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| Titel |
Distant electric coupling between nitrate reduction and sulphide oxidation investigated by an improved nitrate microscale biosensor |
| VerfasserIn |
U. Marzocchi, N. P. Revsbech, L. P. Nielsen, N. Risgaard-Petersen |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250069444
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| Zusammenfassung |
| Bacteria are apparently able to transmit electrons to other bacteria (Summers et al. 2010) or to
electrodes (Malvankar et al. 2011) by some kind of nanowires (Reguera et al. 2005, Gorbi et
al. 2006). Lately it has been shown that such transfer may occur over distances of centimetres
in sediments, thereby coupling sulphide oxidation in deeper layers with oxygen reduction
near the surface (Nielsen 2011). The finding of these long-distance electrical connections
originated from analysis of O2, H2S, and pH profiles measured with microsensors. Nitrate is
thermodynamically almost as good an electron acceptor as O2, and we therefore set up an
experiment to investigate whether long-distance electron transfer also happens with
NO3-.
Aquaria were filled with sulphidic marine sediment from Aarhus Bay that was
previously used to show long-distance electron transfer to O2. The aquaria were
equipped with a lid so that they could be completely filled without a gas phase. Anoxic
seawater with 300 μM NO3- was supplied at a constant rate resulting in a steady
state concentration in the aquatic phase of 250 μM NO3-. The reservoir with the
nitrate-containing water was kept anoxic by bubbling it with a N2/CO2 mixture and was kept
at an elevated temperature. The water was cooled on the way to the aquaria to keep
the water in the aquaria undersaturated with gasses, so that bubble formation by
denitrification in the sediment could be minimised. Profiles of NO3-, H2S, and
pH were measured as a function of time (2 months) applying commercial sensors
for H2S and pH and an improved microscale NO3- biosensor developed in our
laboratory.
The penetration of NO3- in the sediment was 4-5 mm after 2 months, whereas sulphide
only could be detected below 8-9 mm depth. The electron acceptor and electron
donor were thus separated by 4-5 mm, indicating long distance electron transfer. A
pH maximum of about 8.6 pH units at the NO3- reduction zone similar to a pH
maximum observed in the O2 reduction zone of electro-active sediments could be
observed. This pH maximum was the strongest evidence for long-distance electron
transfer in oxic sediments, but cannot be taken as proof in denitrifying sediments as
conventional denitrification may also produce elevated pH. We are now searching for the
NO3- reducing bacteria that may be active in long-distance electron transfer in our
sediment.
Gorby, Y. A., S. Yanina, et al. (2006). Electrically conductive bacterial nanowires
produced by Shewanella oneidensis strain MR-1 and other microorganisms. Proceedings
of the National Academy of Sciences of the United States of America 103(30):
11358-11363.
Malvankar, N. S., M. Vargas, et al. (2011). Tunable metallic-like conductivity in
microbial nanowire networks. Nature Nanotechnology 6(9): 573-579.
Nielsen, L. P., N. Risgaard-Petersen, et al. (2010). Electric currents couple spatially
separated biogeochemical processes in marine sediment. Nature 463(7284): 1071-1074.
Reguera, G., K. D. McCarthy, et al. (2005). Extracellular electron transfer via microbial
nanowires. Nature 435(7045): 1098-1101.
Summers, Z. M., H. E. Fogarty, et al. (2010). Direct Exchange of Electrons Within
Aggregates of an Evolved Syntrophic Coculture of Anaerobic Bacteria. Science 330(6009):
1413-1415. |
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