Study Guide: The Prokaryotes – Bacteria and Archaea

The Prokaryotes: Bacteria and Archaea

Overview of Prokaryotes

Prokaryotes are unicellular organisms lacking a membrane-bound nucleus and organelles. They are divided into two domains: Bacteria and Archaea, as recognized by the Three Domain System of phylogenetic relationships. - Bacteria: Includes a wide variety of species, many of which are pathogenic. - Archaea: Distinct from bacteria, often found in extreme environments.

Three Domain System

The Three Domain System classifies all life into three domains: Bacteria, Archaea, and Eukarya. This system is based on differences in ribosomal RNA and other molecular features. - Bacteria: Prokaryotic, single circular chromosome. - Archaea: Prokaryotic, single circular chromosome, unique membrane lipids. - Eukarya: Eukaryotic, multiple linear chromosomes.

Characteristic	Bacteria	Archaea	Eukarya
Cell type	Prokaryotic	Prokaryotic	Eukaryotic
Chromosomes	Single, circular	Single, circular	Several, linear
Membrane lipids	Ester linkages	Ether linkages	Ester linkages
Ribosomal RNA	Unique	Unique	Unique
Cell wall	Peptidoglycan	No peptidoglycan	Cellulose/chitin (if present)

Domain Bacteria

Bacterial Diversity

The domain Bacteria contains 18 different phyla, with only half containing pathogenic species. Bacteria are classified based on cell wall structure, metabolism, and genetic characteristics.

Representative Groups of Bacteria

Bacteria are grouped into several major phyla, each with unique characteristics.

Deep-Branching Thermophiles

- Aquificae: Hyperthermophiles, grow at high temperatures. - Thermotogae: Thermophiles, anaerobic, grow in hot environments.

Cyanobacteria

- Oxygenic photosynthetic bacteria with thylakoid membranes. - Examples: Anabaena, Spirulina.

Firmicutes and Actinobacteria (Gram-positive)

- Firmicutes: Low GC, gram-positive, includes Bacillus and Clostridium. - Actinobacteria: High GC, gram-positive, includes Streptomyces and Mycobacterium.

Proteobacteria and Nitrospirae (Gram-negative)

- Proteobacteria: Diverse metabolism, includes Escherichia, Salmonella, Rhizobium. - Nitrospirae: Nitrile oxidizers, obligate aerobes.

Bacteroidetes/Chlorobi Group

- Bacteroidetes: Anaerobes, important in gut microbiota. - Chlorobi: Green sulfur bacteria, phototrophic.

Spirochetes

- Narrow coiled cells, motile with axial filaments. - Includes Treponema (syphilis), Borrelia (Lyme disease).

Chlamydiae, Planctomycetes, and Verrucomicrobia

- Chlamydiae: Intracellular pathogens. - Planctomycetes: Unique cell structure, budding reproduction. - Verrucomicrobia: Cells with prosthecae.

Domain Archaea

Characteristics of Archaea

Archaea are prokaryotic organisms with unique membrane lipids (ether linkages) and cell wall structures. They are often found in extreme environments and were first identified as a distinct domain by Carl Woese in the 1970s.

Major Phyla of Archaea

The domain Archaea is divided into four main phyla: - Euryarchaeota - Crenarchaeota - Korarchaeota - Nanoarchaeota

Representative Groups of Archaea

Crenarchaeota

- Includes hyperthermophiles and acidophiles. - Found in hot springs and marine vents.

Euryarchaeota

- Includes methanogens, halophiles, and thermophiles. - Methanogens produce methane in anaerobic environments.

Methanogens

Methanogens are archaea that produce methane as a metabolic byproduct in anaerobic conditions. They are found in environments such as wetlands, digestive tracts of animals, and sewage digesters.

Halophiles

Halophiles are archaea that thrive in highly saline environments, such as salt lakes and salt mines.

Summary Table: Comparison of Bacteria and Archaea

Feature	Bacteria	Archaea
Cell wall	Peptidoglycan	No peptidoglycan
Membrane lipids	Ester linkages	Ether linkages
Habitat	Wide range	Often extreme environments
Pathogenicity	Many pathogenic species	Few pathogenic species

Key Terms and Concepts

- Prokaryote: Organism lacking a nucleus and membrane-bound organelles. - Domain: Highest taxonomic rank in biological classification. - Phylogenetic tree: Diagram showing evolutionary relationships. - Gram-positive: Bacteria with thick peptidoglycan cell wall. - Gram-negative: Bacteria with thin peptidoglycan and outer membrane. - Methanogen: Archaea producing methane in anaerobic conditions. - Halophile: Organism thriving in high salt concentrations.

Additional info:

Some details about metabolic pathways, environmental adaptations, and pathogenicity were inferred from standard microbiology knowledge to provide a complete study guide.