From plastic to protein: Could we eventually eat PET-eating microbes?
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There are microbes that look at a plastic bottle and go, “Yum”. Do you think you’d ever look at a protein powder made from those microbe and go “Yum” too?
Researchers at Michigan Technological University are looking to turn plastic into protein, with funding from the US Defence Advanced Research Projects Agency, or DARPA. In 2023, they described their process in a paper published in the journal Trends in Biotechnology.
So far, in a lab, the plastic has been converted into an oil-like compound using heat to deconstruct the polymer chains. This compound is then fed to oil-eating bacteria, which leave behind a sludge that resembles a yeast byproduct. This sludge is dried out and turned into an edible powder.
Achieving scale should be as simple as putting plastic in at one end and getting powder out of the other, Stephen Techtmann, an assistant professor of biological sciences who is leading the project, has said in a statement.
Eventually, he hopes it could go from food to survive on, in times of disaster and scarcity, to food to thrive on.
It has, after all, been just eight years since plastic-eating microbes were first discovered, in Japan.
In 2016, researchers from the Kyoto Institute of Technology and Keio University, in Japan, published a paper in the journal Science on Ideonella sakaiensis, a rod-shaped bacteria that they had found feeding on polyethylene terephthalate or PET at a bottle recycling plant.
It was a revolutionary find — the first evidence that bacteria could digest our artificial polymers made from oil, gas and coal. “It seems bacteria evolved to be able to degrade plastic in response to the growing presence of plastic in the environment,” says Ronan McCarthy, a professor of biomedical sciences at Brunel University, London.
Except, I. sakaiensis worked slowly, taking up to six weeks to completely break down PET.
This kickstarted research into microbes and their plastic-digesting enzymes. Bioengineers began to manipulate microbes and isolate the responsible enzymes, then engineer the microbes to speed the process up.
By 2018, an international team of researchers led by John McGeehan of the University of Portsmouth linked the two enzymes from I. sakaensis, and speeded the process up further, to just a few days.
New strains were found. In 2020, French biotech startup Carbios announced the creation of a new supercharged bacterial enzyme that could break down plastic bottles in under 10 hours. The original enzyme used to do this was discovered in a heap of composting leaves.
Around the same time, McCarthy of Brunel University, noticed the some of the waste that had washed up on a beach in England was covered with slime. He took samples and found that these were communities of bacteria that were using plastic as a source of carbon.
His lab worked to engineer that Pseudomonas stutzeri strain of bacteria, which were not previously known to consume plastic, and manipulated it to attach to plastic by creating a biofilm around it.
He published his findings in in the journal NPJ Biofilms and Microbiomes, in 2023.
Meanwhile, Carbios set up an industrial demonstration plant in 2021 and has partnered with big plastic producers such as PepsiCo, Nestle Waters and L’Oreal to bio-recycle PET plastic.
In 2022, Epoch Biodesign, started by scientists from the University of Oxford, received $11 million in seed funding, to develop their microbial strains that could break down detergents, plastics, textiles, industrial chemicals and cosmetics.
Eventually, McCarthy says, the engineered bacteria and super-enzymes could just be deployed directly onto polluted sites. “There is always the risk of uncontrolled spread of these bacteria,” he says. “However this can be mitigated by careful design, for example, by programming the bacteria to only survive for a certain amount of time or within a specific controlled environment.”
