Hawaiian Bobtail Squid Depends On Mutually Beneficial Relationship With Luminescent Bacterium

The deceptive Hawaiian bobtail squid is known for its predator-fooling light organ, which it uses to mimic moonlight and camouflage itself to the ocean's surface so that they can hide from monk seals and other predators. In order to accomlish this bit of hocus pocus, the small sea creatures depends on a mutually beneficial relationship with a luminescent bacterium called Vibrio fischeri. A recent study, led by researchers from the University of Hawaii at Manoa, investigates the evolution of this survival technique.

The team of researchers, in partnership with the University of Wisconsin - Madison (UWM), found the luminescent bacterium actually has unique receptors that essentially sense the presence and concentration of fatty acids – a building block of all cell membranes - in surrounding organisms. This phenomenon is known as chemotaxis, according to a news release.

"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," Edward Ruby, one of the study researchers and professor from the University of Hawaii, explained in the university's release.

The bacteria then communicate with other organisms using chemical signals, so that they can decide whom to create a mutually beneficial partnership with. This is also referred to as symbiosis and has been observed among many other species, too. It follows then Hawaiian bobtail squid hatchlings aren't born with Vibrio fischeri, and instead attract the bacterium from their surrounding environment using chemoattractants and capture it in their light organs.

All organisms, including humans, use chemotaxis to attract beneficial microbes to specific tissues, researchers say. Human infants, for example, do this when they are exposed to bacteria in their environment - they essentially signal to particular tissues (gut, skin, teeth, reproductive tract, ect.) that must be colonized by these harmless bacterium and defend against those that are harmful.

Hawaiian bobtail squid (Euprymna scolopes) is native to the shallow coastal waters of Hawaii in the Pacific Ocean. These nocturnal squids are relatively small sea creatures - measuring only 1.4 inches in length - that prefer to feed on crustaceans. Interestingly, a bobtail squid release 90 percent of its bioluminescent bacteria back into the ocean each morning so that the bacteria can replenish itself during the day. Then, when nighttime rolls around, the squid acquires a new crop of bacteria in its light organ to help it evade its ravenous predators.

Researchers plan to further test why Vibrio fischeri is the only bacterial species that can colonize the light organ of the squid. Their findings were recently published in the journal Applied and Environmental Microbiology.

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