A Failed Antibiotic: The Unexpected Weed Killer of the Future

Scientists at the University of Adelaide have repurposed a failed tuberculosis antibiotic as a potent herbicide capable of tackling two invasive weeds prevalent in Australia without harming human or bacterial cells. This approach, involving structural modifications of the molecule to block weed growth, could revolutionize herbicide development and provide a quicker, more cost-effective solution for farmers and homeowners dealing with weed infestations.

Weed killers of the future could soon be based on failed antibiotics.

A molecule initially devised to combat tuberculosis, despite not making it beyond the lab as an antibiotic, is now displaying potential as a powerful foe against invasive weeds that plague our gardens and cause billions of dollars of annual losses for farmers.

While the failed antibiotic wasn’t fit for its original purpose, scientists at the University of Adelaide discovered that by tweaking its structure, the molecule became effective at killing two of the most problematic weeds in Australia, 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 the existing herbicides on the market, costing farmers billions of dollars each year,” said lead researcher Dr. Tatiana Soares da Costa from the University of Adelaide’s Waite Research Institute.

“Using failed antibiotics as herbicides provides a shortcut for faster development of new, more effective weed killers that target damaging and invasive weeds that farmers find hard to control.”

Researchers at the University’s Herbicide and Antibiotic Innovation Lab discovered there were similarities between bacterial superbugs and weeds at a molecular level.

(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, they were able to block the production of the amino acid lysine, which is essential for weed growth.

“There are no commercially available herbicides on the market that work in this way. In fact, in the past 40 years, there have been hardly any new herbicides with new mechanisms of action that have entered the market,” said Dr. Andrew Barrow, a postdoctoral researcher in Dr. Soares da Costa’s team at the University of Adelaide’s Waite Research Institute.

It’s estimated that weeds cost the Australian agriculture industry more than $5 billion each year.

Annual ryegrass in particular is one of the most serious and costly weeds in southern Australia.

“The short-cut strategy saves valuable time and resources, and therefore could expedite the commercialization of much-needed new herbicides,” said Dr. Soares da Costa.

“It’s also important to note that using failed antibiotics won’t drive antibiotic resistance because the herbicidal molecules we discovered don’t kill bacteria. They specifically target weeds, with no effects on human cells,” she 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 weed killers to target pesky weeds growing in our backyards and driveways.

“Our re-purposing approach has the potential to discover herbicides with broad applications that can kill a variety of weeds,” said Dr Barrow.

Dr. Tatiana Soares da Costa and her team are now looking at discovering more herbicidal molecules by re-purposing other failed antibiotics and partnering up with the industry to introduce new and safe herbicides to the market.

Reference: “Repurposed inhibitor of bacterial dihydrodipicolinate reductase exhibits effective herbicidal activity” by Emily R. R. Mackie, Andrew S. Barrow, Marie-Claire Giel, Mark D. Hulett, Anthony R. Gendall, Santosh Panjikar, and Tatiana P. Soares da Costa, 22 May 2023, Communications Biology.
DOI: 10.1038/s42003-023-04895-y

Funding for this research was provided by the Australian Research Council through a DECRA Fellowship and a Discovery Project awarded to Dr. Tatiana Soares da Costa.

The first author on the paper is Emily Mackie, a PhD student in Dr Soares da Costa’s team, who is supported by scholarships from the Grains and Research Development Corporation and 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 that builds capacity for Australia’s agriculture, food, and wine sectors.

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