Fig. 4.

Schematic representation of the energy metabolism of a cable bacterium. The cells in the suboxic and sulfidic zone (red) perform anodic H₂S oxidation. The free energy released by this redox half-reaction is utilized for generating ATP, thus allowing the assimilation of carbon and nitrogen, while the generated electrons are transported toward cells in the oxic zone via conductive fibers in the shared periplasmic space. Cells in the oxic zone (blue) utilize these electrons to perform cathodic O₂ reduction, but this results in very little to no release of free energy and hence no capacity to assimilate carbon and ammonia.