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.