Sulfur Metabolism - Sulfur Reduction

Sulfur Reduction

Sulfur reduction occurs in plants, fungi, and many bacteria. Sulfate can serve as an electron donor in anaerobic respiration and can be reduced for the formation of organic compounds. Sulfate-reducing bacteria reduce sulfate and other oxidized sulfur compounds, such as sulfite, thiosulfate, and elemental sulfur, to sulfide. Sulfate reduction can be dissimilatory or assimilatory. Sulfate reduction by sulfate-reducing bacteria, for example, is dissimilatory; the purpose of reducing the sulfate is to produce energy, and the sulfide is excreted. Dissimilatory sulfate reduction utilizes the enzymes ATP sulfurylase, APS reductase, and sulfite reductase. In assimilatory sulfate reduction, however, the sulfate is assimilated, or incorporated into organic compounds. In some organisms (e.g., gut flora, cyanobacteria, and yeast), assimilatory sulfate reduction is a more complex process that makes use of the enzymes ATP sulfurylase, APS kinase, PAPS reductase, and sulfite reductase.