Microorganisms Classification Quiz

Classification of Microorganisms

• Microorganisms are categorized into five main groups: Bacteria, Archaea, Fungi, Protists, and Viruses.
• Classification is based on characteristics such as cell structure, metabolism, and genetics.

Cell Structure

• Prokaryotes: Lack a nucleus and membrane-bound organelles; DNA is found in the nucleoid. Includes Bacteria and Archaea.
• Eukaryotes: Have a nucleus and membrane-bound organelles. Includes Fungi, Protists, and Animals.

Metabolism

• Autotrophs: Produce their own food using sunlight or chemicals (e.g., plants, algae).
• Heterotrophs: Rely on consuming other organisms or their by-products for nourishment (e.g., animals, fungi, most bacteria).

Genetics

• Domains: Three primary taxonomic classifications: Archaea, Bacteria, and Eukarya.
• Kingdoms: Six kingdoms include Archaea, Bacteria, Fungi, Plantae, Animalia, and Protista.
• Taxonomic hierarchy: Domain > Kingdom > Phylum > Class > Order > Family > Genus > Species.

Bacterial Classification

• Bacteria are classified by:
  • Shape:
    • Cocci (spherical)
    • Bacilli (rod-shaped)
    • Spirilla (spiral)
    • Vibrios (comma-shaped)
  • Cell Wall Composition:
    • Gram-positive: Thick peptidoglycan layer.
    • Gram-negative: Thinner cell wall with an outer membrane.
  • Respiration Mode:
    • Aerobic: Require oxygen.
    • Anaerobic: Do not require oxygen.
  • Nutrition Mode:
    • Autotrophs: Self-sufficient in food production.
    • Heterotrophs: Need to consume other organisms.

Fungal Classification

• Three types of fungi:
  • Filamentous Fungi: Composed of hyphae; can form molds.
  • Yeasts: Unicellular, oval-shaped organisms ranging from 2-60 µm, some capsulated.
  • Dimorphic Fungi: Change form based on temperature; appear filamentous at lower temps and yeasts at higher temps (e.g., Histoplasma capsulatum).

Viral Classification

• Viruses are classified by:

  • Virion Morphology: Size, shape, and presence of an envelope.
  • Genome Properties: Characteristics of viral nucleic acids.
  • Protein Properties: Type of proteins present.
  • Biological Properties: Such as host range.
  • Genome Organization: Structure and replication mechanisms.
  • Antigenic Properties: Immune response characteristics.

• Per the International Committee on Taxonomy of Viruses (ICTV), over 30,000 viruses have been isolated, categorized into more than 3,600 species across 164 genera and 71 families.

Viral Taxonomic Structure

• Taxonomic levels for viruses include:

  • Order (-virales)
  • Family (-viridae)
  • Subfamily (-virinae)
  • Genus (-virus)
  • Species

• Example:

  • Order: Mononegavirales
  • Family: Filoviridae
  • Genus: Filovirus
  • Species: Ebola virus Zaire

Classification by Nucleic Acid

• DNA Viruses:
  • Single-stranded (ssDNA): Parvoviridae.
  • Double-stranded (dsDNA): Papovaviridae, Adenoviridae, Herpesviridae, Iridoviridae, Poxviridae.