Lecture 13 - bacterial interactions with eukaryotes Flashcards
Symbiosis
Intimate association between organisms of different species
Syntrophy
Association requiring two or more partners to complete a metabolic pathway
Synergism
Optional cooperation where both species benefit but are able to grow independently from one another
Commensalism
One partner benefits, while the other is unaffected
Amensalism
One species harms another but is neither affected nor benefited by the action
Mutualism
Each partner benefits from the other
Can mutualistic species grow independent of one another
Sometimes
Example of mutualism
Lichens: composite organism formed by the mutualistic relationship between fungi and cyanobacteria/algae
- fungus is dependent on cyanobacteria/algae for carbohydrate
- fungus provides minerals for cyanobacteria/algae, but is not necessary for their growth
Parasitism
Intimate association where one partner benefit by harming a specific host
Wolbachia
Bacteria that commonly infects insects and nematodes as intracellular symbionts
What kind of relationship does wolbachia have with its hosts?
Mutualistic or parasitic depending on the host
Can wolbachia survive independently?
No. Must reside in the cytoplasm of a host because its genome has been pared down. Unable to live without materials from the host
Relationship between Wolbachia and Brugia malayi
Mutualistic
- wolbachia is required for the growth of brugia (nematode)
How was the relationship between Wolbachia and Brugia confirmed?
Antibacterial therapy that kills Wolbachia was more effective at clearing a Brugia infection than antihelminthic therapy that kills Brugia
What is the result of the relationship between Wolbachia and Brugia?
Brugia blocks lymphatic system in humans –> swelling of extremities
What aspect of Wolbachia is important in its relationship with Brugia?
Wolbachia can make FAD (essential e- carrier) and provide it to brugia
How is Wolbachia passed to new insect hosts?
Inherited through egg cytoplasm (only passed down through females)
How does Wolbachia influence sexual differentiation in insects?
- male killing
- feminization
- parthenogeneis
- cytoplasmic incompatibility
Male killing
Infected males die during larval development
Feminization
Infected males develop into females or infertile pseudo-females
Parthenogenesis
Reproduction of infected females without males
Cytoplasmic infertility
Infected males can’t produce progeny with uninfected females or with females that carry another Wolbachia strain
Outcome of cytoplasmic infertility
Increased proportion of infected progeny in the population
Example of syntrophy
Mixotricha paradoxa
- protozoan that has at least four bacterial symbionts that provide useful materials for it
- lives in the hindgut of termites and provides essential materials for wood breakdown and consumption
What do bacterial symbionts do in Mixotricha paradoxia
- Spirochetes and “anchor bacteria” on the outer surface provide locomotion for Mixotricha
- cytoplasmic symbionts perform mitochondrial functions to provide energy for Mixotricha
What does Mixotricha do to help termites?
Converts wood polysaccharides to acetic acid which is taken up by the termite
Endophytes
Bacteria or fungi that colonize the transport vessels of plants
What do endophytes to to their hosts?
Produce alkaloids and enzymes that deter plant pathogens and root feeding nematodes –> promotes plant growth
What is the problem with endophytic pathogens for us?
Endophytic pathogens live in the vessels of plants and therefore can’t be washed off of raw produce
Rhizoplane
Plant root surface
Rhizosphere
Region of soil outside the rhizoplane that receives substances from the root
Rhizobium
Bacteria that enter cortical cells of legume roots and provide fixed nitrogen to the plant
How do rhizobium enter plant roots?
- attracted to the legume by chemotaxis towards exuded flavonoids
- bacterial Nod factor induces root hair to curl around it and take it up into the infection thread
- rhizobia enter cortical cells and differentiate into bacteroids
What do rhizobia and legumes provide one another?
- rhizobia provides fixed nitrogen
- legumes provide malate and minerals
- legumes also provide leghemoglobin which sequesters O2 and precisely delivers it to electron transfer system of bacteria
Why is leghemoglobin necessary for rhizobia/legume interactions?
Rhizobia use nitrogenase to fix nitrogen. Nitrogenase can’t function in the presence of oxygen, so it must be kept separate
Why is malate important for rhizobia/legume interactions?
Malate is used in the TCA cycle for energy production. Lots of energy is needed for nitrogen fixation.
Why is the rumen important in bovine systems?
Largest digestive chamber that contains a diverse microbial community that aids in breakdown of plant fibers
End product of cellulose breakdown in cows
Bacteria ferment glucose and create short chain fatty acids that can be taken up by the animal
Byproducts of cellulose breakdown in cows
Methane
Influence of starch and sugars on bovine microbiome
Starch and sugars are broken down by gram - bacteria like E. coli. Increased starch/sugar intake promotes their growth and causes dysbiosis
One way to treat gut dysbiosis in cattle
Add fistula to cows to allow transplantation of rumen material between cows
In a healthy population, what aspects of the microbiome are variable and which are constant?
- carriage of microbial taxa is variable (not every individual will have the same amount of each type of bacteria)
- metabolic pathways remain stable
