Finding, cultivating, and bioengineering organisms that may digest plastic not only aids within the removal of pollution, but is now also big business. Several microorganisms that may do that have already been found, but when their enzymes that make this possible are applied at an industrial scale, they typically only work at temperatures above 30 °C. The heating required implies that industrial applications remain costly up to now, and aren’t carbon-neutral. But there’s a possible solution to this problem: finding specialist cold-adapted microbes whose enzymes work at lower temperatures.
Scientists from the Swiss Federal Institute WSL knew where to search for such micro-organisms: at high altitudes within the Alps of their country, or within the polar regions. Their findings are published in Frontiers in Microbiology.
“Here we show that novel microbial taxa obtained from the ‘plastisphere’ of alpine and arctic soils were capable of break down biodegradable plastics at 15 °C,” said first writer Dr Joel Rüthi, currently a guest scientist at WSL. “These organisms could help to cut back the prices and environmental burden of an enzymatic recycling process for plastic.”
Rüthi and colleagues sampled 19 strains of bacteria and 15 of fungi growing on free-lying or intentionally buried plastic (kept in the bottom for one 12 months) in Greenland, Svalbard, and Switzerland. A lot of the plastic litter from Svalbard had been collected through the Swiss Arctic Project 2018, where students did fieldwork to witness the results of climate change at first hand. The soil from Switzerland had been collected on the summit of the Muot da Barba Peider (2,979 m) and within the valley Val Lavirun, each within the canton Graubünden.
The scientists let the isolated microbes grow as single-strain cultures within the laboratory in darkness and at 15 °C and used molecular techniques to discover them. The outcomes showed that the bacterial strains belonged to 13 genera within the phyla Actinobacteria and Proteobacteria, and the fungi to 10 genera within the phyla Ascomycota and Mucoromycota.
Surprising results
They then used a collection of assays to screen each strain for its ability to digest sterile samples of non-biodegradable polyethylene (PE) and the biodegradable polyester-polyurethane (PUR) in addition to two commercially available biodegradable mixtures of polybutylene adipate terephthalate (PBAT) and polylactic acid (PLA).
Not one of the strains were capable of digest PE, even after 126 days of incubation on these plastics. But 19 (56%) of strains, including 11 fungi and eight bacteria, were capable of digest PUR at 15 °C, while 14 fungi and three bacteria were capable of digest the plastic mixtures of PBAT and PLA. Nuclear Magnetic Resonance (NMR) and a fluorescence-based assay confirmed that these strains were capable of chop up the PBAT and PLA polymers into smaller molecules.
“It was very surprising to us that we found that a big fraction of the tested strains was capable of degrade at the very least certainly one of the tested plastics,” said Rüthi.
The most effective performers were two uncharacterized fungal species within the genera Neodevriesia and Lachnellula: these were capable of digest all the tested plastics except PE. The outcomes also showed that the power to digest plastic relied on the culture medium for many strains, with each strain reacting otherwise to every of 4 media tested.
Side-effect of ability to digest plant polymers
How did the power to digest plastic evolve? Since plastics have only been around for the reason that Fifties, the power to degrade plastic almost definitely wasn’t a trait originally targeted by natural selection.
Microbes have been shown to provide a wide range of polymer-degrading enzymes involved within the break-down of plant cell partitions. Specifically, plant-pathogenic fungi are sometimes reported to biodegrade polyesters, due to their ability to provide cutinases which goal plastic polymers due their resemblance to the plant polymer cutin.”
Dr Beat Frey, Last Writer, Senior Scientist and Group Leader, WSL
Challenges remain
Since Rüthi et al. only tested for digestion at 15 °C, they don’t yet know the optimum temperature at which the enzymes of the successful strains work.
“But we all know that the majority of the tested strains can grow well between 4 °C and 20 °C with an optimum at around 15 °C,” said Frey.
“The subsequent big challenge might be to discover the plastic-degrading enzymes produced by the microbial strains and to optimize the method to acquire large amounts of proteins. As well as, further modification of the enzymes may be needed to optimize properties akin to protein stability”.
Source:
Journal reference:
de Freitas, A. S. et al. (2023). Amazonian dark earths enhance the establishment of tree species in forest ecological restoration. Frontiers in Soil Science. doi.org/10.3389/fsoil.2023.1161627.