Chemolithotrophy and Autotrophy

Chemolithotrophic microbes conserve energy from the oxidation of inorganic compounds, and many also fix carbon dioxide autotrophically, a combination that supports life in environments devoid of organic matter.

Definition

Chemolithotrophy is a mode of metabolism in which inorganic compounds serve as electron donors for energy conservation, and autotrophy is the use of inorganic carbon, typically carbon dioxide, as the principal carbon source for biosynthesis.

Scope

This topic covers the oxidation of inorganic electron donors such as hydrogen, reduced sulfur and nitrogen compounds, and ferrous iron; the energetics and ecology of nitrification, sulfur oxidation, and related processes; and the autotrophic pathways, including the Calvin cycle, by which inorganic carbon is converted into cell material. It highlights metabolic capabilities largely restricted to prokaryotes.

Core questions

• Which inorganic compounds can serve as microbial energy sources?
• How is energy conserved from inorganic oxidations?
• How do autotrophs fix carbon dioxide into cell material?
• Why are chemolithotrophs important in biogeochemical cycles?

Key concepts

• Inorganic electron donors
• Nitrification and sulfur oxidation
• Autotrophic carbon fixation
• The Calvin cycle and alternative fixation pathways
• Role in biogeochemical cycles

Key theories

Chemolithotrophy

Winogradsky established that certain microbes obtain energy by oxidizing inorganic compounds rather than organic matter, demonstrating a mode of life independent of preformed organic carbon and central to elemental cycling.

Mechanisms

Chemolithotrophs oxidize inorganic donors such as hydrogen, ammonia, nitrite, sulfide, or ferrous iron, channeling the released electrons through transport chains to generate a proton motive force for ATP synthesis. Because many such organisms cannot use organic carbon, they fix carbon dioxide through autotrophic pathways such as the Calvin cycle, which requires substantial energy and reducing power supplied by their inorganic metabolism.

Clinical relevance

Chemolithotrophic and autotrophic microbes drive key steps of the nitrogen, sulfur, and iron cycles, contribute to soil fertility and to the corrosion and weathering of materials, and sustain ecosystems at deep-sea vents and other settings without sunlight or organic input.

History

Sergei Winogradsky discovered chemolithotrophy in the 1880s through studies of sulfur- and nitrogen-oxidizing bacteria, introducing the concept of microbes that live on inorganic energy sources and founding the field of microbial ecology alongside Martinus Beijerinck.

Key figures

• Sergei Winogradsky
• Martinus Beijerinck

Seminal works

• madigan2018
• willey2020

Frequently asked questions

Are all chemolithotrophs also autotrophs?

Many are, fixing carbon dioxide for biosynthesis, but the two traits are distinct. Chemolithotrophy refers to the energy source (inorganic compounds), while autotrophy refers to the carbon source (inorganic carbon). Some organisms combine them and others do not.