Transcript The Bacteria - De Anza College

4-a The Bacteria
pps. 77 – 106
• The Prokaryotic Cell
• Size, shape, arrangement of cells
• Structures external to cell wall
Animations
Bacterial Motility4
(Bacterial Motility Quiz)
Membrane Transport4
(Membrane Transport Quiz)
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Prokaryote vs Eukaryote
“Prenucleus”
“True nucleus”
One circular chromosome Paired chromosomes
Not in a membrane
In nuclear membrane
No histones
Histones
No organelles
Organelles
(Golgi, ER, cilia, etc.)
Peptidoglycan cell walls
Polysaccharide cell walls
Binary fission
Mitotic spindle
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The Prokaryotic World
Vast heterogeneous group
Include bacteria, archaea
Ubiquitous in nature
Very small
Unicelluar
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Differentiated by many factors
Morphology (shape)
Chemical composition (~staining)
Nutritional requirements
Biochemical activities
Sources of energy
Go through your Lab Manual and list Ex #s
next to each of the factors above
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Morphology, Shapes
• Coccus (plural = cocci; berries)
– Spherical cells
• Bacillus (plural = bacilli; small staffs)
– Rod-shaped, often motile
– Large surface area to volume and adsorption
is more effective
• Coccobacillus
– Cells not perfectly round (as cocci)
– Have ‘blunted’ ends, ‘oval’ shape
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• Spirillum (plural = spirilla)
– Spiral or curved bodies, one or more ‘twists’
– Rigid, fairly inflexible
– Often motile by external flagella
• Spirochetes
– Also ‘spiral’ shaped, but more flexible
– Motile by an internal flagellum, axial filament
• Vibrio
– Comma shaped cells, motile via flagella
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• Average size: 0.2 -1.0 µm  2 - 8 µm
• Basic shapes
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Figures 4.1a, 4.2a, 4.2d, 4.4b, 4.4c
Arrangements, Groupings
• Arrangement & groupings - useful
identification characteristics
• Cells can remain attached to each other as
bacteria divide
• Cocci tend to display more variation in
grouping than rods
– Cocci divide along more than one axis
– Rods only divide along their short axis
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• Diplococci = pairs of cocci
• Streptococci = chains of cocci
• Staphylococci = clusters of geometrically
arranged cocci (sometimes grape-like)
• Tetrads = ‘packets’ of 4 cells
• Sarcinus = ‘packets’ of 8 cells
• Diplobacilli = pairs of cells
• Streptobacilli = chains of cells
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Figures 4.1, 4.2
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Unusual shapes
– Star-shaped Stella
– Square Haloarcula
• Most bacteria are monomorphic
• A few are pleomorphic (Corynebacterium)
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Figure 4.5
Structures External to the Cell Wall
Glycocalyx
Flagella
Axial filaments
Fimbriae, pili
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Pili
Flagellum
Fimbriae
Glycocalyx
Cell wall
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Glycocalyx
• The outer surface covered in
– Polysaccharide, protein, polyalcohols, amino
sugars, spp specific
• Functions include:
– Attachment
– Protection from desiccation
– Protection from ‘attack’
Figure 4.6
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2 Types of Glycocalyx
Capsules
Slime layers
• Capsules are
– Closely associated
with cells
– Does not ‘wash’ off
easily
• Slime layer is
– More diffuse, easily
washed off
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• Glycocalyx can be thick or thin, rigid or
flexible
• Observe with India ink
– See dark cells with ‘clear outline’ around them
– Stain does not penetrate glycocalyx
Stain?
