The growing threat of antimicrobial resistance has prompted researchers to search everywhere for new compounds. This week, a European multinational team reported the discovery of a new antifungal antibiotic called solanimycin at mBio. The compound was originally isolated from a pathogen infecting potatoes and appears to be produced by a range of related plant pathogens.

According to the researchers, solanimycin can fight a wide range of fungi that are known to infect and destroy crops. In laboratory studies, the compound also works against Candida albicans, a fungus that naturally exists in the body, but can lead to dangerous infections. The results indicate that solanimycin and its related compounds are useful in both agricultural and clinical settings.

Soil microbes, particularly those from the phylum Actinobacteria, produce most therapeutic antibiotics used today. Dr. Rita Monson, a microbiologist at the University of Cambridge, said the new findings suggest that plant microbes deserve further study, especially when crops become resistant to existing treatments. She led the study with Dr. Miguel Matilla, a molecular microbiologist.

"We have to observe more microbial populations more broadly," Monson said. "The pathogenic potato bacterium Dickeya solani, which produces solanimycin, was first discovered 15 years ago. Researchers at the laboratory of Dr. George Salmond, a molecular microbiologist at the University of Cambridge, began studying its antibiotic potential about a decade ago.

"These strains emerged quickly and are now widely distributed," Matilla said. Solanimycin is not the first antibiotic found in this organism. In previous work, researchers have found that D. solani produces an antibiotic called oocydin A that is highly active against a variety of plant fungal pathogens.

Matilla says these previous findings, combined with the analysis of the bacterial genome, imply that it may synthesize more antibiotics that also have antifungal potential. The suggestion came back: when they silenced the gene responsible for producing oocydin A, the bacteria continued to show antifungal activity. This observation led to the recognition of solanimycin, as well as the recognition of gene clusters of proteins that constitute the compound.

The researchers found that the bacteria rarely used the compound, but produced it based on cell density. Acidic pH environments, as present in potatoes, also activate the solanimycin gene cluster. It’s almost like a smart protection mechanism, Monson says.

"We believe this is an antifungal that kills competitor fungi and bacteria benefit a lot from it," Monson said. But you won’t open it unless you’re in a potato. Researchers have begun to work with chemists to understand more about the molecular structure of solanimycin and better understand how it works. They then wanted to see continued testing of the compound on plants and animal models.

“Our future work focuses on trying to use this antifungal antibiotic to protect plants,” Matilla said. The team believes this finding is an encouraging sign that plant pathogens, such as D. solani, can be induced to make compounds that can be used to fight plant and human diseases.

"We have to explore everything to find new antibiotics," Matilla said. "

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