bacteria and arcaea PPT

Chapter Overview

• Bacteria and Archaea: Most abundant and diverse life-forms on Earth.

• Key themes include:

  • Gene transfer

  • Metabolism

  • Morphology

  • Ecological diversity.

Phylogenetic Tree of Life

• Three major domains:

  • Bacteria

  • Archaea

  • Eukaryota

• Notable lineages:

  • Spirochetes, Proteobacteria, Cyanobacteria, Methanogens.

Introduction to Bacteria and Archaea

• Characteristics:

  • Most are unicellular and prokaryotic.

  • Lack membrane-bound nucleus.

  • Distinct differences in plasma membranes and cell wall composition.

• Antibiotics affect bacterial ribosomes without impacting archaea or eukaryotes.

Microbiome

• Defined as a community of microbes that inhabit particular areas.

Distinguishing Features of Bacteria and Archaea

• Molecular Features:

  • Bacteria: one type of RNA polymerase (five subunits).

  • Archaea: one type (13 subunits, similar to eukaryotes).

Biological Impact

• Bacteria are ancient and diverse with:

  • Fossils dating back 3.5 billion years.

  • 10,000 known species; likely hundreds of thousands exist.

  • Microbes reside in significant numbers in the human body.

Habitat Diversity

• Bacteria and archaea occupy diverse habitats, including:

  • Hydrothermal vents

  • Extreme pH levels

  • Environments with very low temperatures.

Pathogenic Bacteria

• Pathogens: Bacteria causing diseases; examples include:

  • Clostridium tetani (Tetanus)

  • Staphylococcus aureus (Acne, toxic shock syndrome)

  • Mycobacterium tuberculosis (Tuberculosis)

  • Mycobacterium leprae (Leprosy)

Koch’s Postulates

• Guidelines to establish a microorganism's role in disease:

  1. Microorganism present in diseased organisms.

  2. Isolated and cultured in pure form.

  3. Causes the same disease in a healthy host.

  4. Re-isolation from the diseased host.

Germ Theory of Disease

• Introduced by Robert Koch, highlighting infectious diseases' patterns and transmission.

• Infectious disease transmission methods:

  • Person to person

  • Insect/animal bites

  • Contaminated food/water.

Bacterial Pathogenicity

• Virulence: Heritable ability to cause disease.

• Pathogenic strains (like E. coli) often possess larger genomes due to virulence genes acquisition.

Resistant Endospores in Pathogenic Bacteria

• Endospores: Durable structures formed during environmental stress, resistant to extreme conditions.

Antibiotic Evolution and Resistance

• Antibiotics kill bacteria or inhibit growth; discovered in 1928, widely used since 1940s.

• Extensive use led to drug-resistant bacterial strains.

Biofilms

• Biofilms: Bacterial colonies in a protective polysaccharide matrix, resist antibacterial agents.

Role in Bioremediation

• Bioremediation: Use of bacteria and archaea to clean polluted environments, especially toxic organic solvents.

Bacterial Size and Morphology

• Bacteria size ranges from 0.3 μm to 100 μm.

• Shapes include cocci (spherical), bacilli (rod-shaped), and spirilli (spiral-shaped).

Arrangement of Bacteria

• Arrangements include:

  • Cocci: Diplococcus, Streptococcus, Tetrads, Staphylococcus

  • Bacillus: Diplobacillus, Streptobacillus

  • Spiral: Spirillum, Spirochete

Genetic Variation through Gene Transfer

• Lateral gene transfer allows bacteria to acquire traits:

  • Transformation: Uptaking DNA from the environment.

  • Transduction: DNA transfer via viruses.

  • Conjugation: Direct genetic material transfer between cells.

Cell-Wall Composition

• Gram Staining: Differentiates bacteria:

  • Gram-positive: Thick peptidoglycan (purple).

  • Gram-negative: Thin peptidoglycan with an outer membrane (pink).

The Oxygen Revolution

• Cyanobacteria: First to perform oxygenic photosynthesis, significantly changing Earth's atmosphere.

Nitrogen Fixation and the Nitrogen Cycle

• Essential for protein and nucleic acid synthesis; nitrogen needs conversion from N2 to NH3 through nitrogen-fixing bacteria.

Key Lineages of Bacteria and Archaea

• Bacteria: 29 recognized lineages, classified by morphology and metabolism.

• Archaea: Abundant in extreme conditions; includes groups like Korarchaeota and Euryarchaeota.