Animal symbiosis

Question 1

What is the animal microbiome?

Answer 1

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

Question 2

Who came up with the word microbiome and when was this?

Answer 2

Josh Lederberg 2001

Question 3

Define: microbiota

Answer 3

microbes in a community

Question 4

What are the domains on the tree of life and how were they determined

Answer 4

Carl Woese = Analysis of ribosomal RNA gene determined 3 different kingdoms:
1. Bacteria
2. Archaea
3. Eukaryota

Question 5

What are 2 examples of animal symbioses with bacteria?

Answer 5

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

Question 6

Describe a human microbial symbiosis example

Answer 6

Humans + common commensals
Many body systems contain many microorganisms

Question 7

How many species of termites are there and what differentiates them?

Answer 7

3000 species of termites- differentiated based on symbiotic relationship with different microbes:
- Lower termites- diverged 150mya
- Higher termites- diverged from lower about 60mya

Question 8

Name and define what termites feed on

Answer 8

lignocellulose = cell wall component of woody plants
- can feed on sound wood or decomposed wood depending on termite

Question 9

What is lignocellulose made up of and what are they resistant to?

Answer 9

Cellulose + hemicellulose + lignin
recalcitrant to enzymatic attack

Question 10

Who has faster digestion ruminants or termites and why?

Answer 10

Termites- evolved enzymatic mechanims to break down woody components efficiently

Question 11

What is the termite-microbe symbiosis?

Answer 11

= 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

Question 12

What are the differences between lower and higher termites?

Answer 12

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

Question 13

What are the benefits to the termite and gut microbes?

Answer 13

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

Question 14

What happens if termites do not have hindgut microbes?

Answer 14

They will continue to feed but unable to digest so will die of starvation
vice versa for microbes

Question 15

When a termite is born does it contain necessary microbes?

Answer 15

No, adult termites must feed them otherwise they will die

Question 16

In the hindgut of a termite, what other associations are there?

Answer 16

Associations between protozoan and bacteria- unknown benefit

Question 17

Name an example of a symbiotic association in the hindgut of a termite

Answer 17

Protozoan = streblomastix strix has unknown symbiosis with long, thin bacterial cells creating ridges

Question 18

Describe the termite-microbe symbiosis

Answer 18

1. Wood is chewed thoroughly into small bits by termite and moves into vacuole
2. protists has enzymes + termite enzymes = ferment wood to produce acetate, hydrogen and CO2
3. Acetate is absorbed by termite for oxidation + biosynthesis, as well as a carbon source
4. Methanogenic archaea

Question 19

what is acetate?

Answer 19

= short chained fatty acid

Question 20

What is reductive acetogenesis?

Answer 20

process in which acetate is produced by reduction of CO2/organic acids = bacterial process

Question 21

What other organisms produce methane and how does it compare to termites?

Answer 21

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

Question 22

Describe the pathway of acetogenesis

Answer 22

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

Question 23

What bacteria are acetogenic?

Answer 23

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

Question 24

Name and describe the 2 spirochetes function in termites

Answer 24

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

Question 25

How bacterial cells are there per human cell?

Answer 25

6-10 bacterial cells- more bacteria than human cells 100 trillion vs 10 trillion

Question 26

How many different species in the human gut and what % of body weight do they make up?

Answer 26

over 1000- make up 3% of overall body weight

Question 27

Describe the benefits of microbes in the gut of humans

Answer 27

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

Question 28

Define dysbiosis

Answer 28

= imbalance between organisms present in human microbiome

Question 29

What are the differences between a healthy human gut and a disrupted human gut

Answer 29

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