The Functional Complexity of [NiFe] Hydrogenases in Sulfate Reducing Bacteria (Genus; Desulforvibrio spp)

Abstract

Sulfate-reducing bacteria are categories of bacteria and archaea that can obtain energy by oxidizing organic compounds or molecular hydrogen (H2) while reducing sulfate (SO42−) to hydrogen sulfide (H2S). By analysis, these organisms "respire" sulfate rather than oxygen, a form of anaerobic respiration, the oxidation of hydrogen by the primary genus of Sulfate Reducing Bacteria (Desulfovibrio, Desulfovibrio desulfuricans) is catalyzed by enzymes called Hydrogenases. Three basic types of hydrogenases have been widely isolated from the primary genus of sulfate-reducing bacteria Desulfobibrio which differ in their structural subunits, metal compositions, physico-chemical characteristics, amino acid sequences, immunological activities, structural gene configuration and their catalytic properties. Broadly, hydrogenases can be considered as ‘iron containing hydrogenases and nickel-containing hydrogenases. The iron-sulfur-containing hydrogenase enzyme contains two ferredoxin-type (4Fe-4S) clusters and typical iron-sulfur center believed to be involved in the activation of H2 yet it is the most sensitive domain to CO and NO2−.eventhough it is not featured in all species of genus Desulfovibrio. The nickel-(iron-sulfur)-containing hydrogenases, [NiFe] hydrogenase posses two 4Fe-4S centers and one 3Fe-xS cluster in addition to nickel and have been found in all species of Desulfovibrio with strong resistance to CO and NO2- so far investigated. The genes encoding the large and small subunits of a periplasmic and membrane-bound species of the [NiFe] hydrogenase have been cloned in Escherichia coli and sequenced, however the functional complexity of the hydrogenase system remained unexplored as a result of the metabolic diversity in Desulfovibrio spp. The [NiFe] hydrogenase plays an important role in the energy metabolism of Desulfovibrio spp. Thus, the expression of the encoded structural genes would be an excellent marker for the metabolic functionalities under specific inducible environment.