3月JJ背景 Hawaii bobtailed squid

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Squid’s bacteria give hope for cures
UH researchers study the relationship between a squid and its symbiotic luminescent bacteria

The bobtailed squid is showing University of Hawaii researchers how bacteria interact with animal tissues -- findings that could eventually be applied to human medicine.

They are studying the relationship between the squid and its symbiotic partner, a luminescent bacteria known as Vibrio fischeri.

It is a curious situation because the squid hatches without bacteria, said Spencer Nyholm, graduate assistant leading the work in the Pacific Biomedical Research Center.

It picks it up from sea water. But Vibrio fischeri makes up less than one-tenth of 1 percent of all bacteria in surrounding water, he said. "It's like pulling a needle out of a haystack when the squid is colonized by bacteria."

Investigating the mechanism with Nyholm were postdoctoral researcher Eric Stabb and professors Edward Ruby and Margaret McFall-Ngai. Their findings were published in the recent Proceedings of the National Academy of Sciences, available at www.pnas.org.

The team discovered that the squid uses cilia, little hairlike structures that move food particles, to initiate the relationship.

The appendages beat in unison and create microcurrents that draw sea water near the site where bacteria infect, Nyholm said. The squid secretes a mucuslike substance that forms a matrix suspended from its light organ.

The bacteria aggregate in the matrix, then migrate to the squid's light organ and colonize crypt spaces within it.

In human infection in cystic fibrosis, Nyholm said, patients typically produce a lot of thick mucus in their lungs, and bacteria infect the mucus.

"Here we have an example of being able to colonize an animal through mucus. We're not saying there is a direct link, but in the future it may be possible to use the squid as a model for studying diseases like that."

Habitating the light organ on the squid's underside, Vibrio fischeri produce light, and squid use it as a type of camouflage known as "counter-illumination," Nyholm said.

The light is used to break up a shadow that might be cast by moonlight and starlight so predators below cannot look up and see the squid, he said.

He said the group now wants to look for genes in bacteria that might be involved specifically with colonizing the light organ and using the mucus to attach to the squid cells.

"There's a big problem in medicine," Nyholm said. "It basically focuses on bacteria that cause disease. Yet all animals, including humans, have a very large percentage of their bodies colonized by beneficial bacteria."

Studies focus on how disease-causing bacteria interact with animals, Nyholm said. "We don't understand the normal state of affairs, how they interact with animals."

In humans, he pointed out, 90 percent of cells in the body belong to bacteria mainly living in intestines. So 10 percent of the cells "make up what you'd normally think of as your body," he said.

Different types of Vibrio species might have implications in human medicine, he said. Vibrio cholerae, for example, might have implications for cholera. It does not infect squid but is related to Vibrio fischeri, he said.

University of Hawaii