Which bacterium produces light in a famous symbiosis with the Hawaiian bobtail squid?

Aliivibrio fischeri produces light in a famous symbiosis with the Hawaiian bobtail squid.

The bacterium lives in a specialized light organ of the squid Euprymna scolopes. The squid supplies nutrients and a protected habitat, while the bacteria produce blue-green light through a chemical process called quorum sensing. At high cell density, chemical signals activate genes needed for bioluminescence.

The light helps the squid camouflage itself at night. From below, the glow can match faint moonlight and starlight, reducing the squid’s silhouette against the water. The animal expels much of its bacterial population each dawn, and the light organ is recolonized later from seawater.

The organism was formerly known as Vibrio fischeri, but genetic classification placed it in the genus Aliivibrio. This species is widely used to study bacterial communication, symbiosis, and bioluminescence. Its quorum-sensing system became a classic example of bacteria coordinating group behavior.