A failed antibiotic could be given new life as a weed killer.

A molecule originally developed as an antibiotic for tuberculosis, but never advanced beyond the lab, is now being put forth as a potential breakthrough in combating invasive weeds that wreak havoc in gardens and cost farmers billions of dollars annually.

Researchers at the University of Adelaide have discovered that by modifying the structure of the failed antibiotic, they could effectively eliminate two of Australia's most troublesome weeds, annual ryegrass and wild radish. 

Remarkably, the modified molecule proved lethal to weeds while sparing bacterial and human cells.

Dr Tatiana Soares da Costa, lead researcher at the University of Adelaide's Waite Research Institute, expressed her excitement, saying; “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.” 

“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,” she added.

The Herbicide and Antibiotic Innovation Lab at the University of Adelaide exploited molecular similarities between bacterial superbugs and weeds. 

By chemically modifying the failed antibiotic, they successfully obstructed the production of lysine, an essential amino acid for weed growth.

Dr Andrew Barrow, a postdoctoral researcher in Dr Soares da Costa's team, highlighted the significance of this breakthrough, saying; “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”.

Weeds cost the Australian agriculture industry over $5 billion annually, making this discovery all the more valuable. 

The troublesome annual ryegrass, in particular, poses a serious and costly threat in southern Australia.

Dr Soares da Costa said that the re-purposing approach not only saves time and resources but also eliminates concerns about antibiotic resistance. 

“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. 

The potential benefits of the findings extend beyond farmers. Researchers believe it could lead to the development of new weed killers to tackle unwelcome growth in residential areas.

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

The findings of this research have been published in the journal Communications Biology.

Dr. Soares da Costa and her team are now exploring the re-purposing of other failed antibiotics to discover additional herbicidal molecules. 

They are also seeking partnerships with industry players to introduce new and safe herbicides to the market.