L39: Animal Microbe Interactions Flashcards
explain the role of chemolithoautotrophic bacteria in providing
energy and nutrients to marine and deep sea animals
– animals harness the ability of chemolithoautotrophs to extract
energy from chemical compounds and fix CO2
– chemosynthesis, as opposed to photosynthesis, by bacterial
symbionts to produce organic compounds for host animals
– deep sea hydrothermal vents, estuaries, deep sea cold seeps
(hydrocarbon), whale falls, etc
explain Tube worms and symbionts
habitat: deep sea hydrothermal vents
– Riftia pachyptila worms lack mouth and gut
tube worms and symbionts and the point of sulfur in all this
– contain sulphide-oxidizing bacterial (SOB) symbionts
– held within a “trophosome” (~60% of wet weight)
– red colour due to a special hemoglobin which transports O2 and
H2 S (from the hot vents) to the bacterial symbionts (aerobes)
– recall leghemoglobin, squid light organ (nutrient exchange)
– the SOB symbionts fix CO2 using energy and electrons derived
from H2 S-oxidation, thus they are chemolithoautotrophs
– chemosynthesis, as opposed to photosynthesis, to produce
organic compounds
– 16S rRNA gene sequence analysis indicated that these are
unique Gammaproteobacteria
– nutrients (organic compounds) passed to host worm
Gutless clam and symbionts
– these clams (Solemya reidi, etc) are pathetic!
– estuary habitat is rich in organic C (river) and SO42- (sea)
– gills contain symbiotic aerobic chemolithoautotrophic
sulphide-oxidizing bacteria (SOB’s)
– deeply-branching Gammaproteobacteria related to the sulphide-
oxidizing chemolithoautotrophic Riftia symbionts
draw the thing
Gutless clam ecology & metabolism
– oxidation of organic compounds coupled with SO42- reduction by sulphate-reducing bacteria (SRBs) in the sediments yields H2S (the SRBs are not the symbionts of the clam)
– hydrothermal vents not present to produce H2 S in estuaries
– estuarine sediments are an ideal habitat for SRB’s and thus
these clams, but they are also found in other similar niches
– H2 S rising from sediments is oxidized by both the sulphide-
oxidizing symbionts and the clam’s mitochondria
– ATP generation via sulphide oxidation by both partners
– CO2 -fixation by the chemolithoautotrophic symbionts is fueled
by energy derived from H2 S-oxidation (chemosynthesis)
– the symbionts supply the clam with organic compounds that
are its source of carbon and a major source of energy
– the clam does not need a gut (reduced or absent)!
C. Mytilidae mussels and symbionts
– family of mussels found at deep sea cold seeps and
hydrothermal vents
– both types of vents release H2 S, CH4 and other hydrocarbons
– mussels from both environments have complex microbial communities of specific symbiotic bacteria within their gills
– symbionts obtain nutrients, C and energy from the environment
– hosts obtain nutrients via digestion of the symbiotic bacteria
break down the relation between symbionts and deep sea mussels
– gill symbionts include (but are not limited to) methanotrophic,
methylotrophic, sulfide- and sulfur-oxidizing bacteria
– aerobic chemolithoautotrophs (chemosynthetic)
A. methanotrophic symbionts
– oxidize CH4 as a carbon, electron and energy source
– methane monooxygenase (MMO)
B. sulphide-oxidizing chemolithoautotrophic symbionts
– similar to the SOB’s found in Riftia worms and gutless clam
– oxidize H2 S (electron and energy source)
– fix CO2 (carbon source)
explain Rumen microbial ecology
ruminants (cattle, sheep, goat, giraffe, etc) consume plant
material which is metabolized mainly by microbes in the rumen
– plant material, produced by photosynthesis, mainly consists of cellulose but also contains starch, hemicellulose, lignin,
proteins, lipids, etc
– 1-5% of rumen bacteria and protozoa produce extracellular
cellulases that break down cellulose to sugars
– sugars are fermented to organic acids and CO2 by many species
– the various organic acids are interconverted by fermenters
– cattle rumen:
– 100 L volume
– 80 L gas belched per day
draw pyramid of rumen trophic pyramid
animal apex consumption
microbial 1^0, 2^0, 3^0 consumption
Plant 1^0 production
What are the stages of rumen metabolism
1) Degradation of cellulose and other complex carbohydrates
2) Fermentation of sugars and acids (organic, fatty, amino)
3) Absorption of organic acids by rumen tissue
4) Methanogenesis using fermentation products H2 and CO2
5) Predation by protozoa (ciliates) on bacteria
6) Digestion of proteins & microbes in the lower GI tract
What is the goal of rumen metabolism + equation
the goal is to convert cellulose into C energy and energy sources for the animal
57.5 C6 H12 O6 ==> 65 acetate + 20 propionate + 15 butyrate
+ 60 CO2 + 35 CH4 + 25 H2 O
What are Rumen Products
1) Organic acids absorbed by the ruminant:
– acetate (47-60%), propionate (18-23%), butyrate (19-29%)
– also referred to as volatile fatty acids (VFA)
– ruminant oxidizes acetate and butyrate via TCA cycle for energy
– propionate is the only gluconeogenic (biomass-building carbon
source) organic acid substrate supplied to the animal
2) Gasses:
– CO2 (60-70%)
– CH4 (30-40%)
3) Heat
Break down the rumen microbial community
- Rumen bacteria: diverse community allows metabolic adaptation to diet
–-> Degrade: cellulose, starch, hemicellulose, proteins, lipids etc.
–->Ferment: sugars, organic and fatty acids. - Rumen archaea are primarily methanogens
–-> some methanogens are symbionts of rumen protozoa - Rumen protozoa: i.e., ciliates, degrade plant material and ferment sugars
–-> prey on rumen bacteria and archaea
–-> store carbohydrates that are are readily digested in the lower GI tract - Saprophytic fungi degrade plant material, ferment sugars
- Parasitic fungi parasitize ciliates (very little known about these)
– i.e., Sagittospora cameroni parasitizes Diplodinium minor
Discuss the population numbers in rumen microbial communities
– early estimates were of up to 10^10 microbial cells per g
– DGGE showing diversity (right)
– qRT-PCR revealed (per g):
=>5.17x1011 bacteria
=>3.17x109 archaea (methanogens)
=>4.02x107 protozoa (ciliates)
What are the benefits of rumen microbes
– abundant supply of food and other necessary compounds
– saliva rich in PO4- (P source, pH buffer)
– constant pH
– even temperature
– re-chewing and movement in rumen mixes contents
– absorption of toxic waste products by ruminant tissues
– low [O2 ] perfect for anaerobes
