Succession of cable bacteria and electric currents in marine sediment

Abstract

Filamentous Desulfobulbaceae have been reported to conduct electrons over centimetre-long distances, thereby coupling oxygen reduction at the surface of marine sediment to sulphide oxidation in sub-surface layers. To understand how these 'cable bacteria' establish and sustain electric conductivity, we followed a population for 53 days after exposing sulphidic sediment with initially no detectable filaments to oxygen. After 10 days, cable bacteria and electric currents were established throughout the top 15 mm of the sediment, and after 21 days the filament density peaked with a total length of 2 km cm À 2 . Cells elongated and divided at all depths with doubling times over the first 10 days of o20 h. Active, oriented movement must have occurred to explain the separation of O 2 and H 2 S by 15 mm. Filament diameters varied from 0.4-1.7 lm, with a general increase over time and depth, and yet they shared 16S rRNA sequence identity of 498%. Comparison of the increase in biovolume and electric current density suggested high cellular growth efficiency. While the vertical expansion of filaments continued over time and reached 30 mm, the electric current density and biomass declined after 13 and 21 days, respectively. This might reflect a breakdown of short filaments as their solid sulphide sources became depleted in the top layers of the anoxic zone. In conclusion, cable bacteria combine rapid and efficient growth with oriented movement to establish and exploit the spatially separated half-reactions of sulphide oxidation and oxygen consumption.

Anodes Stimulate Anaerobic Toluene Degradation via Sulfur Cycling in Marine Sediments

“…The same families (Desulfobulbaceae and Desulfobacteraceae) have been reported previously to be enriched on anodes during bioelectrochemical benzene degradation in sulfide-rich groundwater (21). Organisms related to Desulfobulbus propionicus were able to produce current in sulfide-rich marine sediment (64,65). Similarly, in our work, organisms from the family Desulfobulbaceae were found at significantly higher relative abundances in the microbial communities of the anodic biofilms than in those of the bulk anolyte.…”

Rapid Redox Signal Transmission by “Cable Bacteria” beneath a Photosynthetic Biofilm

“…To confirm the presence of the cable bacteria, catalyzed reporter deposition-fluorescence in situ hybridization (CARD-FISH) was performed, using the oligonucleotide probe DSB706 (7). Detailed methods are given in Malkin et al (8), with the modification that preservation of the sediment samples was accomplished by addition of ethanol to a final concentration of 50%.…”

“…Close microscopic examination of sediments exhibiting this geochemical signature revealed that long filamentous bacteria belonging to the family Desulfobulbaceae were associated with the long-distance electron transport (6,7). These so-called "cable bacteria" have been observed to exceed 8 mm in length and are thought to span the entire suboxic zone (6,7). Perturbation experiments further suggested that cable bacteria were directly implicated in the longdistance electron transport (6).…”

“…In sediments with high rates of sulfate reduction, all detectable free sulfide can be removed by this process from a suboxic zone up to about 30 mm (5,7,8). Moreover, electrogenic sulfur oxidation appears to be competitively successful over other microbial sulfur oxidation strategies in laboratory experiments when organic-rich coastal sediments are incubated with oxygenated overlying water (5, 9).…”

“…This novel microbial lifestyle enabling sulfur oxidation by long-distance electron transport can be distinguished by a distinct geochemical fingerprint of microsensor depth profiles (5). Close microscopic examination of sediments exhibiting this geochemical signature revealed that long filamentous bacteria belonging to the family Desulfobulbaceae were associated with the long-distance electron transport (6,7). These so-called "cable bacteria" have been observed to exceed 8 mm in length and are thought to span the entire suboxic zone (6,7).…”