Notes on Microbial Diversity and Ecology

Microbial Diversity and Ecology

  • Key Concepts of Microbial Metabolism

    • All living organisms require sources of:
    • Energy
    • Electrons (reducing power)
    • Carbon
    • Classifications based on sources:
    • Energy: phototrophs (light), chemotrophs (chemical)
    • Electrons: lithotrophs (inorganic), organotrophs (organic)
    • Carbon: autotrophs (CO₂), heterotrophs (organic compounds)

  • Redox Reactions

    • Importance in metabolism:
    • Organisms oxidize compounds to harvest energy.
    • Electron donors and acceptors vary by organism.
    • Examples of terminal electron acceptors:
      • Oxygen ($O_2$)
      • Nitrate ($NO_3^-$)
      • Sulfate ($SO_4^{2-}$)

  • Types of Phototrophic Microorganisms

    • Heliobacteria:
    • Only known Gram-positive phototrophs
    • Type I anoxygenic phototrophs, obligate anaerobes
    • Photoorganoheterotrophs (require organic compounds for carbon and electron sources)
    • Purple Non-Sulfur Bacteria:
    • Type II anoxygenic phototrophs
    • Can be either lithotrophs or organotrophs, auto- or heterotrophs
    • Capable of both aerobic respiration and phototrophic growth

  • Metabolic Pathways Handling CO₂

    • Organotrophs: Oxidize organic compounds into $CO_2$.
    • Autotrophs: Reduce CO₂ into organic compounds.

  • Energy Sources and Electron Transfer

    • For organisms using $H_2S$ (hydrogen sulfide):
    • Utilized as a terminal electron donor in respiration and carbon fixation
    • Understanding sulfide reducers and oxidizers:
    • Sulfate reducers: use $SO_4^{2-}$ as electron acceptor for anaerobic respiration.
    • Sulfide oxidizers: use HS$^-$ as electron donor for respiration and carbon fixation.

  • Myxobacteria

    • Characteristics:
    • Obligate aerobes, Gram-negative, capable of gliding motility
    • Aggregate to form fruiting bodies in response to starvation
    • Myxospores develop within structures for dispersal

  • Bdellovibrio Bacteriovorus

    • Characteristics:
    • Obligate intracellular predators
    • Attack phase involves catabolism and biosynthesis without cell division
    • Invasion through exoenzymes to penetrate host cell membrane
    • Growth phase: elongation into filament using host cell nutrients

  • Caulobacter

    • Unique prosthecate bacterium:
    • Features a stalk (prostheca) for nutrient uptake
    • Life cycle involves swarmer cells and stalked cells
    • Adaptations for oligotrophic environments include increased surface area and efficient nutrient uptake
    • Morphological polarity aids in nutrient acquisition and growth mechanism.

  • Overview of Microbial Diversity Contributions:

    • Each group contributes uniquely to ecology and energy cycles:
    • Decomposers, energy sources in food webs, and contributors to biogeochemical cycles.