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Microbial Metabolism. Overview of metabolism (you should know about TCA cycle, Embden-Meyerhof pathway-glycolysis, Proton motive force etc.) Overview of nutrition Culture media Energetics Enzyme catalysis Oxidation and reduction Electron carriers Energy conservation. Metabolism.

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microbial metabolism
Microbial Metabolism
  • Overview of metabolism (you should know about TCA cycle, Embden-Meyerhof pathway-glycolysis, Proton motive force etc.)
  • Overview of nutrition
  • Culture media
  • Energetics
  • Enzyme catalysis
  • Oxidation and reduction
  • Electron carriers
  • Energy conservation
energy classes of microbes
Energy classes of microbes
  • microbes need three things to grow:
    • Energy source
    • Nutrients (C)
    • Suitable environmental conditions
  • Energy source
    • Phototroph (light)
    • Chemotroph (chemicals)
      • Chemoorganotroph (organic chemicals)
      • Chemolithoautotroph (inorganic chemicals)
macronutrients
Macronutrients
  • Carbon (CO2 or organic compounds)
  • Hydrogen (H2O or organic compounds)
  • Oxygen (H2O or organic compounds)
  • Nitrogen (NH3, NO3-, organic N-compounds)
  • Phosphorus (PO43-)
  • Sulfur (H2S, SO42-, organic compounds)
  • Potassium (K+)
  • Magnesium (Mg2+, salts)
  • Sodium (Na+)
  • Calcium (Ca2+, salts)
  • Iron (Fe3+, Fe2+, or salts)
iron as a nutrient
Iron as a nutrient
  • Needed for aerobic metabolism (cytochromes, iron-sulfur proteins)
  • Insoluble under aerobic conditions
    • Fe(OH)3, FeOOH
    • Solubilized by siderophores
micronutrients and growth factors
Micronutrients and growth factors
  • Micronutrients: Metals and metalloids
    • Generally not necessary to add to medium
    • Deficiencies can arise when medium constituents are very pure
  • Growth factors: organic requirements
    • Vitamins, amino acids, purines, pyrimidines, acetate
culture media
Culture media
  • Defined: all chemicals are ostensibly known
  • Complex (undefined): contains substances with unknown chemistries, such as peptones, yeast extract, lake water, soil extract, etc.
energetics
Energetics
  • Gibbs Free-Energy (G)
  • Reaction has a free-energy change
    • Negative: exergonic
    • Positive: endergonic
    • Zero: equilibrium
  • Standard concentrations—tables of ΔGf°’
redox reactions
Redox Reactions
  • Reactions can be written as half-reactions
    • Oxidation: removal of electrons
      • S → P + e- or H2 → 2H+ + 2e-
    • Reduction: addition of electrons
      • S + e- → P or O2 + 4H++ 4e- → 2H2O
  • Energetics of redox reactions can be considered as electrical potentials (see electron tower)
calculation of reaction energetics
Calculation of reaction energetics
  • First, must write balanced equation
    • E.g., 2H2 + O2 → 2H2O
  • Calculation of ΔG°’ for a reaction
    • ΔG°’ = ΔGf°’products - ΔGf°’reactants
    • ΔG°’ = 2 x (-237.2 kJ/mol) – (2 x 0 + 0)
  • Calculation of ΔG for a reaction
    • ΔG = ΔG°’ + RT x ln(k)
electron tower
Electron Tower
  • A redox reaction needs a reducing and oxidizing half-reaction
  • Reactions with stronger tendency to give up electrons are higher (more negative) on the tower
  • To determine which direction the reactions go, see which is “higher” on the electron tower
  • Note the position of important electron carriers (NAD, FAD, cytochrome a) and external electron donors/acceptors (H2, organic compounds, O2)
nad as electron carrier
NAD as electron carrier
  • NAD+ + ED → EDox + NADH
  • NADH + EA → EAred + NAD+
  • Overall reaction:
    • ED +EA → EDox + EAred
high energy compounds
High-energy compounds
  • ATP is the energy currency of the cell
    • High energy released when phosphate is hydrolyzed (ATP, ADP, AMP)
  • Acetyl phosphate
  • Acetyl coenzyme A
  • Phospho-enol pyruvate
modes of e conservation atp
Modes of E Conservation-ATP
  • Fermentation: in which redox reaction ocurs WITHOUT a terminal electron acceptor (couple oxiation with subsequent reduction of an organic product generated from initial substrate)
  • Respiration: in which O2 or another oxidant serves as an electron acceptor
more modes of e generation
MORE Modes of E generation
  • Anaerobic Respiration
  • Chemolitho(auto)trophy
  • Photo(auto)trophy
  • WHAT DO ALL THESE HAVE IN COMMON?