How to Glow in the Dark: Squid Style

Bioluminescence* has been witnessed in all kingdoms of life, from fungi to plants to bacteria, however the origins of it are not yet well understood. This beautiful phenomenon is best witnessed in the depths of the ocean, at more than 1000m, where no sunlight can be found, meaning the only light to penetrate the complete darkness is that of bioluminescent creatures.

Cephalopods, which are a group of organisms including squid and octopus, can be founding spanning all depths of the earth’s oceans, but many species have chosen to occupy the darkest depths which has led them to develop bioluminescent characteristics.

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This somewhat crazy characteristic comes with a multitude of uses. It can enable the organism to become camouflaged in its surroundings, mimic other species to avoid predation and can be used in defence such as to startle another organism.

So, back to the origin of these glow in the dark creatures. A recent study has traced the origin of the gene responsible for bioluminescence in cephalopods to a bacterium known as Vibrio fischeri.

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Vibrio fischeri (in a petri dish)

 This tiny bacterium lives in a relationship with the cephalopod which is known as ‘symbiotic’. Essentially this means that they live closely together and regularly interact, whether this be in a positive, negative or neutral way for either party involved.

Vibrio fischeri originally had the gene for bioluminescence known as Reflectin. It is thought that the reflectin gene may have become part of the cephalopod through horizontal gene transmission* from the bacteria into an ancient cephalopod.

The reflectin proteins are able to assemble themselves into blocks and then these are grouped together in the cephalopods skin to allow them to rapidly change colour and emit light under a variety of different circumstances.

We may not know the origin of bioluminescence in every creature we see it in, but it seems we now have quite a good idea of how it came about in our tentacled ocean friends and who knows, maybe it’ll help to take us one step closer to being able to glow ourselves some day…

 

Glossary
Bioluminescence*
The biochemical emission of light by living organisms
Horizontal Gene Transfer*
Movement of genetic material from one organism to another, usually between a single celled organism such as a bacterium and a multicellular organism such as a mammal.

Source
Origin of the Reflectin Gene and Hierarchical Assembly of Its Protein (Guan et al, 2017). 

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