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).