Chemoautotrophe

Chemoautotrophs, also called chemolithoautotrophs, are organisms that obtain energy by oxidizing inorganic compounds and use carbon dioxide as their primary carbon source. They are distinct from photoautotrophs, which rely on light energy to fix carbon. In chemoautotrophy, energy comes from redox reactions involving inorganic electron donors such as ammonia, nitrite, hydrogen sulfide, elemental sulfur, ferrous iron, or molecular hydrogen. The captured energy drives the fixation of CO2 into organic matter via carbon fixation pathways that can include the Calvin cycle, the reverse tricarboxylic acid cycle, or other autotrophic routes.

Chemoautotrophs occupy a wide range of environments, particularly those devoid of sunlight. They are key primary producers in deep-sea hydrothermal vent communities, cold seeps, acidic springs, and many subsurface or terrestrial habitats. By converting inorganic carbon into biomass, they form the base of microbial food webs and contribute to global biogeochemical cycles of carbon, nitrogen, sulfur, and iron.

Representative groups include nitrifying bacteria, such as Nitrosomonas (ammonia-oxidizing) and Nitrobacter (nitrite-oxidizing); sulfur-oxidizing bacteria like Thiomicrospira and Thiomargarita namibiensis; and iron-oxidizing bacteria such as Acidithiobacillus ferrooxidans. Archaea also include chemoautotrophs, for example some Sulfolobus and Ferroplasma species. Some microorganisms can switch between lithotrophic and heterotrophic metabolisms depending on environmental conditions.

Overall, chemoautotrophs are a diverse and ecologically important group that enables life in environments where light cannot sustain photosynthesis, and they play a major role in cycling essential elements.