With his "Bestiary", Jeremie Brugidou brings bioluminescence into the light of nature

Once upon a time, there was a bacterium, Vibrio fischeri , and a small cuttlefish, Euprymna scolopes , from the Sepioladae family, living on the Hawaiian coasts. They do not love each other tenderly. Their union is of interest. Buried in the sand during the day, hunting at night, the cuttlefish feeds on crustaceans, annelids and fish. But it must protect itself from barracudas and the nasty Hawaiian monk seal. It does this by a very clever camouflage strategy. The animal emits, in fact, a luminosity from its ventral surface, the intensity of which it can, thanks to a complex optical device – the photophore – vary until it “corresponds perfectly to the ambient luminosity (in this case that produced by the moon on the surface)”, so that each time its body, opaque during the day, transforms at night into a luminous body, it appears and disappears at the same time, “melted” in the moonlight – and therefore invisible to the eye of seals and hawk-moths. This is a rather decent life for a cuttlefish. Except that without its companion, the bacterium, it would not have been able to lead it. At birth, in fact, Euprymna scolopes is not luminescent, and hardly has a photophore. As soon as it emerges from the egg, it must immediately receive external care, precisely the help of Vibrio fischeri : but how can we find this bacterium, "which represents less than 0.1 % of the total bacteria present in this environment, in the immensity of the sea that