Cable bacteria can respire electrodes without oxygen and grow about as fast as they do in air

What happened

Cable bacteria are filamentous, sulphide-oxidising bacteria that carry electrons along conductive fibres over centimetre distances in sediment, normally to reach oxygen. The researchers show that the freshwater species Electronema aureum GS can instead pass electrons to insoluble acceptors outside the cell when no oxygen is present, and that it grows at rates comparable to aerobic respiration when doing so.

Electrochemical and molecular analyses indicate two routes to an electrode: direct transfer, and transfer mediated by riboflavin, which accumulated in the bioelectrochemical systems. Transfer worked even at +600 mV versus Ag/AgCl, a redox potential the authors call unusually high for electroactive bacteria. They identified two cell-surface redox components that are metal-dependent, pH-sensitive and heat-labile, consistent with outer-membrane cytochromes.

Why it matters

Cable bacteria were known for long-distance conduction to oxygen. Finding that one species can also respire solid surfaces without oxygen reveals a respiratory flexibility, and widens the picture of how these organisms conserve energy where redox conditions keep changing.

Caveats

This entry is based on the abstract. The results concern a single freshwater species in laboratory bioelectrochemical systems. The surface redox components are described as consistent with cytochromes, not identified as specific proteins.