Na(+) as coupling ion in energy transduction in extremophilic Bacteria and Archaea

For microorganisms to live under extreme physical conditions requires important adaptations of the cells. In many organisms the use of Na(+) instead of protons as coupling ion in energy transduction is associated with such adaptation. This review focuses on the enzymes that are responsible for the generation and utilization of Na(+) gradients in extremophilic microorganisms. Aspects that are dealt with include: bioenergetics and ion homeostasis in extremophilic Bacteria and Archaea; the molecular mechanism of Na(+) translocation; and (dis)advantages of Na(+) as coupling ion in energy transduction.