There's a new squid in town, and it promises to be a novel and important biomedical model, says Roger Hanlon,director of the MBL's Marine Resources Center. For the first time outside of Hawaii, MRC scientists have successfully cultured this squid, a Hawaiian species called Euprymna scolopes, throughout its life cycle, paving the way for its use as a model research system.

What interests scientists most about Euprymna is not its nerve cell (which, in the local Woods Hole squid Loligo, has intrigued neurobiologists for decades) but the animal's unique symbiosis with the luminous marine bacterium Vibrio fischeri. Vibrio enjoys a mutually beneficial relationship with Euprymna, living within the large light organ found in the squid's mantle cavity. Although scientists are still mystified by the squid-bacterium relationship, they do know that Vibrio produces 1000 times more light when living within the squid's light organ than it does when cultured outside of the organism. Scientists believe that the light produced by Vibrio within the light organ may help disguise the squid, through a light-diffusing behavior known as counterillumination, from predators swimming below them. How the bacterium benefits from its relationship with the squid remains unclear, although studies show that this symbiosis does have an effect on Vibrio's growth rate and life cycle.

Scientists, including Paul Dunlap of the Woods Hole Oceanographic Institution and Margaret McFall-Ngai and Ned Ruby of the University of Southern California, believe that understanding how this curious symbiosis works will have a biomedical benefit for human health as well. Although the species of bacterium living within Euprymna is harmless, many species of Vibrio are not. In fact, some species of VibriO, including the one that causes cholera and the species that causes paralytic shellfish poisoning, can be deadly. Understanding how the Euprymnal Vibrio symbiosis works will provide scientists with information about how bacteria and other microbesÑwhether harmless or pathogenicÑare able to recognize and colonize specific tissues in its host.

Scientists' ability to develop this model has been enhanced considerably, thanks to the MRC's recent success in culturing Euprymna from egg to egg. Now investigators can study both the squid and the bacterium in culture separately to learn how each organism functions independently of the other, as well as how they live successfully together as a symbiotic pair.