The gas vesicles confer of buoyancy to prokaryotic
cells and are involved in the regulation of buoyancy.
This regulation allows microorganisms to position
themselves at an optimal depth in the water column or
to make vertical migrations based on gradients favorable
to their development. The production of gas vesicles is
dependent on the light in phototrophic organisms,
nutrients and oxygen gradients, temperature, salinity, or
pH in chemolithotrophic or chemoorganotrophic vacuolated prokaryotes living in aquatic environments.
9.7.2.2 Adaptation to Supports
In aquatic environments, the majority of prokaryotic
microorganisms are living on fixed supports, like particles
suspended in the water, borders and banks, sediments and
dumped materials, etc. Prokaryotes can colonize these
substrates by forming biofilms (cf. Sect. 9.7.3) or move at
their surface by gliding. Microorganisms that move by
gliding are usually filamentous; this is the group of gliding
filamentous bacteria. The gliding velocity is much lower
than that obtained when moving based on flagellar movement. These bacteria move slowly and the speed of movement depends on the length of the filament. However, many
nonfilamentous bacteria can also move by gliding on
supports (McBride 2001). Gliding mechanisms are complex.
Chemoorganotroph unicellular filamentous prokaryotes
such as Cytophaga, some Flavobacterium, or some
Myxococcus may have different sliding modes. For example,
Flavobacterium (formerly Cytophaga) johnsoniae colonizes
the surface of plant debris on the soil or sediment; it has
particulate structures (proteins) inserted into envelopes.
A series of proteins anchored in the cytoplasmic membrane
is in contact with a second set of proteins inserted into
the outer membrane (Fig. 9.29a). The cytoplasmic membrane proteins are activated through the proton motive
force and induce activation of proteins of the outer membrane which are set in motion and which, positioned and
moving on the support, move the cell in the opposite
direction by gliding (Fig. 9.29b). Myxococcus, a gliding
unicellular bacterium, moves to the surface of the supports
(particulate organic debris) by secreting a detergent that
reduces the surface tension and allows the bacteria to glide.
These bacteria are well adapted to their organic materials
that biodegrade slowly by excreting cellulases, chitinases,
and other extracellular enzymes capable of hydrolyzing the
solid polymers.
Other unicellular prokaryotes and some multicellular filamentous prokaryotes move on their support by means of the
activation of pili that vibrate and advance the filament.
These pili called type IV pili allow cell adhesion to the
supports and induce advance of the cell by retracting rhythmically. This type of motility is called motility by pulling or
jerking (“twitching motility”). Many nonflagellated but also
flagellated bacteria can move on supports such as biological
surfaces (cells, tissues), organic (biofilms, etc.), or inert and
inorganic (sediment, metals, concrete, etc.), in aquatic
sediments or biofilms by using this type of motility with
type IV pili in polar position (Mattick 2002). The type IV
pili have a diameter of 5–7 nm and a length of 1 to several
microns. They are activated by a protein basal body and are
made up of a protein (pilin). They act by retracting and
extending rhythmically through a “back-and-forth” movement that allows the cells to move on the supports and also
aggregating and moving out of the bacterial colonies. This
mode of movement is mistakenly called “gliding motion,”
but should instead be called “moving by jerking or by rhythmic contractions” (Mattick 2002).
Multicellular filamentous prokaryotes such as Beggiatoa,
Thiothrix, or Leucothrix as well as filamentous cyanobacteria excrete exopolysaccharides (EPS) from pores on
their outer membrane at the junction of septa between
cells. These filaments form exopolymer mucoid layers
around the filament. This layer, adhering to the support,
also allows gliding displacement of these filamentous bacteria by movement due to the excretion of filaments of
exopolysaccharides (McBride 2001). These bacteria
agglomerating together form mucoid masses that adhere
to and colonize surfaces. For example, sulfur-oxidizing
filamentous bacteria such as Beggiatoa or Thiothrix form
complex clumps that adhere to the walls of sulfur thermal
water pools (cf. Sect. 14.4.4, Fig. 14.38). Branched filamentous actinobacteria (Streptomyces) are well suited to
supports (organic particles, plant debris) on which they
grow without moving, but by developing a filamentous network that little by little colonizes all the support.
9.7.3 Adhesion to Surfaces, Biofilms,
and Microbial Mats
9.7.3.1 Mechanisms of Adhesion
Most prokaryotes live by adhering to surfaces in the natural
environment. Cells can join individually or form mono- or
multispecies biofilms, more or less thick (Fig. 9.30).
Many bacteria in aquatic environments adhere to surfaces
in response to stress (survival method), especially
Gram-negative bacteria. Some bacteria (Caulobacter,
Myxococcus) include a phase of adhesion in their cell
cycle. Others need to bind to solid particles for feeding,
such as bacteria that degrade cellulose plant debris, bacteria
that degrade lipid droplets in an aquatic environment, etc.
Ionic Interactions
Prokaryotes can adhere through ionic interactions (electric
charges). Cell surface is negatively charged, which allows
binding to positively charged surfaces.
