Extracellular pyruvate: sensing, uptake, and significance for gamma-proteobacteria

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Pyruvate, a central metabolite, is excreted by many bacteria into the environment as a result of overflow metabolism. In previous studies we identified a network of pyruvate sensors and transporters, which is activated in Escherichia coli and other gamma-proteobacteria under nutrient limitation to reuptake this metabolite. The first part of the project is dedicated to the detailed elucidation of the structure and function of key components of this network in E. coli. The studies shall focus (1.) on the investigation of the unusual phosphorylation-independent signal transduction within the pyruvate-sensing histidine kinase/response regulator systems BtsS/BtsR and YdpA/YpdB of E. coli and their structural analysis. (2.) The 3D structures of the two pyruvate transporters BstT and CstA of E. coli shall be resolved. Both transporters belong to the poorly investigated CstA transporter family. CstA, the name-giving protein of the family, will be biochemically characterized with respect to substrate specificity, kinetics and energization for the first time. Although the pyruvate sensory network is widespread in gamma-proteobacteria, there are significant differences in design and functionality among genera. For example, bacteria of the genus Vibrio excrete significantly more pyruvate than Escherichia, but have a very simple system for pyruvate sensing and uptake. Therefore, in the second part of the project, the studies will be extended to Vibrio campbellii (previously V. harveyi), a model bacterium for quorum sensing. The work shall focus (3.) on the clarification of the biological significance of pyruvate sensing and transport in V. campbellii. Furthermore, (4.) V. campbellii will be used as a model organism to investigate the relevance of extracellular pyruvate for microbial interactions. We will address the question whether bacteria compete for pyruvate as a nutrient or use the compound to attract and kill other species. Work on this project is expected to contribute to a better understanding of sensing and uptake of the primary metabolite pyruvate and its significance for microbial interactions.