These apparently ancient cells generate a proton gradient across a membrane (we’ll come to how they do that), reproducing exactly what alkaline hydrothermal vents provide for free. The proton gradient drives the acetyl CoA pathway, by way of an iron–sulphur protein embedded within the membrane – the energy-converting hydrogenase, or Ech for short. This protein funnels protons through the membrane on to another iron–sulphur protein, called ferredoxin, which in turn reduces CO2