See Ch 3, Fig 3.13a, p 72 & LM
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Functions
Attachment
• Streptococcus mutans
– Produces a slime layer
– Forms a surface that allows other bacteria to
aggregate on tooth surfaces
– Results in dental plaque
• Vibrio cholerae
– Attach to intestinal villi of host
– Results in cholera
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Avoid Desiccation
• Capsules and slime layers are hydrophilic
– Bind ‘extra’ water in the environment
– Contribute to protection from desiccation
• Also provide protection from loss of nutrients
– Holds nutrients within the layer
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Avoid Phagocytosis
It is difficult to engulf a bacterium that
has a capsule
• Streptococcus pneumoniae
– Able to cause pneumonia and ‘kill’ patient
– Non-encapsulated cannot cause pneumonia
• Klebsiella colonize respiratory tract
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Capsules and Virulence
Bacteria
Disease
1. Bacillus anthracis
2. Streptococcus
pneumoniae
3. Klebsiella
4. Streptococcus
mutans
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Flagella
• A tail-like structure
– Projects from the cell body of bacteria
– Functions in movement
• Bacterial example:
Figure 4.6
– Helicobacter pylori
• Uses multiple flagella to propel itself
• Through mucus lining to reach stomach
epithelium
Singular: Flagellum; whip
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Flagella are Helical Filaments
Rotate like screws
Provide several kinds of bacterial motility
•
•
•
•
•
Consist of protein: flagellin
Attach to a protein ‘hook’
Connects to ‘basal body’ rings
Gram + microbes have 2 basal body rings
Gram negative have 4 rings
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Gram negative bacterium
Note: 4 rings
vs 2 in Gram +
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Figure 4.8b
Flagella and Motility
• Via rotation of the basal body
• Rotational ‘speed’ can increase or
decrease
• Moves bacteria through liquid media
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Flagella Variation
• Monotrichous (polar)
– One flagellum
– Vibrio cholera
• Amphitrichous
– Have a single flagellum on each end
– Only one operates at a time
– Allows bacteria to reverse course rapidly
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• Lophotrichous (one or both ends of cell)
– Have multiple flagellum at same ‘spot’
– Act in concert to move bacteria in single direction
• Peritrichous
– Have a flagella projecting in all directions
– Escherichia coli
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Flagella Arrangement
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Flagella: Run, Tumble
• Move in one direction called a ‘run’
• Change in direction called ‘tumbles’
– Interruptions in a run, changes direction
– Caused by reversal of flagella rotation
• Bacteria with many flagella
– Proteus
– Swarms, wavelike movement across media
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Running and Tumbling
View animation:
Bacterial Motility4
Figure 4.9
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Taxis
• Move toward or away from stimuli: TAXIS
– Due to chemical stimuli: chemotaxis
– Or, light: phototaxis
• If toward the stimuli, called an attractant
– And the bacteria moves towards it with many
‘runs’ and few ‘tumbles’
• If away from the stimuli, called a repellent
– The frequency of ‘tumbles’ increases as it moves
away from the stimulus
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Flagella and Virulence
The flagellar protein called H antigen is
used to identify serovars
– Among Gram negative bacteria
– (e.g., E. coli O157:H7)
– At least 50 different H antigens for E. coli
– Associated with foodborne epidemics
(Ch 1, p. 20)
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Axial Filaments
• Endoflagella,
movement only
• In spirochetes
• Anchored at one
end of a cell
• Rotation causes
cell to move in
spiral motion
Fig 4.10
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Axial Filaments and Virulence
• Spirochetes
– Move through body
fluids
– Treponema pallidum
• Syphilis
– Borrelia burgdorferi
• Lyme disease
Fig 26.10
Fig 23.13
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Fimbriae & Pili
• Are short, thin
appendages
• Fimbriae allow
attachment to initiate
disease
• Pili join cells to
transfer DNA from
one cell to another
called: Conjugation
Fig 4.11
Fig 8.25
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Fimbriae vs Pili
These structures consist of a protein
called pilin
Divided into 2 types, different functions
Fimbriae
Pili
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Fimbriae Characteristics
•
•
•
•
Occur at poles of cells, or all over
Number from a few to >hundreds
Enable a cell to adhere to surfaces
Example:
– Neisseria gonorrhoreae
– Causes gonorrhea
Fig 4.11
– Fimbriae helps colonize mucus
membranes
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Pili Characteristics
Usually longer than fimbriae
Number only one or 2
Pili join cells to transfer DNA
Process called conjugation
Fig 8.25
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Q’s
1. The structure used by bacteria to
transfer genetic information is:
a. Flagella
b. Pili
c. Glycocalyx
d. Ribosome
2. Prokaryotic cells
a.
b.
c.
d.
e.
Have a single chromosome
Lack a nuclear membrane
Divide by binary fission
Have cell walls containing peptidoglycan
All of the above
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Q’s
1. Which is not a function of glycocalyx
a. It forms pseudopodia for faster mobility of an
organism
b. It can protect a bacterial cell from drying out
c. It can contribute to the disease-causing
process
d. It allows a bacterium to stick to a host
2. All of these are involved in bacterial
attachment except:
a. Fimbriae
b. Pili
c. Capsules
d. Axial filaments
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Q’s
1. The cell arrangement shown here is:
a.
b.
c.
d.
e.
Streptococcus
Staphylococcus
Diplococcus
Tetrads
Sarcinae
2. The plane in which a bacterium
divides determines the arrangement.
True
False
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Q’s
1. What is taxis?
a.
b.
c.
d.
Movement towards a stimulus
Movement toward or away from a stimulus
Movement towards light
Movement away from a stimulus
2. What are the 3 parts of a flagellum?
a.
b.
c.
d.
Tubulin, flagellin, basal body
Flagellin, filament, hook
Filament, hook, basal body
Tubulin, hook, filament
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Q’s
1. Which of the following is NOT a
structure found in prokaryotic cells?
a. Flagella
b. Pili
c. Cilia
d. Axial filaments
e. Peritrichous flagella
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