Lecture 13 - bacterial interactions with eukaryotes

Question 1

Symbiosis

Answer 1

Intimate association between organisms of different species

Question 2

Syntrophy

Answer 2

Association requiring two or more partners to complete a metabolic pathway

Question 3

Synergism

Answer 3

Optional cooperation where both species benefit but are able to grow independently from one another

Question 4

Commensalism

Answer 4

One partner benefits, while the other is unaffected

Question 5

Amensalism

Answer 5

One species harms another but is neither affected nor benefited by the action

Question 6

Mutualism

Answer 6

Each partner benefits from the other

Question 7

Can mutualistic species grow independent of one another

Answer 7

Sometimes

Question 8

Example of mutualism

Answer 8

Lichens: composite organism formed by the mutualistic relationship between fungi and cyanobacteria/algae
- fungus is dependent on cyanobacteria/algae for carbohydrate
- fungus provides minerals for cyanobacteria/algae, but is not necessary for their growth

Question 9

Parasitism

Answer 9

Intimate association where one partner benefit by harming a specific host

Question 10

Wolbachia

Answer 10

Bacteria that commonly infects insects and nematodes as intracellular symbionts

Question 11

What kind of relationship does wolbachia have with its hosts?

Answer 11

Mutualistic or parasitic depending on the host

Question 12

Can wolbachia survive independently?

Answer 12

No. Must reside in the cytoplasm of a host because its genome has been pared down. Unable to live without materials from the host

Question 13

Relationship between Wolbachia and Brugia malayi

Answer 13

Mutualistic
- wolbachia is required for the growth of brugia (nematode)

Question 14

How was the relationship between Wolbachia and Brugia confirmed?

Answer 14

Antibacterial therapy that kills Wolbachia was more effective at clearing a Brugia infection than antihelminthic therapy that kills Brugia

Question 15

What is the result of the relationship between Wolbachia and Brugia?

Answer 15

Brugia blocks lymphatic system in humans –> swelling of extremities

Question 16

What aspect of Wolbachia is important in its relationship with Brugia?

Answer 16

Wolbachia can make FAD (essential e- carrier) and provide it to brugia

Question 17

How is Wolbachia passed to new insect hosts?

Answer 17

Inherited through egg cytoplasm (only passed down through females)

Question 18

How does Wolbachia influence sexual differentiation in insects?

Answer 18

• male killing
• feminization
• parthenogeneis
• cytoplasmic incompatibility

Question 19

Male killing

Answer 19

Infected males die during larval development

Question 20

Feminization

Answer 20

Infected males develop into females or infertile pseudo-females

Question 21

Parthenogenesis

Answer 21

Reproduction of infected females without males

Question 22

Cytoplasmic infertility

Answer 22

Infected males can’t produce progeny with uninfected females or with females that carry another Wolbachia strain

Question 23

Outcome of cytoplasmic infertility

Answer 23

Increased proportion of infected progeny in the population

Question 24

Example of syntrophy

Answer 24

Mixotricha paradoxa
- protozoan that has at least four bacterial symbionts that provide useful materials for it
- lives in the hindgut of termites and provides essential materials for wood breakdown and consumption

Question 25

What do bacterial symbionts do in Mixotricha paradoxia

Answer 25

- Spirochetes and "anchor bacteria" on the outer surface provide locomotion for Mixotricha - cytoplasmic symbionts perform mitochondrial functions to provide energy for Mixotricha

Question 26

What does Mixotricha do to help termites?

Answer 26

Converts wood polysaccharides to acetic acid which is taken up by the termite

Question 27

Endophytes

Answer 27

Bacteria or fungi that colonize the transport vessels of plants

Question 28

What do endophytes to to their hosts?

Answer 28

Produce alkaloids and enzymes that deter plant pathogens and root feeding nematodes --> promotes plant growth

Question 29

What is the problem with endophytic pathogens for us?

Answer 29

Endophytic pathogens live in the vessels of plants and therefore can't be washed off of raw produce

Question 30

Rhizoplane

Answer 30

Plant root surface

Question 31

Rhizosphere

Answer 31

Region of soil outside the rhizoplane that receives substances from the root

Question 32

Rhizobium

Answer 32

Bacteria that enter cortical cells of legume roots and provide fixed nitrogen to the plant

Question 33

How do rhizobium enter plant roots?

Answer 33

- attracted to the legume by chemotaxis towards exuded flavonoids - bacterial Nod factor induces root hair to curl around it and take it up into the infection thread - rhizobia enter cortical cells and differentiate into bacteroids

Question 34

What do rhizobia and legumes provide one another?

Answer 34

- rhizobia provides fixed nitrogen - legumes provide malate and minerals - legumes also provide leghemoglobin which sequesters O2 and precisely delivers it to electron transfer system of bacteria

Question 35

Why is leghemoglobin necessary for rhizobia/legume interactions?

Answer 35

Rhizobia use nitrogenase to fix nitrogen. Nitrogenase can't function in the presence of oxygen, so it must be kept separate

Question 36

Why is malate important for rhizobia/legume interactions?

Answer 36

Malate is used in the TCA cycle for energy production. Lots of energy is needed for nitrogen fixation.

Question 37

Why is the rumen important in bovine systems?

Answer 37

Largest digestive chamber that contains a diverse microbial community that aids in breakdown of plant fibers

Question 38

End product of cellulose breakdown in cows

Answer 38

Bacteria ferment glucose and create short chain fatty acids that can be taken up by the animal

Question 39

Byproducts of cellulose breakdown in cows

Answer 39

Methane

Question 40

Influence of starch and sugars on bovine microbiome

Answer 40

Starch and sugars are broken down by gram - bacteria like E. coli. Increased starch/sugar intake promotes their growth and causes dysbiosis

Question 41

One way to treat gut dysbiosis in cattle

Answer 41

Add fistula to cows to allow transplantation of rumen material between cows

Question 42

In a healthy population, what aspects of the microbiome are variable and which are constant?

Answer 42

- carriage of microbial taxa is variable (not every individual will have the same amount of each type of bacteria) - metabolic pathways remain stable