Vibrio fischeri and squid

inoculation of symbiont

Young squids are infected in the crypt with almost pure cultures

crypts

house symbionts have micro ills to increase the surface area

expelling symbiont

every morning most of the symbionts are expelled and become VBNC

LuxR and LuxI

quorum sensing system ensure enough population to bioluminesce

cell density

10⁹-10¹⁰

luciferase

Monooxygenase encoded by LuxAB uses O2 and FmNH2 to oxidize aldehyde tetradecanal making light

fatty acid reductase

luxCDE code for the protein regenerates tetradecanal

oxidoreductase

LuxG encodes, protein regenerates FMNH2

3-oxyhexanol homoserine lactone

made by AI synthitase (LuxI), autoinducer high concetration at high density, binds LuxR leading to expression

left operon

luxR

right operon

LuxICDABEG

catabolite expression

[CAMP-CRP] controlled, high when starving

host nutrient supply

the squid feeds the bacteria just enough to survive but still produce starvation response

[CAMP-CRP] binding

binds LuxR leading to an activated operon

autoinducer control

the population density, need [AI-LuxR] threshold to activate LuxI (luciferase)

overexpression control

luxR repression at very high [AI-luxR] levels to prevent overexpression and keep light steady