Serratia marcescens

1
Serratia marcescens
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Swarming in Serratia marcescens
Wetting agents and surfactants play a critical
role in surface motility
3
Vibrio parahaemolyticus has two different types
of flagella
Laf
Pof
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S. marcescens, E. coli, S. typhimurium, Proteus
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Signals
Not
Slowed motor
Iron starvation
Specific amino acids
pH changes
Oxygen gradients
Known autoinducers
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• Null hypothesis Density dependence is related to
  generating wetness through some means other that
  quorum sensing.

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Two major classes of swarming-defective mutants
?
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Mutants in the chemotaxis pathway are
swarming-defective in S.marcescens, E. coli S.
typhimurium
ORear et al., 1992 Harshey Matsuyama, 1994
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Cell expressing only a serine binding mutant of
Tsr
0.7 agar
0.3 agar
Burkart et al., PNAS, 1998
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The chemotaxis signaling pathway in E.
coli/Salmonella
V. Sourjik, Trends Microbiol., 2004
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che mutants are developmentally impaired
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The chemotaxis signaling pathway modulates motor
bias
V. Sourjik, Trends Microbiol., 2004
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Model for CheY as swarming regulator
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How does Che system control swarmer cell
development?

• 1. Genome-wide expression profiles of WT vs Dche
• 2. Genetic suppressor analysis of DcheY

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Sensing wetness A new role for the bacterial
flagellum Wang et al., 2005
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Time course of swarming in wild-type S.
typhimurium
100 x
25 x
Flagellar genes is not upregulated during swarming
Tim Wang
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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
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Lawn morphologies and fluid retention
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Microarray Salmonella WT vs CheY Cells On Plates
WT Red (Cy5)/ CheY Green (Cy3).
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Genome-wide expression profiles of WT vs DChe
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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).
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Class III FlgM External checkpoint for flagellar
biogenesis
OM
CM
flgM
FliA
M
M
M
M
FliA
fliC
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Prediction FlgM levels should be lower
outside/higher inside
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Prediction restoration of hydration should
restore external FlgM
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Prediction restoration of hydration should
restore flagellation
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Prediction flgM mutation should restore class 3
gene expression
It does
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(No Transcript)
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Testing regulation of flagellar length model
Flagella stained with Texas Red-conjugated
antibody
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Testing quick response model
After shearing
Flagellate non-flagellate controls
Rosu Hughes, J. Bact. 2006
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FlgM secretion after shearing (blending)
IC Intracellular EC - Extracellular
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Class 3 FlgM as drought sensor Regulation in
reverse
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But why are che mutant colonies dry?
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Suppressors of a cheY null mutant map to the
switch complex
0.3 agar
0.7 agar
Mariconda et al., Mol. Microbiol. 2006
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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
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Model for CheY as swarming regulator
How does motor switching control control surface
wetness?
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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
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Flagellum as a sensor (and generator) of external
wetness
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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 (AcetylP) And CheYP was
sufficient for movement The sophisticated
machinery for chemotaxis system evolved later
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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