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General Microbiology II

Resource Utilization and Succession

Groups of microbes often utilize the "waste" others, thus establishing commensalistic relationships; this is clearly seen in environments with a mixture of limited amounts of oxidants that can serve as terminal electron acceptors, such as oxygen, iron (or manganese), nitrate, sulfate and carbon dioxide (e.g., Winogradsky column)

Example of a succession based on terminal electron acceptor availability:

• aerobes predominate initially, because using oxygen as terminal electron acceptor yields more energy than any other scheme, and oxygen inhibits both nitrate and sulfate reduction
• microaerophiles and then facultative (an)aerobes begin to predominate as oxygen concentration decreases
• anaerobes predominate when oxygen is exhausted, but facultative (an)aerobes may persist and lead to accumulation of fermentation products (hydrogen, organic acids), especially by syntrophic bacteria
  • iron reducers (Shewanella, etc.) predominate at first because the most energy can be derived from anaerobic respiration (catabolism) of organic compounds if iron is the terminal electron acceptor
  • nitrate reducers (Pseudomonas, etc.) predominate next because the next most energy can be derived from anaerobic respiration (catabolism) of organic compounds if nitrate is the terminal electron acceptor
  • sulfate reducers (Desulfovibrio, etc.) predominate next because the next most energy can be derived from anaerobic respiration (catabolism) of organic compounds if sulfate is the terminal electron acceptor ... and because they compete better for hydrogen (frequently generated by syntrophic bacteria) than methanogens (but only if the sulfate concentration is high)
  • carbon dioxide reducers (methanogens) predominate next because the next most energy can be derived from reduction of carbon dioxide to methane (after the sulfate supply is exhausted) using hydrogen (frequently generated by syntrophic bacteria)
  • sulfur reducers ( , etc.) predominate next, because the next most energy can be derived from anaerobic respiration (catabolism) of organic compounds if sulfur is the terminal electron acceptor
  • carbon dioxide respirers (homoacetogens) predominate next because the next most energy can be derived from reduction of carbon dioxide to acetate using hydrogen (frequently generated by syntrophic bacteria)