Lithoautotrophs

Lithoautotrophs are organisms that derive energy from the oxidation of inorganic molecules and fix carbon dioxide to synthesize organic biomass. The term combines litho (inorganic minerals) with auto (self-sustaining carbon fixation). They are a subset of chemolithoautotrophs and can inhabit environments with little or no organic carbon.

Energy sources for lithoautotrophs include hydrogen gas, reduced sulfur compounds (such as hydrogen sulfide and thiosulfate), ferrous iron, and, in some cases, ammonia or nitrite. Electron donors are inorganic, which distinguishes lithoautotrophs from photoautotrophs that rely on light for energy.

Carbon fixation pathways among lithoautotrophs vary. The Calvin cycle is common in many bacteria, while some archaeal and bacterial lineages use the reverse tricarboxylic acid (rTCA) cycle, the reductive acetyl-CoA (Wood–Ljungdahl) pathway, or the hydroxypropionate cycle.

Habitats for lithoautotrophs include deep-sea hydrothermal vents, cold seeps, iron- or sulfur-rich springs, acid mine drainage environments, and subsurface rocks. They form the base of primary production in dark ecosystems and contribute to global biogeochemical cycles of carbon, sulfur, and nitrogen.

Notable examples include sulfur-oxidizing bacteria such as Thiobacillus and Acidithiobacillus; iron-oxidizers like Leptospirillum and Mariprofundus; and hydrogen-oxidizing bacteria and nitrifying bacteria. Research on lithoautotrophs informs our understanding of early life on Earth and the potential for life on other rocky planets.