The Bacteria and Archaea

Foundations in Microbiology

Chapter

4

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Fifth Edition

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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