Chapter 1
The structure and function of prokaryotes
• Pili and fimbriae
• Flagella
• The bacterial endospore

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.

• 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

Peritrichous
Polar/monotrichous
Lophotrichous
Amphitrichous

Filament : from cell surface to the tip
Basal body : embedded in the cell
Hook : link the filament to its basal body
Basal body :
G + :
S (peptidoglycan),
M(plasma membrane)
The E. coli
Flagellar
Structure
G-:
L (out membrane),
P (peptidoglycan layer),
S-M(contact the plasma membrane)

Rotatal movement counterclockwiae: forward on clockwise: tumble

Bacteria-bound experiment flagella antibody cell
Glass lide

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 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.

MCPs: methyl-accepting chemotaxis proteins

• 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.

• 1. Light Microscope by staining
• 2. Electron microscope
• 3. Feature of colony
• 4. Culture in semi-solid medium

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

芽孢
胞）
C
A B
Taxomony-relative

Mature free endospore

exosporium
cortex coat outer membrane
Inner membrane

Spore formation: lack of nutrients. 7 stages

A
A. Life Cycle of endospore
B. Formation of endospore in
Bacillus megaterium
B

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.

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 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?

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