Download التركيب الدقيق للخلية البكتيرية Structure of bacterial cell

PowerPoint to accompany
Foundations
in
Microbiology
Fifth Edition
Talaro
Chapter
4
Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Prokaryotic Profiles:
the Bacteria and the Archaea
Chapter 4
Fig. 4.1
3
flagella
• 3 parts
– filament – long, thin, helical structure composed of
proteins
– hook- curved sheath
– basal body – stack of rings firmly anchored in cell
wall
• rotates 360o
• 1-2 or many distributed over entire cell
• functions in motility
4
Fig 4.2b
5
Flagellar arrangements
1. monotrichous – single flagellum at one end
2. lophotrichous – small bunches arising from
one end of cell
3. amphitrichous – flagella at both ends of cell
4. peritrichous – flagella dispersed over surface
of cell, slowest
6
7
8
Fig 4.5
Chemotaxis
9
Fig 4.6
axial filaments
• periplasmic, internal flagella, enclosed
between cell wall and cell membrane of
spirochetes
• motility
10
11
Fig 4.7a b
fimbrae
• fine hairlike bristles from the cell surface
• function in adhesion to other cells and
surfaces
12
pili
• rigid tubular structure made of pilin protein
• found only in Gram negative cells
• Functions
– joins bacterial cells for DNA transfer (conjugation)
– adhesion
13
Conjugation
14
glycocalyx
•
•
Coating of molecules external to the cell wall,
made of sugars and/or proteins
2 types
1. capsule - highly organized, tightly attached
2. slime layer - loosely organized and attached
•
functions
–
–
–
attachment
inhibits killing by white blood cells
receptor
15
Fig 4.10
16
2 Types of Glycocalyx
17
Biofilms
18
Peptidoglycan
• unique macromolecule composed of a
repeating framework of long glycan chains
cross-linked by short peptide fragments
• provides strong, flexible support to keep
bacteria from bursting or collapsing because
of changes in osmotic pressure
19
Peptidoglycan
20
4 groups based on cell wall
composition
1.
2.
3.
4.
Gram positive cells
Gram negative cells
Bacteria without cell walls
Bacteria with chemically unique cell walls
21
Gram positive
Gram negative
22
Fig 4.16
23
Gram positive cell wall
• Consists of
– a thick, homogenous sheath of peptidoglycan
20-80 nm thick
– tightly bound acidic polysaccharides, including
teichoic acid and lipoteichoic acid
– cell membrane
• Retain crystal violet and stain purple
24
Gram positive wall
25
Gram negative cell wall
• Consists of
– an outer membrane containing
lipopolysaccharide (LPS)
– thin shell of peptidoglycan
– periplasmic space
– inner membrane
• Lose crystal violet and stain red from
safranin counterstain
26
Gram negative cell wall
27
Cytoplasm
• dense gelatinous solution of sugars, amino
acids, & salts
• 70-80% water
• serves as solvent for materials used in all
cell functions
28
Chromosome
• single, circular, double-stranded DNA
molecule that contains all the genetic
information required by a cell
• DNA is tightly coiled around a protein,
aggregated in a dense area called the
nucleoid
29
plasmids
•
•
•
•
•
small circular, double-stranded DNA
free or integrated into the chromosome
duplicated and passed on to offspring
not essential to bacterial growth & metabolism
may encode antibiotic resistance, tolerance to
toxic metals, enzymes & toxins
• used in genetic engineering- readily manipulated
& transferred from cell to cell
30
ribosomes
• made of 60% ribosomal RNA & 40%
protein
• consist of 2 subunits: large & small
• procaryotic differ from eucaryotic
ribosomes in size & number of proteins
• site of protein synthesis
• All cells have ribosomes.
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ribosomes
32
Inclusions, granules
• intracellular storage bodies
• vary in size, number & content
• bacterial cell can use them when
environmental sources are depleted
• Examples: glycogen, poly-b-hydroxybutyrate,
gas vesicles for floating, sulfur and
polyphosphate granules
33
Inclusions
34
endospores
• Resting, dormant cells
• produced by some G+ genera: Clostridium, Bacillus
& Sporosarcina
• Have a 2-phase life cycle – vegetative cell & an
endospore
• sporulation -formation of endospores
• germination- return to vegetative growth
• hardiest of all life forms
• withstand extremes in heat, drying, freezing,
radiation & chemicals not a means of reproduction
35
endospores
• resistance linked to high levels of calcium
& dipicolinic acid
• dehydrated, metabolically inactive
• thick coat
• longevity verges on immortality 25, 250
million years.
• pressurized steam at 120oC for 20-30
minutes will destroy.
36
endospores
37
3 shapes of bacteria
• cocci - spherical
• bacilli - rod
• spiral - helical, comma, twisted rod,
spirochete
38
39
Methods in bacterial
identification
1.
2.
3.
4.
5.
6.
Microscopic morphology
Macroscopic morphology – colony appearance
Physiological / biochemical characteristics
Chemical analysis
Serological analysis
Genetic & molecular analysis
•
•
•
G + C base composition
DNA analysis using genetic probes
Nucleic acid sequencing & rRNA analysis
40
Major Taxonomic Groups of
Bacteria per Bergey’s manual
• Gracilicutes – gram-negative cell walls,
thin-skinned
• Firmicutes – gram-positive cell walls, thick
skinned
• Tenericutes – lack a cell wall & are soft
• Mendosicutes – archaea, primitive
procaryotes with unusual cell walls &
nutritional habits
41
• species –a collection of bacterial cells which share
an overall similar pattern of traits in contrast to
other bacteria whose pattern differs significantly
• strain or variety – a culture derived from a single
parent that differs in structure or metabolism from
other cultures of that species (biovars, morphovars)
• type – a subspecies that can show differences in
antigenic makeup (serotype or serovar),
susceptibility to bacterial viruses (phage type) and
in pathogenicity (pathotype).
42
Procaryotes with unusual
characteristics
Rickettsias
• very tiny, gram-negative bacteria
• most are pathogens that alternate between mammals
and fleas, lice or ticks
• obligate intracellular pathogens
• cannot survive or multiply outside of a host cell
• cannot carry out metabolism on their own
• Rickettsia rickettisii – Rocky Mountain spotted fever
• Rickettsia prowazekii – epidemic typhus
• Coxiella burnetti – Q fever
44
Chlamydias
•
•
•
•
tiny
obligate intracellular parasites
not transmitted by arthropods
Chlamydia trachomatis – severe eye
infection and one of the most common
sexually transmitted diseases
• Chlamydia psittaci – ornithosis, parrot fever
• Chlamydia pneumoniae – lung infections
45
Mycoplasmas
•
•
•
•
naturally lack a cell wall
stabilized by sterols, resistant to lysis
extremely small
range in shape from filamentous to coccus
or doughnut shaped
• Mycoplasma pneumoniae – atypical
pneumonia in humans
46
Free-living nonpathogenic
bacteria
• Photosynthetic bacteria
– Cyanobacteria
– Green & purple sulfur bacteria
• Gliding, fruiting bacteria
• Appendaged bacteria
– produce an extended process of the cell wall in
form of a bud, stalk or long thread
47
Archaea: the other procaryotes
• constitute third Domain Archaea
• seem more closely related to Domain Eukarya than to
bacteria
• contain unique genetic sequences in their rRNA
• have unique membrane lipids & cell wall construction
• live in the most extreme habitats in nature,
extremophiles
• adapted to heat salt acid pH, pressure & atmosphere
• includes: methane producers, hyperthermophiles,
extreme halophiles, and sulfur reducers
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