Long-distance electron transport occurs globally in marine sediments

Recently, long filamentous bacteria have been reported conducting electrons over centimetre distances in marine sediments. These so-called cable bacteria perform an electrogenic form of sulfur oxidation, whereby long-distance electron transport links sulfide oxidation in deeper sediment horizons to oxygen reduction in the upper millimetres of the sediment. Electrogenic sulfur oxidation exerts a strong impact on the local sediment biogeochemistry, but it is currently unknown how prevalent the process is within the seafloor. Here we provide a state-of-the-art assessment of its global distribution by combining new field observations with previous reports from the literature. This synthesis demonstrates that electrogenic sulfur oxidation, and hence microbial long-distance electron transport, is a widespread phenomenon in the present-day seafloor. The process is found in coastal sediments within different climate zones (off the Netherlands, Greenland, the USA, Australia) and thrives on a range of different coastal habitats (estuaries, salt marshes, mangroves, coastal hypoxic basins, intertidal flats). The combination of a widespread occurrence and a strong local geochemical imprint suggests that electrogenic sulfur oxidation could be an important, and hitherto overlooked, component of the marine cycle of carbon, sulfur and other elements.