Solanimycin, which is produced by Dickeya solani, the enterobacterial pathogen of potato, is active against a broad range of plant-pathogenic fungi and the human pathogen Candida albicans.
Model for the structure of the first enzyme-free precursor of solanimycin. Image credit: Matilla et al., doi: 10.1128/mbio.02472.
Many important drugs for treating microbial infections are derived from natural products produced by microorganisms.
In an era of increasing antimicrobial resistance, there is an urgent need for discovery of new antibiotics for use in medicine and agriculture.
Several antifungal drugs derived from natural products, or that mimic natural products, have been approved.
However, the number of natural product-derived antifungal antibiotics developed in the last 40 years is significantly lower than that of their antibacterial counterparts.
“The new discovery suggests plant-based microorganisms are worth a closer look, especially as crops develop resistance to existing treatments,” said Dr. Rita Monson, a microbiologist at the University of Cambridge.
“We have to look more expansively across much more of the microbial populations available to us.”
The solanimycin-producing pathogenic bacterium Dickeya solani was first reported in European seed potato stocks from 2005 to 2006, and it is now recognized as a prominent plant pathogen worldwide.
In a previous work, the researchers found that it produces an antibiotic called oocydin A, which is highly active against multiple fungal plant pathogens.
“Those previous discoveries, together with the analysis of the genome of the bacterium, hinted that it might synthesize additional antibiotics, said, also with antifungal potential,” said Dr. Miguel Matilla, a molecular microbiologist at the Spanish Research Council’s Estación Experimental del Zaidín.
“That hint paid off — when we silenced the genes responsible for the production of oocydin A, the bacterium continued to show antifungal activity.”
“That observation led to the identification of solanimycin and the identification of the gene clusters responsible for the proteins that make the compound.”
The researchers found that Dickeya solani uses the compound sparingly, producing it in response to cell density.
An acidic pH environment — as that present in a potato — also activates the solanimycin gene cluster.
“It almost looks like a clever protective mechanism,” Dr. Monson said.
“It’s an antifungal that we believe that will work by killing fungal competitors, and the bacteria benefit so much from this. But you don’t turn it on unless you’re in a potato.”
“Our future steps are focused on trying to use this antibiotic antifungal for plant protection,” Dr. Matilla added.
The findings were published in the journal mBio.
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Miguel A. Matilla et al. Solanimycin: Biosynthesis and Distribution of a New Antifungal Antibiotic Regulated by Two Quorum-Sensing Systems. mBio, published online October 10, 2022; doi: 10.1128/mbio.02472
