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Other Adaptive Responses

Other Adaptive Responses. Chemotaxis or controlled movement Quorum sensing Biofilm. E. Chemotaxis. Synthesis of flagella often induced by nutrient limitation (expression of early genes induced). Synthesis requires expression of 3 sets of genes Middle make basal boy, hook

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Other Adaptive Responses

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  1. Other Adaptive Responses • Chemotaxis or controlled movement • Quorum sensing • Biofilm

  2. E. Chemotaxis Synthesis of flagella often induced by nutrient limitation (expression of early genes induced) • Synthesis requires expression of 3 sets of genes • Middle make basal boy, hook • Late - filament σ28 Fig 12.33 Bact. Phy & Met Chilcottand Hughes Microbiol. Mol. Biol. Rev. 64:694-708, 2000

  3. E. Chemotaxis Directed movement in response to an external chemical stimuli or effectors Movement can be towards or away Cells can response to a several different chemical substances Different nutrients (food sources) Metals (many are toxic) See section 12.2.11 in Bact. Phy and Met.

  4. E. Chemotaxus In bacterial cells with flagella, chemotaxis mediated by controlling length of runs (on) • See Part (b) of figure • if going towards attractant, runs long • If going away, runs short

  5. E. Chemotaxis Attractant or repellent will create a concentration gradient in environment Bacterial cells need to sense if moving towards or away from source of attractant or repellent Toward or away from highest concentration Turn off flagella when going in wrong direction How do they do this? Sense change in concentration over time by adaptive methylation

  6. E. Chemotaxis Components besides flagella (Fig 12.34) Transmembranechemoreceptors or methyl-accepting chemotaxis proteins (MCPs) Sense attractant or repellant 2. CytoplasmicSignalling Proteins CheA, CheY, CheW and CheZ – Control flagella rotation (on or off) 3. Enzymes for Adaptive methylation CheB and CheR Mediate sensing of conc. gradient

  7. 1. Methyl-accepting chemotaxis proteins (MCPs) Each cell has several different type of MCPs (Five in E. coli: Tsr, Tar, Trg, Tap and ?) • Each methyl-accepting chemotaxis receptor protein or MCP can sense multiple compounds • Tar senses attractants maltose and aspartate and repellants cobalt and nickel Fig 13.10 Microbe

  8. 1. Methyl-accepting chemotaxis proteins (MCPs) MCPs are located in cell or inner membrane of bacteria • For some chemicals (substrates), substrate binding proteins in periplasm binds chemical and then interacts with MCP receptor protein (see figure 12.34) Fig 12.34 Bact. Phy & Met

  9. 2. Signaling Proteins Signaling proteins CheA and CheW form complex with MCPs • CheA (histidinekinase) can autophosphoryl-ate itself Fig 12.34 Bact. Phy & Met

  10. 2. Signaling Proteins PhosphorylatedCheA-P can phosphorylateCheY and High levels of phosphorylatedCheY (CheY-P) causes flagellum to turn clockwise (tumble) CheZ removes phosphates off CheY inactivating it Fig 13.10 Microbe

  11. 2. Signaling Proteins Key factor determining flagella turning is how much of CheY is phosphorylated (CheY-P) • PhosphorylatedCheA-PphosphorylatesCheY • CheZ is constantly acting to remove phosphates from CheY activity is constitutive Fig 12.34 Bact. Phy & Met

  12. 2. Signaling Proteins When the MCP binds to an attractant, it adopts an conformation that decreases CheAautophosphorylation • When the MCP is not binding an attractant or binds an repellant, it adopts a conformation that stimulatesCheAphosphorylation Fig 12.34 Bact. Phy & Met

  13. 3. Adaptive Methylation Each MCP has 5 glutamate residues that can be methylated Methylation state becomes a memory of previous concentration • CheR adds methyl groups at a constant rate Fig 12.34 Bact. Phy & Met

  14. 3. Adaptive Methylation PhosphorylatedCheB (CheB-P) removes methyl groups from MCP CheA-P phosphorylatesCheB (in addition to CheY) • CheB-P loses its phosphate over time (becomes not active) • Only phosphorylatedCheB removes methyl groups Fig 12.34 Bact. Phy & Met

  15. 3. Adaptive Methylation When going towards an attractant or away from a repellent, the MCPs become more methylated Methylated MCPs are more likely to stimulate CheAautophorylation (need more attractant to prevent) Once a MCP becomes fully methylated it can not prevent CheAautophosphorylation (tumble and system reset) • During tumble,CheB-P becomes active and removes methyl groups – partially resets system

  16. Chemotaxis Overview System integrates signal from multiple different MCPs Amount of phospho-CheA is barometer of # of MCPs bound to attractant and not repellent Methylation state indicates level of attractant previous If encounter attractant, need more MCPs to bind attractant to prevent tumble (less sensitive to attractant)

  17. Chemotaxis Overview Has three short lived opposing reactions CheAphosphorylation and dephosphorylation CheYphosphorylation and dephosphorylation MCP methylation and demethylation Also integrates response to multiple stimuli

  18. Chemotaxis Overview Parkinson 2003 J. Bacteriol. 185:1493 Green pro-mote CW turning (Off) Red promote CCW turning

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