Vibrio fischeri
Stephanie Maiden

Vibrio fischeri is a heterotrophic gram-negative bacteria found in temperate and subtropical waters. It has a bunch of polar flagella that assist it in moving. It is most famous for its bioluminescence. V. fischeri is routinely found in fish, and its bioluminescence is thought to not only explain a glow seen on decomposing fish, but also glowing fish sticks! This feature has been used to study toxicity of aquatic environments and helps protect certain symbionts.

V. fischeri’s bioluminescence has been found to be caused by five genes, luxCDABE, that are regulated by luxR and luxI. The emission of light happens from the oxidation of organic compounds. Differences in the amount of light produced can therefore be correlated to the organisms metabolism. This is how researchers use this bacteria to study water toxicity. The reduction of light emitted is proportional to the toxicity of the aquatic sample.

V. fischeri is most often found has a symbiont of Euprymna scolopes, a small shallow water squid found on the shores of Hawaii. This nocturnal feeder has a light organ that protects it from predators by eliminating its shadow caused by the moonlight above. The light from the light organ comes from the squid’s symbiosis with the bacteria. When the squid hatches it contains no symbionts. It must acquire them from the surrounding water in order to use its light organ. The presence of the bacteria influence the development of the host squid. Within several hours, the bacteria change. They decrease in size, lose their flagella, and emit light. In fact, they emit a thousand times more light inside the squid than they do otherwise! After several weeks, the squid’s light organ is fully developed. Then, every morning, the squid released 90% of the V. fischeri population in its light organ back into the water. This is probably done to insure that new hatches of squid have the bacteria available to them.

Even though this bacterium is also known to be pathogenic to some invertebrates, it is very useful to the Euprymna scolopes and researchers testing water samples. Another example of a helpful bacterium!


*Disclaimer - This report was written by a student participaring in a microbiology course at the Missouri University of Science and Technology. The accuracy of the contents of this report is not guaranteed and it is recommended that you seek additional sources of information to verify the contents.


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