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Serratia marcescens

Serratia marcescens serrawettin 0.75% agar Broth Plate Alberti & Harshey, 1992 Swarming in Serratia marcescens Wetting agents and surfactants play a critical role in surface motility H + Ab that tether Pof Mot mutations Na+ channel blockers i.e. slow motor rotation Low Iron Na +

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Serratia marcescens

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  1. Serratia marcescens

  2. serrawettin 0.75% agar Broth Plate Alberti & Harshey, 1992 Swarming in Serratia marcescens Wetting agents and surfactants play a critical role in surface motility

  3. H+ Ab that tether Pof Mot mutations Na+ channel blockers i.e. slow motor rotation Low Iron Na+ High viscosity Low viscosity H+-driven Lateral flagella Na+-driven Polar flagellum Na+-driven Polar flagellum McCarter et al., 1988, 1989 Kawagishi et al 1996 Vibrio parahaemolyticus has two different types of flagella Laf Pof

  4. S. marcescens, E. coli, S. typhimurium, Proteus…

  5. Signals… Not Slowedmotor Ironstarvation Specificaminoacids pHchanges Oxygengradients Knownautoinducers

  6. Null hypothesis: Density dependence is related to generating wetness through some means other that quorum sensing.

  7. Chemotaxis LPS Surfactant? Wetting Two major classes of swarming-defective mutants ?

  8. The chemotaxis system, but not chemotaxis, is essential for swarming Burkart et al., 1998 Mutants in the chemotaxis pathway areswarming-defective in S.marcescens, E. coli & S. typhimurium O’Rear et al., 1992 Harshey & Matsuyama, 1994

  9. Cell expressing only a serine binding mutant of Tsr 0.7% agar 0.3% agar Burkart et al., PNAS, 1998

  10. The chemotaxis signaling pathway in E. coli/Salmonella V. Sourjik, Trends Microbiol., 2004

  11. che mutants are developmentally impaired

  12. The chemotaxis signaling pathway modulates motor bias V. Sourjik, Trends Microbiol., 2004

  13. Model for CheY as swarming regulator

  14. How does Che system control swarmer cell development? • 1.Genome-wide expression profiles of WT vs Dche • 2. Genetic suppressor analysis of DcheY

  15. Sensing wetness: A new role for the bacterial flagellum Wang et al., 2005

  16. Time course of swarming in wild-type S. typhimurium 100 x 25 x Flagellar genes is not upregulated during swarming Tim Wang

  17. Che mutants are developmentally impaired only on the surface WT(B) WT(P) cheY(B) cheY(P) cheZ(B) cheZ(P) 3.5h 2.5h 1.5h

  18. Lawn morphologies and fluid retention

  19. Induced Repressed Not changed Microarray: Salmonella WT vs CheY Cells On Plates WT Red (Cy5)/ CheY Green (Cy3).

  20. Che mutants specifically down-regulate class 3 motility genes Genome-wide expression profiles of WT vs DChe

  21. A Model connecting the dots… 1. Inhibition of Class 3 genes in Che mutants is due to FlgM 2. FlgM accumulates intracellularly because it cannot be exported outside 3. Export is blocked because dry external conditions slow filament growth (short flagella).

  22. Class III FlgM: External checkpoint for flagellar biogenesis CM OM flgM FliA M M M M FliA fliC

  23. Prediction: FlgM levels should be lower outside/higher inside

  24. Prediction: restoration of hydration should restore external FlgM

  25. Prediction: restoration of hydration should restore flagellation

  26. Prediction: flgM mutation should restore class 3 gene expression It does

  27. Testing ‘regulation of flagellar length’ model Flagella stained with Texas Red-conjugated antibody

  28. Testing ‘quick response’ model After shearing Flagellate & non-flagellate controls Rosu & Hughes, J. Bact. 2006

  29. FlgM secretion after shearing (blending) IC – Intracellular; EC - Extracellular

  30. Class 3 FlgM as drought sensor: Regulation in reverse

  31. 1. Genome-wide expression profiles of WT vs DChe • 2. Genetic suppressor analysis of DcheY Susana Mariconda But why are che mutant colonies dry?

  32. Suppressors of a cheY null mutant map to the switch complex 0.3% agar 0.7% agar Mariconda et al., Mol. Microbiol. 2006

  33. Swarming can be correlated with the ability to switch motor direction Mariconda et al., Mol. Microbiol. 2006 mM IPTG Chemoreceptor-less strain expressing a inducible CW signaling fragment

  34. Model for CheY as swarming regulator How does motor switching control control surface wetness?

  35. Switch and Stir model 1. Flagella stick to surfaces 2. Motor switching helps them un-stick 3. Freely rotating flagella stir-up the surface moisture, combining it with secreted carbohydrates to generate ‘slime’ that is so essential for movement

  36. Flagellum as a sensor (and generator) of external wetness

  37. We may have discovered an ancient role for the chemotaxis system! In the beginning, there was CheY CheY could be phophorylated by other phospho donors (Acetyl~P) And CheY~P was sufficient for movement The sophisticated machinery for chemotaxis system evolved later

  38. H+ Na+ High viscosity Low viscosity H+-driven Lateral flagella Na+-driven Polar flagellum Na+-driven Polar flagellum Flagellum as a mechanosensor Ab that tether Pof Mot mutations Na+ channel blockers i.e. slow motor rotation Low Iron Motor speed Laf Pof McCarter et al., 1988, 1989

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