Study Notes on Microbial Interactions and Host-Microbe Relationships

Majority of microbes typically live freely and are generally harmless.
Host-microbe relationships can shift from:
- Neutral (commensal) to host
- Beneficial (mutualist or symbiont)
- Harmful (pathogen or parasite)
Example of Escherichia coli:
- Produces vitamins and protects from pathogen invasion (beneficial).
- Produces toxins and causes bloody diarrhea (harmful).

Defined as a relationship where one organism benefits at the expense of another.

Obligatory Mutualism: Both species depend on each other for survival. Examples include:
- Buchnera aphidicola (bacteria) and aphids:
- Bacteria provide essential amino acids to host aphids.
- Evolved together (coevolution) as mutual dependence grew.
- Trichonympha sp. (protist) and Termites:
- Protists assist in the digestion of cellulose, allowing termites to feed on wood.
- Relationship shared with Elusimicrobium bacteria, which also aids digestion.
- Coral Symbiosis with Dinoflagellates:
- Symbiodinium provides energy through photosynthesis, while coral provides nitrogen compounds.
- Coral bleaching linked to the loss of these dinoflagellates, making corals susceptible to pathogens.
- Tube Worms and Bacterial Endosymbionts:
- Tube worms rely on bacteria for organic carbon intake; bacteria benefit from a stable environment provided by the worm.

Defined as a beneficial but non-obligatory interaction.
The Fungal Highway:
- Network of fungal hyphae facilitates dispersal of bacteria across nutrient-dense environments.

One organism benefits while the other is unaffected.
Often involves syntrophy where the growth of one organism is improved by growth factors from another nearby organism.
- E.g., modifications in the environment make it suitable for another organism.

Predation: Killing for benefit.
- Microbe predation strategies:
  - Epibiotic predators attach to surfaces and lyse prey.
  - Endobiotic predators invade cytoplasm to consume internal contents.
- Example: Grazing by protozoans transfers carbon from bacteria to larger organisms.
Parasitism: Exploitation of another organism while alive, often leads to a relationship where one may die if the equilibrium is disturbed.
- Example: Wolbachia bacteria infecting mosquitoes can inhibit the replication of viruses like West Nile.
Competition: Organisms compete for shared resources, leading to adaptive evolution.
- Competition can involve both contact-dependent and independent growth inhibition strategies.

A specific type of antagonism where one organism negatively impacts another through the release of compounds, such as:
- Antibiotic production by fungi and bacteria (e.g., Penicillium producing penicillin which inhibits bacterial growth).

Utilizing Wolbachia infected mosquitoes to disrupt the lifecycle and propagation of the West Nile virus in wild populations.
Steps include:
- Release of Wolbachia-infected mosquitoes into the wild.
- Establishment of Wolbachia in the wild mosquito population, reducing viable offspring of West Nile virus carriers.

Interactions between microbes and their hosts are complex and evolve over time.
Recognizing these interactions can lead to microbial management in both natural and man-made environments.

Nitrogen-fixing Rhizobia and Legumes: Mutualistic relationship where bacteria convert nitrogen for the plant.
Staphylococcus epidermidis on Human Skin: A commensal that benefits from skin cells without impacting host health.
Plasmodium and Malaria: Example of parasitism, illustrating how environmental changes can shift a relationship from mutualistic to parasitic.

Discussion on how symbiotic relationships can change due to environmental influences.