10. Microbial associations with animals

Question 1

What is the association between microbes and herbivores? 5

Answer 1

1. Animals cannot digest cellulose alone, as they lack the cellulytic enzymes
2. Herbivores depend on cellulytic/fermentative microbes in the gut
3. Anaerobic bacteria, protozoa, archaea and the only group of anaerobic fungi live in animals
4. The digestive tracts of the animals have specialized modifications for the microbes
5. there are two classes of these herbivores, hind gut fermenters and ruminants

Question 2

Descrobe hind gut fermenters. 6

Answer 2

1. Icl horses, rabbits, rodents, elephants, rhinos and buffalo
2. Have a modified extension at the base of the lower small intestine called a caecum
3. This is an elongated chamber which carries hon to form the large intestine
4. Comes after the stomach
5. Fossil records tell us they were the first herbivores to evolve
6. Poor efficiency compared to ruminants

Question 3

Decscribe rumen fermenters. 5

Answer 3

1. Incl cows, sheep, goats and deer
2. Modification of lower oesophagus - part of 4 chambered stomach system
3. Rumen - main fermentation chamber for microbes at pH5-7
4. Comes beofre the main absorption chamber (stomach), the abdomasum (acidic) so is more efficient
5. Evolved to become quite successful and took over and main herbivore

Question 4

Describe ruminant digestion. 6

Answer 4

1. Grass is chewed, breaking plant fibers into smaller pieces and increasing SA:vol for easier digestion
2. Moves into a small chamber called the reticulum, then the rumen
3. After rumen, grass goes backwards to mouth through esophagus as cud and is chewed again
4. The second grinding has microbes and enzymes for digestion already there, so is more efficient
5. Then goes back through esophagus directly to omasum, then to abomasum
6. Abomasum to small intestine, then large intestine

Question 5

Describe hind gut digestion. 3.

Answer 5

1. plant material enters stomach and undergoes some digestion by acids secreted by animal
2. Moves to caecum, where microbiota secrete (endo)cellulases
3. The enzymes break cellulose into simple sugars for absorption

Question 6

Describe what happens biochemically during the ruminant digesiton process. 6

Answer 6

1. Plant materials are 70-80% cellulose with some starch and sugars
2. Some microbes produce (endo)cellulases which breakdown cellulose to sugars eg. glucose and other hexoeses
3. Sugars fermented by anaerobic, fermentative microbes to a range of fatty acids eg. acetate, proprionate and butyrate
4. These travel across rumen and abomasum wall ninto bloodstream as energy source
5. Also releases co2 and methane, which are released by belching
6. Fermentation process leads to a lot of gas, 65% co2 and 35% methane.

Question 7

What are mycotoxins and how do they affect ruminants? 6

Answer 7

1. Grass, especially dry grass, is often infected with a range of fungi.
2. Fungi called endophytes as they live within plant tissue - we don’t know what most are or what they do
3. Some of the endophytes produce a range of chemicals that are toxic to insects
4. Some - tremorgens - can affect animals that eat infected grass, by inhibiting and exciting smooth muscle, inhibiting rumen contractions, reducing efficiency of digestion and rumen and causing weight loss
5. Also affects skeletal smooth muscle, causing ryegrass staggers
6. The fungi may act as a deterrent to insects

Question 8

What are termites? 6

Answer 8

1. Insects which also lack necessary enzymes to break down plant material, but eat wood
2. Build underground chambers containing fungal gardens
3. Termites deposit plant material (wood) as dung
4. Fungi eats cellulose, termites eat fungi
5. termite mounds up to 6m tall form above chambers for ventilation
6. 6M species of termite

Question 9

What are termite mounds? 4

Answer 9

1. co2 and methane are released from the chambers, which are removed through mound
2. They allow cool air to be drawn into fungal garden
3. Air channels can be closed at night
4. This keeps the temperature even

Question 10

What are termitomyces? 4

Answer 10

1. This mycelium is eaten and cellulases produced by it remain active in the termites’ stomachs
2. Produce less ch4 than cows as less anaerobic than rumen (volume difference)
3. the termites have a very small gut so it is not anaerobic due to large SA:Vol
4. The fungal ball is of a two type clade. It is only associated with termites.

Question 11

What are the problems connecting termites and nitrogen? 3

Answer 11

1. Wood has a very low n content
2. n fixing spirochetes inhabit the intestines of termites, providing up to 60% of the n
3. n is vital so termites need fungus and spirochetes

Question 12

Describe the global annual production of methane. 4

Answer 12

1. Biogenic sources incl ruminants, termites, paddy fields and other natural things.
2. Abiogenic sources incl burning fossil fuels and biomass, cars and industrial losses
3. 81-86% of methane produced pa comes from biogenic sources
4. This is mostly from ruminants, more worrying than other sources

Question 13

What are attine/leaf cutting ants? 6

Answer 13

1. Primary herbivore of tropical forest, where they are widespread and partake in large-scale defoliation
2. Ants chew up food with mandibles and push into mycelium, where the cellulose is degraded
3. Ants eat mycelium
4. Every ant species has one fungus species, strong host specificity. Evolved over 50M years ago
5. Both completely dependent on each other
6. The fungi contain/produce lipids that the insects eat

Question 14

What is the role of ant defoliation? 3

Answer 14

1. Defoliation is very important in tropical forests
2. Removal of large pieces of leaf over large area breaks the canopy
3. This allows light in, leading to regeneration and regrowth

Question 15

How do ants interact with their fungal garden? 4

Answer 15

1. As ants tend their garden, hyphae swell at tips on surface of mycelium (bromatia)
2. These contain large quantities of lipid droplets, which the ants feed on
3. There is a third ‘partner’ - streptomycetes, on insect cuticle, which produces antibiotics
4. This inhibits other microbes so parasitic fungi doesn’t affect/attack fungal garden

Question 16

What role do beetles have when interacting with microbes? 6

Answer 16

1. Now appears majority of insects are dependent on microbial partners
2. The ambrosia beetle is native to Asia, and has been imported worldwide via trees
3. It bores galleries into trees and seeds with ambrosia fungus, but the galleries don’t go deep enough to cause any damage
4. They lay eggs which hatch, carrying a fungus which is seeded on inside of galleries - digests gallery surface and grazes on mycelium
5. Beetle became a vector for other parasitic fungi, which do damage trees
6. Ambrosia fungus doesn’t damage tree or insect

Question 17

What is Dutch Elm disease? 5

Answer 17

1. Devastated elm trees in USA and Europe between 1930s and 80s, 90%+ were lost
2. Caused by transmission of fungus ophiostoma ulmi, parasite which was rare but came common when beetles could pass it along
3. To prevent spread through xylem,three produces intrusions (tyloses) which block vessel to prevent fungus trasnport
4. Yeast rapidly taken up through xylem, what flow is blocked
5. If enough vessels are blocked, tree will wilt and die

Question 18

Describe the bioluminescence of the anglofish. 6

Answer 18

1. Anglofish have bio-luminescent lures, which are due to bacteria
2. Some have lures in different places eg to attract prey or mates
3. Only females have these lures
4. They are full of biolumiscent bacteria
5. Some flash, we don’t know how
6. Not all bioluminescence is due to other bacteria eg. fireflies

Question 19

Describe vibrio fisheri. 4

Answer 19

1. Widespread marine bioluminescenct bacteria, captured by some animal in photophores (light organs)
2. Can be used as a lure eg. anglofish
3. Hawaiian squid hunts surface at night
4. Has bioluminescent ring so prey think it is the moon