Animal symbiosis Flashcards
What is the animal microbiome?
totality of microorganisms and their collective genetic material within particular environment
- some only refer to it as being the full collection of all microbial genes
Who came up with the word microbiome and when was this?
Josh Lederberg 2001
Define: microbiota
microbes in a community
What are the domains on the tree of life and how were they determined
Carl Woese = Analysis of ribosomal RNA gene determined 3 different kingdoms:
1. Bacteria
2. Archaea
3. Eukaryota
What are 2 examples of animal symbioses with bacteria?
animal-bacteria e.g. bobtail squid forms symbiosis with vibrio fischeri (bacteria)- bacteria produces light and is integrated in nocturnal squid and migrates to light organ- bacteria used to create shadowing effect to prevent predation
animal-bacteria e.g. Panamanian yellow frog = endangered because it is covered in fungus but association with bacteria on skin produces antimicrobial substances which prevent fungus growth
Describe a human microbial symbiosis example
Humans + common commensals
Many body systems contain many microorganisms
How many species of termites are there and what differentiates them?
3000 species of termites- differentiated based on symbiotic relationship with different microbes:
- Lower termites- diverged 150mya
- Higher termites- diverged from lower about 60mya
Name and define what termites feed on
lignocellulose = cell wall component of woody plants
- can feed on sound wood or decomposed wood depending on termite
What is lignocellulose made up of and what are they resistant to?
Cellulose + hemicellulose + lignin
recalcitrant to enzymatic attack
Who has faster digestion ruminants or termites and why?
Termites- evolved enzymatic mechanims to break down woody components efficiently
What is the termite-microbe symbiosis?
= decompostion of dead wood due to mutualistic symbiotic bacteria in hind gut of termites
- termite comprise of all 3 kingdoms- bacteria, archaea + single celled eukaryotes
What are the differences between lower and higher termites?
Lower:
- protozoan flagellates (eukaryotes), bacteria + archaea in hindgut
- small wood particles taken up by protists by phagocytosis into digestive vacuoles
- Diet = sound + decomposing wood
Higher:
- Lost protozoa when they diverged
- Contain bacteria + archaea and have evolved seperate digestion of cellulose = variation in diet
What are the benefits to the termite and gut microbes?
Termite:
+ Production of food- hydrolysis of cellulose + lignin
Gut microbes:
+ Provide favourable environment- redox tension = anoxic conditions for archaea cannot survive in oxygen, humidty- 4/5 bacteria = water, nutrition
What happens if termites do not have hindgut microbes?
They will continue to feed but unable to digest so will die of starvation
vice versa for microbes
When a termite is born does it contain necessary microbes?
No, adult termites must feed them otherwise they will die
In the hindgut of a termite, what other associations are there?
Associations between protozoan and bacteria- unknown benefit
Name an example of a symbiotic association in the hindgut of a termite
Protozoan = streblomastix strix has unknown symbiosis with long, thin bacterial cells creating ridges
Describe the termite-microbe symbiosis
- Wood is chewed thoroughly into small bits by termite and moves into vacuole
- protists has enzymes + termite enzymes = ferment wood to produce acetate, hydrogen and CO2
- Acetate is absorbed by termite for oxidation + biosynthesis, as well as a carbon source
- Methanogenic archaea
what is acetate?
= short chained fatty acid
What is reductive acetogenesis?
process in which acetate is produced by reduction of CO2/organic acids = bacterial process
What other organisms produce methane and how does it compare to termites?
Cows lose 10-20% of electrons in food as methane via mouth/faeces = huge waste of energy
- emits 500l of methane a day = 10% of energy lost
Termites = only small amount of energy lost to methane = reductive acetogenesis
Describe the pathway of acetogenesis
Wood Ljungdahl pathway:
= fixation of 2 molecules of CO2 with 4 molecules of hydrogen- 2 carbon joined = acetate + ATP
- ATP for bacterial growth and acetate for termite
What bacteria are acetogenic?
bacteria in hindgut = many different types but many were spiral-shaped either attached to protist flagellates or swimming around protozoa
= spirochetes that are good at moving in liquid- always present in healthy termites but cannot be grown in vitro
Name and describe the 2 spirochetes function in termites
Treponema primitia = key role in fermentation of wood in termite for nutritional value- converts CO2 to acetate
Treponema azotonutricium = wood hard to eat with low nutritional value (no protein + low nitrogen)- exhibits diazotrophic growth = grows with atmospheric nitrogen to produce protein to feed insect
+ generates hydrogen from catalysis of sugars to feed other bacteria for acetogenesis
How bacterial cells are there per human cell?
6-10 bacterial cells- more bacteria than human cells 100 trillion vs 10 trillion
How many different species in the human gut and what % of body weight do they make up?
over 1000- make up 3% of overall body weight
Describe the benefits of microbes in the gut of humans
MUTUALISTIC INTERACTION:
Benefit to host =
- protection against pathogens
- interaction with immune system- can stimulate immune response e.g. antigen presenting cells
- Digestive enzyme activity that we cannot produce
- synthesis of vitamins- vitamin B and K
Benefit to microbiome =
- favourable stable environment
- Nutrition
Define dysbiosis
= imbalance between organisms present in human microbiome
What are the differences between a healthy human gut and a disrupted human gut
Healthy = common commensals present as well as some pathogens, but commensals produce antimicrobial compounds like bacteriocin which kills closely related bacteria and outcompete pathogens as they take nutrition + suppress virulence factors by stimulation of immune system
Disturbed = common commensals lost via antibiotics = overgrowth of pathobionts e.g. C. difficile always present but without common commensals they produce toxins which damage epithelial and enter bloodstream causing sepsis
