BIOS104 Symbiosis

What does symbiosis mean?

a host (large) and symbiont (small) living together

How common are symbiotic interactions?

very common, can be any combination between kingdoms

What is an endosymbiont?

lives inside the body → maybe intracellular

What is a gut symbiont?

lives in the colon/hindgut lumen, villi/attached to epithelia, rumen

How can symbiotic relationships form?

through horizontal or vertical transmission

What are the types of symbiont?

• obligate → required

• facultative → not required by beneficial

• parasite → not nice

how long can some symbioses last?

millions of years

What ‘services’ do symbionts do to their hosts?

• nutrients

• defence

• offense

What nutrients can symbionts help take up?

• micronutrients → phosphate, nitrate

• photosynthate → algae

what fungus acquires phosphate and other micronutrients in the soil?

mycorrhiza

What are the two main types of mycorrhizal fungi?

• arbuscular → inside

• ectomycorrhizae → outside

What is meant by ‘wood wide web’?

ectomycorrhiza joins trees in a forest together

What do algal symbionts acquire?

sucrose

How do symbionts aid in digestion?

degradation of complex polysaccharides → cellulose, lignin

→ short chain fatty acids (SCFAs)

How can symbionts detox diet?

gut microbes may break down toxic secondary compounds and extend dietary sources

How can symbionts aid in anabolism?

• essential amino acid synthesis

• other amino acid synthesis

• B vitamin synthesis

What are examples of defensive symbiosis?

• avoiding predation → counter shading, toxicity

• inhibiting natural enemies → body guards

• protection against microbial attack → external

• protect against viral attack

• protect against parasites

What is an example of offence symbiosis?

nematodes releasing bacteria and killing off the insect host to use as food source for other nematodes

How would animals and plants perform in an axenic world?

very poorly

Are humans made of more bacteria or human cells?

we have more bacterial cells than human cells → 56% bacteria by number

How can human gut microbiome impact our biology?

• digestion through microbial action

• pathogen resistance → diverse community inhibits pathogens taking over

• metabolic integration → development, gut/brain axis