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Chapter 1
The structure and function of prokaryotes
Special structure
• Pili and fimbriae
• Flagella
• The bacterial endospore
Pili and fimbriae
G-, short, fine, hairlike appendages
that are not involved in motility.
Fimbriae/fimbria:1000piece/cell,
adhesion to host epithelium
Sex pili/pilus: 1-10piece/cell,
sexual conjugation, they are
genetically determined by sex factors
or conjugative plasmids and are required
for bacterial mating.
Receptors of some bacterial viruses.
Fimbriae and Pilli
FLAGELLA
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Some bacteria are motile
Locomotory organelles- flagella
Taste environment
Respond to food/poison
– chemotaxis
• Flagella
– embedded in cell membrane
– project as strand
– Flagellin (protein) subunits
– move cell by propeller like action
The majority of motile prokaryotes
move by means of flagella
Flagellar Arrangements
Peritrichous
Polar/monotrichous
Lophotrichous
Amphitrichous
Flagellar ultrastructure
Filament: from cell surface to the tip
Basal body: embedded in the cell
Hook: link the filament to its basal body
The E. coli
Basal body:
Flagellar
+
G:
Structure
S (peptidoglycan),
M(plasma membrane)
G-:
L (out membrane),
P (peptidoglycan layer),
S-M(contact the plasma membrane)
The mechanism of flagellar movement
Rotatal movement
counterclockwiae: forward on
clockwise: tumble
Bacteria-bound experiment
cell
flagella
antibody
Glass lide
Bacterial Behavior
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Chemotaxis, Phototaxis, and Other Taxes
Prokaryotes encounter gradients of physical
and chemical agents in nature, and the motility
machinery in the cell is designed to respond in
a positive or negative way to these gradients
by directing the movement of the cell either
toward or away from the signal molecule,
respectively.
Such directed movements are called TAXES.
Chemotaxis: a response to chemicals.
Phototaxis: a response to light.
Chemotaxis in Bacteria
• Chemotaxis is the
movement of an
organism toward (an
attractant) or away from
(a repellent) a chemical.
The Chemotaxis
Process
(a) In the absence of a
chemical attractant the
cell swims randomly
in runs, changing
direction during
tumbles.
(b) In the presence of an
attractant runs become
biased, and the cell
moves up the gradient
of the attractant.
Mechanism of Chemotaxis
MCPs: methyl-accepting chemotaxis proteins
Phototaxis
• Accumulation of the phototrophic bacterium at light
wavelengths at which its pigments absorb.
• Phototaxis of an entire colony toward the light source on the
right.
How to judge wether a cell
have flagella
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1. Light Microscope by staining
2. Electron microscope
3. Feature of colony
4. Culture in semi-solid medium
The bacterial endospore
A number of G+ bacteria can form a
special resistent, dorment structure, be
resistant to enviroment stresses such as heat,
ultraviolet radiation, gamma radiation,
chemical disinfectants, and desiccation.
1.Sterilize
2.Spore formation
Morphology of Endospores (芽孢/胞）
A
B
Taxomony-relative
C
Endospore Structure
Mature free endospore
The endospore
exosporium
coat
outer
membrane
cortex
Inner
membrane
Spore formation: lack of nutrients. 7 stages
B
A. Life Cycle of endospore
B. Formation of endospore in
Bacillus megaterium
A
The mechnism of heat and other
kethal agents resistantance
1. Calcium dipicolinic acid
2. Heat stable enzyme
3. High G+C%
4. Less water
5. Amino acid containing surfur(cys)
Spore germination
1. Activation – Usually results from treatments like heating.
2. Germination – Breaks spore’s dormant state. This process
is characterized by spore swelling, loss of resistance to heat and
other stresses, loss of refractility and increase in metabolic activity.
3. Outgrowth – The spore protoplast makes new components
and develops once more into an active bacterium.
Paraspore crystal as biopesticide
Parasporal Crystal
Toxic crystals
(Spore-companioned crystal)
Several Bacillus species, most notably
B.popilliae and B. thuringiensis, produce
intracellular crystals of toxic glycoproteins
when they sporulate.
What we have learned so far?
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what is Pili and fimbriae? Their function?
What is Flagella? Its Arrangements, ultrastructure?
The mechanism of flagellar movement
Describe the structure and function of a bacterial
flagellum.
• What is the energy source for the flagellum?
• Bacteria-bound experiment?
• Chemotaxis, Phototaxis?
• How to judge wether a cell have flagella?
• What is endospore? Its structure, signifance.
• Spore formation, Life Cycle.
• The mechnism of heat and other kethal agents
resistantance?
• What is paraspore crystal? Its signifance?
Summary
1, Prokaryotic genetic material is located in
an area called the nucleoid and is not
enclosed by a membrane.
2, Most bacteria have a cell wall outside the
plasma membrane to give them shape and
protect them from osmotic lysis.
Bacterial walls are chemically complex and
usually contain peptidoglycan or murein.
3, Bacteria often are classfied as either gram
positive or gram negative based on differences in
cell wall structure and their response to Gram
staining.
Gram-positive walls have thick,homogeneous
layers of peptidoglycan and teichoid acid. Gramnegative bacteria have a thin peptidoglycan layer
surrounded by a complex outer membrane
containing lipopolysaccharides and other
components
4, Some bacteria are motile, usually by means of
flagella, and bacterial species differ in the number
and distribution of their flagella.
5, Structures such as capsules, fimbriae, and sex
pili are found outside of some bacterial cell wall.
6, Some bacteria survive adverse environmental
conditions by forming endospores, dormant
structures resistant to heat,desiccation and many
chemicals