Phenotypic heterogeneity generated by histidine kinases based signaling networks

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More and more studies reveal that phenotypic heterogeneity is a common feature in bacterial populations. This project focuses on the comparative analysis of histidine kinases based signaling networks to unravel design principles that generate phenotypic heterogeneity. The multi-input histidine kinases based quorum sensing cascade in Vibrio harveyi was studied in correlation with phenotypic heterogeneity in the first funding period. Our results clearly indicate that this signaling cascade with three parallel bifunctional histidine kinases and a sRNA-regulated switch has the inherent property to cause phenotypic heterogeneity. Specifically, the ratio between kinase to phosphatase activities of the quorum sensing histidine kinases, which is differentially influenced by the three autoinducers, and the copy number of the master regulator LuxR were found to be crucial for the degree of phenotypic heterogeneity. Finally, exposure of V. harveyi to an artificial high concentration of all autoinducers caused the switch into a homogeneous population, which produced less biofilm than a heterogeneous one. We will focus on the multi-input histidine kinases nutrient sensing network in Escherichia coli in the second funding period. This network is composed of two histidine kinases and two transporters. It senses the level of several intra- and extracellular metabolites, transduces this information by protein-protein interactions and induces phenotypic heterogeneity. This nutrient sensing network is also found in other members of the Enterobacteriaceae including many pathogens, e.g., Klebsiella, Cronobacter, Citrobacter. All available data strongly suggest that the individuals of the E. coli population sense the available carbon sources through this network and develop bet-hedging strategies to adapt and survive during nutrient transitions. These bet-hedging strategies could result in different cellular fates, such as growing and dividing cells, biofilm-forming cells, or persister cells. We will compare the quorum sensing and the nutrient sensing networks in correlation with phenotypic heterogeneity by quantitative analysis and mathematical modeling with a specific focus on robustness, the molecular mechanism of signal transduction and the role of sRNA switches. Finally, we will analyze the impact of nutrient availability and metabolism on individual cellular fates of E. coli. In addition, we will investigate the biological significance of nutrient sensing and phenotypic heterogeneity during host colonization of uropathogenic E. coli. We aim to manipulate these E. coli populations by specific diets to become homogeneously and therefore, easier accessible to the immune response or antibiotic treatments.