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- 2Biology of sulfur and disulfide respiration
- 3Chemistry of elemental sulfur, polysulfide, and organic disulfides
- 4Polysulfide as a possible intermediate of sulfur respiration
- 5Sulfur respiration of Wolinella succinogenes
- 6Sulfur respiration in hyperthermophilic archaea
- 7Disulfide respiration in methanogenic archaea
Anaerobic respiration with elemental sulfur/polysulfide or organic disulfides is performed by several bacteria and archaea, but has only been investigated in a few organisms in detail. The electron transport chain that catalyzes polysulfide reduction in the Gram-negative bacterium Wolinella succinogenes consists of a dehydrogenase (formate dehydrogenase or hydrogenase) and polysulfide reductase. The enzymes are integrated in the cytoplasmic membrane with the catalytic subunits exposed to the periplasm. The mechanism of electron transfer from formate dehydrogenase or hydrogenase to polysulfide reductase is discussed. The catalytic subunit of polysulfide reductase belongs to the family of molybdopterin-dinucleotide-containing oxidoreductases. From the hyperthermophilic archaeon Pyrodictium abyssi isolate TAG11 an integral membrane complex has been isolated which catalyzes the reduction of sulfur with H2 as electron donor. This enzyme complex, which is composed of a hydrogenase and a sulfur reductase, contains heme groups and several iron-sulfur clusters, but does not contain molybdenum or tungsten. In methanogenic archaea, the heterodisulfide of coenzyme M and coenzyme B is the terminal electron acceptor of the respiratory chain. In methanogens belonging to the order Methanosarcinales, this respiratory chain is composed of a dehydrogenase, the membrane-soluble electron carrier methanophenazine, and heterodisulfide reductase. The catalytic subunit of heterodisulfide reductase contains only iron-sulfur clusters. An iron-sulfur cluster may directly be involved in the reduction of the disulfide substrate.