Fundamentals of Microbial Metabolism

Sep 30, 2024

Lecture: Basics of Microbial Metabolism

Introduction to Microbial Metabolism

  • Metabolism: Sum of all chemical reactions in a living organism.
    • Comprises two processes: catabolic (breaking down molecules) and anabolic (building up molecules).
  • Microbial Metabolic Diversity: Allows microbes to thrive in diverse environments: Antarctic ice, deserts, hydrothermal vents, human body, compost bins.
  • Energy Sources:
    • Chemotrophs: Use chemicals (organic or inorganic) for energy.
    • Phototrophs: Use light energy.

Types of Chemotrophs

  • Chemoorganotrophs (Chemoheterotrophs):
    • Use organic compounds; common in labs.
    • Obtain energy through oxidation, trapping energy as ATP.
  • Chemolithotrophs:
    • Oxidize inorganic compounds (e.g., hydrogen gas, hydrogen sulfide, iron, ammonia).
    • Often live in association with chemoorganotrophs.

Phototrophs

  • Convert light energy into chemical energy using pigments.
  • Photosynthesis Types:
    • Oxygenic Photosynthesis: Produces oxygen (e.g., cyanobacteria, algae).
    • Anoxygenic Photosynthesis: Does not produce oxygen (e.g., purple and green bacteria).

Metabolic Processes

  • Catabolic Reactions: Break down large molecules (e.g., carbohydrates, proteins) to release energy; involve oxidation.
  • Anabolic Reactions: Use simple molecules to build complex ones; require energy (ATP); involve reduction.
  • Redox Reactions: Coupled oxidation and reduction processes; essential for energy transfer.

ATP and Energy Transfer

  • ATP (Adenosine Triphosphate):
    • Formed by adding phosphate to ADP (phosphorylation).
  • Phosphorylation Types:
    • Substrate-Level Phosphorylation: Direct transfer of high-energy phosphate.
    • Oxidative Phosphorylation: Electrons transferred through electron transport chain, releasing energy to form ATP.
    • Photophosphorylation: Light energy converts to chemical energy in photosynthesis.

Metabolic Pathways

  • Glycolysis: Breakdown of glucose and other macromolecules.
    • Entry point for various pathways; interconnected to Krebs cycle.
  • Krebs Cycle (Citric Acid Cycle):
    • Oxidizes molecules, releasing CO2; linked to electron transport system.

Importance of Redox Reactions

  • Central to microbial metabolism and physiology.
  • Involve electron transfer between molecules.

Fun Fact

  • Pseudomonas putida CBB5:
    • Can metabolize caffeine.
    • Genes used to engineer E. coli for water decontamination.

Further Reading

  • Chapter 5 on microbial metabolisms in the Tortura text.