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Bad drug, good weedkiller: "Failed" antibiotic repurposed as herbicide

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Just as antibiotic resistance is a problem for human health, herbicide resistance represents a huge problem for the agricultural sector. Researchers have devised a novel strategy to address the issue by repurposing a "failed" antibiotic as a herbicide.

Farmers have a lot to contend with when it comes to protecting their crops: the insects that eat the plants, the microbes that infect leaves, shoots, and roots, and invasive weeds that compete with crops for soil and Sun.

Herbicide options are decreasing because of the spread of herbicide-resistant weeds and understandable legislative bans or restrictions on using existing herbicides due to safety and environmental concerns. These issues, coupled with the fact that there hasn't been a new type of herbicide produced for many years, have led to concerns about the future of sustainable agriculture.

Now, researchers at the University of Adelaide in South Australia have come up with a novel solution.

Effective herbicides - such as the widely used glyphosate - prevent plants from making certain amino acids (proteins) needed for a variety of plant processes, including growth. The researchers understood that a new herbicide had to inhibit the molecular pathway that led to the biosynthesis of the amino acid lysine.

Coincidentally, medical researchers have been focused on developing antibiotics that inhibit lysine biosynthesis over the past three decades. However, most have not entered the market because they've been ineffective against pathogens. But, given the molecular similarity between bacteria and plants, the researchers explored the use of "failed" antibiotics as herbicides.

By modifying the molecular structure of an antibiotic candidate for treating tuberculosis, which failed to move beyond the lab, the researchers found it could block lysine production.

"There are no commercially available herbicides on the market that work in this way," said Andrew Barrow, one of the study's co-authors. "In fact, in the past 40 years, there have been hardly any new herbicides with new mechanisms of action that have entered the market."

Importantly, the researchers say that using failed antibiotics as herbicides won't contribute to antibiotic resistance in humans because they don't kill bacteria and have no effect on human cells.

The researchers are aware of the untapped potential of their discovery.

"The discovery is a potential game changer for the agricultural industry," said Tatiana Soares da Costa, corresponding author of the study. "Many weeds are now resistant to the existing herbicides on the market, costing farmers billions of dollars each year. Using failed antibiotics as herbicides provides a short-cut for faster development of new, more effective weed killers that target damaging and invasive weeds that farmers find hard to control."

And, they say, the discovery might benefit more than farmers; it may lead to the development of weed killers for household use.

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

The study was published in the journal Communications Biology.

Source: University of Adelaide

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