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What role does oxygen play in bioluminescent chemical reactions?

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time-lapse photo of fireflies — Bioluminescence Time-lapse image of fireflies in the Catskill Mountains, New York. Firefly light is a cold light, with approximately 100 percent of the energy given off as light and only a minute amount as heat. Only light in the visible spectrum is emitted.

In bioluminescent chemical reactions, molecular oxygen acts as a critical oxidizing agent that facilitates the emission of light.12

The process generally involves the enzyme luciferase catalyzing the oxidation of a substrate called luciferin. In many organisms, such as fireflies, the reaction involves the formation of a complex that subsequently reacts with oxygen to liberate enough energy to shift the molecule into a high-energy excited state; as this complex returns to its ground state, it releases a photon of visible light. In bioluminescent bacteria, oxygen reacts with reduced flavin mononucleotide and luciferase to form an intermediate complex that eventually emits light upon reacting with an aldehyde.132

Beyond its role in light production, it has been suggested that bioluminescence may have originally evolved as a mechanism to remove oxygen that was toxic to primitive bacteria. In these early organisms, the metabolic consumption of oxygen through this reaction likely provided a survival advantage before such organisms developed more complex systems for utilizing oxygen.4