Following the tracks of an extremely adaptive bacterium

Diversity in the genome reflects adaptability

The plant pathogen Pseudomonas syringae causes major damage in agriculture. However, it also produces a large number of biologically active natural products. These could help the bacterium to adapt to changing environmental conditions and displace competitors. In a comprehensive genomic analysis, the researchers examined 18 representative strains of the bacterial species and analyzed their genetic potential to produce natural products using state-of-the-art bioinformatics methods.

They were able to identify a total of 231 so-called biosynthetic gene clusters. These gene clusters contain enzyme-coding genes that are responsible for the synthesis of natural products. Genes for nonribosomal peptide synthetases (NRPS) were particularly abundant. NRPS produce natural products that, for example, help the bacterium to assert itself against competitors and adapt to its environment.

Natural products with special properties

Through a combination of bioinformatic analyses, chemical structure determination and biological activity tests, two new families of natural products were identified and characterized: the syrilipamides and the secimides. Both are low molecular weight compounds produced by Pseudomonas syringae. These molecules show remarkable toxicity towards competing microorganisms, especially against fungi and also amoebae. Their selective effect could be used in the future for the protection of plants or as a starting point for the development of new bioactive substances.

SecA enzyme expands chemical repertoire

“We have also discovered a previously unknown enzyme: SecA,” says Shuaibing Zhang, first author of the study. “SecA adds chlorine atoms to specific organic compounds, which increases the structural complexity and activity of the resulting compounds,” adds Pierre Stallforth, head of the project. He is a professor at the University of Jena and head of department at the Leibniz-HKI. Such chlorinated natural products play an important role in pharmaceutical research and could be used in the future for the development of new antibiotics, cancer therapies or plant protection products.

New perspectives for biotechnology

With their effect against amoebae and fungi, the newly discovered natural products could be of interest to both agriculture and pharmaceutical research. First of all, however, the team was interested in the ecological function of these molecules. They help Pseudomonas syringae, a versatile bacterium, plant pathogen, and producer of bioactive compounds, to defend itself against predators and competition and to adapt to niches in its natural habitat. The formation of microbial consortia in nature and the function of the natural products involved contribute to the understanding of the complex ecological interactions in our environment and are the research focus of the Jena Cluster of Excellence “Balance of the Microverse”. Scientists from the Leibniz Institute for Natural Product Research and Infection Biology – Hans Knöll Institute (Leibniz-HKI) and the Friedrich Schiller University Jena were involved in the work.

The project was funded by the Werner Siemens Foundation, the Leibniz Association and the German Research Foundation as part of the Collaborative Research Center ChemBioSys and the Cluster of Excellence “Balance of the Microverse”.