Anoxygenic photosynthesis

Anoxygenic photosynthesis converts light energy into chemical energy using electron donors other than water, so it does not release oxygen.

Bacteriochlorophyll: A family of photosynthetic pigments that absorbs light in many anoxygenic phototrophs. Its light absorption drives the reaction centers used by many anoxygenic phototrophs.
Hydrogen sulfide: A colorless, toxic gas with the chemical formula H₂S that can serve as an electron donor. Sulfur bacteria oxidize it instead of splitting water for photosynthetic electrons.
Great Oxidation Event: A major rise in atmospheric oxygen beginning about 2.4 billion years ago. Oxygenic photosynthesis transformed an atmosphere previously shaped by oxygen-free metabolisms.
Microbial fuel cell: An electrochemical device in which microorganisms help convert chemical energy into electrical energy. Researchers investigate anoxygenic phototrophs as light-responsive components in bioelectrochemical systems.
Sulfur cycle: The movement and transformation of sulfur through organisms, rocks, water, and the atmosphere. Oxidation of sulfide by anoxygenic phototrophs links light capture to sulfur transformations.
Photosynthetic reaction center: A pigment-protein complex that converts absorbed light into charge separation and initiates electron transfer. Its architecture determines how anoxygenic cells harvest light and move electrons.
Elemental sulfur: A naturally occurring form of sulfur with oxidation state zero. Some phototrophs deposit it when they oxidize hydrogen sulfide.
Archean Eon: A geological eon lasting from about 4.0 to 2.5 billion years ago. Anoxygenic phototrophy likely operated in Earth's largely oxygen-poor early environments.
Photobiological hydrogen production: The production of hydrogen gas by light-driven biological processes. Some anoxygenic phototrophs can generate hydrogen under suitable conditions.
Carbon cycle: The movement of carbon among living organisms, the atmosphere, oceans, and Earth's crust. Anoxygenic phototrophs can fix carbon and influence local carbon flows.

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