A Dangerous Bacterium Discovered in Potato Produces New Antibiotics

Antimicrobial resistance is becoming more of a problem, so researchers are looking for new substances everywhere. This week in mBio, a global research team from Europe reports the discovery of the novel antifungal antibiotic solanimycin.

The chemical, which was discovered from a pathogenic bacterium that infects potatoes, appears to be produced by a diverse group of closely related plant pathogenic bacteria. Solanimycin, the researchers discovered, inhibits a wide range of fungi known to harm and infect agricultural crops. The substance also inhibited the growth of Candida albicans, a fungus that normally lives in the body but can cause potentially harmful infections, in laboratory tests. The findings suggest that solanimycin and related drugs could be beneficial in both clinical and agricultural settings.

Antimicrobial resistance is becoming more of a problem, so researchers are looking for new substances everywhere. The majority of antibiotics used today are produced by soil microorganisms, specifically those of the phylum Actinobacteria. According to University of Cambridge scientist Rita Monson, PhD, the new discovery shows that plant-based microbes are worth further investigation, especially as crops become resistant to current treatments.

She co-led the study with molecular microbiologist Miguel Matilla, PhD, at the Spanish Research Council's Estacion Experimental del Zaidn in Granada. "We have to investigate more broadly across far more of the microbial populations available to us," Monson said. Dickeya solani, a pathogenic potato bacterium discovered more than 15 years ago, produces solanimycin.  Scientists in molecular microbiologist George Salmond's group at the University of Cambridge began investigating the substance's antibiotic potential about ten years ago.

"These strains evolved quickly and are now widely disseminated," Matilla says. Solanimycin is not the first antibiotic derived from bacteria. Previously, scientists discovered that D. solani produces the antibiotic oocydin A, which is extremely effective against a wide range of fungal plant infections. According to Matilla, who also examined the organism's genome, previous findings suggested that the bacterium could produce other antibiotics with antifungal properties.

That tip paid off: Matilla, Monson, Salmond, and their colleagues discovered that the bacteria retained antifungal activity even after silencing the genes required for oocydin A production. As a result of that observation, the chemical solanimycin and the gene clusters in charge of the proteins that produce it were discovered. The bacterium produces the chemical in response to cell density and uses it sparingly, according to the researchers.

An acidic pH environment, such as that found in potatoes, also activates the solanimycin gene cluster. According to Monson, it almost appears to be a clever protection system. According to Monson, the antifungal "will function by destroying fungal competitors, and the bacteria will benefit greatly from this." You can't turn it on unless you're inside a potato. Scientists have begun working with chemists, according to Monson, to better understand the molecular makeup of solanimycin and how it functions. She went on to say that she and Matilla hoped for more research on the substance to be conducted using plant and animal models.

According to Matilla, the next step will be to try to use this antibiotic antifungal for plant protection. The study's findings are interpreted as a positive sign that plant pathogens like D. solani can be encouraged to produce chemicals that can be used to treat both plant and human diseases. 

(Source: American Society for Microbiology)