Classification of Microorganisms: Taxonomy, Domains, and Kingdoms

Classification of Microorganisms

Taxonomy and Systematics (Phylogeny)

Taxonomy is the science of classifying organisms, while systematics (phylogeny) involves studying the evolutionary relationships among organisms. These fields provide a framework for organizing biological diversity and understanding how organisms are related.

• Taxonomy: The science of naming, describing, and classifying organisms.

• Systematics (Phylogeny): The study of evolutionary relationships among organisms.

• Example: The classification of Escherichia coli within the domain Bacteria, phylum Proteobacteria.

Historical and Current Methods of Classification

Organisms have been classified using various methods, from observable characteristics to molecular techniques.

• Historical Methods: Morphology, physiology, and biochemical tests.

• Current Methods: Genetic sequencing, molecular markers, and phylogenetic analysis.

• Example: Ribosomal RNA sequencing is used to determine evolutionary relationships.

Binomial Nomenclature

Binomial nomenclature is the formal system of naming species using two names: genus and species.

• Format: Genus name (capitalized) + species name (lowercase), both italicized.

• Example: Staphylococcus aureus

Classification System and Levels

The classification system organizes organisms into hierarchical levels.

• Levels (in order): Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species

• Mnemonic: "Dear King Philip Came Over For Good Soup"

The Three Domains of Life

All living organisms are classified into three domains based on cellular organization and genetics.

• Bacteria: Prokaryotic cells, peptidoglycan cell walls, diverse metabolic types.

• Archaea: Prokaryotic cells, unique membrane lipids, often extremophiles.

• Eukarya: Eukaryotic cells, includes fungi, algae, protozoa, and animals.

• Prokaryotic Domains: Bacteria and Archaea

• Eukaryotic Domain: Eukarya

Kingdoms in the Eukarya Domain

The domain Eukarya is divided into four kingdoms, each with distinct characteristics.

• Kingdom Fungi: Non-photosynthetic, cell walls of chitin, includes yeasts and molds.

• Kingdom Plantae: Photosynthetic, cell walls of cellulose, includes algae.

• Kingdom Animalia: Multicellular, no cell walls, includes helminths (parasitic worms).

• Kingdom Protista: Mostly unicellular, includes protozoa and some algae.

Definition of Species

Species definitions differ between eukaryotes and prokaryotes.

• Eukaryotic Species: A group of organisms that can interbreed and produce fertile offspring. Example: Homo sapiens

• Prokaryotic Species: A population of cells with similar characteristics.

Prokaryotic Reproduction and Clones

Prokaryotes reproduce primarily by binary fission, producing genetically identical cells called clones.

• Binary Fission: Asexual reproduction where a cell divides into two identical cells.

• Clone: A group of cells derived from a single parent cell.

Prokaryotic Strains

Strains are subgroups within a species that have distinct characteristics.

• Strain: A genetic variant or subtype of a microorganism.

• Differentiation: Strains are differentiated by biochemical, genetic, or antigenic properties.

• Strain Letters: Letters and numbers indicate specific variants (e.g., E. coli O157:H7).

Classification of Viruses

Viruses are classified based on their genetic material, structure, and host range.

• Viral Strain: A variant of a virus with distinct genetic or antigenic properties.

• Example: Influenza virus strains (H1N1, H3N2).

Domain Archaea

Archaea are prokaryotes with unique characteristics, often found in extreme environments.

• Characteristics: No peptidoglycan in cell walls, unique membrane lipids, extremophiles.

• Examples: Methanogens, halophiles, thermophiles.

Domain Bacteria

Bacteria are prokaryotes with diverse morphologies and metabolic capabilities.

• Characteristics: Peptidoglycan cell walls, various shapes (cocci, bacilli, spirilla).

• Examples: Streptococcus, Escherichia, Bacillus

• Bacterial Morphology: Shapes include cocci (spherical), bacilli (rod-shaped), spirilla (spiral).

Kingdom Fungi

Fungi are eukaryotic organisms that include yeasts, molds, and mushrooms.

• Characteristics: Non-photosynthetic, cell walls of chitin, decomposers.

• Yeast vs. Mold: Yeasts are unicellular, molds are multicellular and filamentous.

• Examples: Saccharomyces cerevisiae (yeast), Aspergillus (mold)

Phylum Protozoa

Protozoa are unicellular eukaryotes, often motile and found in aquatic environments.

• Characteristics: Unicellular, motile, heterotrophic.

• Examples: Amoeba, Paramecium, Plasmodium

Phylum Algae

Algae are photosynthetic eukaryotes found in aquatic environments.

• Characteristics: Unicellular or multicellular, photosynthetic, cell walls of cellulose.

• Examples: Chlamydomonas, Spirogyra, Volvox

Eukaryotic Animal Parasites

Animal parasites are multicellular eukaryotes, often causing disease in hosts.

• Characteristics: Multicellular, lack cell walls, parasitic lifestyle.

• Examples: Helminths such as Ascaris (roundworm), Taenia (tapeworm)

Viruses

Viruses are acellular entities that require a host cell for replication.

• Characteristics: Genetic material (DNA or RNA), protein coat, obligate intracellular parasites.

• Examples: Influenza virus, HIV, bacteriophages

Summary Table: Domains and Kingdoms

The following table summarizes the main domains and kingdoms, their cell types, and examples.

Domain	Kingdom/Group	Cell Type	Characteristics	Examples
Bacteria	---	Prokaryotic	Peptidoglycan cell wall, diverse shapes	Escherichia coli, Streptococcus
Archaea	---	Prokaryotic	No peptidoglycan, extremophiles	Methanogens, halophiles
Eukarya	Fungi	Eukaryotic	Chitin cell wall, decomposers	Aspergillus, Saccharomyces
Eukarya	Plantae	Eukaryotic	Cellulose cell wall, photosynthetic	Algae
Eukarya	Animalia	Eukaryotic	No cell wall, multicellular	Helminths
Eukarya	Protista	Eukaryotic	Mostly unicellular, diverse	Protozoa, some algae
---	Viruses	Acellular	DNA or RNA, protein coat	Influenza, HIV

Additional info: This summary expands on brief points by providing definitions, examples, and a comparative table for clarity. It is suitable for exam preparation and covers all major learning objectives from the provided material.