[34] Hydrogen-sulfur oxidoreductase complex from Pyrodictium abyssi

Sulfur plays an important role in the metabolism of many hyperthermophilic archaea. The obligate heterotrophic strains of Pyrococcus and Thermococcus grow on organic compounds. In the presence of elemental sulfur (S°), or polysulfides, H2S is formed. Chemolithoautotrophic archaea such as Pyrodictium utilize the redox couple H2/S° as an energy-yielding reaction. The genus Pyrodictium comprises the three species P. occultum, P. brockii, and P. abyssi. Although the growth of P. occultum and P. brockii is stimulated by yeast extract, both species are strictly dependent on H2 and are able to grow by H/S ° autotrophy. In contrast, P. abyssi (type strain AV2) is an obligate heterotroph growing anaerobically by the fermentation of proteins. This chapter reports the purification and characterization of an extremely thermostable, membrane-bound, sulfur-reducing enzyme complex isolated from the P. abyssi isolate TAG11. It is proposed to contain the entire electron transport chain required for the reduction of S° with H2 to H2S, including a hydrogenase, a sulfur reductase, and electron-transferring components.