The polar microbes that could save the planet from plastic

Although millions of households around the world conscientiously separate plastic and store it separately in their waste, current recycling systems have now clearly failed. In the world, recycling is estimated at 9 percent of the total; in the USA, this percentage is about 5 percent, and is decreasing, due both to the fact that plastic sent to China was previously counted as “recycled”, and to the decrease in the cost of virgin plastic obtained from hydrocarbons and of the increase in production.

To make the picture worse, data derived from a very recent study have been added: the recycling process, which involves extensive washing of plastic waste, is actually responsible for releasing huge quantities of microplastics into the environment, which also filters through the water purification systems of the plants; although it is possible to think of filtering systems capable of breaking down even microplastics, this would make the process even more uneconomical, probably further affecting the decrease in the total recycled percentage.

As a result, new ways need to be found, to avoid turning the planet into an even more dumping ground than we already have.
One of the most promising directions of research consists in making plastics biodegradable, not, however, by creating new types of plastics, but by identifying and cultivating microorganisms capable of degrading current plastics. Finding, cultivating, and engineering organisms that can digest plastic not only helps remove pollution, it’s now big business, too. Several microorganisms capable of doing this have already been found, but when their enzymes that make it possible are applied on an industrial scale, they typically only work at temperatures above 30°C. The need to maintain such a constant temperature makes the process energetically and financially onerous, but there is a possible solution: to find microbes adapted to colder environments, whose enzymes are able to operate at lower temperatures.

Now, a team of Swiss researchers has managed to identify just this type of microbe in the Alps and in some polar regions. The researchers sampled 19 strains of bacteria and 15 of fungi that had grown on loose or intentionally buried plastic (kept in soil for a year) in Greenland, Svalbard and Switzerland. Individual microbial cells were then isolated and allowed to grow as pure cultures in the laboratory in the dark at 15°C. Once the genomes of the strains grown were examined, 13 different genera were identified in the phyla Actinobacteria and Proteobacteria and 10 genera of microscopic fungi in the phyla Ascomycota and Mucoromycota.

Each type of microorganism was then tested for its ability to digest sterile samples of non-biodegradable polyethylene (PE) and biodegradable polyester-polyurethane (PUR), as well as two commercially available biodegradable blends of polybutylene adipate terephthalate (PBAT) and polylactic acid ( PLA); these are common plastic polymers, present in an enormous variety of commonly used objects and packaging.

So far, no strains capable of digesting polyethylene have been identified, but 11 types of fungi and 8 of bacteria were able to digest PUR at 15°C, while 14 types of fungi and 3 of bacteria were able to degrade the plastic mixtures of PBAT and PLA: the digestion capacities depended on the culture medium used, indicating how they constituted a nutritional adaptation dependent on the energy sources available for the microbes. In particular, two as yet uncharacterized species belonging to the fungal genera Neodevriesia and Lachnellula have been shown to digest every type of plastic tested, except polyethylene.

These promising initial results open up a number of future possibilities: first of all, we will try to identify the microbial enzymes responsible for the measured degradative activities. This will allow both their direct use and above all the engineering of more manageable and therefore more easily industrialized microbes.

Moreover, it will be possible to try to optimize the enzymes themselves from the point of view of the optimal temperature required for their work: today, they are active between 4 and 20°C, with an optimum at 15°C, but their engineering could bring the optimal room temperature. Contrary to the economic failure that the current plastic recycling strategy has encountered, plastic-eating microorganisms and their enzymes also seem promising for the market: it is worth recalling some examples in this sense here.

As of April 2021, Carbios has developed an agreement with Michelin to develop fully recyclable tyres, exploiting microbial enzymes potentially capable of completely degrading them. Carbios itself, in June 2021, following an agreement previously made with L’Oréal, Nestlé, PepsiCo and other companies, announced the production of the first plastic bottles for food use, entirely biodegradable from its own battery of microbial enzymes.

In October 2021, researchers from the National Renewable Energy Laboratory of the USA have announced the development of a bacterium capable of degrading polyethylene into useful material to produce a type of high-performance nylon.

In November 2022, SeedLab entered into an agreement with MIT, Harvard University and other prestigious institutions, to carry out experiments on their microbes capable of degrading plastic. If, in the end, we manage to have systems for biodegrading plastic available on an industrial scale, then the differentiation and recycling process can become effective and economical, with the advantage that, using microbes, not even microplastics will escape; but for this to happen, as always, the main road is solid scientific research, even in our country.