Chapter 4 Part 4 Surface structures and inclusions of
prokaryotes Slide 2 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 resistance to
desiccation Slide 3 Capsules and Slime Layers Polysaccharide layers
Assist in attachment to surfaces Aid in evasion of immune system
Resist dessication Slide 4 Capsule Observed by using a negative
stain The dye does not penetrate the capsule but is seen on a dark
background Slide 5 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)
Slide 6 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 Slide 7 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 Slide 8
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 Slide 9 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
Slide 10 Differences between Endospores and Vegetative Cells Slide
11 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 Slide 12 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 Slide 13 Spore
structure Slide 14 Sporulation or Sporogenesis Process of endospore
formation within a vegetative (parent) cell Germination = return of
an endospore to its vegetative state Slide 15 Spore Germination
Activation by heat and nutrients Ca-dipicolinate and cortex
components disappear SASPs degrade Swelling with H 2 O 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 Slide 16 Microbial locomotion Slide 17 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 Slide 18 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
Slide 19 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 Slide 20 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 m/sec Myxobacteria and Cyanobacteria examples Slide 21
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 Slide 22 Gliding motility: movement of
proteins Motility proteins in the cytoplasmic and outer membranes
propel the cell Slide 23 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
Slide 24 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 Slide 25 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 Slide 26 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 Slide 27 Chemotaxis
