Research on fungi at the University of Kansas has helped turn hard-to-recycle plastic waste from the Pacific Ocean into key ingredients for the pharmaceutical industry.
The biochemical approach to transform polyethylene uses an everyday soil fungus called Aspergillus nidulans that has been genetically altered. The results were recently reported in the article “Conversion of Polyethylene to Fungal Secondary Metabolites” published in Angwandt KimiJournal of the German Chemical Society.
“What we’ve done in this paper is first digest the polyethylene using oxygen and some metal catalysts — things that aren’t particularly harmful or expensive — and that breaks down the plastic into a diacid,” said co-author Pearl Oakley, Irving S. • Johnson Distinguished Professor of Molecular Biology at Kuwait University.
Then, long chains of carbon atoms from the decomposing plastics were fed to the transgenic Aspergillus fungus. Fungi, as designed, metabolized them into a range of pharmacologically active compounds, including commercially viable crops of asperbenzaldehyde, cytrioperidine and motilene.
Unlike previous methods, Oakley said, the fungi digested the plastic products quickly, like “junk food.”
“What’s different about this approach is that it’s two things – chemical and innate,” he said. “But it’s also relatively fast. With a lot of these tries, the fungus can digest the material, but it takes months because plastic is hard to break down. But this breaks down the plastic quickly. Within a week you can have the finished product.”
The researcher at Kuwait University added that the new approach was “strangely” effective.
“Of the mass of the diacid that goes into the culture, 42% returns as the final compound,” he said. “If our technology was a car, it would run 200 miles an hour, get 60 miles per gallon, and run on recovered cooking oil.”
Oakley previously worked with corresponding author Clay Wang of the University of Southern California to produce about a hundred secondary metabolites from fungi for a variety of purposes.
“It turns out that fungi make a lot of chemical compounds, which are beneficial to fungi in that they inhibit the growth of other organisms — penicillin being the canonical example,” Oakley said. “These compounds are not required for the organism’s growth, but help either protect it from or compete with other organisms.”
For a while, scientists thought they had fully exploited the potential of fungi to produce these compounds. But Oakley said the era of genome sequencing has opened up new possibilities for using secondary metabolites to benefit humanity and the environment.
“There was a realization that there are many, many combinations of genes that make secondary metabolites that no one has discovered — and there are millions of species of fungi,” Oakley said. “A lot of companies have done a good job over the years, but it’s been pretty patchy, because they were just growing things in an incubator and screening them to make new compounds — but 95 percent of the gene pools have been silent since then they’ve only been ‘turned on’.” When needed. They didn’t do anything. So, there are a lot of things to discover.”
KU’s Oakley lab has refined gene-targeting procedures to alter gene expression in Aspergillus nidulans and other fungi, producing new compounds.
“Now we have sequenced the genomes of a group of fungi, and we can identify the fingerprints of gene clusters that make chemical compounds,” he said. “We could change the expression of genes; we could remove them from the genome; we could do all sorts of things to them. We could see that there were a lot of these secondary metabolite gene clusters, and our gene targeting procedures allowed us, at least in principle, to turn on some of those clusters.” .
Co-authored by Oakley, Wang Chris Rabot, Yuhao Chen, Swati Bilani, Ye-Ming Chiang, and Travis Williams of the University of Southern California and Elizabeth Oakley of Kuwait University.
The researchers focused on developing secondary metabolites for the digestion of polyethylene plastics because these plastics are difficult to recycle. For this project, they harvested polyethylene from the Pacific Ocean that was collected at Port Catalina on Santa Catalina Island, California.
“There have been many attempts to recycle plastic, and some of it has been recycled,” Oakley said. “A lot of it is basically melted down and wrapped into fabric and goes into various other plastic things. Polyethylene doesn’t get recycled very much, even though it’s a major plastic.”
The KU investigator said the long-term goal of the research is to develop procedures for breaking down all plastics into products that can be used as food by fungi, eliminating the need to sort them during recycling. He added that the work symbolizes the theme of earth, energy and environment research at Kuwait University, and is directed towards “increasing understanding to help preserve the life of our planet and its inhabitants.”
“I think everyone knows plastic is a problem,” Oakley said. “It accumulates in our environment. There’s a big area in the North Pacific where it tends to accumulate. But you also see plastic bags flying around – they’re in rivers, they’re hanging in trees. The squirrels around my house have even learned to stack their nest with plastic bags. One of the things that’s needed is economical disposal.” of plastic, and if one can make something useful out of it at a reasonable price, that makes it more economically viable.”