How do chemoautotrophic bacteria make food without sunlight?

Chemoautotrophic bacteria, or chemosynthetic organisms, produce their own food without sunlight by deriving energy from the oxidation of inorganic chemical compounds. Instead of relying on light, these bacteria utilize inorganic substances—such as hydrogen sulfide, ammonia, hydrogen gas, or ferrous ions—as electron donors.123

By oxidizing these chemicals, the bacteria generate the energy necessary to drive their metabolism and fix carbon dioxide into organic compounds, such as sugars and other cell constituents. This process is often facilitated by metabolic pathways like the Calvin cycle, which allows the bacteria to convert energy-poor carbon dioxide into energy-rich organic matter.32

In ecosystems such as deep-sea hydrothermal vents, these bacteria serve as the primary producers. They support diverse communities of organisms, including mussels and worms, either as free-living populations or through symbiotic relationships, effectively replacing the role that plants and algae play in sunlit environments.1