Old & Odd: Archaea, Bacteria & Protists - CrashCourse

Introduction to Single-Celled Organisms

• Importance of single-celled organisms in understanding life on Earth.

• Two of the three taxonomic domains are single-celled: Archaea, Bacteria, and Protists.

• These organisms represent the world's oldest living lineages, originating from the first signs of life on Earth.

Overview of Archaea, Bacteria, and Protists

• Archaea: Often found in extreme environments; examples include:

  • Methanogens (produce methane)

  • Extremophiles (thermophiles, halophiles)

• Bacteria: Most abundant prokaryotes; evolving rapidly,

  • Horizontal gene transfer leads to antibiotic resistance.

• Protists: Eukaryotic, larger diversity, and complexity of life.

• Key roles in ecosystems; some cause disease while others support life.

Prokaryotic vs. Eukaryotic Cells

• Prokaryotes (Archaea and Bacteria): No nucleus, DNA in plasmids.

• Eukaryotes (Protists): Have a nucleus with chromosomal DNA.

• Common features include plasma membranes and ribosomes for protein synthesis.

Age of Archaea

• Fossils dating back 3.5 billion years imply archaea's long history on Earth.

• Found in extreme habitats: hydrothermal vents, oil wells, volcanic springs.

Types of Archaea

• Methanogens: Live in swamps; derive energy from hydrogen and carbon.

• Extremophiles: Adapted to extreme conditions:

  • Thermophiles: Survive high temperatures (e.g., Pyrolobus fumarii).

  • Halophiles: Thrive in high salinity environments (e.g., Great Salt Lake).

Bacteria: Diversity and Adaptability

• Bacteria classified by cell membrane characteristics:

  • Gram-positive: Thick membranes (e.g., Staphylococcus, Streptococcus).

  • Gram-negative: Thinner membranes (e.g., Proteobacteria, Cyanobacteria).

• Bacteria are diverse and adaptable, leading to rapid evolution and developing antibiotic resistance.

Methods of Genetic Exchange in Bacteria

• Horizontal Gene Transfer: Method for bacteria to exchange genetic information, essential for antibiotic resistance.

• Bacteria reproduce asexually but can share traits with neighbors, increasing genetic diversity.

Types of Bacteria

• Proteobacteria: Diverse forms, involved in nitrogen fixation and diseases.

• Cyanobacteria: Only prokaryotes that perform photosynthesis, critical in aquatic ecosystems.

• Spirochetes: Corkscrew-shaped, some are pathogens (e.g., Lyme disease).

• Chlamydias: Uniquely parasitic, significant for human infections.

Protists: A Complex Group

• Protists evolved from bacteria approximately 1.7 billion years ago, combining attributes of both plants and animals.

• Types of Protists:

  • Protozoa: Animal-like, heterotrophic, capable of movement using flagella or cilia.

  • Algae: Plant-like, perform photosynthesis; unicellular and multicellular varieties.

    • Sailor's Eyeball: The largest single-celled organism.

  • Fungus-like Protists: Includes slime molds; can move and absorb nutrients.

Characteristics of Protists

• Require wet environments to thrive (e.g., bogs, bodies of water).

• Diversity in reproduction: some unicellular, some multicellular, and a few capable of sexual reproduction.

Conclusion

• The diversity and adaptability of archaea, bacteria, and protists underline the complexity of life on Earth.

• These organisms are crucial for understanding the fundamental aspects of biology, evolution, and ecology.

• Encourage further exploration into the uniqueness and functions of these fascinating organisms.

Introduction to Single-Celled Organisms

Understanding single-celled organisms is fundamental to comprehending the complexity of life on Earth. These organisms not only represent the earliest form of life but also play significant roles in ecological systems. Two of the three taxonomic domains are comprised solely of single-celled organisms: Archaea and Bacteria, alongside the more complex Protists. Together, they represent some of Earth’s oldest living lineages, tracing back to the first signs of life approximately 3.5 billion years ago.

Overview of Archaea, Bacteria, and Protists

Archaea

• Often found in extreme and inhospitable environments, archaea demonstrate unique metabolic pathways.

• Types of Archaea include:

  • Methanogens: Microorganisms that produce methane as a metabolic byproduct, often found in anaerobic environments like swamps and the guts of ruminants.

  • Extremophiles: Organisms that thrive in extreme conditions, divided into categories such as:

    • Thermophiles: Archaea that can withstand high temperatures, such as Pyrolobus fumarii, which can survive above 100°C.

    • Halophiles: Species that exist in high-salinity environments like salt lakes, adapting to osmotic pressures.

Bacteria

• As the most abundant prokaryotic organisms, bacteria exhibit remarkable diversity and adaptability, rapidly evolving to various conditions.

• Characteristics of Bacterial Cell Membranes:

  • Gram-positive: Thick peptidoglycan layers, making them more susceptible to antibiotics (e.g., Staphylococcus, Streptococcus).

  • Gram-negative: Thinner peptidoglycan layers with an outer membrane, often more resistant to antibiotics (e.g., Proteobacteria, Cyanobacteria).

Protists

• Protists are eukaryotic and include a diverse range of organisms, both unicellular and multicellular, often exhibiting complex life cycles.

• Key Types of Protists:

  • Protozoa: Animal-like protists that are heterotrophic, feeding on bacteria and other small particles, often mobile via cilia, flagella, or pseudopodia.

  • Algae: Plant-like protists that conduct photosynthesis, ranging from unicellular forms, like Chlorella, to large multicellular forms, like kelp.

  • Fungus-like Protists: Such as slime molds, exhibit characteristics of fungi with the ability to move and absorb nutrients as well as reproduce asexually or sexually.

Prokaryotic vs. Eukaryotic Cells

• Prokaryotes (Archaea and Bacteria): Lack a nucleus; their DNA is typically circular and organized in plasmids, allowing for rapid replication and mutation.

• Eukaryotes (Protists): Possess a defined nucleus containing chromosomal DNA and various organelles like mitochondria and chloroplasts, allowing for compartmentalized cellular functions.

Methods of Genetic Exchange in Bacteria

• Horizontal Gene Transfer (HGT): A critical process where bacteria exchange genetic material, which contributes to genetic diversity and the development of antibiotic resistance. This mechanism includes transformation, transduction, and conjugation.

Conclusion

The extraordinary diversity and adaptability of archaea, bacteria, and protists are a testament to the complexity of life on Earth. These single-celled organisms not only provide insights into the origins of life but also serve vital functions in ecosystems across the globe. Understanding their evolution, ecological roles, and interactions enhances our knowledge of biology, evolution, and ecology, prompting further inquiry into the unique functionalities of these fascinating organisms.