Photobacterium phosphoreum is a Gram-negative, bioluminescent bacterium living in symbiosis with deep-sea marine organisms, such as anglerfish.

[1] It can emit bluish-green light (490 nm) due to a chemical reaction between FMN, luciferin and molecular oxygen catalysed by an enzyme called luciferase.

P. phosphoreum appears to be distributed worldwide in oceans and is found in a variety of different marine habitats.

P. phosphoreum colonizes a wide variety of deep-sea fishes which generally occur in the mesopelagic and bentho-pelagic zones.

[1] P. phosphoreum is the most frequently used luminescent bacterium in water quality assessment.