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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. Metabolism.

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Microbial Metabolism

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  1. 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

  2. Metabolism

  3. 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)

  4. 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)

  5. Iron as a nutrient • Needed for aerobic metabolism (cytochromes, iron-sulfur proteins) • Insoluble under aerobic conditions • Fe(OH)3, FeOOH • Solubilized by siderophores

  6. Siderophore

  7. Iron uptake

  8. 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

  9. 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.

  10. Energetics • Gibbs Free-Energy (G) • Reaction has a free-energy change • Negative: exergonic • Positive: endergonic • Zero: equilibrium • Standard concentrations—tables of ΔGf°’

  11. 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)

  12. 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)

  13. 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)

  14. Chemical kinetics and enzyme catalysis

  15. Electron carriers: NAD

  16. NAD+ as co-enzyme

  17. NADH as co-enzyme

  18. NAD as electron carrier • NAD+ + ED → EDox + NADH • NADH + EA → EAred + NAD+ • Overall reaction: • ED +EA → EDox + EAred

  19. 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

  20. 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

  21. MORE Modes of E generation • Anaerobic Respiration • Chemolitho(auto)trophy • Photo(auto)trophy • WHAT DO ALL THESE HAVE IN COMMON?

  22. Overview of fermentation

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