Carbon source driven virulence factors generation by Pseudomonas aeruginosa, implications for application in bioelectrochemical systemsv

  • Kohlenstoffquellen gesteuerte Bildung der Virulenzfaktoren von Pseudomonas aeruginosa; Folgen für Anwendung in bioelektrochemischen Systemen

Bosire, Erick M.; Agler-Rosenbaum, Miriam (Thesis advisor); Blank, Lars Mathias (Thesis advisor)

Aachen (2017)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2017

Abstract

Pseudomonas aeruginosa, the ubiquitous quintessential pathogen, produces a wide array of virulence factors to propagate pathogenicity. In polymicrobial infections and competitive environmental niches, a concerted action of the virulence factors ensures its competitiveness and often dominance. The quorum sensing system controls the genes coding for these virulence factors ensuring a timely production to avoid unnecessary virulence activation.P. aeruginosa virulence factors, especially phenazines, have gained attention for biotechnological application, such as bioremediation or in bioelectrochemical systems (BES). For the latter, especially phenazine redox mediators and other pathogenicity factors like rhamnolipids and siderophores might play an important role in enabling biofilm formation on the electrodes. In mixed culture BES, bacteria metabolise substrates and liberated electrons are shuttled to an external electron acceptor (anode) via soluble redox mediators among other modes of electron transfer. P. aeruginosa plays a key role in these processes and displays tremendous metabolic versatility and nutrition influences its virulence generation. Like in natural communities, microorganisms often build synergistically interacting microbial consortia in wastewater BES. In these interactions, consumption of fermentation products from fermenters by P. aeruginosa leads to increased phenazine mediator production and consequently increased electroactivity of the whole community. Understanding the signalling mechanisms behind this natural phenomenon may allow the design of co-cultures for increased current production in BES or engineering phenazine redox mediator-based BES biocatalysts. Also, a detailed understanding of how the phenazines are employed under varying ecological conditions across the P. aeruginosa strains and their capacity as redox mediators in BES is yet to be fully achieved. This thesis first explored the applicability of the P. aeruginosa strains (PA14, KRP1 and PAO1) as redox mediator producers in BES. Next, the influence of one of the important BES parameters-electrochemical potential on the phenazine physiology and electric current generation of strain PA14 was examined. To further decipher how fermentation products influence the virulence generation, 2,3-butanediol (2,3-BD) metabolism pathway mutants were generated and their virulence generation assessed. Finally, the two-component systems involved in the perception of 2,3-BD were identified. Remarkable differences among the three strains in the production of phenazines, rhamnolipids and the tendency to form biofilms under the BES conditions and different substrates were revealed. Comparing all strains and carbon sources, the BES isolate KRP1 was the most electroactive when supplied with the three carbon sources considered. Phenazine-1-carboxylic acid (PCA) was found to play a major role in redox cycling under the BES conditions. The production and use of PCA in electron shuttling depended on the applied potential as well as the substrate. Overall the electrochemical potential impacts the electron transfer, growth and biofilm formation. These findings on the influence of the applied potential will enable appropriate poising of the electrode to harness the redox cycling potential of the phenazines. The RcsC/RcsB and PvrS/PvrR two-component systems were identified as, most likely, being responsible for the perception and regulation of the of 2,3-BD-stimulated virulence factors production; mutants lacking these systems exhibited reduced production of phenazines. These results provide fundamental insights that will lead to a more thorough understanding of carbon-source based virulence factor regulation and can be useful in designing synergistically interacting co-cultures, where P. aeruginosa is the redox mediator producer.