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2015 ; 81
(17
): 6003-11
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Cable Bacteria in Freshwater Sediments
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Risgaard-Petersen N
; Kristiansen M
; Frederiksen RB
; Dittmer AL
; Bjerg JT
; Trojan D
; Schreiber L
; Damgaard LR
; Schramm A
; Nielsen LP
Appl Environ Microbiol
2015[Sep]; 81
(17
): 6003-11
PMID26116678
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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.
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