Cable Bacteria in Freshwater Sediments

Abstract

In marine sediments cathodic oxygen reduction at the sediment surface can be coupled to anodic sulfide oxidation in deeper anoxic layers through electrical currents mediated by filamentous, multicellular bacteria of the Desulfobulbaceae family, the so-called cable bacteria. Until now, cable bacteria have only been reported from marine environments. In this study, we demonstrate that cable bacteria also occur in freshwater sediments. In a first step, homogenized sediment collected from the freshwater stream Giber Å, Denmark, was incubated in the laboratory. After 2 weeks, pH signatures and electric fields indicated electron transfer between vertically separated anodic and cathodic half-reactions. Fluorescence in situ hybridization revealed the presence of Desulfobulbaceae filaments. In addition, in situ measurements of oxygen, pH, and electric potential distributions in the waterlogged banks of Giber Å demonstrated the presence of distant electric redox coupling in naturally occurring freshwater sediment. At the same site, filamentous Desulfobulbaceae with cable bacterium morphology were found to be present. Their 16S rRNA gene sequence placed them as a distinct sister group to the known marine cable bacteria, with the genus Desulfobulbus as the closest cultured lineage. The results of the present study indicate that electric currents mediated by cable bacteria could be important for the biogeochemistry in many more environments than anticipated thus far and suggest a common evolutionary origin of the cable phenotype within Desulfobulbaceae with subsequent diversification into a freshwater and a marine lineage.

Transient bottom water oxygenation creates a niche for cable bacteria in long‐term anoxic sediments of the Eastern Gotland Basin

“…Densities of cable bacteria measured in the EGB sediment (1.3–33 m cm −2 ) are within the range of in situ values reported from freshwater (40 m cm −2 , Risgaard‐Petersen et al ., ), mangroves (77 m cm −2 , Burdorf et al ., ) and marine bioturbated sediments (0.15–56 m cm −2 , Malkin et al ., ). They are however substantially lower as compared with other coastal sites with cohesive sediments, i.e.…”

Microbial Communities Are Well Adapted to Disturbances in Energy Input

“…Temporal strategies that do not rely on internal clocks include resource storage (9), hibernation and dormancy (10), and persister cells (11). Strategies organized over space can also increase fitness, such as diel vertical migration (12), luxury uptake (13), chemotaxis (14), and spatially executed redox reactions via cell gliding (15) or bacterial cables (16). …”

Long-distance electron transport by cable bacteria in mangrove sediments

“…Cable bacteria, which perform e-SOx through long-distance electron transport, have to date mostly Seitaj et al (2015), (5) Schauer et al (2014), (6) Nielsen et al (2010), (7) Risgaard-Petersen et al (2015) been found in fine-grained muddy sediments characterized by high organic carbon content and a high supply of sulphide through sulphate reduction . Therefore, it is not unsurprising that mangrove sediments also sustain cable bacteria activity: mangrove sediments have a high organic carbon content due to litterfall (Aller et al 2004, Deborde et al 2015, and in most cases sulphate reduction is the most important pathway of organic matter mineralization (Kristensen et al 2008).…”