Metabolic Diversity Summary

Metabolic Diversity

  • Definition: Classification of microorganisms based on their metabolism.
Oxygen Requirements
  1. Aerobes: Require oxygen for growth (e.g., Legionella).
  2. Anaerobes: Do not require oxygen for growth (e.g., Clostridium).
  3. Facultative Aerobes: Can grow with or without oxygen, but oxygen enhances growth (e.g., E. coli).
Energy, Electron, and Carbon Sources
  • Energy Sources: Can be either chemicals or light.
  • Electron Donors: Can be from organic (e.g., glucose) or inorganic compounds (e.g., H2S).
  • Carbon Sources: Can be organic compounds (e.g., glucose) or inorganic (e.g., CO2).
Metabolic Types
  • Heterotrophs: Obtain carbon from organic compounds.
  • Autotrophs: Obtain carbon from carbon dioxide (CO2).
Categories of Microorganisms
  • Chemoorganotrophs: Organic chemicals for energy, electrons, and carbon (e.g., protozoa, fungi).
  • Chemolithoheterotrophs: Inorganic chemicals for energy and electrons, organic compounds for carbon.
  • Chemolithoautotrophs: Inorganic chemicals for energy and electrons, CO2 for carbon.
  • Photoheterotrophs: Light energy, organic/inorganic chemicals for electrons, organic compounds for carbon.
  • Photoautotrophs: Light energy, inorganic chemicals for electrons, CO2 for carbon.
Processes in Metabolism
  • Aerobic Respiration: Uses oxygen; produces energy from glucose via glycolysis, TCA cycle, and electron transport chain.
  • Anaerobic Respiration: Uses other electron acceptors instead of O2; specific cytochromes involved.
  • Fermentation: Energy production without oxygen.
Terminal Electron Acceptors in Anaerobic Respiration
  • Common terminal electron acceptors include nitrates, sulfates, and organic compounds.
  • Denitrification: Loss of nitrogen in gaseous form (NO, N2O, N2) from the environment; beneficial in sewage treatment.
  • Sulfate Reduction: Involves using sulfur compounds as electron acceptors.
Photosynthesis Types
  • Anoxygenic Photosynthesis: Utilizes light without producing oxygen (e.g., purple bacteria, green sulfur bacteria).
  • Oxygenic Photosynthesis: Uses light energy to oxidize H2O producing O2 (e.g., cyanobacteria).
Calvin Cycle in CO2 Fixation
  • Overall stoichiometry: 6 CO2 + 12 NADPH + 18 ATP → glucose and other products.
  • Involves the enzyme RubisCO for the initial reaction with CO2.
  • Plants and algae perform this process in chloroplasts; prokaryotes in the cytoplasm.