Rotten potatoes could be your next antibiotic, here's why

The new discovery suggests plant-based microorganisms are worth a closer look, especially as crops develop resistance to existing treatments, says microbiologist Rita Monson, Ph.D., at the University of Cambridge.

“We have to look more expansively across much more of the microbial populations available to us,” Monson adds.

The antibiotic potential was first discovered 15 years ago

Solanimycin is produced by the pathogenic potato bacterium Dickeya solani, which was discovered more than 15 years ago. About ten years ago, scientists in the lab of molecular microbiologist George Salmond, at the University of Cambridge, started looking into the substance's antibiotic potential.

“These strains emerged rapidly, and now they are widely distributed,” said Miguel Matilla, a molecular microbiologist Miguel Matilla, Ph.D., at the Spanish Research Council’s Estación Experimental del Zaidín, in Granada.

Previous discoveries, as well as an analysis of the bacterium's genome, suggested that it could synthesize additional antibiotics with antifungal properties, according to Matilla.

Matilla, Monson, Salmond, and their colleagues discovered that when they silenced the genes responsible for oocydin A production, the bacterium retained antifungal activity.

A bright future for the study

Monson said the researchers have begun collaborating with chemists to learn more about the molecular structure of solanimycin and better understand how it works. Monson and Matilla explain that they hope to see continued testing of the compound in plant and animal models.

“Our future steps are focused on trying to use this antibiotic antifungal for plant protection,” Matilla said. The research team sees the discovery as an encouraging sign that plant pathogens—like D. solani—could be coaxed to make compounds used against diseases in plants and people.

“We have to [be] open to the exploration of everything that’s out there to find new antibiotics,” Matilla said.

Abstract:

The increasing emergence of drug-resistant fungal infections has necessitated a search for new compounds capable of combating fungal pathogens of plants, animals, and humans. Microorganisms represent the main source of antibiotics with applicability in agriculture and in the clinic, but many aspects of their metabolic potential remain to be explored. This report describes the discovery and characterization of a new antifungal compound, solanimycin, produced by a hybrid polyketide/nonribosomal peptide (PKS/NRPS) system in Dickeya solani, the enterobacterial pathogen of potato. Solanimycin was active against a broad range of plant-pathogenic fungi of global economic concern and the human pathogen Candida albicans. The genomic cluster responsible for solanimycin production was defined and analyzed to identify the corresponding biosynthetic proteins, which include four multimodular PKS/NRPS proteins and several tailoring enzymes. Antifungal production in D. solani was enhanced in response to experimental conditions found in infected potato tubers and high-density fungal cultures. Solanimycin biosynthesis was cell density dependent in D. solani and was controlled by both the ExpIR acyl-homoserine lactone and Vfm quorum-sensing systems of the bacterial phytopathogen. The expression of the solanimycin cluster was also regulated at the post-transcriptional level, with the regulator RsmA playing a major role. The solanimycin biosynthetic cluster was conserved across phylogenetically distant bacterial genera, and multiple pieces of evidence support that the corresponding gene clusters were acquired by horizontal gene transfer. Given its potent broad-range antifungal properties, this study suggests that solanimycin and related molecules may have potential utility for agricultural and clinical exploitation.