prokaryotic profiles: the bacteria and the...
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Prokaryotic Profiles: the Bacteria and the Archaea
Chapter 4
Fig. 4.1
flagella• 3 parts
– filament – long, thin, helical structure composed of proteins
– hook- curved sheathhook 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
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Fig 4.2b
Flagellar arrangements
1. monotrichous – single flagellum at one end
2 lophotrichous – small bunches arising2. 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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Fig 4.5
Chemotaxis
Fig 4.6
axial filaments
• periplasmic, internal flagella, enclosed between cell wall and cell membrane of spirochetes
• motility• motility
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Fig 4.7a b
fimbrae
• fine hairlike bristles from the cell surface• function in adhesion to other cells and
surfaces
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
glycocalyx• Coating of molecules external to the cell wall,
made of sugars and/or proteins• 2 types
1. capsule - highly organized, tightly attached2 li l l l i d d tt h d2. slime layer - loosely organized and attached
• functions– attachment– inhibits killing by white blood cells– receptor
Fig 4.10
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2 Types of Glycocalyx
Biofilms
Peptidoglycan
• unique macromolecule composed of a repeating framework of long glycan chains cross-linked by short peptide fragments
• provides strong flexible support to keep• provides strong, flexible support to keep bacteria from bursting or collapsing because of changes in osmotic pressure
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Peptidoglycan
4 groups based on cell wall composition
1. Gram positive cells2. Gram negative cells3. Bacteria without cell walls4. Bacteria with chemically unique cell walls
Gram positive Gram negative
Fig 4.16
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Gram positive cell wall
• Consists of – a thick, homogenous sheath of peptidoglycan
20-80 nm thick– tightly bound acidic polysaccharides includingtightly bound acidic polysaccharides, including
teichoic acid and lipoteichoic acid– cell membrane
• Retain crystal violet and stain purple
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
Gram negative cell wall
Cytoplasm
• dense gelatinous solution of sugars, amino acids, & salts
• 70-80% waterl t f t i l d i ll• 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• DNA is tightly coiled around a protein, aggregated in a dense area called the nucleoid
plasmids
• small circular, double-stranded DNA• free or integrated into the chromosome• duplicated and passed on to offspring• not essential to bacterial growth & metabolism• 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
ribosomes• made of 60% ribosomal RNA & 40%
protein• consist of 2 subunits: large & small
procaryotic differ from eucaryotic• procaryotic differ from eucaryotic ribosomes in size & number of proteins
• site of protein synthesis• All cells have ribosomes.
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ribosomes
Inclusions, granules
• intracellular storage bodies• vary in size, number & content• bacterial cell can use them when• bacterial cell can use them when
environmental sources are depleted• Examples: glycogen, poly-β-
hydroxybutyrate, gas vesicles for floating, sulfur and polyphosphate granules
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
endosporep• 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
endospores
• resistance linked to high levels of calcium & dipicolinic acid
• dehydrated, metabolically inactive• thick coatthick coat• longevity verges on immortality 25, 250
million years.• pressurized steam at 120oC for 20-30
minutes will destroy.
endospores
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3 shapes of bacteria
• cocci - spherical• bacilli - rod• spiral - helical, comma, twisted rod,
i h tspirochete
Methods in bacterial identification
1. Microscopic morphology2. Macroscopic morphology – colony appearance3. Physiological / biochemical characteristics4. Chemical analysisy5. Serological analysis6. 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
• species –a collection of bacterial cells which share an overall similar pattern of traits in contrast to other bacteria whose pattern differs significantlysignificantly
• 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).
Procaryotes with unusual characteristics
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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
Chlamydias
• tiny• obligate intracellular parasites• not transmitted by arthropods• Chlamydia trachomatis severe eye• Chlamydia trachomatis – severe eye
infection and one of the most common sexually transmitted diseases
• Chlamydia psittaci – ornithosis, parrot fever
• Chlamydia pneumoniae – lung infections
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
Glidi f iti b t i• Gliding, fruiting bacteria• Appendaged bacteria
– produce an extended process of the cell wall in form of a bud, stalk or long thread
Archaebacteria• New Kingdom
– so unique• Live in extreme environments• Three groups
– Methanogens• Make methane • Don’t need oxygen• Don t need oxygen• Purify water
– Thermoacidophiles• Hot and acidic• Thermal vents• Hot Springs
– Extreme halophiles• Salty• Dead Sea American society or
Microbiology
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