Topic 9 The Ecology of Prokaryotes

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Topic 9The Ecology of Prokaryotes

• Biology 1001
• October 19, 2005

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4.3 Diversity of Metabolic Pathways

• Nutritional Modes of Prokaryotes

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4.3 Diversity of Metabolic Pathways

• Oxygen metabolism
• Obligate aerobes require O2 for cellular
  respiration for energy
• Facultative anaerobes use O2 if available but use
  fermentation in an anaerobic environment
• Obligates anaerobes are poisoned by O2 and use
  either fermentation or anaerobic respiration for
  energy

Alcohol fermentation
Clostridium botulinum
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9.2 Essential Ecological Roles

• Chemical Recycling
• Chemoheterotrophs are decomposers, returning
  carbon and other nutrients to the soil
• Cyanobacteria (photoautotrophs) produce O2 and
  convert CO2 to an organic form of carbon
• Bacteria are important in the nitrogen cycle
• Nitrogen fixing bacteria N2 ? NH3
• Ammonifying bacteria organic N ? NH4
• Nitrifying bacteria NH4 ? NO2- or NO2- ? NO3-
• Denitrifying bacteria NO3- ? N2

Figure 54.17
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9.2 Essential Ecological Roles

• Symbiotic Relationships
• Metabolic cooperation with other prokaryotes
• Symbiosis refers to an ecological relationship
  between two organisms of different species in
  direct contact. In a symbiotic relationship with
  a eukaryote the prokaryote is the symbiont while
  the eukaryote is the host
• Mutualism both organisms benefit
• Commensalism one benefits, the other is
  unharmed
• Parasitism one benefits, the other is harmed
• Most relationships between humans and bacteria
  are mutualistic!

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9.3 Bacteria and Disease

• Pathogenic prokaryotes are parasitic to humans
• Account for half of all human diseases
• Cause illness by producing poisons, called toxins
• Exotoxins are proteins secreted by prokaryotes
• Endotoxins are components of the
  lipopolysaccharide outer membrane of
  gram-negative bacteria
• Gram-negative bacteria tend to resist antibiotics
  because the outer membrane impedes their entry

Lyme Disease Borrelia burgdorferi
Clostridium botulinum
Endospore