L32: Microbe Animal Interactions Flashcards
Name examples of bioluminescent things
Vibrio and Allivibrio (squid +fish)
photobacterium fish
xenorhabus terrestial
Describe general characteristics of luminscent bacteria
G+, with symbiotic associations, produce light for the host in return for something
How does light benefit the host in Vibrio Fischeri
what: counter illumination protects the squid from predators
how: light from above silhouttes the squid so downward bioluminescene counteracts that effect. If there is light downards there no shadow will be cast so prey cannot see
What is innoculation
a highly specific interaction where host and symbiont can recognise each other despite low concentration
this allows light organs to develop in baby squid, it will not develop if not infected with bacteria
What does the host provide the lighty bacteria
organic + amino acids
Where and how do bacteria form in the squid, what does the bacteria produce to help
they form in crypts as a pure culture very near the blood supply
the crypts have microvili to increase SA => more contact
this creates a biofilm so the infection can persits
the bacteria synthesises a lot of cellulose and polysaccharides
Explain the freshness of the bacteria on the squid throughout the day
in the morning 90% of symbiont population in expelled and that bacteria become VBNC, but can still infect
this is a way for the bacterial to save energy
if u culture in light it grows back to full density in 12h, so u have fresh density by nightfall
How is the light produced, outline the role of cell density and quorum sensing
involves luxR/I genes
the light is produced when population reaches 10^9 to 10^10 quorum
high density and starvation coincide because high density deplete nutrients => meaning high density only occur in symo conditions but there are exceptions
Discuss light production in relation to other bacterial species
it was the first SQ system discovered
encoded by LuxR-luxI gene, homologs of this gene are in many bacterial species
=>they are N acyl homoserine lactone autoinducers
What is the exception of milky seas
density and starvation starvation
virbo produce some light growing on decomposing agal blooms and it looks milky
they are everywhere
Chemically explain the light yielding reaction
FMNH2 + O2 + R-CHO => R-COOH + FMN + H2O + light
- luciferase is a monooxygenase encoded by luxAB genes
*it consumes O2 and FMNH2 in oxidation of aldehyde-tetradecanal the R-CHO
*then a photon of light is the by-product - a fatty acid reductase encoded by luxCDE regenerated the tetradecanal, consuming ATP and NADPH
- an oxidoreductase encoded by luxG regenerated FMNH2 via electron transfer from NADPH
There is consumption of O2, ATP, NAD(P)H so its costly in terms of reducing power
Explain autoinduction and QS, discuss AI and density
- AI is diffusible and membrane permeable
made of 3 oxyhexanoyl homoserine lactone - synthesized by AI synthase that is encoded by luxI
*[AI] proportional to cell density/the quorom, meaning [AI] inside and outside the cell is the same
*it is detected by LuxR then AI-LuxR binds to LuxI gene promoter, this requires high cell density => begins luxICDABEG operon expression
Explore AI signalling and quorum sensing in other bacteria
- present in all bacterial species
*N acly homoserine lactone are the most common in G(-)
QS required in pathogen to induce virulence genes that cause diseases for example in Agrobacterium tumor formation is dependant on cell density => will only form when there is enough Agrobacterium
