Lithoautotrophic

Lithoautotrophic refers to organisms that derive energy by oxidizing inorganic compounds (litho-) and use carbon dioxide or bicarbonate as their sole carbon source (autotrophic). They are chemoautotrophs that rely on inorganic electron donors rather than organic nutrients. Lithoautotrophs occupy diverse environments, from deep-sea hydrothermal vents to acidic mine drainage and rock surfaces, and they form the base of primary production in ecosystems where light is scarce or absent.

Energy metabolism involves the oxidation of inorganic substrates such as molecular hydrogen (H2), reduced sulfur compounds (H2S, S0, thiosulfate), ferrous iron (Fe2+), or ammonia (NH3). The electrons released are transferred to terminal acceptors, commonly oxygen in aerobic lithoautotrophy or nitrate, sulfate, or ferric iron in anaerobic variants. The captured energy powers the fixation of CO2 via pathways such as the Calvin cycle, the reverse tricarboxylic acid cycle, or the Wood-Ljungdahl pathway.

Ecology and importance: Lithoautotrophs contribute to biogeochemical cycles—carbon, sulfur, nitrogen, and iron—and support communities in dark environments and harsh conditions. They are essential for applications such as bioleaching, bioremediation, and primary production in ecosystems without photosynthesis.

Taxonomy and examples: Bacteria and archaea include ammonia-oxidizing bacteria (e.g., Nitrosomonas), sulfur-oxidizing bacteria (e.g., Thiobacillus and Thiomicrospira), iron-oxidizing bacteria (e.g., Acidithiobacillus), and hydrogen-oxidizing species, as well as several archaeal groups such as Sulfolobales. These organisms illustrate the diversity of lithoautotrophy.

Comparison: Lithoautotrophs use inorganic electron donors for energy, unlike photoautotrophs that rely on light, and unlike chemoorganoautotrophs that use organic electron donors.