Luminescent Bacteria

Question 1

What process do luminescent bacteria use to produce light?

Answer 1

Bioluminescence

Light is produced through a simple chemical reaction catalyzed by the enzyme bacterial luciferase.

Question 2

Which two genera of marine bacteria are known for producing light?

Answer 2

Photobacterium and Vibrio

These bacteria are capable of bioluminescence in marine environments.

Question 3

What substrates are used in the bioluminescence reaction?

Answer 3

A fatty acid and O2

These are the substrates for the enzyme bacterial luciferase involved in light production.

Question 4

What type of relationship do some luminescent bacteria form with fish or squid?

Answer 4

Symbiotic relationship

The bacteria grow in special light organs of the host, protected from competition.

Question 5

How can fish utilize the light emitted by luminescent bacteria?

Answer 5

To attract prey, signal other fish, or obscure their shadow

The emitted light serves multiple ecological functions for the fish.

Question 6

What is the significance of luminescent bacteria enticing fish to swallow them?

Answer 6

Access to nutrient-rich environment of the fish gut

Ingested bacteria benefit from the nutrients available in the fish’s digestive system.

Question 7

What is unique about the light production in Vibrio fischeri?

Answer 7

Light is produced only at high population density

Low-density populations of V. fischeri do not luminesce.

Question 8

What regulatory mechanism do V. fischeri cells use to monitor population density?

Answer 8

Quorum sensing

This mechanism involves a self-produced extracellular signal molecule called autoinducer.

Question 9

What must occur for luminescence to be activated in V. fischeri?

Answer 9

High concentration of autoinducer

A sufficient number of autoinducer-producing cells must be present.

Question 10

Why is light production considered an energy-expensive process?

Answer 10

It requires significant metabolic resources

This is why V. fischeri limits light production to high-density populations.

Question 11

What materials are needed for the first period of the experiment?

Answer 11

1 Sea Water Complete (SWC) agar plate and 1 sterile swab

These materials are used to isolate luminescent bacteria.

Question 12

What is the main purpose of swabbing the gills of the salt-water fish?

Answer 12

To streak the SWC agar plate for bacterial isolation

This is the initial step in isolating luminescent bacteria from the fish.

Question 13

What should be done with the swab after streaking the agar plate?

Answer 13

Discard in a biohazard container

This is necessary for safe disposal of potentially contaminated materials.

Question 14

At what temperature should the agar plate be incubated?

Answer 14

~12°C

A low temperature is used for the incubation of luminescent bacteria.

Question 15

What should be done after identifying a luminescent colony during examination?

Answer 15

Re-streak for isolation onto an SWC plate

This allows for further isolation of the luminescent bacteria.

Question 16

How should the plate be examined for luminescent colonies?

Answer 16

In a dark room, allowing eyes to dark adapt

Staying in the dark for up to 5 minutes may be necessary to see luminescence.

Question 17

What type of staining is performed on an isolated colony?

Answer 17

Gram stain

This helps differentiate between Photobacterium and Vibrio based on their cell morphology.

Question 18

How do Photobacterium cells appear after Gram staining?

Answer 18

Gram-negative rods

This is a characteristic morphology of Photobacterium.

Question 19

What is the range of shapes for Vibrio cells after Gram staining?

Answer 19

Gram-negative straight rods to slightly curved (bent) rods

This variability in morphology is characteristic of the Vibrio genus.