SB

Chapter 16

Introduction to Microbial Life

  • Microorganisms in and on the human body outnumber human cells.
  • Disruption of microbial communities may lead to:
    • Increased susceptibility to infections
    • Predisposition to certain cancers
    • Conditions such as asthma, allergies, irritable bowel syndrome, Crohn’s disease, and autism.

Overview of Prokaryotes

16.1 Prokaryotic Diversity and Impact

  • Prokaryotic cells are smaller than eukaryotic cells.
  • Prokaryotes comprise a biomass at least 10 times that of all eukaryotes.
  • They have significant effects on the environment and human health.
  • Two main types of prokaryotes: Archaea and Bacteria.

16.2 Prokaryotic Cell Shape and Structure

  • Cell shape helps in identifying prokaryotes:
    • Cocci: Spherical shape
    • Bacilli: Rod-shaped
    • Spirilla: Short, rigid spiral
    • Spirochetes: Long, flexible spiral
  • Most prokaryotes have a protective cell wall.
  • Categorized by:**
    • Gram + (thick peptidoglycan wall)
    • Gram - (different wall structure)
  • Additional structures include:
    • Sticky capsules
    • Flagella (for movement)
    • Fimbriae (for attachment)

16.3 Adaptation and Genetic Variation in Prokaryotes

  • Rapid reproduction generates genetic variation.
  • Some form endospores for survival in harsh conditions.

16.4 Nutritional Diversity of Prokaryotes

  • Prokaryotes show extensive nutritional diversity allowing them to thrive in various environments.
  • Two energy sources:
    • Phototrophs (capture sunlight)
    • Chemotrophs (harness energy from chemicals)

16.5 Biofilms and Microbial Associations

  • Prokaryotes can form organized biofilm communities, leading to medical and environmental challenges.

16.6 Environmental Cleanup via Prokaryotes

  • Bioremediation: Using organisms to remove pollutants.
  • Common in sewage treatment processes.

16.7 Evolution of Prokaryotes

  • Advances in genetics show some prokaryotes are more closely related to eukaryotes.
  • First major split in life history: divergence of Bacteria and then Archaea from Eukarya.

16.8 Archaea's Unique Habitats

  • Archaea thrive in extreme conditions:
    • Halophiles: Salt-loving
    • Thermophiles: Heat-loving
    • Methanogens: Live in anaerobic (without oxygen) environments.

16.10 Pathogenic Bacteria and Disease

  • Exotoxins: Secreted proteins causing disease.
  • Endotoxins: Released upon death of gram-negative bacteria.
  • Some pathogens are used as biological weapons (e.g., anthrax).

Overview of Protists

16.12 Diversity of Protists

  • Protists are mostly unicellular eukaryotes found in damp habitats.
  • Categories include:
    • Autotrophic: Algae
    • Heterotrophic: Protozoans
    • Mixotrophic: Capable of photosynthesis and heterotrophy.

16.13 Protist Phylogeny and Supergroups

  • Protists organized into multiple clades, some related to plants, fungi, or animals.
  • Recognized supergroups:
    • SAR
    • Excavata
    • Unikonta
    • Archaeplastida

16.15 Algae as a Renewable Energy Source

  • Fossil fuels derive from ancient organisms.
  • Diatoms could provide a future source of biofuels.
  • Research focuses on cultivating diatoms and other algae for energy.

16.16 Mitochondrial Adaptations in Excavates

  • Excavata group includes:
    • Giardia (parasitic)
    • Trichomonas vaginalis
    • Trypanosomas (pathogenic protists)
    • Also includes Euglena (mixotrophic) and termite endosymbionts.

16.19 Evolution of Multicellularity in Eukaryotes

  • Multicellularity allows for specialized cells.
  • Evolved in:
    • Stramenopiles (brown algae)
    • Unikonts (fungi, animals)
    • Archaeplastids (red and green algae, land plants).