9 Adaptations of Prokaryotes to Their Biotopes and to Physicochemical Conditions. . .
341
cells and are involved in the regulation of buoyancy.
This regulation allows microorganisms to position
themselves at an optimal depth in the water column or
to make vertical migrations based on gradients favorable
to their development. The production of gas vesicles is
dependent on the light in phototrophic organisms,
nutrients and oxygen gradients, temperature, salinity, or
pH in chemolithotrophic or chemoorganotrophic vacuolated prokaryotes living in aquatic environments.
9.7.2.2 Adaptation to Supports
In aquatic environments, the majority of prokaryotic
microorganisms are living on fixed supports, like particles
suspended in the water, borders and banks, sediments and
dumped materials, etc. Prokaryotes can colonize these
substrates by forming biofilms (cf. Sect. 9.7.3) or move at
their surface by gliding. Microorganisms that move by
gliding are usually filamentous; this is the group of gliding
filamentous bacteria. The gliding velocity is much lower
than that obtained when moving based on flagellar movement. These bacteria move slowly and the speed of movement depends on the length of the filament. However, many
nonfilamentous bacteria can also move by gliding on
supports (McBride 2001). Gliding mechanisms are complex.
Chemoorganotroph unicellular filamentous prokaryotes
such as Cytophaga, some Flavobacterium, or some
Myxococcus may have different sliding modes. For example,
Flavobacterium (formerly Cytophaga) johnsoniae colonizes
the surface of plant debris on the soil or sediment; it has
particulate structures (proteins) inserted into envelopes.
A series of proteins anchored in the cytoplasmic membrane
is in contact with a second set of proteins inserted into
the outer membrane (Fig. 9.29a). The cytoplasmic membrane proteins are activated through the proton motive
force and induce activation of proteins of the outer membrane which are set in motion and which, positioned and
moving on the support, move the cell in the opposite
direction by gliding (Fig. 9.29b). Myxococcus, a gliding
unicellular bacterium, moves to the surface of the supports
(particulate organic debris) by secreting a detergent that
reduces the surface tension and allows the bacteria to glide.
These bacteria are well adapted to their organic materials
that biodegrade slowly by excreting cellulases, chitinases,
and other extracellular enzymes capable of hydrolyzing the
solid polymers.
Other unicellular prokaryotes and some multicellular filamentous prokaryotes move on their support by means of the
activation of pili that vibrate and advance the filament.
These pili called type IV pili allow cell adhesion to the
supports and induce advance of the cell by retracting rhythmically. This type of motility is called motility by pulling or
jerking (“twitching motility”). Many nonflagellated but also
flagellated bacteria can move on supports such as biological
surfaces (cells, tissues), organic (biofilms, etc.), or inert and
inorganic (sediment, metals, concrete, etc.), in aquatic
sediments or biofilms by using this type of motility with
type IV pili in polar position (Mattick 2002). The type IV
pili have a diameter of 5–7 nm and a length of 1 to several
microns. They are activated by a protein basal body and are
made up of a protein (pilin). They act by retracting and
extending rhythmically through a “back-and-forth” movement that allows the cells to move on the supports and also
aggregating and moving out of the bacterial colonies. This
mode of movement is mistakenly called “gliding motion,”
but should instead be called “moving by jerking or by rhythmic contractions” (Mattick 2002).
Multicellular filamentous prokaryotes such as Beggiatoa,
Thiothrix, or Leucothrix as well as filamentous cyanobacteria excrete exopolysaccharides (EPS) from pores on
their outer membrane at the junction of septa between
cells. These filaments form exopolymer mucoid layers
around the filament. This layer, adhering to the support,
also allows gliding displacement of these filamentous bacteria by movement due to the excretion of filaments of
exopolysaccharides (McBride 2001). These bacteria
agglomerating together form mucoid masses that adhere
to and colonize surfaces. For example, sulfur-oxidizing
filamentous bacteria such as Beggiatoa or Thiothrix form
complex clumps that adhere to the walls of sulfur thermal
water pools (cf. Sect. 14.4.4, Fig. 14.38). Branched filamentous actinobacteria (Streptomyces) are well suited to
supports (organic particles, plant debris) on which they
grow without moving, but by developing a filamentous network that little by little colonizes all the support.
9.7.3 Adhesion to Surfaces, Biofilms,
and Microbial Mats
9.7.3.1 Mechanisms of Adhesion
Most prokaryotes live by adhering to surfaces in the natural
environment. Cells can join individually or form mono- or
multispecies biofilms, more or less thick (Fig. 9.30).
Many bacteria in aquatic environments adhere to surfaces
in response to stress (survival method), especially
Gram-negative bacteria. Some bacteria (Caulobacter,
Myxococcus) include a phase of adhesion in their cell
cycle. Others need to bind to solid particles for feeding,
such as bacteria that degrade cellulose plant debris, bacteria
that degrade lipid droplets in an aquatic environment, etc.
Ionic Interactions
Prokaryotes can adhere through ionic interactions (electric
charges). Cell surface is negatively charged, which allows
binding to positively charged surfaces.
9 Adaptations of Prokaryotes to Their Biotopes and to Physicochemical Conditions. . .
341