Microbial Symbioses

Question 1

Parasitic

Answer 1

symbioses with an expense to the host

Question 2

Pathogenic

Answer 2

symbioses that causes disease/death to host

Question 3

Commensal

Answer 3

symbioses with no impact on host

there is not evidence of this existing in life

Question 4

Mutualistic

Answer 4

symbioses that benefits both the host and microorganism

Question 5

Root Nodule Symbiosis

Answer 5

mutualistic symbioses between legumes and nitrogen-fixing bacteria

Question 6

What is formed that characterizes Root Nodule Symbiosis? What does it do?

Answer 6

nodules on the root of legumes are formed which houses the bacteria that fix nitrogen

Question 7

Which bacteria is best known as the nitrogen-fixing bacteria involved in Root Nodule Symbiosis?

Answer 7

Rhizobia bacteria

Question 8

What are the steps of root nodule formation?

Answer 8

1. recognition and attachment of bacterium to root hairs mediated by Rhicadhesin
2. excretion of nod factors by the bacterium
   
   • induce root hair curling
3. Bacterial invasion of the root hair and multiply w/in an infection thread
4. travel to the main root via the infection thread
   
   • nod genes induce nearby plant cells to divide
5. formation of bacteroid state by bacteria
6. continued plant and bacterial division, forming the mature root nodule

Question 9

What are nod factors?

Answer 9

species specific oligosaccharides produced by nodABC genes in bacteria

induce root hair curling and plant cell division

Question 10

Of the nod genes, what is specific about nodD?

Answer 10

nodD is the transcriptional activator for other nod genes and is activated by plant flavanoids

if in the wrong plant, flavanoids become co-repressors

Question 11

In the Root Nodule Symbiosis, what does the plant give the bacterium?

Answer 11

electron donors like succinate, malate, fumarate

Question 12

In the Root Nodule Symbiosis, what do the bacterium give the plant?

Answer 12

ammonia which is converted to glutamine via glutamine synthetase w/ Nitrogenase

(N2 -> NH3 -> Glutamine Asparagine)

Question 13

What is Leghemoglobin? and What is its job in Root Nodule Symbiosis?

Answer 13

Leghemoglobin is produced by legumes for root nodulators once bacteroid begins to form

has Fe core which binds to O2 to keep the O2 levels low which allows the symbiosis to be better

Question 14

Crown Gall Disease

Answer 14

parasitic symbiosis between Agrobacterium tumefaciens and plants causing grown gall tumors

Question 15

How are Crown Gall Tumors induced?

Answer 15

1. A.tumefaciens cells attach to wound site on plant
2. cellulose microfibrils are synthesized by the attached cells
3. ATP is used to produce activated VirG protein
4. VirG expresses rest of Vir genes
5. VirD nicks Ti (tumor induction) plasmid
6. VirE transfers 1 plasmid strand to VirB
7. VirB makes secretion system which infects plants w/ the T-DNA

Question 16

What is the Ti Plasmid and what is its make-up?

Answer 16

Ti (tumor induction) plasmid

• contains…
  
  • T-DNA which is transferred into host genome
  • tumor formation genes
  • modified amino acid (opine) biosynthetic genes

Question 17

What are mycorrhizae?

Answer 17

mutualistic associations of plant roots and fungi

Question 18

What are the 2 classes of mycorrhizae?

Answer 18

Ectomycorrhizae

and

Endomycorrhizae

Question 19

What are ectomycorrhizae?

Answer 19

• extensive sheath around the outside of the root
• only a little penetration into the root tissue
• found primarily in forest trees, mainly boreal and temperate forests

Question 20

What are endomycorrhizae?

Answer 20

• fungal mycelium becomes deeply embedded w/in the root tissue
• more common than ecomycorrhizae
• found in >85% of terrestrial plant species

Question 21

How do mycorrhizal fungi assist plants?

