Transcript التركيب الدقيق للخلية البكتيرية Structure of bacterial cell

PowerPoint to accompany
Foundations
in
Microbiology
Fifth Edition
Talaro
Chapter
4
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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
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7
8
Fig 4.5
Chemotaxis
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Fig 4.6
axial filaments
• periplasmic, internal flagella, enclosed
between cell wall and cell membrane of
spirochetes
• motility
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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
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Conjugation
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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
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Fig 4.10
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2 Types of Glycocalyx
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Biofilms
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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
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Peptidoglycan
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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
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Gram positive
Gram negative
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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
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Gram positive wall
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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
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Gram negative cell wall
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Cytoplasm
• dense gelatinous solution of sugars, amino
acids, & salts
• 70-80% water
• serves as solvent for materials used in all
cell functions
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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
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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
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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
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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
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Inclusions
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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
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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.
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endospores
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3 shapes of bacteria
• cocci - spherical
• bacilli - rod
• spiral - helical, comma, twisted rod,
spirochete
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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
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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
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• 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).
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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
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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
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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
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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
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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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