Chemolithotrophy

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Author:
cornpops
ID:
111572
Filename:
Chemolithotrophy
Updated:
2011-11-09 02:32:37
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PMB 112 midterm2
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general microbiology midterm 2
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  1. chemolithotrophy
    the oxidation of inorganic electron donors to obtain energy

    • ATP synthesis is coupled to oxidation of the inorganic electron donor
    • Reducing power is obtained directly from the inorganic compound or from reverse electron transport
  2. energetics and carbon flow
    • electron transport leading to proton motive force
    • energy can be generated from electron transport from electron donors to electron acceptors
  3. autotrophs
    carbon source is CO2
  4. mixotrophs
    carbon source is an organic compound
  5. energetics of chemolithotrophy
    • both electron donor and electron acceptor determine energetics
    • difference in reduction potential of the two couples needs to be sufficient to produce ATP - requires ~32 kJ/mol

    • DGo’= -nF DEo’
    • n= number of electrons
    • F= Farraday constant (96.48 kJ/V)
    • DEo’=Eo’ of electron acceptor couple minus Eo’ of electron donor couple
  6. concept of chemolithotrophy conceived by Winogradsky
    • observations of Beggiatoa, colorless sulfur bacteria - large, filamentous, could observe directly:
    • only observed these bacteria in H2S-rich springs
    • if deprived of H2S, lose sulfur granules, continue to grow
    • if H2S then supplied, grow sulfur granules form

    • concluded H2S -> S0
    • S0 acts as energy source
    • S0 is oxidized to sulfate
  7. electron flow in sulfur chemolithotrophs
    can use standard electron transport system components
  8. anaerobic corrosion of iron
    • route 1: H2 -> H2S + Fe0 -> FeS(precipitate) + H2(recycled)
    • iron loses electrons, acts as donor

    route 2: 4Fe0 + SO42- + 4H20 -> FeS + 3Fe2+ + 80H-
  9. hydrogen as inorganic electron donor
    • hydrogen-oxidizing chemolithotrophs:
    • oxygen as electron acceptor
    • anaerobic using something else as electron acceptors

    • aerobic H2 bacteria are autotrophs and fix CO2 via Calvin Cycle
    • Generation of ATP during H2 oxidation is catalyzed by hydrogenase - oxygen-sensitive, thus grows best under microoxic conditions

    can also grow chemoorganotrophically with organic compounds as energy sources - thus are facultative chemotlithotrophs depending on environmental conditions
  10. iron bacteria and energy from ferrous ion oxidation*
    chemolithotrophs that use ferrous iron (Fe2+) as their sole energy source

    only a small amount of energy is available from oxidation of Fe2+ - lots must be oxidized

    • under neutral conditions, Fe2+ is oxidized non-biologically
    • under acidic conditions Fe2+ is stable and soluble and available to be oxidized
    • - most iron-oxidizing bacteria are obligately acidophilic
    • "natural" PMF across membrane, so ATP synthesis can occur as long as Fe2+ available - low ATP yield, limited growth

    oxidizing ferric iron forming insoluble ferric hydroxide and complex ferrous salts known as "yellow boy"

    specialized oxidoreductase: rusticyanin

    • some anoxygenic phototrophs oxidize ferrous iron
    • uses reverse electron flow

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