Biodiversity II - Three Domains of Life and Bacteria

Three Domains of Life

  • Eucarya/Eukaryotes

    • Cells contain nuclei: compartments that house DNA.
    • Eukaryote cells are compartmentalized with specialized organelles.

  • Archaea

    • Prokaryotic cells without nuclei or compartments.
    • Often found in extreme environments; termed extremophiles.

  • Bacteria

    • Prokaryotic cells lacking nuclei and compartments.
    • Distinct biochemical differences from Archaea, which are not covered in detail.

Bacterial Classification by Shape

  • Bacteria are classified primarily by their shape:
    • Cocci: Dot-shaped bacteria.
    • Bacilli: Rod-shaped bacteria.
    • Spirilla: Spiral-shaped bacteria.
    • Vibrio: Comma or bean-shaped.
    • Spirochaetes: Long spiral-shaped; include bacteria such as those causing Lyme disease and syphilis.

Growth Forms of Bacteria

  • Bacteria also categorized by their grouping during growth:
    • Staphylococci: Cocci in clusters (Greek "staphylos" = "bunch of grapes").
    • Diplococci: Cocci in pairs (Greek "diplo" = "double").
    • Streptococci: Cocci in chains (Greek "streptos" = "twisted").

Bacterial Structure

  • Cells consist of:

    • Cell Membrane (CM): Flexible outer boundary.
    • Cell Wall (CW): Rigid structure that provides support (contains peptidoglycan).

  • Peptidoglycan: A protein-sugar compound crucial for bacterial cell wall integrity.

    • Antibiotics like penicillin inhibit peptidoglycan synthesis, affecting bacterial survival without harming human cells.

Capsules and Reproduction

  • Capsule: A potential outer layer that influences infection capability, visible as "halos" under a microscope.

  • Reproduction:

    • Primarily through binary fission (asexually splitting in two).
    • Conjugation: A form of sexual reproduction involving the exchange of genetic material.

  • Endospores: Some bacteria form resistant endospores to survive harsh conditions. Examples include Bacillus anthracis (anthrax). Endospores can remain dormant for years and reactivate under favorable conditions.

Importance of Bacteria

  • Pathogen Identification: Bacterial shape, size, growth form, and cell wall structure assist in identifying pathogens causing infections in humans, plants, and animals.

    • Notable bacterial diseases: syphilis, gonorrhea, cholera, Lyme disease, food poisoning, tuberculosis, strep throat.

  • Toxins:

    • Exotoxins: Released by bacteria (e.g., tetanus, botulism).
    • Endotoxins: Components of cell walls that are toxic (e.g., salmonella).

Bacteria: Beyond Diseases

  • Most bacteria are harmless and play vital roles in ecosystems:

    • Aerobic bacteria: Require oxygen for survival.
    • Anaerobic bacteria: Do not require oxygen and may be inhibited by it.
    • Decomposers: Break down dead organisms and recycle nutrients back into the environment.

  • Cyanobacteria (Blue-Green Bacteria): Photosynthetic bacteria that significantly contribute to global oxygen production.

    • Prochlorococcus: A major photosynthetic bacterium, comprising ~20% of global photosynthesis.

Beneficial Bacteria

  • Applications in food industry include:

    • Converting milk into buttermilk, yogurt; fermenting beer and vinegar.
    • Creating flavors in cheeses and aiding in fermentation processes (e.g., sauerkraut).

  • Environmental benefits:

    • Waste breakdown in sewage treatment, oil spill cleanup, and recovery of metals from mining waste

  • Nitrogen-fixing bacteria live in roots of legumes, converting nitrogen gas into usable forms, enhancing soil fertility.

  • Probiotics: Beneficial bacterial supplements; research ongoing for their health benefits for humans.