Bacterial Physiology and Metabolism

Bacterial Physiology and Metabolism - Fueling the Minions

• Growth Essentials:
  • Nutrients: Macronutrients (📌 CHONPS: C, H, O, N, P, S), Micronutrients (Fe, Zn, Mn).
  • Growth Factors: Vitamins, amino acids (e.g., Haemophilus needs X & V factors).
  • Environment:
    • Temperature: Psychrophiles (<20°C), Mesophiles (20-40°C), Thermophiles (>45°C).
    • pH: Acidophiles, Neutrophiles, Alkaliphiles.
    • Oxygen: Aerobes (need $O_2$), Anaerobes ($O_2$ toxic), Facultative (flexible), Microaerophilic (low $O_2$).
• Bacterial Growth Curve:

  ⭐ The four phases of a typical bacterial growth curve are lag, log (exponential), stationary, and death phase; generation time is shortest in the log phase.

![Bacterial Growth Curve Phases](https://ylbwdadhbcjolwylidja.supabase.co/storage/v1/object/public/notes/L1/Microbiology_General_Microbiology_Bacterial_Physiology_and_Metabolism/03ab5d88-390c-4650-949f-18a0b2b2c756.jpg)

• Metabolism & Energy:
  • Catabolism: Breakdown for energy (ATP). Pathways: Glycolysis, Kreb's cycle (TCA), Oxidative phosphorylation (aerobes).
  • Anabolism: Biosynthesis using energy.
  • Fermentation: Anaerobic ATP generation, organic end products (e.g., lactate, ethanol).

Bacterial Physiology and Metabolism - Gateway Guardians

• Nutrient Uptake Mechanisms: Crucial for bacterial survival and growth.
  • Passive Transport: No energy required.
    • Simple Diffusion: Movement of small molecules (e.g., $O_2$, $CO_2$) down concentration gradient.
    • Facilitated Diffusion: Carrier protein mediated (e.g., glycerol transport); no metabolic energy.
  • Active Transport: Energy-dependent; moves solutes against gradient.
    • Primary Active Transport: Uses ATP directly (e.g., ABC transporters).
    • Secondary Active Transport: Uses ion gradients (e.g., symport, antiport).
    • Group Translocation: Substrate is chemically modified during transport.

      ⭐ The phosphotransferase system (PTS) is a unique group translocation mechanism in many bacteria, which chemically modifies the substrate (e.g., glucose by phosphorylation) as it is transported across the cell membrane.

• Key Metabolic Pathways: Glycolysis, TCA cycle, Oxidative phosphorylation (brief overview).

Bacterial Physiology and Metabolism - Powerhouse Pathways

• Primary Goal: Efficient ATP synthesis via nutrient catabolism.
• Aerobic Respiration: Key pathway for maximal energy extraction.
  • 1. Glycolysis (EMP pathway): Glucose breakdown to Pyruvate.
    • Location: Cytoplasm.
    • Net yield: 2 ATP, 2 NADH.
  • 2. Pyruvate Decarboxylation (Link Reaction): Pyruvate to Acetyl-CoA.
    • Yields: NADH, CO₂.
  • 3. TCA Cycle (Krebs Cycle): Acetyl-CoA fully oxidized to CO₂.
    • Location: Cytoplasm (prokaryotes).
    • Generates: ATP (as GTP), multiple NADH, FADH₂.
  • 4. Oxidative Phosphorylation:

    ⭐ In prokaryotes, the Electron Transport Chain (ETC) and ATP synthesis are coupled on the cytoplasmic membrane, generating a Proton Motive Force (PMF). This differs from eukaryotes (mitochondria).

    • Electrons from NADH/FADH₂ pass through ETC; O₂ is terminal acceptor.
    • PMF powers ATP synthase, producing ~30-32 ATP per glucose.

Bacterial Physiology and Metabolism - Life Without Air

• Anaerobic Respiration:

  • Final electron acceptor: Inorganic molecules ($NO_3^-$, $SO_4^{2-}$, $CO_2$), not $O_2$.
  • ATP yield: > Fermentation, < Aerobic.

• Fermentation:

  • No ETC; ATP via substrate-level phosphorylation.
  • Low ATP yield (e.g., 2 ATP/glucose).
  • Regenerates $NAD^+$ from $NADH$ for glycolysis.
  • End products: Acids (lactic), alcohols (ethanol), gases.

  ⭐ Fermentation regenerates $NAD^+$, enabling glycolysis without $O_2$, yielding minimal ATP (typically 2 ATP/glucose).

• Oxygen Tolerance:

  • Obligate Anaerobes: $O_2$ toxic (e.g., Clostridium). Lack catalase, SOD. (📌 ABC: Actinomyces, Bacteroides, Clostridium)
  • Aerotolerant: Tolerate $O_2$, don't use it.
  • Facultative: Switch metabolisms (e.g., E. coli).

High‑Yield Points - ⚡ Biggest Takeaways

• Growth curve: Lag, Log, Stationary, Death phases.
• Obligate aerobes (e.g., M. tb) need O2; Obligate anaerobes (e.g., Clostridium) killed by O2.
• Facultative anaerobes (e.g., E. coli) prefer O2, can grow without. Aerotolerant ignore O2.
• ATP generation: Substrate-level phosphorylation and oxidative phosphorylation are key.
• Fermentation: Anaerobic, regenerates NAD+, yields diverse organic end products.
• Bacterial spores (Bacillus, Clostridium): Dormant, highly resistant, contain calcium dipicolinate.
• Nutrient transport: Includes active transport, passive/facilitated diffusion, and group translocation (e.g., PTS).