18. Lifestyles of the Small and Numerous

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cornpops
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109642
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18. Lifestyles of the Small and Numerous
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2011-11-08 21:56:55
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PMB 112 midterm2
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general microbiology midterm 2
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  1. differentiation
    the generation of phenotypically different cells that are genetically identical
  2. How does differentiation occur in bacterial systems?
    • After division, two daughter cells can become different from each other by:
    • 1) containing different proteins
    • 2) activating different proteins
    • 3) turning on the expression of different sets of genes
  3. sporulation by gram positive bacteria
    • most endospore forming bacteria live in the soil and sporulate when nutrients are limiting
    • mature spores are dormant/metabolically inactive and resistant to damage
    • generated by asymmetric cell division - one cell becomes the spore and the other cell helps to build the spore and then disintegrates
  4. How do bacteria make the decision to sporulate?
    two-component system called a phosphorelay

    • Histindine kinases KinA-E
    • intermediate response regulator Spo0F
    • histidine phosphotransferase Spo0B
    • DNA-binding response regulator Spo0A
  5. What regulates sporulation?
    • DNA damage blocks KinA
    • GTP blocks KinB and activates RapA
    • Cell density blocks RapA
    • RapA blocks Spo0F, cause dephosphorylation
    • Spo0E blocks Spo0A, cause dephosphorylation
  6. σF transcription cascade
    • SpoIIAB binds σF, making it inactive
    • SpoIIAA binds SpoIIAB and displaces σF
    • SpoIIAB-ATP phosphorylates SpoIIAA to make SpoIIAA~P
    • SpoIIAA~P and SpoIIAB-ADP unbind
    • after nucleotide exchange, SpoIIAB-ATP can rebind σF

    activation of SpoIIE phosphatase in the prespore compartment only keeps SpoIIAA unphosphorylated, releasing σF and turning on σF-dependent transcription in the prespore
  7. σF
    • activated in prespore after polar septation
    • drives expression of SpoIIR, which signals to the mother cell to cleave pro-σE
    • drives expression of σG, which remains inactive until after engulfment

  8. σE
    • activated by proteolytic cleavage
    • drives expression of engulfment genes
    • drives expression of pro-σK, which remains inactive until signal from prespore
  9. σG
    • activated after engulfment is complete
    • drives expression of proteins that package the chromosome and protect it from radiation, proteins necessary for metabolic dormancy
    • drives expression of SpoIVB, which promotes cleavage of pre-σK in mother cell
  10. σK
    • activated by proteolytic cleavage upon signal from prespore
    • drives expression of proteins that make the spore cortex, protecting it from dessication, heat, chemicals
    • when the spore is complete, the mother cell disintegrates
  11. Nostoc
    a lack of N triggers heterocyst development

    perform oxygenic photosynthesis and nitrogen fixation

    photosynthesis liberates oxygen - toxic to the nitrogenase enzyme required for nitrogen fixation

    • physically separates the two metabolic pathways:
    • vegetative cells - photosynthesis
    • heterocysts - nitrogen fixation
  12. How doe heterocysts achieve a microoxic environment?
    • 1) dismantle PSII, the photosynthetic enzyme that produces O2
    • 2) produce special cell envelope that limits the influx of gases
    • 3) produce oxidases that consume O2

    • vegetative cells fix CO2 and pass it to heterocysts as sucrose
    • heterocysts fix N2 as ammonium and pass it to vegetative cells as glutamate
  13. Nostoc symbioses with plants*
    • plants and fungi form symbioses with Nostoc to have a ready source of fixed nitrogen
    • have developed ways to bypass the normal controls on heterocyst development, taken over some control of the genes

    • 1) form heterocysts at levels of fixed nitrogen that inhibit heterocyst formation in free-living cells
    • 2) form more heterocysts per vegetative cell
    • 3) perform far less photosynthesis themselves and rely on fixed carbon from the plant

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