Photobacterium phosphoreum

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

Source: Wikipedia — Photobacterium phosphoreum (CC BY-SA 4.0)