New Antibiotics of Leaf Dwellers

A team of ETH researchers led by Julia Vorholt and Jörn Piel have discovered new antibiotic substances in bacteria that colonize the leaf surfaces of a native wild plant.

On leaf surfaces lives a rich microbial community that produces many unexplored natural products. (Image: Gerd Innerebner / Roger Wepf, ScopeM)

On leaves of plants lives a variety of different microorganisms such as bacteria or fungi. Leaf surfaces are densely populated, although few nutrients are found on them. To keep the competition away, many of the leaf dwellers rely on chemical warfare: they have developed antibiotic substances that stop growth and reproduction of other roommates.

A group of researchers led by ETH Zurich professors Julia Vorholt and Jörn Piel from the Institute of Microbiology discovered a particularly productive bacterium during a systematic search on leaves of thale cress (Arabidopsis thaliana): Brevibacillus sp. Leaf 182.

In experiments it inhibited half of all 200 strains that the researchers had isolated from leaf surfaces. The bacterium produces and secretes at least four antibiotic chemical compounds. Brevibacillus sp. Leaf 182. Two of these compounds were already known, while a substance called Macrobrevin had a previously unknown chemical structure.

Antibiotic interactions revealed

“Using bioinformatic methods, we searched for groups of genes that could generally control the production of substances and thus affect other bacteria,” explains Vorholt. At the same time, the researchers tested in the laboratory which of these strains have an antibiotic effect against others, ie ensure that certain bacteria no longer reproduce. Overall, they found over 700 such antibiotic interactions between different microbial strains.

The goal of the project funded by the SNSF and ERC Grant was to find new antibiotics in a previously unstudied habitat. “So far, research has focused on the soil as a habitat, but that’s where we always find the same connections,” says Vorholt.

Defuse antibiotic crisis

Antibiotic-induced inhibition zones in a bacterial lawn (Image: Eric JN Helfrich, ETH Zurich)

However, the search for new antibiotics is becoming increasingly difficult. Piel speaks of the antibiotic crisis: “We have hardly any antibiotics against which at least one pathogen is resistant.” Companies have more or less stopped the search for new substances because they are not profitable enough.

With their project, the ETH researchers are opening up a new reservoir with high potential. “We will now clarify whether Macrobrevin and other newly discovered substances also act against bacteria that cause disease in humans,” says Piel. Even higher than this possibility, he estimates the success of having shown that there are still many natural substances for antibiotics to be discovered in the hitherto under – researched microcosm of leaf surfaces: “This incredibly diverse ecosystem can certainly be very many new approaches for the Deliver medicine. Our results confirm that it is worth expanding the search for a

Source : ETH Zurich