🌱 Lesson 1: Microbial Metabolism, Diversity & Ecology

🔑 Part I: The Foundations of Metabolism

• Metabolism = Life’s engine
  • Catabolism: breaking down molecules → releases energy (⚡exergonic).
  • Anabolism: building cell parts → needs energy (⚡endergonic).
• Free Energy (∆G0′)
  • Negative = energy released (exergonic).
  • Positive = energy required (endergonic).
  • Example: Glucose respiration → ∆G0′ = –2895 kJ/mol → up to ~38 ATP ⚡.
• Reducing Power = electron supply (e–).
  • Oxidation = loss of e–.
  • Reduction = gain of e–.
  • Redox reactions move e– from donors → acceptors (e.g., glucose → O2).

👉 Key idea: Catabolism makes ATP + reducing power, anabolism spends them.

🔋 3.2 Electron Transfer Reactions

• Redox couples (written Oxidized/Reduced, e.g. NO₃⁻/NO₂⁻).
• Reduction potential (E0′) decides who donates vs. who accepts.
• The Redox Tower shows strongest donors at top, acceptors at bottom.
  • Bigger “drop” in tower = more energy released.
  • O₂ is the best acceptor (+0.82 V).
• NAD+/NADH = universal electron shuttle 🚋.
  • NADH = good donor, NAD+ = weak acceptor.
  • Cycles between enzymes to transfer e–.

🧮 3.3 Calculating Free Energy

• Two ways:
  1. From ∆E0′ (redox potentials) → ∆G0′ = –nF∆E0′.
  2. From free energy of formation (products – reactants).
• Real life ≠ standard lab conditions: actual ∆G depends on concentrations.
  • Example: Propionate oxidation is unfavorable in lab, but in wetlands methanogens consume H₂ → makes it favorable 🌿.

⚡ 3.4 Cellular Energy Conservation

• ATP = energy currency. Needs –31.8 kJ/mol (standard) to form.
• Other energy-rich compounds: phosphoenolpyruvate, acetyl-CoA (thioesters).
• Three ways to make ATP:
  1. Substrate-level phosphorylation: direct transfer of phosphate (e.g. glycolysis).
  2. Oxidative phosphorylation: e– transport → proton motive force → ATP synthase.
  3. Photophosphorylation: light powers proton motive force (photosynthesis 🌞).

🔬 3.5 Enzymes = Catalysts

• Speed up reactions by lowering activation energy.
• Highly specific (substrate binds active site).
• Helpers:
  • Prosthetic groups (tightly bound, e.g. heme).
  • Coenzymes (loosely bound, often vitamins, e.g. NADH).

🍞 Part II: Catabolism – Chemoorganotrophs

• Fermentation = anaerobic, organic molecule is both donor & acceptor (no external e– acceptor needed).
• Respiration = donor oxidized, external acceptor used (O₂ or others).

🌍 Unit 4: Metabolic Diversity of Microorganisms

• Microbes = masters of metabolism.
• Energy sources:
  • Phototrophs: light (oxygenic 🌿 vs anoxygenic 🌊).
  • Chemotrophs: chemicals.
    • Chemoorganotrophs: organic fuels (e.g. glucose).
    • Chemolithotrophs: inorganic fuels (e.g. H₂, NH₃, Fe²⁺).
• Carbon sources:
  • Heterotrophs: organic C.
  • Autotrophs: CO₂ → “primary producers.”
• Special case: Iron bacteria (Leptothrix ochracea) oxidize Fe²⁺ but risk being trapped in rust. They avoid this by pushing iron oxide away into sheaths 🚰.

🌱 Unit 5: Microbial Ecology & Environments

20.1 General Ecological Concepts

• Population = one species in one place.
• Community = many species together.
• Richness = how many species.
• Abundance = how many individuals per species.
• Ecosystem = community + abiotic environment.
• Habitats vary: soils (high richness), extremes (low richness but high abundance).

20.2 Biogeochemistry & Nutrient Cycles

• Microbes = key players in cycles (C, N, S, Fe).
• Cycles run mostly via redox reactions.
  • Ex: Sulfur cycle → H₂S oxidized to SO₄²⁻, then reduced back by bacteria.
  • Nitrogen cycle = microbial driven 🌿.
• Microbes form guilds = groups using same resources. Guilds shape niches in communities.

20.3 Microenvironments

• Microbes experience very small-scale environments (their “neighborhood” = microenvironment).
• Each species has:
  • Fundamental niche = all possible conditions.
  • Realized niche = where it actually thrives.

🎯 Quick Review Questions (test yourself!)

1. Why do cells need both ATP and reducing power?
2. What does a bigger “drop” in the redox tower mean?
3. Which energy conservation method do fermenters rely on?
4. Difference between richness and abundance in ecology?