12- Microbiology of animals Flashcards
What does the body of animals provide?
The bodies of animals provide a warm, wet and potentially highly nutritious environment for bacteria that have evolved ways to colonize it. There is an evolutionary pressure to do so.
• Temperature, pH, nutrient supply, the immune system (genetic factor) and other
factors influence the richness and the abundance of the microorganisms on an individual.
• As the animal develops, various body surfaces become progressively colonized: the
individual acquires its normal microbiome.
What are commensal residents?
microorganisms routinely found on the bodies of most healthy individuals. Commensals normally colonize the body without causing an infection.
What is the relationship btw microorganisms and animals?
• At first, most microorganisms may seem to be commensals. They take advantage of the host (nutrients, shelter) and they do not harm the host.
• But, commensals can also be beneficial:
– Provide host with vitamins and metabolic pathways (gut).
– Provide protection against new incoming microbial populations (occupy the territory).
– Teach the immune system.
• Also parasitism: some commensals can become pathogenic under specific conditions (and commensals of one species may cause infectious diseases in another).
Harmful relationships with microorganisms (6)?
Pathogens, infection, disease, pathogenicity, virulence, opportunistic pathogen
- Pathogens: microbial parasites that are able to cause infection.
- Infection: situation in which a microorganism is established and growing in a host, causing damage.
- Disease: damage or injury to the host that impairs host function (infectious diseases, autoimmune diseases, cancer, etc.)
- Pathogenicity: the ability of a parasite to inflict damage to the host.
- Virulence: measure of pathogenicity.
- Opportunistic pathogen: causes disease only in the absence of normal host resistance. The normal microbiome contains opportunistic pathogens.
Where are the vast majority of microorganisms found? Herbivore, carnivores, omnivores
• In animals, the vast majority of microorganisms are found in the gastrointestinal (GI) tract.
• Herbivores – animals that consume mostly plants • Carnivores – animals that consume mostly meat • Omnivores – animals that consume both
• Phylogenetic studies suggest that different lineages evolved a herbivorous lifestyle
Gastrointestinal tract of herbivores? Name two digestive strategies
- Herbivores live on plant material rich in cellulose and other insoluble polysaccharides (lignin, hemicellulose, pectin).
- Animals lack the enzyme (cellulase) that is required to degrade cellulose.
• Microorganisms present in the GI tract of herbivores are able to degrade cellulose
and provides the host with nutrients (mutualism, symbiotic relationship).
• Two digestive strategies have evolved in herbivorous animals
– Foregut fermentation: fermentation chamber precedes the acidic stomach.
– Hindgut fermentation: uses cecum and/or large intestine as fermentation
chambers.
The rumen of ruminant animals: explain
• Food is chewed minimally, swallowed, and passes into the rumen (foregut fermentation
chamber).
• Rumen – Cow: 100-150L, sheep: 6L. – 39-40 °C – pH: 5-7 – Anaerobic environment • pH of the rumen is maintained by saliva which contains sodium bicarbonate and sodium phosphate.
- Only a small proportion of the rumen’s microorganisms produces cellulases
- Fermentation in the rumen is mediated by cellulolytic microbes that hydrolyze cellulose to free glucose and cellobiose, that are then available to all microorganisms for growth.
- The sugars are then fermented, producing volatile faay acids (VFAs: acetic, propionic, butyric), CH4 and CO2.
- Fatty acids pass through the rumen wall into the bloodstream and are utilized by the animal as its main energy source
- Ciliated protozoa, bacteria, archaea (300-400 species, SSU rRNA sequencing)
- Contains 1010–1011 microbes/g of rumen content.
Tell me more about methalogens, what do they produce? Inhibit?
Methanogens produce CH4. Strict anaerobe.
4H2 + CO2 à CH4 + 2H2O + energy
CH3COOH à CH4+ CO2 + energy
• CH3COOH = acetate.
• Acetate used by methanogens is not available to the host. Up to 10% of the energy
value of the feed can be lost as CH4.
• Monensin inhibits methanogenesis and is routinely added to feed to reduce production of CH4.
The rumen… (2). After digestion…?
After several hours of microbial digestion, small portions of the rumen contents are regurgitated, well chewed and then swallowed again. Smaller food particles are collected by the reticulum and moved to the omasum, where excess water is collected.
• The material then goes into the stomach (abomasum) and from there, to the intestines. The mass of microbial cells are subjected to digestion and serves as a major source of amino acids and vitamins.
Tell me about the non-ruminant herbivore.
- Fermentation takes place in the caecum, provides organic acids absorbed by the animal.
- The microbial mass that grows on cellulose and other polysaccharides are not digested, and they are excreted.
- These animals have a higher dietary requirement for amino acids and vitamins than do ruminants.
- Rabbits and hares get around this problem by consuming the faecal pellets they produce (coprophagy).
The Hawaiian Bobtail Squid example- animal/miroorg.
A mutualistic symbiosis between the marine bacterium Aliivibrio fischeri and the Hawaiian bobtail squid is a
model for how animal–bacterial symbioses are established
• The squid harbors large populations of the bioluminescent A. fischeri in a specialized structure (light organ)
- Bacteria emit light that resembles moonlight penetrating marine waters, which camouflages the squid from predators.
- Transmission of bacterial cells is horizontal.
Tell me about termites
- Termites decompose cellulose and hemicellulose
- Diverse community of anaerobes including cellulolytic anaerobes
- Anaerobic bacteria and cellulolytic protists.
Ruminococcus?
Have the cellulase- cellulose enzyme that degrades cellulose in ruminent
