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4110notes3 - Biol4110 Microbial Physiology Notes#3 11/1...

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Biol4110 Microbial Physiology Notes #3 11/1- 12/6/2007 11/1/07: Signal transduction Two component signaling: The components of a basic two component signaling system in bacteria include a sensor kinase and response regulator. A sensor histidine kinase is usually a membrane protein. The extracellular domain senses a particular stimulus and causes the intracellular domain to phosphorylate itself on a histidine residue. The phosphate is then transferred to an aspartyl residue on a response regulator protein. This causes a conformational change in the protein resulting in activation of its output domain that may activate transcription of target genes or may have various enzymatic activities. Functions of two component signaling systems: Nutrient acquisition * nitrogen * phosphorus * carbon Energy metabolism * electron transport systems * uptake and catabolic machinery Virulence * plasmid transfer * toxin production * adherence factors Adaptation to physical or chemical aspects of the environment * pH * osmolarity * light quality Complex developmental pathways * sporulation * fruiting body development * swarmer cell production Example of two-component systems: The E. coli osmolarity-response system consists of a histidine protein kinase and osmosensor, EnvZ, and a response regulator transcription factor OmpR. EnvZ autophosphorylates using ATP as the phosphate donor. The phosphate from EnvZ is then transferred to an Asp residue in OmpR, thereby affecting the promoter interactions of the OmpR DNA-binding module, which regulates the transcription of two porin genes, ompF and ompC . E. coli chemotaxis signaling pathway In this system the methyl accepting chemotaxis protein (MCP) binds attractant on the outside of the cell. The CheA Histidine Protein Kinase autophosphorylates then phosphorylates either of two different response regulators: CheY or CheB. CheY-P causes the flagella to spin clockwise, promoting changes in swimming direction. CheB-P promotes sensory adaptation by demethylating the MCP. Quorum sensing: Bacteria are able to sense when they are near other cells (in a community) by sensing the presence of small, secreted molecules called acyl-homoserine lactones. Bacteria secrete these molecules continually but only when they get to high enough concentrations do they act as a signal. When do bacteria experience quorum sensing? It is now widely recognized that most bacteria found in natural, clinical and industrial settings persist in association with surfaces. Planktonic bacteria, like those grown in the laboratory are quite rare in nature. The surface growing bacteria are typically associated with a community called a biofilm. A biofilm is a complex community of bacteria that can contain one species or more than one species. Biofilm bacteria have
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properties that make them different from planktonic bacteria. For example, biofilm bacteria are much more resistant to antibacterial treatments such as detergents and bleaching agents (up to 1000-fold more resistant). The PhoP-PhoQ two component system
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4110notes3 - Biol4110 Microbial Physiology Notes#3 11/1...

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