Regulation of the transition between motile planktonic and sessile biofilm-associated lifestyles in Pseudomonas aeruginosa

Many bacteria are able to adopt two fundamentally different lifestyles. While the planktonic mode of growth enables dissemination and exploration of novel niches, growing within multicellular, matrix-encased biofilms offers protection and survival in unfavorable environments. The aim of this thesis was to elucidate how the opportunistic pathogen Pseudomonas aeruginosa integrates and translates extra- and intracellular signals to regulate the transition between motile and sessile lifestyles in order to give an appropriate response to a changing environment. In this context, we characterized the chemotaxis methyltransferase CheR1 and demonstrated that its activity is not only essential for flagella-mediated chemotaxis but that it is also important for the formation and maintenance of biofilm structures. Another aim of this thesis was the identification of proteins that bind the small di-nucleotide c-di-GMP – an important bacterial second messenger which governs the switch between motility and sessility. We used immobilized c-di-GMP to perform affinity pull down experiments in which isolated proteins were identified by high-resolution mass spectrometry. This chemical proteomics approach proved to be sufficient for the isolation of c-di-GMP binding proteins harboring known but also novel c-di-GMP binding motifs in the model organism P. aeruginosa. To understand how environmental cues can influence bacterial behavior at the level of transcription, we identified the global regulon of the stationary phase sigma factor RpoS by performing chromatin immunoprecipitation experiments in combination with DNA-microarray analysis. Our results provide evidence that RpoS controls transcription of genes directly linked to biofilm formation but also of genes encoding components of other regulatory systems that trigger the formation of biofilms. Overall, this thesis contributes to our understanding of adaptive pathways leading to the development and maintenance of bacterial biofilms.