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Foundations in Microbiology
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4
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Prokaryotic Profiles: the Bacteria and the Archaea
Chapter 4
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Fig. 4.1
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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
5Fig 4.2b
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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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Fig 4.5
9Fig 4.6
Chemotaxis
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axial filaments
• periplasmic, internal flagella, enclosed between cell wall and cell membrane of spirochetes
• motility
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Fig 4.7a b
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fimbrae
• fine hairlike bristles from the cell surface
• function in adhesion to other cells and surfaces
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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 types1. capsule - highly organized, tightly attached2. slime layer - loosely organized and attached
• functions– attachment– inhibits killing by white blood cells– receptor
16Fig 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. Gram positive cells
2. Gram negative cells
3. Bacteria without cell walls
4. Bacteria with chemically unique cell walls
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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, 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--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. Microscopic morphology2. Macroscopic morphology – colony appearance3. Physiological / biochemical characteristics4. Chemical analysis5. 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
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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).
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
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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