• Biosynthesis of signal molecules and related metabolites by Pseudomonas aeruginosa

    Bacteria use cell-to-cell communication (quorum sensing, QS) systems based on chemical signal molecules to coordinate their behavior within the population. Pseudomonas aeruginosa, an opportunistic pathogen, regulates its virulence via a complex quorum sensing (QS) network. Besides N-acylhomoserine lactone-mediated QS circuits, it possesses an alkylquinolone (AQ) dependent QS system which uses PQS (the Pseudomonas quinolone signal) and its biosynthetic precursor HHQ (2-heptyl-4(1H)-quinolone) as signal molecules. AQ signaling is involved in the regulation of a number of virulence factors. 2-Alkyl-4-hydroxyquinoline-N-oxides (AQNOs), potent inhibitors of respiratory electron transport, also derive from the AQ biosynthetic pathway.

    We aim at characterizing the Pqs proteins involved in the biosynthesis of the various products of the AQ biosynthetic pathway. Because these metabolites have multiple biological activities and significantly contribute to the virulence and competitiveness of P. aeruginosa, deciphering how the enzymes of the AQ biosynthetic pathway fine-tune their production will advance our knowledge on how P. aeruginosa manipulates its biotic environment, and will also contribute to the development of anti-virulence agents.

    Support: German Research Foundation (DFG)

  • Quorum quenching enzymes

    Bacteria use cell-to-cell communication (quorum sensing) systems based on chemical signal molecules to coordinate their behavior within the population. These systems are potential targets for antivirulence therapies, because many bacterial pathogens control the expression of virulence factors via quorum sensing networks.

    One possibility to interfere with quorum sensing is signal inactivation by enzymatic degradation or modification. Such quorum quenching enzymes are wide-spread in the bacterial world and have also been found in eukaryotes. Lactonases and acylases that hydrolyze N-acylhomoserine lactone (AHL) signaling molecules have been investigated most intensively.

    Rhodococcus erythropolis strain BG43, an isolate from soil of the Botanical Garden of the University of Münster, is the first bacterium described to be able to degrade alkylquinolone-type quorum sensing signals. In the opportunistic pathogen Pseudomonas aeruginosa, the alkylquinolone signal PQS significantly contributes to the regulation of virulence gene expression. We aim at characterizing the PQS-cleaving enzymes of strain BG43 and also of related bacteria, especially with respect to their potential to interfere with quorum sensing and virulence factor production of P. aeruginosa.

    Support: German Research Foundation (DFG)

  • Bacterial secondary metabolism: Reaction cascades and enzyme mechanisms

    Microorganisms produce a wealth of bioactive compounds, many of which have been and continue to be crucial for medical, environmental or technological applications. This is reflected by the simple fact that, despite major efforts in pharmaceutical chemistry, the majority of registered drugs still originates from natural sources.

    However, bacterial secondary metabolism also involves a multitude of enzymes with unique properties, so that even well-known biosynthetic pathways can reveal exciting, uncharted reactions. In contrast, a multitude of biosynthetic gene clusters cannot be associated with particular metabolites, probably due to lacking gene expression, precursor supply, instability of the respective pathway products, or analytical challenges.

    Working with the opportunistic pathogen Pseudomonas aeruginosa and related bacteria, our project aims at the analysis of uncharacterized biosynthetic pathways in these species with an enzyme-centered approach. Such a bottom-up strategy can provide useful hints on the identities of yet unknown metabolites or metabolite substructures. Reconstituting and assembling key reactions and reaction cascades occurring within these pathways discloses the fascinating mechanisms and properties of the enzymes involved. It can also provide useful details for the biotechnological, synthetic or semisynthetic production of metabolites for further applications.

    In addition, numerous bacteria have the capability to transform or even detoxify antimicrobial secondary metabolites by chemical modification. Identification of the enzymes involved in such reactions is the subject of another project, which may open up perspectives for the development of new bioactive compounds.