Cable bacteria are filamentous bacteria, found in aqueous sediments, which form chains that conduct electricity. They transfer electrons across distances over 1cm (poss. more) in sediment and groundwater aquifers. They enable the reduction of oxygen and/or nitrates at the sediment's surface to the oxidation of sulphides in the deeper, oxygen-free, sediment layers. Their electrical activity is predicted to have profound impacts on mineral deposition - and they very probably play an important role in maintaining marine ecosystems in coastal areas. Laboratory cultures have shown that there can be more than 2km of conductive 'cables' in a single cubic cm. of sediment. 1)
“Long-distance electrical conductance in sediment was first observed in 2010 as a spatial separation of sulfide oxidation and oxygen reduction in marine sediment that was interrupted and re-established at a rate faster than could be explained by chemical diffusion. It was later found that this electrical conductance could be observed across a non-conductive layer of glass microspheres, where the only possible conductive structures were filamentous bacteria belonging to the family Desulfobulbaceae.”
The exact mechanisms by which the chains of bacteria conduct electricity are under investigation. How they evolved is currently unexplained.