Other Extracellular Layers Outer membrane Capsule Sheath Cell Appendages Filamentous, small: Fimbriae, Pili, & Spinae Filamentous, large: Flagella Outer.

Other Extracellular Layers

Outer membraneCapsuleSheath

Cell AppendagesFilamentous, small: Fimbriae, Pili, & SpinaeFilamentous, large: Flagella

Outer MembraneMost common in Gram negative bacteria, often associated

with a fairly thin peptidogylcan layerA second lipid bilayer, but NOT water and ion impermeable

(permeable largely due to the presence of channel proteins called porins). The outer membrane IS abarrier to large solutes such as glucose.

Often is an asymmetric bilayer, where the outer leaflet containsthe unusual lipid LPS (LipoPolySaccharide). LPS can beshed from the outer membrane and is a major endotoxin

Cell Layers in a Gram Negative Bacterium

Lipopolysaccharide (LPS) Structure

CapsulesA thick layer of secreted polysaccharide which surrounds the cellgenerally a defensive structure, often involved in pathogenicity

Protein JacketsLike capsules are secreted by the cell and built around the cellMuch more complex than capsules mostly made of proteinOften associated with multicellular bacteria

Fimbriae, Pili, & Spinae

Frimbriae & Pili both refer to filamentous projections from the cellsurface made of protein (Frimbriae is the more general term)

There is an ongoing attempt to classify different types of pili: Type I --- adhesive Type II --- involved in general secretion of proteins to the

outside of the cell Type IV --- defined by assembly pathway

and so on . . .

Spinae, as the name implies are spine-like projections composed of protein often used to increase the cell’s surface area

Two Types of Bacterial Motility

Swimming: ability to move through liquids--- usually employing a spiral propeller (flagellum)--- some bacteria can move over surfaces with flagella--- all bacterial flagella are genetically similar

(Horizontal Gene Transfer)

Surface (Gliding) Motility: movement over surfaces--- cells lack flagella--- gliding cells generally cannot swim --- multiple systems have arisen among

different groups of bacteria

aaa

(Halobacterium salinarium)polar in at least one archaeon

aa

(R. sphaeroides)

aaa

Styles of Flagellation

peritrichouspolar

equatorial

(E. coli, S. typhimurium)(A. serpens)

Swimming Bacteria

All bacteria haveessentially the sameflagellar genes (homologous)

The Archea have an analogousstructure that is not geneticallysimilar to the bacterial flagellum

FlagellaUsed for bacterial locomotion (usually swimming)requires tremendous energy input (up to 20% of cellular

energy budget for multiply flagellated cells)can serve as a model system for intracellular signaling

Flagellar Factoids -“flagellum” is a misnomer from early microscopy, the filament is

helical and appears to move in a wave-like manner as it rotates, it is actually quite rigid

- each flagellar filament is composed primarily of one protein, flagellin (FliC), in about 1 million copies, flagellin is also an important antigen for the immune system

- the flagellar filament is a passive structure, basically a propeller

- the flagellum is driven entirely at it’s base by a complex of proteins that function as a proton driven rotary motor

The flagellar motor is fueled by the trans-membrane ion gradient

a

H+

inner membrane

outer membrane

peptidoglycan(hundreds/rev)

~ 300 rev/sec

CheY- P

MotA/B TorqueGenerators (Stator Complex)

The flagellar motor is reversible

CCW: run CW: tumble

E. coli responds to chemical gradients by biasing its random walk

No stimulus Gradient of chemoattractant

[Asp], e.g.

Chemotaxis

- the ability to sense and respond to extracellular concentration gradients of solutes

Chemoreceptors

Input

Output:motor bias,CCWCW rotation

CheY – P- CW signal- 3 sec. lag

bacterial cell