adhere to surfaces, and to resist more or less effectively to
environmental stresses. In some pathogenic bacteria, the
capsule confers an additional pathogenicity, increasing the
resistance to phagocytosis by the host organism.
Finally, some bacteria and archaea have a layer of
proteins or glycoproteins on the outer surface of their
walls, called S-layer that increases the protection of cells
against environmental constraints.
3.1.1.2 Cytoplasm and Nucleoid
The cytoplasm is an aqueous solution of mineral salts and
organic molecules necessary for the metabolic activity. It
contains ribosomes, small particles of 15 nm in diameter,
composed of proteins and ribosomal RNAs. Ribosomes are
the site of the cellular protein synthesis and are composed of
two subunits: the 50S subunit formed by proteins and 23S and
5S rRNAs and 30S subunit that consists of protein and 16S
rRNA. The cytoplasm may contain inclusions of organic
substances of reserves (glycogen, poly-β-hydroxyalkanoates,
lipids) or inorganic compounds (polyphosphate, sulfur, iron)
depending on the microbial type and metabolic activity. Other
inclusions are more specific to some bacterial groups:
1. Cyanophycin granules, polypeptides constituting reserves
of nitrogen in cyanobacteria.
2. Gas vacuoles for buoyancy of some prokaryotes.
3. Bacterial microstructures as carboxysomes, small particles
containing ribulose 1,5-bisphosphate carboxylase necessary to the CO 2 fixation in some autotrophic prokaryotes.
4. Magnetosomes (cf. Sect. 14.5.2, Fig. 14.46) (containing
magnetite). These structures provide magnetotactic bacteria the ability to move in a magnetic field.
5. Thylakoids, membrane structures forming flattened
vesicles, location of the photosynthetic activity in
cyanobacteria.
6. Chlorosomes, ovoid structures adjacent to the cytoplasmic membrane in phototrophic green bacteria, containing
photosynthetic pigments (Fig. 3.27).
In some bacteria, protein filaments forming filamentous
structures (cytoskeleton) in the cytoplasm under the cytoplasmic membrane may be involved in cell shape
(Carballido-Lo ´pez 2006).
In a more or less central area of the cytoplasm, there is the
nucleoid, consisting of a single double-stranded DNA molecule. It is the bacterial chromosome, usually single, circular,
folded in on itself, and associated with proteins. Besides the
chromosome, plasmids, small DNA molecules, can be present
and transferred between cells in prokaryotes. Chromosome
and extrachromosomal elements such as plasmids are part of
the bacterial genome. Plasmids have few genes that are
associated with specific properties of resistance (antibiotics,
pollutants), virulence, or metabolism (biodegradation of
xenobiotics). In bacteria belonging to the order Planctomycetales, an intracytoplasmic membrane divides the cytoplasm into two compartments, the peripheral paryphoplasm
containing no ribosome and the central riboplasm containing
ribosomes and the nucleoid (Fig. 14.32). In some of them, a
)
)
)
)
)
)
)
)
-
-
-
-
-
i
ADP
ATP
ATP ATP
Oxidized
terminal
acceptor
Oxidized
Reduced
Reduced
substrate
Substrate
+
+
+
+
+
+
+ P
Synthase
CYTOPLASM
H
+
H
+
H
+
H
+
H
+
+
H
+
H
+
H
+
H
Cyto pla sm ic m e m b r a n
e
OUTER ENVIRONMENT
t1
t2
t3
tn
Na
Basal body
of flagellum
Flagellum
Fig. 3.4 Different modes of
active transport and formation of
a membrane proton gradient. t1 to
tn: electron carriers (Drawing:
M.-J. Bodiou)
30
R. Matheron and P. Caumette
environmental stresses. In some pathogenic bacteria, the
capsule confers an additional pathogenicity, increasing the
resistance to phagocytosis by the host organism.
Finally, some bacteria and archaea have a layer of
proteins or glycoproteins on the outer surface of their
walls, called S-layer that increases the protection of cells
against environmental constraints.
3.1.1.2 Cytoplasm and Nucleoid
The cytoplasm is an aqueous solution of mineral salts and
organic molecules necessary for the metabolic activity. It
contains ribosomes, small particles of 15 nm in diameter,
composed of proteins and ribosomal RNAs. Ribosomes are
the site of the cellular protein synthesis and are composed of
two subunits: the 50S subunit formed by proteins and 23S and
5S rRNAs and 30S subunit that consists of protein and 16S
rRNA. The cytoplasm may contain inclusions of organic
substances of reserves (glycogen, poly-β-hydroxyalkanoates,
lipids) or inorganic compounds (polyphosphate, sulfur, iron)
depending on the microbial type and metabolic activity. Other
inclusions are more specific to some bacterial groups:
1. Cyanophycin granules, polypeptides constituting reserves
of nitrogen in cyanobacteria.
2. Gas vacuoles for buoyancy of some prokaryotes.
3. Bacterial microstructures as carboxysomes, small particles
containing ribulose 1,5-bisphosphate carboxylase necessary to the CO 2 fixation in some autotrophic prokaryotes.
4. Magnetosomes (cf. Sect. 14.5.2, Fig. 14.46) (containing
magnetite). These structures provide magnetotactic bacteria the ability to move in a magnetic field.
5. Thylakoids, membrane structures forming flattened
vesicles, location of the photosynthetic activity in
cyanobacteria.
6. Chlorosomes, ovoid structures adjacent to the cytoplasmic membrane in phototrophic green bacteria, containing
photosynthetic pigments (Fig. 3.27).
In some bacteria, protein filaments forming filamentous
structures (cytoskeleton) in the cytoplasm under the cytoplasmic membrane may be involved in cell shape
(Carballido-Lo ´pez 2006).
In a more or less central area of the cytoplasm, there is the
nucleoid, consisting of a single double-stranded DNA molecule. It is the bacterial chromosome, usually single, circular,
folded in on itself, and associated with proteins. Besides the
chromosome, plasmids, small DNA molecules, can be present
and transferred between cells in prokaryotes. Chromosome
and extrachromosomal elements such as plasmids are part of
the bacterial genome. Plasmids have few genes that are
associated with specific properties of resistance (antibiotics,
pollutants), virulence, or metabolism (biodegradation of
xenobiotics). In bacteria belonging to the order Planctomycetales, an intracytoplasmic membrane divides the cytoplasm into two compartments, the peripheral paryphoplasm
containing no ribosome and the central riboplasm containing
ribosomes and the nucleoid (Fig. 14.32). In some of them, a
)
)
)
)
)
)
)
)
-
-
-
-
-
i
ADP
ATP
ATP ATP
Oxidized
terminal
acceptor
Oxidized
Reduced
Reduced
substrate
Substrate
+
+
+
+
+
+
+ P
Synthase
CYTOPLASM
H
+
H
+
H
+
H
+
H
+
+
H
+
H
+
H
+
H
Cyto pla sm ic m e m b r a n
e
OUTER ENVIRONMENT
t1
t2
t3
tn
Na
Basal body
of flagellum
Flagellum
Fig. 3.4 Different modes of
active transport and formation of
a membrane proton gradient. t1 to
tn: electron carriers (Drawing:
M.-J. Bodiou)
30
R. Matheron and P. Caumette