Symbiosis

Symbiosis

Adaptations of microbes to the intimate presence of other species

Types of symbiotic relationships

1. Mutualism

2. Synergism

3. Commensalism

4. Amensalism

5. Parasitsm

mutalism

Two organisms grow in an intimate species relationship in which both partner species benefit and may fail to grow independently

• ex) lichens consist of fungi and algea growing together in a complex layered structure. Each species requires the presence of the other.

Synergism

Both species benefit through growth, but the prtners are easily seperated, and either partner can grow indepently of the other

• ex) human colon bacteria ferment releasing hydrogen and carbon dioxide which methanogens convert to methane. The methanogens gain energy, and the bacteria benefit energetically from the removal of their fermentation products.

Commensalism

one species benefits, while the other species is neither harmed nor benefits.

ex) beggiatoa bacteria oxidize H2S for energy. removal ofH2S enables growth of other microbes for whom H2S is toxic. The other micorobes dont benefit bggiatoa.

Amensalism

One species benefits by harming another. Nonspecific relationship.

• Streptomyces secrete antibiotics that lyse other species, that streptomyces consumes for energy

Parasitism

the parasite benefits at the expense of the other, a specifc host. the relationship is usually obligatory for the parasite.

• ex)legionella pneumophelia parasitizes amebas, and infects lung macrophages causing Legionarie’s disease.

Extreme example of mutualism

Lichens

• fungus + algea or fungus + cyanobacterium or all three

• where fungi provide protective cup for algea while the photobiont produces carbohydrates.

• the partner species may require each other

Mutualism checklist

1. Removal of one partner leads to death or reduced growth of the other

2. The genomes of each species show advanced degeneration

3. Products produced by one partern are utilized by the other

Cow rumen microbiome

Rumen bacteria in the cow gut ferment complex polysaccharides from grass producing H2and CO2, methanogens convert these gases into methane preventing the accumulation of H₂, which would otherwise inhibit bacterial fermentation and methanogens use these gases as energy sources.

• synergism

Checklist for synergism

1. Each partner benefits from the other

2. partners are easily separated and grown indepently of each other

Beggiatoa and other sulfer spring microbes

In ecosystems with high concentrations of toxic H2S microbial mats containing sulfer oxidizers like Beggiatoa reduce ecosystem toxicity and allow growth of other species

• Beggiatoa is not doing this out of the goodness of their heart, they are doing it to get energy. 

• this is commensalism

Streptomyces and other soil bacteria

streptomyces produces natural antibitoics to kill and lyse other bacteria in the soil, releasing their nutrients and the streptomyses consume these.

• Streptomyces is bacteria but carries out its life cycle in a fungal way. They make spores.

• Amensalism

Checklist for amensalism

1. one species benfits

2. the other species is harmed by the interaction

3. The interaction is non specific

Checklist for parasitism

1. One species benfits

2. the other species is harmed by the interaction

3. The interaction is specific, and usually obligatory for the parasite.

Endosymbiosis

Many insect species are infected by intracellular bacteria (endosymbionts)

• ex) Wolbachia infects ~50% of insect species.
  🔹 Used to fight malaria & mosquito-borne viruses by competing with parasites.
  🔹 Shortens mosquito lifespan, reducing disease transmission.

Synergism

• they can exist independent of each other

Parsitism

Barry Marshall

Barry Marshall swallowed H. pylori to prove it causes stomach ulcers.
🔹 His experiment confirmed the bacterial cause, overturning prior beliefs.
🔹 Led to effective antibiotic treatments for ulcers

H. pylori infections of young children

protects them from the development of allergies and asthma so in this case its not parasitic, but instead synergism.

Commensalism

• in the bottom case we see synergism

Endosymbiosis

• One of the closest relatives nowadays to mitochondria is called riketsia. It speaks a chemical language that mitochondria understands.