Sulfur metabolism

Sulfur is metabolized by all organisms, from bacteria and archaea to plants and animals. Sulfur is reduced or oxidized by organisms in a variety of forms. The element is present in proteins, nucleic acids, sulfate esters of polysaccharides, steroids, phenols, and sulfur-containing coenzymes.

Reduced sulfur compounds are oxidized by most organisms, including higher animals and higher plants. Some organisms can conserve energy (i.e., produce ATP) from the oxidation of sulfur. Sulfur is the sole energy source for some lithotrophic bacteria and archaea. Reduced sulfur compounds, such as hydrogen sulfide, elemental sulfur, sulfite, thiosulfate, and various polythionates (e.g., tetrathionate), are used by various lithotrophic bacteria and are all oxidized by Acidithiobacillus.

Sulfur oxidizers utilize enzymes such as sulfur oxygenase and sulfite oxidase to oxidize sulfur compounds to sulfate. Lithotrophs that can produce sugars through chemosynthesis make up the base of some food chains. Food chains have formed in the absence of sunlight around hydrothermal vents, which emit hydrogen sulfide and carbon dioxide. Chemosynthetic archaea use hydrogen sulfide as an energy source for carbon fixation, producing sugars.

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