nuclear envelope consisting of a double membrane surrounds
the nucleoid inside the riboplasm, surprising discovery in
prokaryotes, although this structure is not a true nucleus in
the eukaryotic sense (Ward et al. 2006).
3.1.1.3 Spores and Cellular Appendages
Some bacteria are able to produce endospores of resistance
when their environmental conditions become unfavorable.
The endospores are resistant structures to extreme conditions
(temperature, UV, pH, redox potential, drought, etc.). They
are a means of survival and can stay alive for very long
periods estimated at thousands of years. The endospore
contains genetic material and a very dehydrated cytoplasm
that are protected by a complex system consisting of several
resistant envelopes (Fig. 3.6a). Other structures of resistance
exist in prokaryotes such as akinetes* of Cyanobacteria,
cysts of Azotobacter and Myxobacteria, or exospores of
Actinobacteria.
Flagella are filamentous structures 15–20 nm in diameter
in the form of rigid spirals, which are composed of proteins,
principally flagellin (Fig. 3.6b). They are inserted on a basal
body formed of protein rings included in the envelopes of the
Lipoprotein
LPS
Cytoplasm
Cytoplasm
Porin
Lipid A
Teichoic
acids
Peptidoglycan
Periplasmic space
Peptidoglycan
Outer
membrane
Cytoplasmic
Membrane
1: Gram-positive bacterium
2: Gram-negative bacterium
Protein
Phospholipids
b
Lipopoly -
saccharides
Periplasmic
space
Phospholipid
Membrane Cytoplasm
Protein
Porin
Polysaccharide
Lipid A
Lipoprotein
Peptidoglycan
(1)
AG AM AG AM
AG AM
AG AM AG AM
AG AM
TP
TP
TP
TP
TP
TP
AG = N-acetylglucosamine
AM = N-acetylmuramic acid
TP = Tetrapeptide
a
Pentaglycine bridge
c
Fig. 3.5 The cell wall of
bacteria. (a) Structure of
peptidoglycan. (b) Cell wall
structure of Gram-positive and
Gram-negative bacteria. (c)
Structure of the outer membrane
of Gram-negative bacteria. (1)
Pentaglycine bridges (Grampositive bacteria) or direct bond
between two amino acids of
tetrapeptides (Gram-negative
bacteria) (Drawing:
M.-J. Bodiou)
3 Structure and Functions of Microorganisms: Production and Use of Material and Energy
31
the nucleoid inside the riboplasm, surprising discovery in
prokaryotes, although this structure is not a true nucleus in
the eukaryotic sense (Ward et al. 2006).
3.1.1.3 Spores and Cellular Appendages
Some bacteria are able to produce endospores of resistance
when their environmental conditions become unfavorable.
The endospores are resistant structures to extreme conditions
(temperature, UV, pH, redox potential, drought, etc.). They
are a means of survival and can stay alive for very long
periods estimated at thousands of years. The endospore
contains genetic material and a very dehydrated cytoplasm
that are protected by a complex system consisting of several
resistant envelopes (Fig. 3.6a). Other structures of resistance
exist in prokaryotes such as akinetes* of Cyanobacteria,
cysts of Azotobacter and Myxobacteria, or exospores of
Actinobacteria.
Flagella are filamentous structures 15–20 nm in diameter
in the form of rigid spirals, which are composed of proteins,
principally flagellin (Fig. 3.6b). They are inserted on a basal
body formed of protein rings included in the envelopes of the
Lipoprotein
LPS
Cytoplasm
Cytoplasm
Porin
Lipid A
Teichoic
acids
Peptidoglycan
Periplasmic space
Peptidoglycan
Outer
membrane
Cytoplasmic
Membrane
1: Gram-positive bacterium
2: Gram-negative bacterium
Protein
Phospholipids
b
Lipopoly -
saccharides
Periplasmic
space
Phospholipid
Membrane Cytoplasm
Protein
Porin
Polysaccharide
Lipid A
Lipoprotein
Peptidoglycan
(1)
AG AM AG AM
AG AM
AG AM AG AM
AG AM
TP
TP
TP
TP
TP
TP
AG = N-acetylglucosamine
AM = N-acetylmuramic acid
TP = Tetrapeptide
a
Pentaglycine bridge
c
Fig. 3.5 The cell wall of
bacteria. (a) Structure of
peptidoglycan. (b) Cell wall
structure of Gram-positive and
Gram-negative bacteria. (c)
Structure of the outer membrane
of Gram-negative bacteria. (1)
Pentaglycine bridges (Grampositive bacteria) or direct bond
between two amino acids of
tetrapeptides (Gram-negative
bacteria) (Drawing:
M.-J. Bodiou)
3 Structure and Functions of Microorganisms: Production and Use of Material and Energy
31