Lux operon

Question 1

What does transcription of the lux operon achieve? What is required?

Between what organisms does the symbiotic relationship take place?

What is the autoinducer/signalling molecule in the bacteria?

In the bacterial lux operon, what do the following do:

luxR

Promotor

operator/lux box

promotor

luxI

lux C,D,E

lux A,B

lux G

Answer 1

Bioluminescence - high density of bacteria

Between hawaiian squid & bacterium Vibrio fischeri

3-oxo-c6

encodes protein activator tha binds to 3-oxo-c6

promotor of luxR

controls transcription of downstream genes

initiates transcription of downstream genes

encodes 3-oxo-c6 synthetase & produces 3-oxo-c6

encodes fatty acid reductase complex - provides enzyme to make the aldehyde substrate for luciferase

encodes 2 subunits of luciferase

encodes flavin reductase (reduces FMN to FMNH2)

Question 2

What are the 3 steps of autoinduction?

How is bioluminescence produced?

Answer 2

1. RNA polymerase transcription of LuxI produces 3-oxo-c6 through its synthetase
2. LuxR produces activator which binds to 3-oxo-c6
3. Complex binds to lux box which increases affinity for RNA polymerase & induces transcription of downstream genes

Luciferase (coded by A & B) with reduced FMNH2 (by G), oxygen & aldehyde substrate (C, D, E)

Question 3

What is the symbiosis between bacteria & squid?

What does the swelling allow for bacteria?

What does the squid do during the day?

What is the total reaction?

Answer 3

More bacteria means crypt cells of light organ expand - bacteria activate the squid gene that causes the swelling

House more bacteria

Buries into sand & ejects 95% bacterial population so at night the bacteria replenished after division in day

FMNH2 + O2 + Aldehyde R-CHO -> FMN + carboxylic acid R-COOH + H2O + light