A failed antibiotic: the unexpected herbicide of the future

Pull weeds

Scientists at the University of Adelaide have repurposed a failed TB antibiotic as a powerful herbicide that can tackle two invasive weeds prevalent in Australia without harming human or bacterial cells. This approach, which involves structural modifications of the molecule to stop weed growth, could revolutionize herbicide development and provide a faster and more cost-effective solution for farmers and homeowners dealing with weed infestations.

The herbicides of the future may soon be based on failed antibiotics.

A molecule originally designed to fight tuberculosis, despite failing to push the limits of the laboratory as an antibiotic, is now showing potential as a potent enemy against the invasive weeds that plague our gardens and cause billions of dollars in annual losses for farmers.

Although the failed antibiotic was not suited to its original purpose, scientists at the University of Adelaide found that by modifying its structure, the molecule became effective at killing two of Australia’s most problematic weeds, annual ryegrass and wild radish, without harming bacterial and human cells.

This discovery is a potential game changer for the agricultural industry. Many weeds are now resistant to existing herbicides on the market, which cost farmers billions of dollars each year, said lead researcher Dr. Tatiana Soares da Costa of the University of Adelaides Waite Research Institute.

The use of failed antibiotics as herbicides provides a shortcut to faster development of new, more effective herbicides that target harmful and invasive weeds that farmers find difficult to control.

Researchers at the university’s Herbicide and Antibiotic Innovation Lab found that there were similarities between bacterial superbugs and weeds at the molecular level.

Emily Mackie, Andrew Barrow and Tatiana Soares da Costa

(From left) Emily Mackie, Dr. Andrew Barrow and Dr. Tatiana Soares da Costa. Credit: University of Adelaide

They exploited these similarities and, by chemically modifying the structure of a failed antibiotic, succeeded in blocking the production of the amino acid lysine, which is essential for weed growth.

There are no commercially available herbicides on the market that work this way. In fact, over the past 40 years, there have been almost no new herbicides with novel mechanisms of action that have entered the market, said Dr. Andrew Barrow, postdoctoral researcher in Dr. Soares da Costas at the University of Adelaides Waite Research Institute.

Weeds are estimated to cost the Australian agricultural industry more than $5 billion a year.

Annual ryegrass in particular is one of South Australia’s most serious and costly weeds.

The shortcut strategy saves valuable time and resources and thus could accelerate the commercialization of much-needed new herbicides, said Dr. Soares da Costa.

It is also important to note that the use of failed antibiotics will not lead to antibiotic resistance because the herbicidal molecules we have discovered do not kill bacteria. They specifically target weeds, with no effect on human cells, he said.

It’s not just farmers who could reap the benefits of this discovery. Researchers say it could also lead to the development of new herbicides to target the pesky weeds growing in our patios and driveways.

Our repurposing approach has the potential to uncover herbicides with broad applications that can kill a variety of weeds, Dr Barrow said.

Dr. Tatiana Soares da Costa and her team are now trying to discover more herbicidal molecules by repurposing other failed antibiotics and collaborating with industry to bring new and safe herbicides to market.

Reference: Reproposed Bacterial Dihydrodipicolinate Reductase Inhibitor Shows Effective Herbicidal Activity By Emily R. Mackie, Andrew S. Barrow, Marie-Claire Giel, Mark D. Hulett, Anthony R. Gendall, Santosh Panjikar, and Tatiana P. Soares da Costa, May 22, 2023, Communication biology.
DOI: 10.1038/s42003-023-04895-y

Funding for this research was provided by the Australian Research Council through a DECRA grant and discovery project awarded to Dr Tatiana Soares da Costa.

The first author of the paper is Emily Mackie, a doctoral student on Dr. Soares da Costas’ team, who is supported by grants from the Grains and Research Development Corporation and the Research Training Program. Co-authors include Dr Andrew Barrow, Dr Marie-Claire Giel, Dr Anthony Gendall and Dr Santosh Panjikar.

The Waite Research Institute stimulates and supports research and innovation across the University of Adelaide and its partners building capacity for Australia’s agriculture, food and wine sectors.

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