Mechanistic investigations of the syntrophy between Pseudomonas aeruginosa and 2,3-butanediol fermenters within the context of optimized phenazine-based current generation in bioelectrochemical systems

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In the past, exploiting microbial reactions for biotechnological applications was mainly limited to pure cultures. In nature, however, microorganisms typically act in concert because synergistic collaborations are able to overcome metabolic and energetic challenges. Unfortunately, our knowledge on specific microbial interactions is still scarce. Bioelectrochemical systems (BESs) can utilize collaborative microorganisms for the anaerobic conversion (oxidation) of organic matter to carbon dioxide and electric current. Thereby, key microbial players with specific metabolic functions like organics hydrolysis, fermentation, redox mediator shuttling or direct extracellular electron transfer have already been identified. One major challenge for the successful application of BES is the development of optimized microbial BES catalysts. A clear path to achieve this goal is to understand how these key players interact together and to design communities to exploit these interactions.Previous work has shown an important synergistic current production between the 2,3-butanediol fermenter Enterobacter aerogenes and the electron-mediator producer Pseudomonas aeruginosa. In this co-culture, the fermenter digests sugars to mainly 2,3-butanediol, which in turn, is taken up by P. aeruginosa. P. aeruginosa uses 2,3-butanediol to produce increased amounts of the virulence factor pyocyanin, a redox mediator, which enables increased current production at a BES anode. This proposal strives for an ecological and molecular understanding of this synergistic interaction, which seems to be mediated by the fermentation product 2,3-butanediol. Further, these two organisms (but also P. aeruginosa with similar fermenters) encounter one another in soil environments and during lung infections, making implications of this synergism much broader than just BES applications.In the proposed work, we will conduct a thorough ecological evaluation of the synergism between P. aeruginosa and various 2,3-butanediol fermenters: we will study the extent of interspecies communication and physiological responses in both partners and the effect on P. aeruginosa quorum sensing and virulence factor formation, whereby BES will be used as an in-situ analytical tool to quantify pyocyanin. We will further determine ideal physiological conditions for optimum synergistic behavior of P. aeruginosa : fermenter co-cultures in BES, i.e. we will learn to control the binary co-culture. For a comprehensive understanding of the synergism, the related physiological processes in P. aeruginosa will be investigated to answer the following questions: How is 2,3-butanediol sensed?; How is the quorum sensing regulatory network influenced?; Is there a metabolic effect beyond just signaling? Finally, we will integrate all observed phenotypic and physiological results in an physio-ecological model of the co-culture synergism, which will serve as a foundation for future, more complex microbial networks in BES.