Answer 21

they improve nutrient absorption due to the greater surface area provided by the fungal mycelium

Question 22

What do phylogenetics suggest about mammal nutrient lifestyle (i.e. herbivore, omnivore, carnivore)?

Answer 22

suggest that the first mammal ancestor was a carnivore and evolution took mammals to omnivores and then herbivors

Question 23

What are the 2 digestive plans that have evolved in herbivorous mammals?

Answer 23

Foregut Fermentation and Hindgut Fermentation

Question 24

What is Foregut Fermentation?

Answer 24

• where the microbial fermentation chamber is before the small intestine
• includesz sheep, cows, goats, birds etc.

Question 25

What is Hindgut Fermentation?

Answer 25

• where the fermentation chamber (cecum) and large intestine are after the stomach and small intestine
• includes horses, rabbits, primates, rodents, reptiles etc.

Question 26

Why have foregut and hindgut digestive plans developed in herbivorous animals?

Answer 26

because the plants that are eaten contain cellulose that cannot be digested normally

Question 27

What are the most successful group of foregut fermenters and the most dominant herbivores?

Answer 27

The Ruminants which are herbivorous mammals that havea special digestive organ - Rumen

Question 28

What is the pathway that food takes in a ruminant?

Answer 28

1. food enters the Reticulum-Rumen through the Esophagus
2. smaller food particles are sent to the Omasum
3. larger food particles are regirtitated as Cud and re-digested by rumen bacteria
4. small particles in Omasum are sent to the Abomasum (similar to stomach, where chemical digestion begins)
5. food in Abomasum is sent to the small intestine and through rest of digestion

Question 29

What are primary symbionts?

Answer 29

• required for host reproduction
• obligate symbionts
• exhibit extreme gene reduciton (only have those needed for host fitness)
• high AT content
• high mutation rates

Question 30

What are secondary symbionts?

Answer 30

• not required for host reproduction
• facultative symbionts
• not always present in every individual host
• must provide a benefit to the host

Question 31

What are the microbes in Higher Termites and Lower Termites?

Answer 31

Higher Termites - diverse community of anaerobes to decompose cellulose (hemi-)

Lower Termites - anaerobic bacteria and cellulolytic protists

Question 32

What is the symbiont for Leaf Cutter Ants?

Answer 32

worker ants chew up leaves and feed to fungus in the nest, the ants then eat the fungus

Question 33

What is the symbiosis with Hawaiian Bobtail Squid?

Answer 33

• symbiont = Aliivibrio fischeri (A.fischeri)
  
  • bioluminescent
• held in specialized structure = light organ
• used to camouflage the squid from predators
• transmission of symbiont is horizontal = 1st colonized just after sqiud hatches
• light organ 1st produces special mucus that is bound by gram negative bacteria
• A.fischeri dominates gram negative bacteria b/c tolerates high levels of NO

Question 34

What is the symbiosis with Hydrothermal Vent Invertebrates?

Answer 34

• symbiont = chemolithotrophic prokaryotes
• helpful for vent invertebrates = symbionts like the reduced inorganic materials emitting from the vents
• helpful for symbionts = vents invertebrates have trophosome, specialized hemoglobins and high blood CO2 content

Question 35

What is the symbiosis with Reef-Building Corals?

Answer 35

• symbiont = phototrophic cyanobacteria, rhodopytes, chlorophytes, dinoflagellates, and diatoms
• coral skeleton is very efficient light-gathering structure = good for symbiont

Question 36

What is the symbiosis with Lichens?

Answer 36

• symbiosis = btwn fungus (Lichen) and cyanobacterium/alga
• phototroph is photosynthetic and produces organic matter
• fungus provides strucure w/in phototroph can grow and protection from dryness

Question 37

What is the symbiosis called Consortia or “Chlorochromatium aggregatum”?

Answer 37

• symbiosis between microbes in freshwater
• incapable of being separated
• w/ green sulfur bacteria (epibionts) (obligate anaerobic phototroph) and flagellated rod-shaped bacterium (provides movement)
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