Bacterial Classification and Staining Quiz

Microbial World

• Prokaryotic microorganisms are characterized by simple cellular organization.
• They are classified into two domains: Bacteria and Archaea.
• Prokaryotes are a group of unicellular microorganisms that lack a nucleus and membrane-bound organelles.

Prokaryotes

• Bacteria
• Archaea

Evolutionary Tree of Life

• Bacteria, Archaea, and Eucarya all share a universal ancestor.

Prokaryotic Microorganisms

• Prokaryotic microorganisms are characterized by their simple cellular organization.
• They are classified into two domains: Bacteria and Archaea.

Bacteria Domain

• The Bacteria domain comprises several groups, including:
  • Gram-positive bacteria
  • Gram-negative bacteria
  • Mycoplasma
  • Cyanobacteria

Gram-positive Bacteria

• The cell wall of gram-positive bacteria is distinguished by the following characteristics:
  • Multiple layers of peptidoglycan
  • Presence of teichoic acid
  • Absence or presence of minimal protein
• Gram-positive bacteria include the following groups:
  • Cocci
  • Spore-forming bacilli
  • Non spore-forming bacilli
  • Actinomycetes.

Gram-negative Bacteria

• The cell wall of gram-negative bacteria comprises three layers:
  • Mucopeptide layer (peptidoglycan)
  • Lipopolysaccharide
  • Lipoproteins
• Gram-negative bacteria can be classified into different groups based on their oxygen requirements:
  • Facultative anaerobes (e.g., Escherichia coli)
  • Obligate aerobes (e.g., Rhizobium and Azotobacter)
  • Microaerophilic bacteria (e.g., Helicobacter pylori)
  • Obligate intracellular bacteria (e.g., Rickettsia group and Chlamydia group)
• Spirochetes
  • Spirochetaceae family (e.g., genus Critispira)
  • Treponemaceae family (e.g., Treponema pallidum)

Mycoplasma

• Mycoplasma is a genus of bacteria characterized by their lack of a cell wall.
• They are highly resistant to many common antibiotics.
• They have a flexible shape and are among the smallest bacteria. (0.2 - 0.3 µm).
• They can infect humans, animals, and plants.
  • Mycoplasma pneumoniae causes respiratory infections in humans, and other species may infect the urogenital tract.

Cyanobacteria

• Formerly known as blue-green algae.
• They are photosynthetic (oxygen-producing bacteria) and are widespread in nature.
• They have a cohesive outer wall made up of peptidoglycan.
• They contain a blue pigment (Phycocyanin).
• Cyanobacteria exhibit a range of cellular organizations, from unicellular to complex multicellular forms.
• Unicellular cyanobacteria (e.g., Prochlorococcus and Chroococcus).
• Colonial cyanobacteria (e.g., Merismopedia and Microcystis).
• Filamentous cyanobacteria (e.g., Anabaena, Oscillatoria, and Nostoc).

Archaea Domain

• Archaea are a distinct domain of single-celled prokaryotic microorganisms.
• They differ from bacteria and eukaryotes.
• Archaea possess cell walls that are devoid of peptidoglycan, but may have other complex structures for strength and protection (e.g., S-layer and pseudomurein).
• Their cell membranes contain ether-linked lipids, which are more stable than ester-linked lipids found in bacteria.
• Archaea are renowned for their ability to flourish in diverse habitats, including some of Earth's most extreme environments (e.g., hot springs, and salt lakes).
  • Methanogens
  • Thermophiles
  • Halophiles.