Another round of microbes versus plastic

Scientists continue in the quest to conscript microbes in the battle against burgeoning plastic waste.

Cosmos has reported previously on research focussing on the well-known polyethylene terephthalate (PET) plastics used in drink bottles.

Now a German team says it has identified and characterised a strain of bacteria capable of degrading some of the chemical building blocks of the equally prolific and problematic polyurethane.

Writing in the journal Frontiers in Microbiology, the researchers describe a strain of an extremophile group of bacteria that is capable of ingesting toxic organic compounds as its sole source of carbon, nitrogen and energy.

They stress, however, that the work is preliminary, with more knowledge needed before commercial developments are possible. 

Led by the Helmholtz Centre for Environmental Research in Leipzig, the project is part of the European Union program P4SB (From Plastic waste to Plastic value using Pseudomonas putida Synthetic Biology), which is attempting to find useful microorganisms that can bioconvert oil-based plastics into fully biodegradable ones.

In this case, the researchers isolated a bacterium, Pseudomonas sp. TDA1, from a site rich in brittle plastic waste that shows promise in attacking some of the chemical bonds that make up polyurethane plastics.

They performed a genomic analysis to identify the degradation pathways at work, making preliminary discoveries about the factors that help the microbe metabolise certain chemical compounds in plastic for energy. 

They also conducted other analyses and experiments to understand the bacterium’s capabilities.

Co-author Christian Eberlein says this strain is part of a group of bacteria well known for their tolerance of toxic organic compounds and other forms of stress. “That trait is also named solvent-tolerance and is one form of extremophilic microorganisms,” he says.

Colleague and corresponding author Hermann J Heipieper says the next step in any future research would be to identify the genes that code for the extracellular enzymes that are capable of breaking down certain chemical compounds in polyester-based polyurethanes. 

Extracellular enzymes, also called exoenzymes, are proteins secreted outside of a cell that cause a biochemical reaction.

The potential is to engineer these or other enzymes using synthetic biology techniques for bioplastic production. That could involve, for instance, genetically converting the bacteria into mini-factories capable of transforming oil-based chemical compounds into biodegradable ones for planet-friendly plastics.

Polyurethane, which accounted for 3.5 million tonnes of the plastic produced in Europe in 2015, is difficult and energy-intensive to recycle or destroy because is usually does not melt when heated.