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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

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

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
Signals…

Not

Slowedmotor

Ironstarvation

Specificaminoacids

pHchanges

Oxygengradients

Knownautoinducers

slide6
Null hypothesis: Density dependence is related to generating wetness through some means other that quorum sensing.
slide7

Chemotaxis

LPS

Surfactant?

Wetting

Two major classes of swarming-defective mutants

?

slide8

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

slide9

Cell expressing only a serine binding mutant of Tsr

0.7% agar

0.3% agar

Burkart et al., PNAS, 1998

slide14

How does Che system control swarmer cell development?

  • 1.Genome-wide expression profiles of WT vs Dche
  • 2. Genetic suppressor analysis of DcheY
slide16

Time course of swarming in wild-type S. typhimurium

100 x

25 x

Flagellar genes is not upregulated during swarming

Tim Wang

slide17

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

slide19

Induced

Repressed

Not changed

Microarray: Salmonella WT vs CheY Cells On Plates

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

slide20

Che mutants specifically down-regulate class 3 motility genes

Genome-wide expression profiles of WT vs DChe

slide21

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).

slide28

Testing ‘regulation of flagellar length’ model

Flagella stained with Texas Red-conjugated antibody

slide29

Testing ‘quick response’ model

After shearing

Flagellate & non-flagellate controls

Rosu & Hughes, J. Bact. 2006

slide30

FlgM secretion after shearing (blending)

IC – Intracellular; EC - Extracellular

slide32

1. Genome-wide expression profiles of WT vs DChe

  • 2. Genetic suppressor analysis of DcheY

Susana Mariconda

But why are che mutant colonies dry?

slide33

Suppressors of a cheY null mutant map to the switch complex

0.3% agar

0.7% agar

Mariconda et al., Mol. Microbiol. 2006

slide34

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
Model for CheY as swarming regulator

How does motor switching control control surface wetness?

slide36

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

slide38

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

slide39

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