There can also be good things in “bad guys”, a study makes clear: researchers have discovered an active ingredient in a bacterial pathogen of potatoes that shows potential in the fight against fungal infections in both plants and humans: the so-called solanimycin from the pathogen that causes “blackleg”. Effective against various known agricultural pathogens as well as against the human pathogenic fungus Candida albicans. The study thus clarifies the hitherto hardly noticed potential of plant-associated bacteria as a source of antimicrobially active substances, say the scientists.
Substances directed against bacteria are usually the focus of attention – antibiotics. However, new active ingredients are also urgently needed against another group of microbial pathogens: fungal infections are an important issue – both in agriculture and in medicine. Various types of fungi attack plants, causing gigantic yield losses worldwide. Better control agents and alternatives to the agents that are increasingly failing due to the development of resistance are therefore in demand. Similar to plants, however, humans and animals can also be attacked by certain types of fungi – with sometimes life-threatening consequences. So far, however, only comparatively few substances have been available for treatment. As with antibiotics, there is therefore also a considerable need for development in antimycotics.
Search the arsenal of microbes
Certain bacteria, which mostly live peacefully in the soil, have proven to be a particularly productive source of antimicrobial substances. The scientists led by Miguel Matilla and Rita Monson from the University of Cambridge, on the other hand, are now turning their attention to so-called phytopathogenic bacteria. She specifically focuses on the pathogen Dickeya solani, which causes so-called “blackleg” in potato plants and can infect the tubers. The bacterium is currently on the rise and is causing major damage in potato cultivation. However, the researchers are not dedicated to fighting it, but are interested in a possible secret of the bacterium’s success: As known from other microbes, it could specifically “poison” competitors such as other bacteria or fungi in its environment in order to gain advantages.
So the team began investigating Dickeya Solani’s antimicrobial weaponry. They came across a substance called oocydin A, which was effective against several fungal plant pathogens. “However, this earlier discovery and the analysis of the genome of the bacterium indicated that there are more active substances to discover,” says Matilla. During their further investigations, the scientists then came across the substance that they call solanimycin. They finally succeeded in isolating this active ingredient in order to use it for efficacy tests. It was investigated to what extent the substance can suppress the growth of certain microbes on culture medium. If this is the case, characteristic zones of inhibition form around the site of application of the active ingredient.
Potential for agriculture and medicine
As the tests showed, this was the case for a number of fungal organisms: Solanimycin shows potential for action against important pathogens on various crops that are a major problem for agriculture worldwide. The scientists were also able to show the potential for human medicine using the example of the fungus Candida albicans. Solanimycin caused clear zones of inhibition on culture media on which this potentially dangerous pathogen grew. Candida albicans can cause significant health problems and even life-threatening systemic infections in humans under certain circumstances.
Interestingly, through their genetic studies, the researchers were also able to show that the bacterium only produces the compound when it makes sense. Accordingly, an environment with a certain level of acidity – as found in a potato – leads to the formation of the substance. As the researchers explain, the production of the active substance is complex for the protozoa and therefore they only produce it when they are in their victim and only want to benefit from its nutrients there. “It’s an antifungal that we think is supposed to kill fungal competitors, which can be very beneficial to the bacteria,” says Monson.
The researchers emphasize that the extent to which the active ingredient is actually suitable for agricultural or clinical use must first be clarified by further studies. They’ve already started working with chemists to learn more about the molecular structure of solanimycin and better understand how it works. Tests of the active substance in plant and animal models could then follow. Above all, however, the researchers see a fundamental significance in their study: it becomes clear that there is also potential in plant pathogens for the discovery of substances that can be used against diseases in plants and humans. “We have to be open to exploring everything that’s out there to find new antimicrobials,” says Matilla.
Quelle: American Society for Microbiology, Fachartikel: mBio, doi: 10.1128/bio.02472-22