Letter

Nature 463, 1071-1074 (25 February 2010) | doi:10.1038/nature08790; Received 11 September 2009; Accepted 18 December 2009

Electric currents couple spatially separated biogeochemical processes in marine sediment

Lars Peter Nielsen1, Nils Risgaard-Petersen2, Henrik Fossing3, Peter Bondo Christensen3 & Mikio Sayama4

  1. Department of Biological Sciences,
  2. Center for Geomicrobiology, Aarhus University, Ny Munkegade 114, DK-8000 Aarhus C, Denmark
  3. Department of Marine Ecology, National Environmental Research Institute, Aarhus University, Vejlsøvej 25, DK-8600 Silkeborg, Denmark
  4. National Institute of Advanced Industrial Science and Technology, 16-1 Onogawa, Tsukuba 305-8569, Japan

Correspondence to: Lars Peter Nielsen1 Correspondence and requests for materials should be addressed to L.P.N. (Email: biolpn@biology.au.dk).

Some bacteria are capable of extracellular electron transfer, thereby enabling them to use electron acceptors and donors without direct cell contact1, 2, 3, 4. Beyond the micrometre scale, however, no firm evidence has previously existed that spatially segregated biogeochemical processes can be coupled by electric currents in nature. Here we provide evidence that electric currents running through defaunated sediment couple oxygen consumption at the sediment surface to oxidation of hydrogen sulphide and organic carbon deep within the sediment. Altering the oxygen concentration in the sea water overlying the sediment resulted in a rapid (<1-h) change in the hydrogen sulphide concentration within the sediment more than 12mm below the oxic zone, a change explicable by transmission of electrons but not by diffusion of molecules. Mass balances indicated that more than 40% of total oxygen consumption in the sediment was driven by electrons conducted from the anoxic zone. A distinct pH peak in the oxic zone could be explained by electrochemical oxygen reduction, but not by any conventional sets of aerobic sediment processes. We suggest that the electric current was conducted by bacterial nanowires combined with pyrite, soluble electron shuttles and outer-membrane cytochromes. Electrical communication between distant chemical and biological processes in nature adds a new dimension to our understanding of biogeochemistry and microbial ecology.

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