Download endospore

Chapter 4 Part 4
Surface structures and inclusions of
prokaryotes
Glycocalyx
• Substance that surrounds the cell
• Gelatin polymer containing sugars and
proteins
• If firmly attached to the cell wall = capsule
• If loosely attached to the cell wall = slime
layer
• Functions
– attachment
– protection of pathogen from host immune
system
– protection from phagocytosis
Capsules and Slime Layers
– Polysaccharide layers
– Assist in attachment to surfaces
– Aid in evasion of immune system
– Resist dessication
Capsule
• Observed by using a
negative stain
• The dye does not
penetrate the capsule
but is seen on a dark
background
S layer
• Cell surface layer composed of protein
• Almost always in archaea (cell wall type)
and in many bacteria (associates with cell
wall, cell memrane, or LPS)
• Function not precisely known
• May act as a selectively permeable barrier
• bacteria: may provide protection from host
defense (pathogens)
Fimbriae and Pili
• Hairlike appendages that
are shorter than flagella
• Used for attachment
• Pili: longer than fimbriae
– Conjugation with pili
• Join bacterial cells in
preparation for the transfer
of DNA from one cell to
another
Inclusion bodies
• Function as energy reserves or as a reservoir of
structural building blocks
• Differ in different organisms
• Carbon storage polymers
• Polyphosphates
• Sulfur globules
• Magnetosomes
• Gas vesicles
Endospores
• Resting structures formed by some bacteria for
survival during adverse environmental conditions
– Example: when essential nutrients are depleted
• The endospore is a highly resistant differentiated
bacterial cell that are highly resistant to heat, and
drying out and are difficult to destroy
Endospores
• Endospores can remain dormant indefinitely but
germinate quickly when the appropriate trigger is
applied
• Endospores differ significantly from the
vegetative, or normally functioning, cells
Differences between Endospores and
Vegetative Cells
Important spore proteins
• Dipicolinic acid
– Located in the core
– Calcium-dipicolinic acid complexes reduces
water available and helps dehydrate spores
– Interculates into the DNA and stabilizes it to
heat denaturation
Important spore proteins
• Small acid-soluble proteins (SASPs)
– Bind to the DNA in the core and protect it from
damage
– Function as a carbon and energy source when
forming vegetative (normal) cells from spore
cells
Spore structure
Sporulation or Sporogenesis
• Process of endospore
formation within a
vegetative (parent) cell
• Germination = return
of an endospore to its
vegetative state
Spore Germination
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Activation by heat and nutrients
Ca-dipicolinate and cortex components disappear
SASPs degrade
Swelling with H2O
Cell begins to divide like normal
Bacillus anthracis (and Clostridium) produces
endospores
– Easily aerosolized and spread
– Relatively easy and inexpensive to prepare in laboratory
– Can be easily transported without detection
Microbial locomotion
Flagella
• Long filamentous appendages that propel
the bacteria in movement
• made of several proteins, most of which are
anchored in the cell wall and cytoplasmic
membrane
• The flagellum filament, rotates which drives
the flagellar motor
Different types of flagella
• In peritrichous
flagellation, the
flagella are inserted at
many locations around
the cell surface
• In polar flagellation,
the flagella are
attached at one or both
ends of the cell.
• In lophotrichous
flagellation, a group of
flagella arise at one
end
3 parts of flagella
 Filament: long outermost
region; flagellin subunits
(Flg units); attached to the
hook
 Hook: base; single
protein, connection to
motor
 Motor (basal body):
anchors the flagellum to
the cell wall and the
plasma membrane
 Flagella moves the cell by
rotating from the motor
either clockwise or
counterclockwise
Gliding motility
• Prokaryotes that move by gliding motility
do not employ rotating flagella but instead
creep along a solid surface by any of several
possible mechanisms
• Movement typically occurs along long axis
of cell
• Slower than flagella; 10 μm/sec
• Myxobacteria and Cyanobacteria examples
Gliding motility: slime secretion
• Polysaccharide slime is secreted on the
outside surface of the cell
• Slimes contacts the cell surface and solid
surface upon which it glides
• As slime adheres, the cell is pulled along
the surface
Gliding motility: movement of
proteins
• Motility proteins in the cytoplasmic and
outer membranes propel the cell
Why do bacteria move?
• Motile bacteria can respond to chemical and
physical gradients in their environment
• Movement toward an attractant
• Movement away from a repellant
• Controlled by the degree to which runs
(counterclockwise) or tumbles (clockwise)
occurs - direction of rotation of the
flagellum
Types of movement
• Taxis: directed movement in response to chemical
or physical gradients
• Chemotaxis: a response to chemicals
• Phototaxis: a response to light
• Aerotaxis: a response to oxygen
• Osmotaxis: a response to ionic strength
• Hydrotaxis: a response to water
Direction of movement
• Counterclockwise rotation moves the cell in
a direction called a run
• Clockwise rotation causes the tuft (group)
of flagella to spread, resulting in tumbling
of the cell
Chemotaxis
• No attractant, random runs and tumbles but
do not move
• When there is an attractant, the runs are
longer and the tumbles are less frequent
• Result is that the organism moves towards
the attractant
Chemotaxis