Notes on Six Kingdom Classification

Taxonomy Shift to 6 Kingdoms

  • The shift from 5 kingdoms to 6 kingdoms is due to:
    • Molecular Phylogenetics: Advances in genetics and biology revealed differences between the old Kingdom Monera (now Eubacteria and Archaebacteria).
    • Diversity of Life: The five-kingdom system did not adequately represent the complexity and diversity of prokaryotic life.
    • Evolutionary Relationships: The six-kingdom system provides a more accurate depiction of the tree of life, giving significant importance to prokaryotes.

Differences Between Archaebacteria and Eubacteria

  • Cell Wall Composition:
    • Archaebacteria: Pseudo-peptidoglycan
    • Eubacteria: Peptidoglycan
  • RNA Polymerase:
    • Archaebacteria: Several kinds of RNA polymerase.
    • Eubacteria: One kind of RNA polymerase.
  • Ribosomal Proteins and RNA:
    • Archaebacteria: Ribosomal RNA has similarities with eukaryotes.
    • Eubacteria: Ribosomal RNA is connected to domain bacteria.
  • Lipid Composition:
    • Archaebacteria: Branched-chain hydrocarbons attached to glycerol by ether linkages.
    • Eubacteria: Straight chain of fatty acids attached to glycerol by ester linkages.
  • Sensitivity to Antibiotics:
    • Archaebacteria: Not sensitive.
    • Eubacteria: Sensitive.
  • Habitat:
    • Archaebacteria: Found in extreme environments (e.g., hot springs, salt lakes, human colon).
    • Eubacteria: Found in optimum, livable environments like soil, water, and the human body.

Cyanobacteria

  • Formerly belonged to Kingdom Monera.
  • Due to the shift to the 6-kingdoms classification, its classification changed.
  • Free-living photosynthetic bacteria.
  • Obtain energy through photosynthesis.
  • Produce oxygen gas in the atmosphere.