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Chapter 4: Prokaryotic Diversity

Where Do They Live?

  • Prokaryotic organisms are found everywhere in the environment, showcasing their adaptability.

  • They can thrive in various conditions, including extreme environments.

Are They All Good?

  • Sun & the Greenhouse Effect:

    • Solar radiation interacts with carbon dioxide and other greenhouse gases.

    • Increased greenhouse gases absorb and re-radiate heat, influencing climate.

    • Understanding this interaction helps in recognizing the biological impact of prokaryotes on ecosystems.

Relationship Between Microbes and Hosts - Symbiosis

  • Types of Symbiotic Relationships:

    • Mutualism: Both organisms benefit (e.g., bacteria in the human colon).

    • Commensalism: One organism benefits, the other is neither harmed nor benefited (e.g., mites in human hair follicles).

    • Amensalism: One organism is harmed while the other is unaffected (e.g., fungus secreting antibiotics).

    • Parasitism: One organism benefits at the expense of the other (e.g., tuberculosis bacteria in human lungs).

    • Neutralism: Neither organism benefits or is harmed.

Prokaryotes & Us: Microbiome and Normal Flora

  • Microbiota Defined:

    • Refers to the community of microorganisms in a specific environment, especially in the human body.

    • Important questions include how we acquire microbiota and its functions in our body.

What is Microbiota?

  • Resident Microbiota vs. Transient Microbiota:

    • Resident microbiota: Permanent microorganisms that reside in different areas of the body.

    • Transient microbiota: Temporary microorganisms that do not persist.

    • These microbiota live in various conditions (pH, temperature) across different body parts.

How Do We Get It?

  • Newborns are initially sterile; they acquire microbiota from the mother during delivery.

    • Common microbes include:

      • 8-12 hours after birth: Streptococci, Staphylococci, Lactobacilli.

Types of Microbiota Acquisition

  • Breastfeeding:

    • Leads to a dominant population of bifidobacterium, which is beneficial for gut health.

  • Bottle-feeding:

    • Results in a mixed population including coliforms, lactobacilli, and enteric bacilli.

The Rest of the Flora

  • Skin flora is influenced by the baby's environment and contact with various surfaces.

  • Flora diversity increases as the baby grows and begins to explore solid foods and develop teeth.

Where Does It "Live" in Our Body?

  • Microbiota location depends on environmental factors:

    • Skin: Bacteria, fungi, arthropods

    • GI Tract: Bacteria, fungi, protozoa

    • Oral Cavity: Bacteria, fungi

    • Large Intestine: Rich in diverse bacterial populations

    • Respiratory Tract: Sterile in the bronchioles and alveoli

    • Genital and Urinary Tracts: Mixed bacteria in some zones, sterile in internal organs.

Some Resident Microbiota (Table 14.2)

  • Upper Respiratory Tract:

    • Genera: Fusobacterium, Haemophilus, Lactobacillus, etc.

    • The microbiota varies between nose, mouth, and trachea; alveolar areas are axenic.

  • Upper Digestive Tract:

    • Genera: Actinomyces, Bacteroides, etc.

  • Lower Digestive Tract:

    • Genera: Bacteroides, Bifidobacterium, Clostridium, etc.

  • Female and Male Urinary and Reproductive Systems:

    • Diverse genera with unique adaptations related to the local environment.

  • Eyes and Skin:

    • Skin is host to different genera while the conjunctiva has fewer resident microbes due to tear flushing.

What Does It Really Do for Us?

  • Microbiota play critical roles in:

    • Preventing growth of harmful microorganisms: Microbial antagonism makes environments unfavorable for pathogens through competition.

Are They Perfect?

  • No, microbiota can be opportunistic and lead to infections:

    • Conditions such as a compromised immune system or entry into sterile body regions can result in disease.