Lecture 32 Flashcards
Can different species of myxobacteria make fruiting bodies together?
No. Only when 1 specie is present.
- Produce extracellular factors (bacteriocins, antibiotics) to inhibit other myxobacteria
- Distance is maintained between fruiting bodies of different species
- Fruiting bodies that contain cells from different strains of a single species (a poluclonal population) produce fewer spores than those of a monoclonal population (lab study)
Explain what is particular withthe bobtail squid?
- Luminescence due to luminescent bacteria
- Vibrio fischeri
What are characteristics of luminescent bacteria?
- Most seem to be Gram negative and have SYMBIOTIC associations
- Produce light for host in return for a benefit
- Vibrio (squid, fish), Photobacterium (fish), Xenorhabdus (terrestrial), Alteromonas etc.
How does the light of Vibrio Fischeri benefits the host animal?
- Counter illumination to protect squid from predators below
- Light coming from above can silhouette a squid
- Downward focused bioluminescence counteracts that effect
- Squid with bioluminescent bacteria will not cast a shadow
- Squid without bioluminescent bacteria will cast a shadow and thus be easy prey
- They can even change the light intensity
How does inoculation of the squid happen?
- It’s a highly-specific interaction
- Host and symbiont are able to recognize each other (despite the low concentrations in ocean)
- Inoculation of baby squid facilitates light organ to develop.
- Does not develop unless infected - Bacteria reside in “crypts’ as pure culture in very close assocaition with host cells and blood supply
- Formation of bacterial biofilm in these crypts is critical and involves the synthesis following by the bacteria:
- Symbiosis polysaccharide => like a key for recognition by the host
- Cellulose => to make biofilm - Host supplies symbionts with organic a.a.
- Feeding of other bacterial species does not occur
Explain the turnover of vibrio fischeri in bobtail squid?
Fresh culture grown every day:
- Every morning 90% of symbionts are expelled
- Expelled bacteria eventually become VBNC
- Still able to infect
- Save energy in VBNC form?
- Culture in light organ grows back to full density in 12 hours
- “fresh” cells at high density by nightfall
True or false, the Vibrio Fischeri Quorum sensing system was the first such system discovered
True
What genes encode the quorum sensing system of vibio fischeri?
LuxR-LuxI genes
When is light produced?
Ligh is only produced when the population collectively sense a high cell density of 10^9 to 10^10 cells/mL (a quorum)
- The Lux genes that encode the light producing luciferase enzyme are only expressed when the cells are starving AND at a high cell density
- High cell density and starvation naturally coincide because denser populations deplete nutrients more rapidly
- High cell density would NORMALLY only occur under symbiotic cdtns, but there are (mysterious) exceptins: milky seas
What is the formula for the light yield reaction?
R-CHO + O2 + FMNH2 + ATP=> R-COOH + hv (light) + H2O +FMN+ AMP + PPi
What enzyme facilitates the light-yield reaction?
Luciferase enzyme
True or false. New tetradecanal (R-CHO) is use everytime in the reaction.
FAlse. It is recycled back by Lux CE, using ATP.
so RCOOH=> RCHO (using Lux CE)
True or false. New tetradecanal (R-CHO) is use everytime in the reaction.
FAlse. It is recycled back by Lux CE, using ATP.
so RCOOH=> RCHO (using Lux CE)
Don’t need a lot of tetradecanal (since recycled)
How does Quorum sensing in Vibrio Fischeri work?
Autoinducer (AI) is a diffusable, membrane-permeable compound : 3-oxyhexanoyl homoserine lactone
- AI synthesized by enzyme AI synthase (encoded by luxI)
- AI concentration is proportional to cell density/the quorum
- AI concentration within and outside of cells is the same
- AI is detected by being bound by the LUXR protein - AI-LUXR binds to the LUXI gene promoter
- This causes the LUXICDABEF operon to be expressed - Light production only occurs at high cell density becasue binding of AI-LUXR to the promoter requires high AI concentration
