L3: Microbial Fermentation

Question 1

Describe the differences b/w non-fermentative & fermentative digestion

Answer 1

Enzymatic hydrolysis of lrg molecules is essential for both fermentative & glandular digestion BUT fermentative enzymes are MICROBIAL in origin -fermentative rate of rxns slower -extent of alteration to lrg molecules greater

Question 2

Describe the different groups of rumen microbes & how the rumen provides an ideal enviro for fermentative digestion

List the requiremenrs for proper fermentation

Answer 2

• Anaerobic conditions
• Temp 39˚C
• pH 6.0 - 6.7 (neutral)
• Ionic strength in optimum range (~300mOsm)
• Suitable substrate (CHD)
• Regular turnover of digesta in/out, mean retention time (MRT)
• Rate of microbe removal = rate of microbe regeneration
• VFA produced removed (toxic)
• Contents well & continuously mixed (contractions)

Question 3

Describe the different groups of rumen microbes & how the rumen provides an ideal enviro for fermentative digestion

Describe rumen fungi & bacteria

Answer 3

• FUNGI
• obligate anaerobes
• survive totally on ingested feed
• digest structural plant polysaccherides (cellulose, starch, hemicelluloses)
• BACTERIA
• strict anaerobes (die in presence of O2)
• synthesise microbial (bacterial) protein
• Spp. present & relative numbers in rumen change greatly w/ feed composition & dietary changes

Question 4

Describe the different groups of rumen microbes & how the rumen provides an ideal enviro for fermentative digestion

Describe methanogens

Answer 4

• CH4 producing archaea
• Produce CH4 as an end product of microbial digestion of feed in rumen
• Larger and more diverse range found in forage-fed than grain-fed
• methanobacterium ruminantium
• methanobrevibacter sp.

Question 5

Describe the different groups of rumen microbes & how the rumen provides an ideal enviro for fermentative digestion

Describe rumen protozoa

Answer 5

• < number than bacteria but = biomass
• > numbers w/ > starch []
• < methane production
• Removal if called defaunation = > bacteria, so > flow of bacterial protein-N from rumen
• Two families:
• *-Holotrich (hairy)** => use starch & soluble sugars, store sugars, fermentation end products are: acetic, butyric, lactic acids
• *-Entodiniomorphid (tufted)** => ingest starch, plant material, bacteria

Question 6

Describe the different groups of rumen microbes & how the rumen provides an ideal enviro for fermentative digestion

Describe mycoplasmas

Answer 6

• Little known importance
• associated w/ respiratory, urinary & gastro disease
• lysis of bacterial & fungal cell walls

Question 7

Describe the different groups of rumen microbes & how the rumen provides an ideal enviro for fermentative digestion

Describe bacteriophages (viruses)

Answer 7

• Destroy other microbes
• involved in protein recycling

Question 8

Summarise the process of microbial fermentation & growth

What does rate of growth of bacterial popn depend on?

Answer 8

• Amount of e available (substrate)
• Bacterial turn over time
• Number of initial cellulose fermenters
• Individual bacteria spp.
• type & amount of inoculant

Question 9

Summarise the process of microbial fermentation & growth

What does bacterial growth require a constant supply of? Draw diagram representing process of fermentation & growth

Answer 9

• Requires constant supply of fermentable CHD for energy (substrates), some form of N for protein synthesis

Question 10

List the substrates of fermentative digestion

Plant cell walls are complex CHD molecules.

More cell wall =?

Answer 10

• < digestibility
• > fermentation
• loss of energy
• < microbial production
• < VFA production
• < protein

Question 11

List the substrates of fermentative digestion

CHD digestion involves 3 groups of plants CHD’s. Describe.

Answer 11

• Storage mono-, oligo- & polysaccherides
• starch, fructans, water-soluble CHD
• Easily digested
• Soluble structural polysaccherides
• gels
• pectins, B-glucans
• Insoluble structural polysaccherides
• cellulose, hemicellulose
• Fermentation

Question 12

List the substrates of fermentative digestion

What is the limiting factor of digestion of plant CHD?

Answer 12

• LIGNIN
• part of cell wall but not a CHD
• Indigestible

Question 13

List the substrates of fermentative digestion

Examples:

Name the bacteria that have a wide range of substrates

Answer 13

• Butyrivibrio spp
• Selenomas spp
• Lactobacilli spp

Question 14

List the substrates of fermentative digestion

Examples:

Name the bacteria that digest cellulose & hemicellulose

Answer 14

• Bacteriodes succinogens
• Ruminococcus spp

Question 15

List the substrates of fermentative digestion

Examples:

Name the bacteria that digest starch

Answer 15

• Bacteriodes amylophilus
• Streptococcus bovis

Question 16

List the substrates of fermentative digestion

Examples:

Name the bacteria that digest mono & di saccherides

Answer 16

• Succinovibrio dextrinosolvens
• Eubacterium
• Lactobacilli

Question 17

List the substrates of fermentative digestion

Examples:

Name the bacteria that digest lactate & simple sugars

Answer 17

• Peptostreptococcus elsdenii
• Selenomonas lactylitica