Bacteria Provide Key to Recycling Durable Plastics

(CN) – Polyurethanes are ubiquitous, composing the material used in many products from microcellular seals to skateboard wheels. One of the reasons the plastic is so popular with material scientists is that it is so durable.

While this is ideal when you’re building elevator parts, a problem emerges when polyurethane parts reach the end of their usefulness and end up in landfills, where they are slow to decompose and often emit dangerous chemicals as they slowly degrade.

They are also stubbornly difficult to recycle.

But a team of German scientists made a recent discovery that could provide a solution to these persistent problems.

In a study published Thursday in the journal Frontiers in Microbiology, researchers reveal they have found a strain of bacteria capable of degrading some of the chemical building blocks of polyurethane.

“The bacteria can use these compounds as a sole source of carbon, nitrogen and energy,” said Dr. Hermann J. Heipieper, a senior scientist at the Helmholtz Centre for Environmental Research-UFZ in Leipzig, Germany, and co-author of the new paper. “This finding represents an important step in being able to reuse hard-to-recycle PU products.”

PU products, or polyurethane products, accounted for 3.5 million tons of waste in Europe alone in 2015, according to the study. The material is found in refrigerators, buildings, footwear and numerous other applications looking for a strong, lightweight and flexible material.

But the material’s strengths also make it hard to recycle or destroy, as it is extremely heat resistant and efforts to melt it down are extremely difficult and energy intensive. Thus, the material has disproportionate representation in landfills around the world and the incremental degradation process releases toxic – and often carcinogenic – chemicals.

Recently, research centering on the use of fungus and bacteria to degrade polymers have yielded promising results. Thursday’s publication represents one of the first studies dedicated primarily to the degradation of polyurethane.

The German scientists concentrated their research on a strain of bacterium called Pseudomonas sp. TDA1. They found the bacterium by scouring a site rich in brittle plastic waste where the promise was shown in attacking some of the chemical building blocks of polyurethane.

After fining the Pseudomonas strain, scientists focused on genetically decoding the strain in a search for the properties that made it particularly effective in degrading brittle plastics. They discovered that the bacteria strip away chemical building blocks from the plastics and metabolize those chemicals to give it the energy it needs to thrive.

The strain is also resistant to stress and other toxic chemicals which situates it to be able to perform the degradation work being studied.

“That trait is also named solvent-tolerance and is one form of extremophilic microorganisms,” said co-author Christian Eberlein, also with the Helmholtz Centre for Environmental Research-UFZ.

The researchers performed the study as part of a broader effort afoot in Europe to identify useful microorganisms capable of converting oil-based plastics into biodegradable material.

The scientific program is called P4SB, which stands for “From Plastic waste to Plastic value using Pseudomonas putida Synthetic Biology.” It is focused on a strain of bacterium called Pseudomonas putida.

Regarding polyurethane degradation, Heipieper said the next step is to drill down on which specific genes in the strain facilitate the destruction of polymer-based polyurethane.

The scientist also said commercialization of the technology is a way off as more studies that investigate the fundamental operations at play in the degradation before industry can make use of bacterium to recycle polyurethane.

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