Long-distance electron transport occurs globally in marine sediments

Abstract

<p><strong>Abstract.</strong> Recently, long filamentous bacteria have been reported to conduct electrons over centimetre distances in marine sediments. These so-called cable bacteria perform a novel "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 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 literature. This synthesis demonstrates that electrogenic sulfur oxidation mediated by long-distance electron transport is a widespread phenomenon in the present-day seafloor. The process is found in different oceanographic regions and climate zones (The Netherlands, Greenland, USA, Australia), and thrives in 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.</p>

Cable bacteria promote DNRA through iron sulfide dissolution

“…As the relative rates of DNRA and denitrification are of global interest as global N loads increase (Gruber and Galloway ; Conley et al ; Steffen et al ), understanding the conditions under which DNRA may be enhanced (or denitrification suppressed) is critical. If cable bacteria are significantly enhancing DNRA, then the stable, seasonally hypoxic systems most closely associated with cable bacteria (Malkin et al ; Seitaj et al ; Burdorf et al , ; Nielsen ) may become more N‐recycling during the seasonal cable bacteria dominance. This is particularly interesting as the Fe‐cycling associated with cable bacteria has been shown to buffer against euxinia (Seitaj et al ).…”

“…This site is usually located in the salt wedge of the estuary, and is characterized by periodical hypoxia in the bottom waters during low rainfall, combined with aphotic sediments due to the high turbidity of the overlying freshwater layer (Roberts et al ). The site has been used previously for studies of the fate of nitrate during nitrate reduction (Roberts et al , ) and investigation of the sediment has shown an in situ population of cable bacteria (Burdorf et al ).…”

“…Cores were incubated in 10 L of oxygenated site water for approximately 3 weeks (with a maximum of 24 cores per bath). Three weeks was chosen as a time where we expect significant cable bacteria activity based on typical dynamics observed in Yarra River and other sediments (Burdorf et al ). Table shows the details of the nitrate reduction experiments performed.…”

“…As a result of long‐distance electron transfer, cable bacteria generate electric fields, which can be measured as an increase in electric potential (EP) with depth (Damgaard et al ). This electrogenic sulfur oxidation (e‐SOx) is potentially widespread, with cable bacteria discovered in marine systems across the globe (Malkin et al ; Burdorf et al , ), and more recently in aquifers (Muller et al ) and freshwater sediments (Risgaard‐Petersen et al ).…”

The life sulfuric: microbial ecology of sulfur cycling in marine sediments

“…The cable bacteria belong to the family Desulfobulbaceae of the Deltaproteobacteria and are currently represented by two candidate Genera , Candidatus Electronema and Candidatus Electrothrix (Trojan et al ., ). The cable bacteria are widespread in shallow marine sediments (Risgaard‐Petersen et al ., ; Malkin et al ., ; Burdorf et al ., ). In situ mass developments of cable bacteria have been documented in a seasonally hypoxic marine basin in the Netherlands (Grevelingen) (Seitaj et al ., ).…”