BIOL 210 The Prokaryotes F21 edt (notes)

The Prokaryotes

Domains:

  • Bacteria: A diverse group that can be found in various environments and play critical roles in ecological processes.

  • Archaea: Often found in extreme environments, showcasing unique adaptations that differentiate them from bacteria.

Prokaryotic Diversity

Prokaryotes exhibit immense diversity, categorized into major groups that include:

  • Animals: Eukaryotic organisms distinct from prokaryotes.

  • Fungi: Includes eukaryotic decomposers; not part of prokaryotic classification.

  • Gram-positive bacteria: Characterized by their thick peptidoglycan cell walls (e.g., Actinobacteria).

  • Gram-negative bacteria: Have thinner peptidoglycan walls and an outer membrane; groups include Proteobacteria (notable for their diverse metabolic capabilities), Chlamydiae, and Cyanobacteria (known for oxygen production through photosynthesis).

  • Archaea: Includes extremophiles such as Crenarchaeota (thermophiles) and Euryarchaeota (methanogens).

  • Miscellaneous: This category encompasses diverse organisms such as slime molds (eukaryotic), algae (can be photosynthetic eukaryotic), protozoa, and spirochaetes.

Notable Prokaryotes

  1. Shewanella

    • Habitat: Thrives in deep-sea environments characterized by low oxygen concentrations.

    • Unique Features: Known for its long appendages that facilitate attachment to surfaces and its remarkable ability to digest toxic waste while generating electricity, which has applications in bioremediation and biosensing.

  2. Alphaproteobacteria

    • Human Pathogens:

      • Bartonella:

        • B. henselae: Responsible for Cat-scratch disease, transmitted through scratches or bites from cats.

      • Brucella:

        • Causes Brucellosis through consumption of unpasteurized milk or undercooked meat. Symptoms include joint/muscle pain, fever, and fatigue.

      • Ehrlichia:

        • Causes tickborne diseases by infecting white blood cells, leading to various symptomatic presentations.

    • Plant Pathogen:

      • Agrobacterium: This genus induces tumors in plants by inserting plasmids into host DNA, particularly affecting plants via horizontal gene transfer.

    • Nitrogen-Fixing Bacteria:

      • Azospirillum: Found in soil, this bacterium associates with plant roots and utilizes various nutrients, contributing to plant growth.

      • Rhizobium: Known for its symbiotic relationship with legume roots, where it fixes atmospheric nitrogen, enriching soil fertility.

  3. Betaproteobacteria

    • Notable Genera:

      • Neisseria:

        • Chemoheterotrophic cocci, includes pathogenic species like N. meningitidis (causes meningococcal disease) and N. gonorrhoeae (causes gonorrhea).

      • Spirillum:

        • Recognized for its helical shape, commonly found in organic matter-rich stagnant waters, playing a role in ecosystems.

  4. Gammaproteobacteria

    • Key Groups:

      • Pseudomonas: Diverse group of opportunistic pathogens involved in various infections; known for their metabolic versatility.

      • Legionella: Primarily associated with water systems; the bacterium causes Legionnaires’ disease.

      • Vibrio: Found in coastal waters with Vibrio cholerae being the pathogen responsible for cholera outbreaks.

      • Enterobacteriales: This order includes medically important species such as Escherichia (some strains are pathogenic), Salmonella (causes foodborne illness), and Yersinia (the causative agent of plague).

  5. Deltaproteobacteria

    • Bdellovibrio:

      • A unique predator of other bacteria, exhibiting a predatory lifestyle that helps control microbial populations.

  6. Epsilonproteobacteria

    • Helicobacter:

      • This genus is linked to significant gastrointestinal diseases, including peptic ulcers and gastric cancer, highlighting its medical importance.

  7. Cyanobacteria

    • Unique Feature:

      • Possess specialized cells called heterocysts for nitrogen fixation and reproduce through binary fission; they are crucial to nitrogen cycling in aquatic ecosystems and can produce oxygen through photosynthesis.

  8. Clostridium

    • Notable characteristic:

      • Known for being endospore-producing, obligate anaerobes, playing roles in various fermentation processes and pathogenicity, e.g., C. botulinum (causes botulism).

  9. Bacillales

    • Includes Staphylococcus:

      • These cocci-shaped bacteria include both pathogenic (e.g., S. aureus) and non-pathogenic species,

  10. Lactobacillales

    • Generally aerotolerant anaerobes; they lack an electron transport chain and are vital in fermentation processes for food production (e.g., yogurt).

  11. Mycoplasmatales

    • Recognized for their wall-less structure, exhibiting a pleomorphic morphology that allows them to adapt to various host environments, notably Mycoplasma pneumoniae (causes atypical pneumonia).

  12. Gemmata obscuriglobus

    • Unique for having a double internal membrane surrounding its DNA, suggesting an exotic arrangement akin to eukaryotic organization.

  13. Chlamydias

    • Major pathogens include Chlamydia trachomatis, which causes trachoma (leading cause of blindness) and sexually transmitted infections (STIs).

  14. Spirochetes

    • Includes genera such as Borrelia, Leptospira, and Treponema, known for causing diseases like Lyme disease and syphilis, exhibiting unique corkscrew motility.

  15. Fusobacteria

    • Commonly found in the human mouth, they are associated with dental diseases and contribute to oral and systemic infections.

Domain Archaea

  • Extremophiles:

    • Encompasses organisms like hyperthermophiles such as Pyrodictium, which thrive in high-temperature environments, and methanogens like Methanobacterium, essential for methane production in anaerobic ecosystems.

Conclusion

Prokaryotes, with their vast diversity and roles in ecological processes, human health, and agriculture, are fundamental components of life on Earth. They participate in nutrient cycling, serve as models for studies in genetics and biochemistry, and play crucial roles in biotechnology applications.