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University of Hawai'i |
(808) 956-8856 Telephone |
For Immediate Release: |
September 19, 2000 |
Contact: Professor Margaret McFall-Ngai, Pacific Biomedical Research
Center, University of Hawai'i at Manoa, (808) 539-7310, mcfallng@hawaii.edu
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E.scolopes, Photo by Margaret McFall-Ngai |
| New study reveals secret of squid-bacterial symbiosis |
Researchers from the University of Hawai'i Pacific Biomedical Research Center have discovered a unique symbiotic relationship between two sea organisms. Graduate assistant Spencer Nyholm, postdoctoral researcher Eric Stabb, and Professors Edward G. Ruby and Margaret McFall-Ngai figured out how the bobtailed squid manages to harvest its symbiotic partner, a luminescent bacterium known as Vibrio fischeri that makes up less than one-tenth of one percent of all the bacteria in the surrounding seawater. Their findings were published in one of last month's issues of the Proceedings of the National Academy of Sciences, which is available at www.pnas.org.
The symbiotic relationship between the two organisms is unusual. The paper, "Establishment of an animal-bacterial association: Recruiting symbiotic vibrios from the environment," is the first to document an invertebrate's use of cilia - tiny hair-like structures usually used to move food particles - and mucus to initiate such a relationship. Certain leguminous plants also secrete a mucus-like substance, or mucigel, as a means of capturing nitrogen-fixing bacteria with which they live symbiotically, suggesting that such mechanisms for facilitating symbiosis may be rather common. Furthermore, the mechanism described here may represent a widespread strategy of aquatic hosts to increase the likelihood of being colonized by rarely encountered symbiotic partners.
In exchange for "room and board" in the light organ located on the underside of the squid, the bacteria provide a light source that the relatively defenseless nocturnal squid uses to make itself invisible to predatory, bottom-dwelling fishes that would otherwise spot it as a dark blob against the brighter ocean surface.
The presence of Vibrio fischeri and similar kinds of bacteria in the seawater causes the squid to secrete a mucus-like substance, which forms a matrix tethered to and suspended below its light organ. Water currents created by fields of cilia draw the bacteria into this matrix. After accumulating in the matrix for several hours, the bacteria start migrating toward the pore of the light organ and colonizing the crypt within.
This work was supported by the National Science Foundation and the National
Institutes of Health.
