Animal Microbiology Part I

Question 1

How can commensal bacteria be beneficial?

How can commensals be harmful?

Answer 1

Provide host with vitamins and metabolic pathways

Provide protection via competition against new incoming microbial populations

Teach the immune system

But commensals of one species may be pathogenic/parasitic in another or under certain conditions

Question 2

Herbivore digestion

Answer 2

Herbivores rely on foods rich in insoluble polysaccharides: cellulose, lignin, hemicellulose and pectin

Animals lack cellulase themselves - only the microbes have cellulose and digest cellulose to provide host with nutrients (mutualistic)

Foregut and hindgut fermentation chambers

Question 3

Foregut vs. Hindgut fermentation chambers

Answer 3

Foregut: fermentation chamber (rumen) precedes acidic stomach
- Ex. ruminants, colobine monkeys, marsupials, hoatzin

Hindgut: cecum or large intestine used as fermentation chamber

Note: appendix is remnant of a cecum in humans

Question 4

Rumen

Digestion

Energy source for ruminants

Answer 4

Food chewed minimally –> rumen –> more chewing
- Small particles then move on to omasum
- 39-40°C inside rumen, anaerobic
- pH 5-7, maintained by saliva with sodium bicarb + sodium phosphate

Contains cellulolytic microbes such as Ruminococcus as well as non-cellulolytic which also feed off nutrients/sugars released (not mutualistic)

Sugars are fermented to produce volatile fatty acids (acetic, butyric, propionic acids) + CH4 (methanogens) + CO2
- FA pass into bloodstream from rumen and act as main energy source for ruminants

Question 5

Cellulosomes

Answer 5

Outside microbes such as Ruminococcus

Collection of 9 cellulase enzymes to degrade large cellulose polymers

Question 6

Energy loss in feeding ruminants

Answer 6

10% energy lost as acetate used by methanogens which produce CH4 and is burped up by cows

Monensin (antibiotic) inhibits methanogenesis and can be added to feeds to reduce CH4 production (good for environment)

Question 7

Digestion beyond the rumen in ruminants

Answer 7

Small particles move from rumen –> reticulum –> omasum

Excess water is collected in omasum

Food material + microbial mass moves from omasum –> abomasum –> intestines
- microbes serve as major source of AA and vitamins

Question 8

Hindgut fermentation

Answer 8

Fermentation occurs in the cecum which is between the SI and large intestine

Microbial mass is not digested but excreted and thus have higher AA/vitamin requirements
- some animals like rabbits and hares consume fecal pellets called coprophagy if they need the nutrients

Question 9

Hawaiian Bobtail Squid symbiosis

Answer 9

Mutualistic symbiosis between Aliivibrio fischeri and hawaiian bobtail squid

A. fischeri is bioluminescent and squid houses large population in light organ
- A fischeri emit light which resembles moonlight to camouflage the squid from predators

Horizontal transmission between individuals

Question 10

Termites example of symbiosis

Answer 10

Diverse community of anaerobes with cellulolytic capacity such as Ruminococcus live within gut of termintes in symbiotic relationship

Termites are then able to decompose cellulose and hemicellulose and receive acetate waste product for energy