The increase in the production of plastics and the mismanagement of their waste is one of the most important environmental problems of this century. In addition to the essential reduction, reuse and recycling measures, in recent years progress has been made in the knowledge and possible future use of living organisms (microbes, fungi, worms) capable of degrading some of the synthetic plastics produced by humans.
The most recent advance in this field has been presented in an article by Swiss researchers published this May in the journal Frontiers in Microbiology. The authors of this research have discovered in the subsoil of the Alps and the Arctic a total of 34 strains (varieties) capable of degrading various types of plastics, that is, something similar to microbes that eat or digest plastic waste.
This is not the first time that microorganisms with this degrading capacity have been discovered, but in this case, the novelty is that they are strains adapted to relatively low temperature conditions (most of the varieties known up to now do not act against plastics at less than 20°C).
"Temperature is a crucial parameter affecting biodegradation rates, but until now microbial degradation of plastic has been studied mainly at temperatures above 20°C. In the now-published study we isolated 34 microbial strains adapted to habitual soil temperatures. alpine and arctic; as well as in laboratory tests capable of degrading plastics", expose the summary of results of this work whose first signatory is Joel Rüthi, from the Swiss Federal Institute for Forestry, Snow and Landscape Research WSL, in Birmensdorf (Switzerland) and the Swiss Federal Institute of Technology ETH, Zurich (Switzerland).
The study now published in Frontiers in Microbiology shows that "new microbial taxa obtained from the plastisphere of alpine and arctic soils were able to decompose biodegradable plastics at 15°C," Joel Rüthi detailed, "These organisms could help reduce costs and the environmental burden of an enzymatic plastic recycling process".
The study author team sampled 19 strains of bacteria and 15 fungi that grow in loose plastic or intentionally buried (kept in the ground for a year) in Greenland, Svalbard and Switzerland.
The scientists allowed the isolated microbes to grow as single-strain cultures in the laboratory in the dark at 15°C, and used molecular techniques to identify them. The results showed that the bacterial strains belonged to 13 genera in the Actinobacteria and Proteobacteria phyla, and the fungi to 10 genera in the Ascomycota and Mucoromycota phyla.
Following initial isolation, the authors used a suite of assays to assess each strain for its ability to digest sterile samples of non-biodegradable polyethylene (PE) and biodegradable polyester-polyurethane (PUR), as well as two commercially available biodegradable mixtures of adipate terephthalate. of polybutylene (PBAT) and polylactic acid (PLA).
None of the strains could digest the PE, even after 126 days of incubation on these plastics. But 19 (56%) of the strains, including 11 fungi and eight bacteria, were able to digest PUR at 15°C, while 14 fungi and three bacteria were able to digest PBAT and PLA plastic mixtures. Nuclear magnetic resonance (NMR) and a fluorescence-based assay confirmed that these strains could cut PBAT and PLA polymers into smaller molecules.
"It was very surprising for us to find that a large fraction of the tested strains were able to degrade at least one of the tested plastics," Rüthi said.
The best results were two uncharacterized fungal species from the genera Neodevriesia and Lachnellula: these were able to digest all plastics tested except PE. The results also showed that the ability to digest plastic was dependent on the culture medium for most of the strains, with each strain reacting differently to each of the four media tested.
