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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