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Updated by Kiara Govender on Sep 22, 2023
Headline for Let there be light - Aliivibrio fischeri
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Let there be light - Aliivibrio fischeri

My adopted bacterium that I am so proud to share is called Aliivibrio fischeri.
My bacterium has bioluminescent properties which allows it to glow in the dark ! and is also controlled by quorum sensing.
My friendly bacterium is found in symbiosis with many marine animals.
My bacterium also provides a quick and cost effective method for testing toxicity.

Gram-negative, rod-shaped Aliivibrio fischeri

Aliivibrio fischeri are motile, gram- negative, rod-shaped bacteria.

Aliivibrio fischeri

My bacterium, Aliivibrio fischeri, showing off its yellowish-green pigment

Aliivibrio fischeri

Aliivibrio fischeri - formerly known as Vibrio fischeri - are yellow bacteria found in marine environments around the world. Free-living A. fischeri survive on decaying organic matter and use flagella as a means of movement. You are most likely to find these bioluminescent bacteria hitching a ride with marine animals such as the Hawaiian bobtail squid (Euprymna scolopes). A. fischeri have symbiotic relationships with a number of marine animals where they provide bioluminescence in exchange for an environment to grow in and nutrients to feed on (for a day).

Aliivibrio fischeri Toxicity Tests (formerly Vibrio Fischeri)

One important method for assessing toxicity quickly and cost effectively is a bioluminescence inhibition assay that employs a marine gram negative bacterium, Aliivibrio fischeri (formerly Vibrio fischeri) as the test species. Light production is directly proportional to the metabolic activity of the bacterial population, and any inhibition of enzymatic activity due to toxicity or cell death causes a corresponding decrease in the bioluminescence produced by the colony. Test samples are exposed to rehydrated bacteria for a pre-determined period and the degree of light emission inhibition is compared to a negative control. In this way, the assay provides a measure of sub-lethal response as well as lethality through the degree of inhibition.

The bioluminescence of A. fischeri

The bioluminescence of A. fischeri is caused by transcription of the lux operon, which is induced through population-dependent quorum sensing.[2] The population of A. fischeri needs to reach an optimal level to activate the lux operon and stimulate light production. The circadian rhythm controls light expression, where luminescence is much brighter during the day and dimmer at night, as required for camouflage.

File:Bacterial Quorum Sensing.png - Wikimedia Commons

Model of quorum sensing in Vibrio fischeri. LuxI produces Acyl Homoserine Lactone (AHL) which makes it possible for LuxR to bind the DNA 'Lux box'. However a high concentration of AHL is required for LuxR-Lux box binding. This is achieved in the squid Vibrio fischeri's light organ. LuxR-Lux box binding activates luciferase genes (luxICDABEG), producing bioluminescent molecules and even more AHL.

Astrosquid!

Off the coast of Hawaii lives a cunning nocturnal hunter with a brilliant trick up its sleeve. Or rather its mantle. Meet the Hawaiian Bobtail squid. The Hawaiian bobtail squid is one organism that plays host to A. fischeri. In exchange, the squid use the bacteria’s bioluminescence to attract prey, deter predators, and communicate with other squid.