Bioenergetics theory and components: Periplasmic electron-transport systems in bacteria

The periplasmic compartment lies between the inner (cytoplasmic) and outer membranes of Gram-negative bacteria. It is frequently termed the ‘periplasmic space’, but this is a misnomer as the term ‘space’ suggests a void and the periplasmic compartment is far from that. In fact, it is a highly metabolically active compartment where many important respiratory electron-transfer proteins are located. In bacteria these periplasmic redox proteins result in a great respiratory diversity, as they can facilitate electron transfer between a range of electron donors (e.g., formate, hydrogen, reduced nitrogen species, and reduced sulfur species) and electron acceptors (e.g., nitrogen and sulfur oxyanions, dimethylsulfoxide, and trimethylamine N oxide). This underlies the success of bacteria in colonizing a wide range of the Earth׳s oxic and anoxic environments and the important contribution of bacteria to critical biogeochemical element cycles, such as the nitrogen, sulfur, and carbon cycles.