Introduction to Prokaryotes: Bacteria and Archaea

Bacteria and Archaea Overview

• Prokaryotes: organisms without true nuclei, evolved ~3.5 billion years ago.

  • Collective biomass is at least 10 times that of eukaryotes.

  • Cause ~50% of human diseases.

Key Concepts

• Microevolution: changes in populations (Chapters 22-26).

• Macroevolution: changes in species (Chapters 27, 29, 30, 32, 34).

Tree of Life

• Prokaryotes, comprising Bacteria and Archaea, are two of the three main branches.

• Themes for study include morphology, movement, reproduction, metabolism, and energy.

Prokaryotic Characteristics

• Generally unicellular and lack membrane-bound nuclei.

• Size: typically 1–10 microns.

• DNA is not contained in a nucleus (nucleoid).

• Possess a single circular chromosome; may have plasmids (smaller DNA rings).

• Cell walls differ: Bacteria have peptidoglycan, while Archaea do not.

Structure • Movement • Reproduction

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

• Cell Wall: Maintains shape and protects from bursting in hypotonic environments.

  • Gram Staining: dyeing system to examine the cell walls

  • Gram-positive: Purple due to thick peptidoglycan.

  • Gram-negative: Pink due to thin peptidoglycan and outer membrane.

• Capsule: sticky layer aiding in adherence and protection from host defenses.

Endospores

• Resistant dormant structures formed during environmental stress (e.g., Clostridium difficile).

• Contain vital cellular components (DNA, ribosomes).

• Resistant to heat, UV radiation, and antibiotics.

Genetic Variation and Evolution

• Rapid reproduction and mutations: allows accumulation of mutations for rapid adaptation.

• Genetic recombination types:

  • Transformation: uptake of foreign DNA.

  • Transduction: gene transfer via bacteriophages. Carry prokaryotic genes from one host cell to another.

  • Conjugation: direct transfer of DNA via pili.

• R-plasmids: carry antibiotic resistance genes, allowing rapid spread of resistance.

• F factor: required for the production of pili ; it enables a bacterium to initiate conjugation by forming a mating bridge to transfer genetic material.

  F+: donor

  F-: recipient

  F plasmid.

Metabolism and Nitrogen Fixation

• Diversity in metabolism: Bacteria and Archaea utilize various pathways for ATP production.

• Oxygen's Role:

  • Obligate aerobes require O2.

  • Obligate anaerobes are poisoned by O2.

  • Facultative anaerobes can switch between modes.

• Nitrogen fixation: Bacteria convert atmospheric N2 into usable NH3. Essential for plant symbiosis (e.g., in root nodules).

Ecological Importance

• Decomposers: recycle nutrients by breaking down dead matter.

• Bioremediation: using prokaryotes to clean up pollutants (e.g., oil spills).

• Metabolic Cooperation: Group interactions maximize resource use, e.g., Anabaena.

Symbiotic Relationships

• Mutualism: both parties benefit. Example: intestinal bacteria aiding nutrient absorption in humans.

• Commensalism: one benefits, the other is unharmed.

• Parasitism: one benefits at the host's expense (pathogens).

Pathogenic Bacteria

• Spread mainly through person-to-person contact, insect bites, and contaminated food/water.

• Antibiotic resistance facilitated by genetic mutations and selection pressure due to antibiotic use.

  • Mycobacterium tuberculosis example with rifampin resistance mutation.

Comparison of Domains of Life

• Bacteria: no introns, peptidoglycan cell wall, circular chromosomes.

• Archaea: similar to Bacteria but distinct in metabolic processes and cell structure.

• Eukarya: contain a nuclear envelope and membrane-bound organelles, different transcription processes.

Research and Education

• Dr. Bartlett’s research focuses on basal transcription factors and RNA polymerase from the Archaeal domain.

• Courses offered include: Introduction to Microbiology, Molecular Genetics, and Theory of Recombinant DNA Techniques to expand understanding of microbial characteristics and applications in various fields.