Bacterial Illumination

Squid Communicate with each other using a wide spectrum of colors and postures. At night they signal with luminescent organs.

The squid's luminescent communications result from communications between bacteria living in special light organs.

Squid, and a variety of fish, have luminescent bacteria housed in special sacs called light organs. The bacteria generate light with an enzyme called luciferase - but not all the time.

When the bacteria Vibrio fischeri swim free in sea water, their population densities are very low and they do not produce light. When they inhabit the light organs of squid, however, the squid cells nurture the bacteria and their populations soar to high levels. When the bacteria are packed tight, they begin to secrete messenger proteins called autoinducer. As this reaches a critical level, it enters the bacteria and activates a protein called LuxR.

Activated LuxR stimulates the bacterial genes to produce the light producing proteins luciferin, luciferase and associated light producing proteins.

The genes are stimulated to produce additional autoinducer messengers and these are released from the bacteria. The additional production of autoinducer messengers, triggered by the active LuxR, stimulate another round of protein synthesis. This positive feedback loop results in rapid production of light producing proteins. When these proteins reach a critical density, they react with each other to liberate that delightfully eerie blue phosphorescence of the sea.