Microbiology Workshop

MICROBIAL ENERGY SOURCES

Microbes need energy for

  • maintenance
  • growth
  • reproduction
A. OBTAINING ENERGY (NUTRITION)

Energy may be obtained by

  • Autotrophy (Autotrophs)- using existing sources of free energy
  • Heterotrophy (Heterotrophs)- using energy rich compounds formed by other organisms

AUTOTROPHY

  • use energy from independent source
  • make energy rich carbon compounds (organic molecules) from inorganic molecules using carbon dioxide as carbon source
  • PHOTOAUTOTROPHS
      - use photosynthesis to convert light energy to chemical energy to produce organic molecules.
      - some bacteria, all algae, some protists
  • CHEMOAUTOTROPHS
      - use chemosynthesis to convert chemical energy into organic compounds
      - important in nutrient recycling
      - only found in bacteria.

HETEROTROPHY

  • use organic compounds, previously formed by either living or dead organisms, to provide energy
  • organic compounds digested and energy made available to organism
  • EXTRACELLULAR DIGESTION
      - food detected
      - enzymes released
      - organic molecules digested
      - breakdown products absorbed
      - waste products left behind
      - used by all fungi, some bacteria, some protists
  • PHAGOCYTOSIS
      - food particles enclosed in food vacuole
      - enzymes released
      - organic molecules digested
      - breakdown products absorbed
      - waste products eliminated
      - used by protists only.
B. USING ENERGY (RESPIRATION)
  • energy obtained by nutrition is used in cellular respiration to provide energy for microbial activity
  • microbes can be classified according to whether or not they use oxygen for cellular respiration as

  • AEROBES
      - use oxygen during respiration
      - have enzymes to prevent oxygen doing damage to the cell
  • ANAEROBES
      - are able to respire in the absence of oxygen
      - obligate anaerobes - lack the enzymes preventing oxygen damage, stop functioning in the presence of oxygen; may even be killed
      - facultative anaerobes - can use oxygen when it is available, can function in the absence of oxygen - fermentation