodegradable plastic. The appeal of this story is that PET is estimated to degrade at a rate of 0,13mg per square centimeter per day, at a temperature of 30ºC, a rate of elimination that becomes 'exceedingly slow'.
Luck smiled on us again in 2018 when researchers at Postmouth University (UK) accidentally designed an enzyme that enhanced bacterial PETase.
At this time, it has been tried to take a further step to amplify its productivity by 'inserting' the mutant enzyme into an extremophile bacterium, capable of withstanding temperatures above 70ºC, a figure where PET is more viscous. This 'transfer' could speed up the degradation process by up to 10%.
All these findings could give us a break and open a window of hope, since the bacteria 'devours plastics' would be part of the solution to the environmental problem caused by plastics.
Mr Jara
Pedro Gargantilla is an internist at El Escorial Hospital (Madrid) and the author of several popular books.
