Microbial Symbioses Flashcards
Parasitic
symbioses with an expense to the host
Pathogenic
symbioses that causes disease/death to host
Commensal
symbioses with no impact on host
there is not evidence of this existing in life
Mutualistic
symbioses that benefits both the host and microorganism
Root Nodule Symbiosis
mutualistic symbioses between legumes and nitrogen-fixing bacteria
What is formed that characterizes Root Nodule Symbiosis? What does it do?
nodules on the root of legumes are formed which houses the bacteria that fix nitrogen
Which bacteria is best known as the nitrogen-fixing bacteria involved in Root Nodule Symbiosis?
Rhizobia bacteria
What are the steps of root nodule formation?
- recognition and attachment of bacterium to root hairs mediated by Rhicadhesin
- excretion of nod factors by the bacterium
- induce root hair curling
- Bacterial invasion of the root hair and multiply w/in an infection thread
- travel to the main root via the infection thread
- nod genes induce nearby plant cells to divide
- formation of bacteroid state by bacteria
- continued plant and bacterial division, forming the mature root nodule
What are nod factors?
species specific oligosaccharides produced by nodABC genes in bacteria
induce root hair curling and plant cell division
Of the nod genes, what is specific about nodD?
nodD is the transcriptional activator for other nod genes and is activated by plant flavanoids
if in the wrong plant, flavanoids become co-repressors
In the Root Nodule Symbiosis, what does the plant give the bacterium?
electron donors like succinate, malate, fumarate
In the Root Nodule Symbiosis, what do the bacterium give the plant?
ammonia which is converted to glutamine via glutamine synthetase w/ Nitrogenase
(N2 -> NH3 -> Glutamine Asparagine)
What is Leghemoglobin? and What is its job in Root Nodule Symbiosis?
Leghemoglobin is produced by legumes for root nodulators once bacteroid begins to form
has Fe core which binds to O2 to keep the O2 levels low which allows the symbiosis to be better
Crown Gall Disease
parasitic symbiosis between Agrobacterium tumefaciens and plants causing grown gall tumors
How are Crown Gall Tumors induced?
- A.tumefaciens cells attach to wound site on plant
- cellulose microfibrils are synthesized by the attached cells
- ATP is used to produce activated VirG protein
- VirG expresses rest of Vir genes
- VirD nicks Ti (tumor induction) plasmid
- VirE transfers 1 plasmid strand to VirB
- VirB makes secretion system which infects plants w/ the T-DNA
What is the Ti Plasmid and what is its make-up?
Ti (tumor induction) plasmid
- contains…
- T-DNA which is transferred into host genome
- tumor formation genes
- modified amino acid (opine) biosynthetic genes
What are mycorrhizae?
mutualistic associations of plant roots and fungi
What are the 2 classes of mycorrhizae?
Ectomycorrhizae
and
Endomycorrhizae
What are ectomycorrhizae?
- extensive sheath around the outside of the root
- only a little penetration into the root tissue
- found primarily in forest trees, mainly boreal and temperate forests
What are endomycorrhizae?
- fungal mycelium becomes deeply embedded w/in the root tissue
- more common than ecomycorrhizae
- found in >85% of terrestrial plant species
How do mycorrhizal fungi assist plants?
they improve nutrient absorption due to the greater surface area provided by the fungal mycelium
What do phylogenetics suggest about mammal nutrient lifestyle (i.e. herbivore, omnivore, carnivore)?
suggest that the first mammal ancestor was a carnivore and evolution took mammals to omnivores and then herbivors
What are the 2 digestive plans that have evolved in herbivorous mammals?
Foregut Fermentation and Hindgut Fermentation
What is Foregut Fermentation?
- where the microbial fermentation chamber is before the small intestine
- includesz sheep, cows, goats, birds etc.
What is Hindgut Fermentation?
- where the fermentation chamber (cecum) and large intestine are after the stomach and small intestine
- includes horses, rabbits, primates, rodents, reptiles etc.
Why have foregut and hindgut digestive plans developed in herbivorous animals?
because the plants that are eaten contain cellulose that cannot be digested normally
What are the most successful group of foregut fermenters and the most dominant herbivores?
The Ruminants which are herbivorous mammals that havea special digestive organ - Rumen
What is the pathway that food takes in a ruminant?
- food enters the Reticulum-Rumen through the Esophagus
- smaller food particles are sent to the Omasum
- larger food particles are regirtitated as Cud and re-digested by rumen bacteria
- small particles in Omasum are sent to the Abomasum (similar to stomach, where chemical digestion begins)
- food in Abomasum is sent to the small intestine and through rest of digestion
What are primary symbionts?
- required for host reproduction
- obligate symbionts
- exhibit extreme gene reduciton (only have those needed for host fitness)
- high AT content
- high mutation rates
What are secondary symbionts?
- not required for host reproduction
- facultative symbionts
- not always present in every individual host
- must provide a benefit to the host
What are the microbes in Higher Termites and Lower Termites?
Higher Termites - diverse community of anaerobes to decompose cellulose (hemi-)
Lower Termites - anaerobic bacteria and cellulolytic protists
What is the symbiont for Leaf Cutter Ants?
worker ants chew up leaves and feed to fungus in the nest, the ants then eat the fungus
What is the symbiosis with Hawaiian Bobtail Squid?
- symbiont = Aliivibrio fischeri (A.fischeri)
- bioluminescent
- held in specialized structure = light organ
- used to camouflage the squid from predators
- transmission of symbiont is horizontal = 1st colonized just after sqiud hatches
- light organ 1st produces special mucus that is bound by gram negative bacteria
- A.fischeri dominates gram negative bacteria b/c tolerates high levels of NO
What is the symbiosis with Hydrothermal Vent Invertebrates?
- symbiont = chemolithotrophic prokaryotes
- helpful for vent invertebrates = symbionts like the reduced inorganic materials emitting from the vents
- helpful for symbionts = vents invertebrates have trophosome, specialized hemoglobins and high blood CO2 content
What is the symbiosis with Reef-Building Corals?
- symbiont = phototrophic cyanobacteria, rhodopytes, chlorophytes, dinoflagellates, and diatoms
- coral skeleton is very efficient light-gathering structure = good for symbiont
What is the symbiosis with Lichens?
- symbiosis = btwn fungus (Lichen) and cyanobacterium/alga
- phototroph is photosynthetic and produces organic matter
- fungus provides strucure w/in phototroph can grow and protection from dryness
What is the symbiosis called Consortia or “Chlorochromatium aggregatum”?
- symbiosis between microbes in freshwater
- incapable of being separated
- w/ green sulfur bacteria (epibionts) (obligate anaerobic phototroph) and flagellated rod-shaped bacterium (provides movement)
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