Structures external to the Cell Wall:

1
Structures external to the Cell Wall

• ( glycocalyx, flagella, axial filaments, and
  pili).
• 1- Glycocalyx and Capsule
• Many bacteria synthesize large amounts of
  extracellular polymers when growing in their
  natural environments.
• These polymers form capsules or glycocalyx.
  Its chemical nature may be
• polysaccharide as in the Pneumococcus or
  polypeptide as in Bacillus
• anthracis .
• When these polymers closely surrounding the
  cell it is called Capsule, But if
• these polymers form a loose meshwork of fibrils
  extending outward from the
• cell it is called glycocalyx

2
Glycocalyx and Capsule

• a

3
a

• Function of capsule or glycocalyx is to protect
  bacterial cells from
• phagocytosis.
• Capsule and glycocalyx can be demonstrated by
  light microscope using of
• capsule stain of bacterial smear
• or India ink wet mount.
• 2-Flagella and motility
• Motile bacteria possess filamentous appendages
  known as flagella, which
• act as organs of locomotion.
• The flagellum is a long, thin filament, twisted
  spirally in an open, regular
• waveform.
• It is about 0.02 µm thick and is usually several
  times the length of the bacterial cell.
• According to the species, there may be one, or
  up to 20, flagella per cell.

4
a

• Flagella may be classified according to there
  arrangement as follow
• 1- Monotrichous (single polar flagellum).
• 2- Lophotrichous (tuft of polar flagella).
• 3- Perituichous (flagella distributed over the
  cell).
• 4- Amphitrichous (one flagellum at each side
  of cell).

5
Flagella are associated with chemotaxis process
(chemical attraction) of bacterial cells that
contribute in disease pathogenesis.

• Monotrichous flagellum
  Lophotrichous flagella
• 
  
• 
  Peritrichous flagella
  

6
3- Axial filaments

• Some types of bacteria have a flagellum that lie
  inside periplasmic space
• (over cell wall peptidoglycan and under the
  outer membrane).
• This flagellum called endoflagellum or axial
  filament.
• The endoflagella are more than half the length of
  the organisms and run along the axial aspect of
  the spiral body.
• They are responsible for rotary motility of
  these organisms.

7
4- Pili and Fimbriae

• Many bacteria possess filamentous appendages
  termed pili or fimbriae.
• These are more numerous than flagella (e.g.
  100-500, being borne surrounding each cell).
• They are from 0.1 to 1.5 µm in length and having
  a uniform width between 4 and 8 nm.
• Pili are important in mediating adhesion between
  the bacteria
• and host cells ( hemagglutination phenomenon).
• Another type of pili called sex pili is longer
  and initiate the
• process of conjugation ( genetic material
  exchange between
• bacteria).

8
Pili and Fimbriae

• a

9
The Bacterial Cell Wall

• The cell envelope
• The layers that surrounding bacterial cell are
  called the cell envelope.
• The Gram-positive cell envelope
• It is composed from three layers the
  cytoplasmic membrane, a thick
• peptidoglycan layer and a variable outer layer
  called capsule.
• The Gram-negative cell envelope
• It is composed from inner membrane (cytoplasmic
  membrane), the outer
• membrane, the peptidoglycan sheet, and capsules
  if present.
• Periplasmic space separates outer and inner
  membrane.

10
The Gram-positive cell envelope
The Gram-negative
cell envelope

• a

11
The cell wall

• It is the outer covering layer of the bacterial
  cell.
• It is a rigid structure consisting of two layers
  in Gram-positive bacteria and
• of three layers in Gram-negative.
• In Gram-positive bacteria, it is composed from
  pepeidoglycan (thick) layer
• and the associated capsule if present.
• Peptidoglycan is long polymers of two sugar
  derivatives, NAG (N-Acetyl
• Glucosamine) and NAM (N-Acetyl Muramic acid) with
  side chains of four
• alternating D and L amino acids attached to NAM.

12
The cell wall structure

• a

13
Structures internal to the Cell WallThe
cytoplasmic membrane

• It is consisting of phospholipids bilayers and
  proteins (integral and peripheral protein).
• The major functions of
• cytoplasmic membrane
• are
• 1- Selective permeability and
• transport of solutes.
• 2- Electron transport by its
• electron transport chain.
• 3- Excretion of hydrolytic
• exoenzymes.

14
Spores and Sporulation

• To enhance survival during periods of
  environmental hostility, some gram-positive rods
  undergo profound structural and metabolic
  changes.
• These results in the formation of a endospores
  inside the original cell.
• Sporulation
• Repackaging a copy of bacterial DNA into a new
  multilayered cellular envelope that contains very
  little water and reduced metabolic activity.

15
Spore Germination

• Destruction of spore coat and cortex due to heat
  or pH variation to produce vegetative bacterial
  cell which begins binary fission.
• Medical significance of sporulation
• Some of the pathogenic bacteria are
  spore-formers.
• Spores of these microbes can remain viable for
  many years.
• If the spore inoculated in wounds, it will
  germinate to produce
• Infection.
• Example of spore forming bacteria
• 1-Bacillus species.
• 2-Clostridium species.

16
Spore morphology

• Endospore structure
  Spores of Bacillus