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).