Ch. 11 Primate Microbiomes

Anthro317 Final

What is the definition of a microbiome?

a community of microscopic organisms within a certain environment

What are the five main components that make up a microbial community?

1. Bacteria: Make up the largest percentage; unicellular, lack nuclei, have peptidoglycan

2. Archaea: Unicellular, lack nuclei, often found in extreme environments

3. Fungi: Heterotrophic (e.g., yeast)

4. Protists: Unicellular eukaryotes (have nuclei)

5. Viruses: Capsules of infectious nucleic acids

What are the four primary ways microbes classify based on how they obtain carbon and energy?

1. Autotrophs: Get carbon from environment CO2

2. Heterotrophs: Get carbon from organic sources

3. Phototrophs: Use light as the primary energy source

4. Chemotrophs: Use chemical reactions for energy

What environmental factors determine where a microbe can live?

• Salinity

• pH

• Temperature

• Oxygen

• Water

• Light

• Pressure

• Chemical Environment

What was the original “Hygiene Hypothesis” proposed by Strachan in 1989?

Decreasing infections in developed countries caused an increase inflammatory diseases (like hay fever and eczema). It noted that children from larger households were less likely to have hay fever.

How does the “Old Friends” hypothesis (Rook, 2003) reframe the Hygiene Hypothesis?

The increase in inflammatory disorders (allergies, IBD, autoimmune disorders) is because humans are decreasingly exposed microorganisms that are necessary to train the immune system during key developmental windows.

What is the relationship between microbial diversity and the immune system?

Higher diversity microbial communities are often associated with normal immune system functions. The microbiome primes immune cells to tolerate microbes.

What is the definition of an antibiotic?

Any chemical substance that kills or prevents bacteria from growing without destroying human cells.

Short-term and long-term effects of antibiotics on the microbiome?

Short-term: Immediate decrease in taxonomic diversity (richness and evenness)

Long-term: Constitution of the microbiome may be permanently different (not all taxa reappear), alterned immune system (if treated at birth), and the spread of antibiotic-resistant genes.

What is a Fecal Microbiota Transplant (FMT) used for?

It is used to treat Clostridium difficile infections, which can expand out of control when the healthy microbiome balance is thrown off by antibiotics.

How does host phylogeny affect the gut microbiome in primates?

Closely related primate species tend to have similar gut microbiomes. Species within the same mammalian order have more similar microbiomes compared to other species.

How does the environment affect the microbiome of sympatric (living in the same area) populations?

Chimpanzee and gorilla populations that share the same environment have more similar gut microbiomes than those that do not, indicating environmental factors shape the microbiome alongside genetics.

What is the relationship between social grooming and the microbiome in baboons?

1. Grooming Strength: Individuals with stronger grooming relationships have more similar gut microbiomes (lower dissimilarity)

2. Social Network: Individuals that are socially distant have more dissimilar microbiomes

3. Centrality: Individuals more centrally located in the social network have more diverse microbiomes

What is the “Gut-Brain Axis”?

A bi-directional relationship where the gut microbiota influences the central nervous system (behavior/mood) and the brain influences the gut (via stress hormones).

Through what mechanisms do gut bacteria influence the back?

1. Vagus Nerve: Microbes release chemicals that bind to receptors on the vagus nerve.

2. Neurotransmitters: Bacterial metabolism produces neurotransmitters (e.g., serotonin, glutamate)

3. Immune System: Bacteria influence the immune system (inflammation), which impacts the brain.

4. SCFAs: Production of short-chain fatty acids

What were the findings of the Carlson et al. 2018 study regarding toddlers and the microbiome?

The cluster of children with the lowest microbiome diversity actually had the highest language skills.

Which gene is commonly used to reconstruct microbial phylogenies and why?

The 16rRNA gene.

It is used because it has slow rates of evolution, and the sequences for its variable regions (V4 - V5) are well known.

What is the difference between Alpha Diversity and Beta Diversity?

Alpha Diversity: Number of microbial taxa (richness) within a single sample

Beta Diversity: Measures how similar or different the microbial composition is between different samples.