Biol 20: Chapter 4

Video 1:

Prokaryotes are microorganisms that exist in diverse environments and are ubiquitous on Earth.
They can be found inside and on the human body, including areas such as the mouth, nasal cavity, throat, ears, gastrointestinal tract, reproductive tract, and skin.
Soil is rich in prokaryotes, with one gram of soil containing up to 10 billion microorganisms, many of which are beneficial, aiding in organic matter breakdown and increasing soil fertility.
Prokaryotes also inhabit the atmosphere, indicating their widespread presence.

Symbiosis refers to interactions between different species within a community, where these interactions can have various effects on those populations.
Four major types of symbiotic relationships:
Mutualism: Both populations benefit (e.g., E. coli in human gut produces vitamin K).
Commensalism: One population benefits, the other is unaffected (e.g., Staphylococcus epidermidis on human skin uses dead skin cells).
Amensalism: One population is harmed while the other is unaffected (e.g., Lucilia sericata produces a protein harmful to Staphylococcus aureus).
Parasitism: One population benefits at the expense of the other (e.g., pathogenic bacteria causing infections).

The microbiome consists of all prokaryotic and eukaryotic microorganisms associated with a host organism, such as humans.
Resident microbiota: Permanent microorganisms living in or on the body.
Transient microbiota: Organisms that are temporarily present and can be removed (e.g., through handwashing).

Prokaryotes are classified into three domains: Bacteria, Archaea, and Eukarya, with a focus on bacteria in this chapter.
Domain Bacteria is further divided into two kingdoms based on the Gram staining technique: Gram-negative and Gram-positive.

Divided into two major phyla: 1) Proteobacteria and 2) Non-Proteobacteria.
Proteobacteria: Named after the Greek god Proteus for their shape-shifting capabilities.

Alpha Proteobacteria:
- Also known as oligotrophs, capable of growth at low nutrient levels.
- Example: Chlamydia trachomatis, causes trachoma and sexually transmitted infections.
Beta Proteobacteria:
- Eutrophs requiring nutrient-rich environments.
- Examples include Neisseria gonorrhoeae (gonorrhea) and Bordetella pertussis (whooping cough).
Gamma Proteobacteria:
- The largest and most diverse subgroup of gram-negative bacteria, includes opportunistic pathogens.
- Key organisms: Pseudomonas aeruginosa (hospital-acquired infections), Haemophilus influenzae (respiratory infections), Vibrio cholerae (cholera).
- Enterics: Reside in the intestinal tract, divided into coliforms (ferment lactose) and non-coliforms (generally pathogenic).
Delta Proteobacteria:
- Predators of other bacteria, reproduce within the periplasm of host cells (e.g., Bdellovibrio bacteriovorus).
Epsilon Proteobacteria:
- Small, slender bacteria; microaerophilic (require minimal oxygen).
- Example: Helicobacter pylori, associated with stomach ulcers and cancer.

This chapter's focus is on the classification of prokaryotes, emphasizing the differences among major groups, particularly in their pathogenic potential and ecological roles.

Video 2:

Long, spiral-shaped bacteria.
Very thin and highly motile.
Difficult to culture.
Possess endoflagella (axial filaments) for movement through host cells and media.
Enable twisting movement of bacteria due to the structure of axial filaments.
Important to recognize their shape and motility mechanisms.

Cytophaga: Motile aquatic bacteria capable of gliding.
Fusobacteria: Common in human mouth; can cause serious infections.
Bacteroides: Largest genus in CFP group; prevalent in the human large intestine.
- Comprises about 30% of normal gut microbiota—very important for understanding human health.

Large and diverse group that uses sunlight for ATP synthesis through photosynthesis.
Two types of photobacteria:
- Oxygenic: Produce oxygen (e.g., cyanobacteria—important for aquatic ecosystems).
- Anoxygenic: Do not produce oxygen; instead produce other compounds like sulfur (e.g., purple and green sulfur bacteria).
- They use different types of bacterial chlorophylls for photosynthesis.

Characterized by thick peptidoglycan cell wall, retaining purple color during Gram staining.

Example: Clostridium:
- Endospore-producing obligate anaerobes that cannot tolerate oxygen.
- Notable species:
  - Clostridium tetani: Causes tetanus.
  - Clostridium botulinum: Causes botulism.
  - Clostridium perfringens: Causes food poisoning.
  - Clostridium difficile: Causes antibiotic-associated diarrhea.
Streptococcus: Spherical cocci in chains.
- Known for producing enzymes that damage human tissues and blood cells.
- Causes various diseases, including bacterial pharyngitis (strep throat).
Staphylococcus: Common species include:
- Staphylococcus aureus: Causes numerous diseases and infections.
- Staphylococcus epidermidis: Generally harmless and resides on human skin.