Serratia marcescens
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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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Slide2 l.jpg

serrawettin

0.75% agar

Broth

Plate

Alberti & Harshey, 1992

Swarming in Serratia marcescens

Wetting agents and surfactants play a critical role in surface motility


Slide3 l.jpg

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



Signals l.jpg
Signals…

Not

Slowedmotor

Ironstarvation

Specificaminoacids

pHchanges

Oxygengradients

Knownautoinducers


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Chemotaxis wetness through some means other that quorum sensing.

LPS

Surfactant?

Wetting

Two major classes of swarming-defective mutants

?


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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


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Cell expressing only a serine binding mutant of Tsr swarming

0.7% agar

0.3% agar

Burkart et al., PNAS, 1998


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The chemotaxis signaling pathway in swarmingE. coli/Salmonella

V. Sourjik, Trends Microbiol., 2004


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che swarming mutants are developmentally impaired


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The chemotaxis signaling pathway modulates motor bias swarming

V. Sourjik, Trends Microbiol., 2004



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How does Che system control swarmer cell development? swarming

  • 1.Genome-wide expression profiles of WT vs Dche

  • 2. Genetic suppressor analysis of DcheY



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Time course of swarming in wild-type swarmingS. typhimurium

100 x

25 x

Flagellar genes is not upregulated during swarming

Tim Wang


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Che mutants are developmentally impaired swarmingonly 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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Induced swarming

Repressed

Not changed

Microarray: Salmonella WT vs CheY Cells On Plates

WT Red (Cy5)/ CheY Green (Cy3).


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Che mutants specifically down-regulate class 3 motility genes

Genome-wide expression profiles of WT vs DChe


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A Model connecting the dots… genes

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 genes

CM

OM

flgM

FliA

M

M

M

M

FliA

fliC





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Prediction: flagellationflgM mutation should restore class 3 gene expression

It does


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Testing ‘regulation of flagellar length’ model flagellation

Flagella stained with Texas Red-conjugated antibody


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Testing ‘quick response’ model flagellation

After shearing

Flagellate & non-flagellate controls

Rosu & Hughes, J. Bact. 2006


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FlgM secretion after shearing (blending) flagellation

IC – Intracellular; EC - Extracellular


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Class 3 flagellationFlgM as drought sensor: Regulation in reverse


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Susana Mariconda

But why are che mutant colonies dry?


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Suppressors of a flagellationcheY 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


Model for chey as swarming regulator35 l.jpg
Model for CheY as swarming regulator direction

How does motor switching control control surface wetness?


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Switch and Stir model direction

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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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


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H system!+

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