New compound could be the next big thing in the world of herbicides.

At a glance:

  • Over the last few decades, weeds have built up resistance to pesticides
  • A team of researchers have discovered the human antibiotic could be used as an effective pesticides to facilitate crop growth

For the past 20 years we have relied on the same herbicides to deal with weeds suffocating crops and over the years, weeds have built up resistance to these herbicides, which is impacting crop growth.

A team of researchers in the School of Chemistry and Biochemistry have discovered an unlikely new compound that could help design the next big thing in the world of herbicides: a human antibiotic.

Ciprofloxacin is a commonly prescribed antibiotic to treat a wide range of infections, from typhoid fever and urinary tract infections to bone and joint infections.

The antibiotic kills bacteria by interfering with the action of an enzyme called gyrase, an essential component of the DNA replication machinery; and it turns out the antibiotic is also effective at killing plants.

“It’s often quite a step for a drug to work in a spray pack. Most drugs aren’t stable enough or able to penetrate through leaves into the plants to do their job. Ciprofloxacin was surprisingly good at it,” says Dr Joshua Mylne.

Vive la résistance!

After discovering the lethal effect this antibiotic had on plants it was important to be learn how it worked. So Dr Mylne, along with Professor Tony Maxwell at the John Innes Centre in the United Kingdom set up an experiment to find a plant resistant to the antibiotic.

Working with model plant Arabidopsis thaliana they created a vast number of mutants, each containing random mutations in their genomes and exposed them to ciprofloxacin.

“On ciprofloxacin, most plants rapidly turn white because their chloroplasts can’t replicate, so they die. We found a plant that stayed green and would grow quite happily on ciprofloxacin. It wasn’t immune, but was highly resistant,” says Dr Mylne.

With this resistant mutant at hand, the team went down the genomics road to identify what gave the plant its resistance. It turned out to be a mutation in the gene coding for the gyrase enzyme.

“A single change in DNA sequence from a G to an A meant a small part of the gyrase protein got bigger, probably blocking the entrance of ciprofloxacin into its active site,” explains Dr Mylne.

However, before we see a ciprofloxacin-inspired herbicide in action some fine-tuning is needed. Currently, Dr Mylne and his team are working on stripping ciprofloxacin of its antibiotic properties so that it won’t affect soil bacteria or animals.

“Ciprofloxacin is an important antibiotic so we need to discover a molecule that is related to it that is plant-specific and no longer affects bacterial gyrase,” says Dr Mylne. 

Ciprofloxacin-resistant (columns 1, 6), wild-type (column 5) and re-sensitised (other columns) Arabidopsis thaliana on a graded range of ciprofloxacin concentrations. Image by J. Leroux.

Image: Ciprofloxacin-resistant (columns 1, 6), wild-type (column 5) and re-sensitised (other columns) Arabidopsis thaliana on a graded range of ciprofloxacin concentrations. Image by J. Leroux

A model of the herbicidal antibiotic ciprofloxacin.

Image: A model of the herbicidal antibiotic ciprofloxacin. Image by J. Mylne. Mylne lab.