HI squid

A Hawaiian bobtail squid. Photo by The Squid and Vibrio Labs

The small but charismatic Hawaiian bobtail squid is known for its predator-fooling light organ. To survive, the nocturnal cephalopod depends on a mutually beneficial relationship with the luminescent bacterium, Vibrio fischeri, which gives it the ability to mimic moonlight on the surface of the ocean, and deceive monk seals and other predators that would happily make a meal of the small creature.

A study published recently in Applied and Environmental Microbiology by Edward “Ned” Ruby, professor at the University of Hawaiʻi at Manoa’s Pacific Biosciences Research Center and colleagues from the University of Wisconsin–Madison revealed that Vibrio fischeri has a novel type of receptors that sense the presence and concentration of fatty acids, a building block of all cell membranes. This class of receptors allows a bacterium to migrate toward short-chain fatty acids — a phenomenon referred to as chemotaxis.

“This is the first example of a receptor for this class of compounds, and this receptor appears to have evolved in, and be restricted to, the Vibrionaceae family of marine bacteria,” Ruby said.

The language of bacteria

Sending and receiving chemical signals allow bacteria to communicate with other organisms, gather information about their environment and determine with whom to create a mutually beneficial partnership — a symbiosis. For example, the Hawaiian bobtail squid hatchlings aren’t born with Vibrio fischeri. They attract it, and only it, from the surrounding seawater using chemoattractants, and capture it in their light organs.

Capillary-tube chemotaxis assay. A tiny glass tube containing a concentrated solution of a chemoattractant (that is, a fatty acid) is placed into a suspension of motile Vibrio fischeri cells. Within a few minutes the bacteria have swum to the tip of the tube, where the concentration of the attractant is highest. The bright area is the cloud of bacteria accumulating around the tip. Photo by Edward Ruby, UH/ PBRC

Capillary-tube chemotaxis assay. A tiny g