Bacteria and Archaea Notes

Bacteria

• Most studied organisms.
• Found almost everywhere except in extreme environments.
• Strong cell walls that contain peptidoglycan.
• Some have a second cell wall, a property used for classification.
• Some, like actinobacteria, are photosynthetic.

Archaea

• Predominate in extreme environments hostile to most other life forms.

Thermocidophiles

• Live in hot, acidic environments.
• Examples: sulfur hot springs, thermal vents on the ocean floor, around volcanoes.
• Thrive in temperatures above $80$ degrees Celsius and pH levels of $1$ to $2$.
• Some cannot survive below $55$ degrees Celsius.
• Many are strict anaerobes (die in the presence of oxygen).

Halophiles

• Live in very salty environments.
• Typical cell salt concentration: $0.9\%$.
• Ocean average salt concentration: $3.5\%$.
• Great Salt Lake and Dead Sea salt concentration: greater than $15\%$.
• Have adaptions to live in salty environments.
• Usually aerobic.
• Some carry out a unique form of photosynthesis using protein instead of chlorophyll.

Methanogens

• Obligate anaerobes (cannot live in the presence of oxygen).
• Use carbon dioxide during respiration and give off methane as a waste product.
• Found in sewage treatment plants, swamps, bogs, and near volcanic vents.
• Thrive in the gastrointestinal tract of humans and other animals, responsible for gases released from the lower digestive tract.

Bacteria vs. Archaea

• Classified in different domains due to many differences.
• Bacteria and archaea are as different from each other as they are from eukaryotic cells.
  • Bacterial cell walls contain peptidoglycan; archaea do not.
  • Different lipids in their plasma membranes.
  • Different ribosomal proteins and RNA.
    • Ribosomal proteins in archaea are similar to those of eukaryotic cells.