By using a soil fungus called Aspergillus nidulans, a team of researchers from the University of Kansas (KU) has recently managed to transform hard to recycle plastic waste from the Pacific Ocean into key components for designing pharmaceutics.
“What we’ve done in this paper is to first digest polyethylenes using oxygen and some metal catalysts – things that are not particularly harmful or expensive – and this breaks the plastics into diacids,” explained study co-author Berl Oakley, a professor of Molecular Biology at KU.
In a second step, long chains of carbon atoms resulting from the decomposed plastics were fed to genetically modified Aspergillus fungi, which metabolized them into a variety of pharmaceutically active compounds, including asperbenzaldehyde, citreoviridin, and mutilin.
Unlike in previous attempts, the fungi managed to digest the plastic products very quickly. “The thing that’s different about this approach is it’s two things – it’s chemical, and it’s fungal. But it’s also relatively fast. With a lot of these attempts, the fungus can digest the material, but it takes months because the plastics are so hard to break down. But this breaks the plastics down fast. Within a week you can have the final product,” Oakley said.
Although Oakley and his team have worked for years to produce about a hundred of secondary metabolites of fungi for various purposes, advances in genome sequencing have now unlocked new possibilities.
“There was a realization there were lots and lots of clusters of genes that made secondary metabolites that nobody had discovered – and there are millions of species of fungi. A lot of companies have done good work over the years, but it was very much incomplete, because they were just growing things in the incubator and examining them for production of new compounds – but 95 percent of the gene clusters were just silent since they are not ‘turned on’ until needed. They weren’t doing anything. So, there are lots more things to discover,” Oakley explained.
By sequencing the genomes of a variety of fungi, the scientists are now able to recognize the signatures of gene clusters that make chemical compounds, and change the expression of these genes, or even remove them from the genome, in order to increase the productivity of the fungi. After focusing on polyethylenes from the Pacific Ocean in the present study, the researchers aim to develop future procedures to break down all plastics into products that can be used as food for fungi, in order to eliminate the need to sort them during recycling.
“I think everybody knows that plastics are a problem. They’re accumulating in our environment. There’s a big area in the North Pacific where they tend to accumulate. But you also see plastic bags blowing around – they’re in the rivers and stuck in the trees. The squirrels around my house have even learned to line their nest with plastic bags. One thing that’s needed is to somehow get rid of the plastic economically, and if one can make something useful from it at a reasonable price, then that makes it more economically viable,” Oakley concluded.
The study is published in the journal Angewandte Chemie.
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