Fungi convert polyethylene waste into pharmacologically useful metabolic products
Plastic waste is one of the most significant ecological and economic problems of our time. In the journal Angewandte Chemie,
a research team has now introduced a chemical–biological method for
upcycling polyethylene waste: catalytic cleavage is used to make
carboxylic diacids that are subsequently converted into
pharmacologically useful natural products by genetically engineered
fungi.
© Wiley-VCH, re-use with credit to 'Angewandte Chemie' and a link to the original article.
Plastics are an unavoidable part of our daily lives. Estimates
predict that worldwide production will rise to 1.1 billion tons annually
by 2040. Accordingly, the amount of waste is rising and ending up in
landfills or in the oceans. This waste is increasingly threatening to
our food supply and ecosystems. Polyethylenes (PE) are particularly
problematic. Although they are the most common plastics, there are
limited recycling processes available. The same properties that make PEs
tough and useful hinder their degradation and recycling. One problem is
their hydrocarbon backbone, which has no good “break point” at which to
split the polymer into pieces of defined length. This leads to broad
mixtures of low-value products.
A team led by Travis J. Williams and Clay C. C. Wang at the
University of Southern California (Los Angeles, CA) and Berl Oakley at
the University of Kansas (Lawrence, KS) has now introduced a combined
chemical–biological method to upcycle PE waste into valuable and complex
compounds of pharmacological interest. In the first step, the team
catalytically converts the PE under O2 to make a wide variety
of different carboxylic diacids (hydrocarbon chains with two acid
groups). In a second step, these are “fed” to fungi that make useful
natural products from them. The team was able to demonstrate this using
actual PE waste from the North Pacific gyre.
After the PE is split apart, any short-chain carboxylic diacids must
be separated from the mixture, as they are toxic to the fungi. These can
be used as feedstocks for the synthesis of biodegradable plastics for
agriculture, for example. Longer chain diacids with more than ten carbon
atoms can be used to feed Aspergillus nidulans fungal cultures.
Fungi grow fast, are inexpensive to cultivate, and are already in broad
use for producing drugs, including antibiotics like penicillin. The team
developed a robust strategy to genetically modify the metabolic
pathways of A. nidulans so that the fungus synthesizes the
desired products in high yield. As example substances, they produced
asperbenzaldehyde, citreoviridin, and mutilin natural products that are
starting materials in the search for drugs to treat diseases such as
Alzheimer’s and cancer, or agents against antibiotic resistant bacteria.
With this strategy, a broad palette of additional bioactive substances
could be generated from PE waste.
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About the Author
Dr.Clay C. C. Wang
is the Department Chair and Professor of Pharmacology and Pharmaceutical
Sciences at the Alfred E. Mann School of Pharmacy and Pharmaceutical
Sciences at the University of Southern California. He is also a
Professor of Chemistry at USC. His research program focuses on the
interface of chemistry and biological sciences. His lab has been
studying Aspergillus nidulans as a general host for the production of fungal natural products.
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