The chemical reaction that is responsible for bio-luminescence is catalyzed by the enzyme luciferase. In the presence of oxygen, luciferase catalyzes the oxidation of an organic molecule called luciferin. Though bio-luminescence across a diverse range of organisms such as bacteria, insects, and dinoflagellates  function in this general manner (utilizing luciferase and luciferin), there are different types of luciferin-luciferase systems. For bacterial bio-luminescence specifically, the biochemical reaction involves the oxidation of an aliphatic aldehyde by a reduced flavin mononucleotide. The products of this oxidation reaction include an oxidized flavin mononucleotide, a fatty acid chain, and energy in the form of a blue-green visible light.
Reaction: FMNH + O + RCHO → FMN + RCOOH + HO + light