Taxonomy, Cellular Domains, and Acellular Agents

Foundations of Microbial Taxonomy and Classification

• Identification vs. Classification

  • Identification: The process of using an organism's specific characteristics to set it apart from all other organisms.

  • Classification: The process of using an organism's characteristics to group them together based on shared traits.

• Subspecies and Strain Nomenclature

  • In microbiology, taxonomy extends below the species level to species strains and subspecies.

  • Subspecies Designation Example: Staphylococcus aureus aureus (possesses a formal subspecies designation).

  • Strain Designation Example: Influenza virus H1N1 (possesses a specific strain designation).

  • Shared Feature: Both subspecies and strains possess a unique trait that sets them apart from the baseline species.

• Categories of Strain Variations

  • Biovars (Biochemical Variants): Strains differentiated by variations in biochemical properties and metabolic pathways.

  • Serovars (Serological Variants): Strains differentiated by variations in surface antigens and serological reactivity.

  • Genovars (Genotypic Variants): Strains differentiated by variations in their genetic code.

  • Phenotypic vs. Genotypic Expression: Biovars and serovars represent phenotypic variations because their differences are outwardly displayed (e.g., biochemical traits or antigen types), whereas genovars represent differences at the underlying genetic code level.

Prokaryotic Domain Comparison

• General Prokaryotic Characteristics

  • Lack a membrane-bound nucleus.

  • Lack membrane-bound organelles.

• Archaea Group

  • Cellular Structure: All are single-celled organisms.

  • Cell Wall: All possess cell walls using pseudopeptidoglycan

  • Reproduction: Asexual reproduction via binary fission.

  • Motility: Some members are motile while others are non-motile; motile forms utilize flagella.

  • Metabolism: Includes both autotrophs and heterotrophs.

  • Habitat: Found in aquatic and terrestrial environments.

  • Genetic Relationships: Genetically more similar to Eukaryotes than to Bacteria.

  • Morphology: Morphogenetically identical to the Bacteria group.

• Bacteria Group

  • Cell Wall Composition: Uses peptidoglycan to build cell walls.

  • Morphology: Morphogenetically identical to the Archaea group.

Structural Organization in Microorganisms

• Colonial Organization

  • Consists of cell clusters where all cells have the same capabilities.

  • Lacks cellular differentiation or specialized tissue functional division.

• Multicellular Organization

  • Defined by cellular specialization, where individual cells perform distinct, dedicated functions.

Eukaryotic Microorganisms and Helminths

• General Eukaryotic Characteristics

  • Possess a true membrane-bound nucleus.

  • Contain complex membrane-bound organelles.

• Fungi

  • Examples: Yeasts, molds, and mushrooms.

  • Cellular Organization: Can be single-celled, colonial, or multicellular.

  • Reproduction: Reproduce via asexual spores or sexual spores.

  • Motility: Non-motile.

  • Metabolism: All are heterotrophs (specifically saprobes and detritivores that absorb organic nutrients).

  • Habitat: Inhabit aquatic and terrestrial environments.

• Protists: Algae

  • Taxonomic Grouping: Part of the Protist group.

  • Cellular Organization: Can be single-celled, colonial, or multicellular.

  • Cell Wall: Possess cell walls.

  • Reproduction: Reproduce via asexual or sexual methods.

  • Motility: Some are motile (utilizing flagella), while others are non-motile.

  • Metabolism: All are autotrophs.

  • Habitat: Primarily aquatic.

• Protists: Protozoa

  • Taxonomic Grouping: Part of the Protist group.

  • Cellular Organization: All are single-celled (1 cell).

  • Cell Wall: Contain no cell walls.

  • Reproduction: Reproduce via asexual or sexual methods.

  • Motility: All are motile, utilizing structures such as cilia or flagella.

  • Metabolism: All are heterotrophs.

  • Habitat: Found in aquatic and terrestrial environments.

• Parasitic Helminths (Worms)

  • Domain: Eukaryotic organisms.

  • Cellular Organization: All are multicellular.

  • Cell Envelope: Contain no cell walls.

  • Reproduction: Exclusively sexual reproduction (note: even species that are hermaphrodites reproduce sexually).

  • Motility: Motile by specialized musculature.

  • Metabolism: Heterotrophs.

  • Lifestyle / Habitat: Live in or on a host organism.

Acellular Infectious Agents

• General Properties

  • Are acellular agents and are not considered alive.

• Viruses

  • Structure: Composed of nucleic acid (have DNA or RNA) enveloped by a protein capsid.

  • Host Range: Infect every living thing.

• Viroids

  • Structure: Composed solely of naked RNA strands.

  • Host Range: Infect only plants.

• Prions

  • Structure: Composed entirely of infectious protein.

  • Host Range: Infect animals (causing conditions such as Mad Cow Disease).