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Applied and Environmental Microbiology, July 2006, p. 4755-4760, Vol. 72, No. 7
0099-2240/06/$08.00+0 doi:10.1128/AEM.00163-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.
Institute for Microbiology, University of Hannover, Schneiderberg 50, 30167 Hannover, Germany,1 Max Planck Institute for Marine Microbiology, Celsiusstr. 1, 28359 Bremen, Germany,2 Department of Microbiology, University of Aarhus, Ny Munkegade, Building 540, 8000 Aarhus C, Denmark3
Received 21 January 2006/ Accepted 26 April 2006
A lithotrophic freshwater Beggiatoa strain was enriched in O2-H2S gradient tubes to investigate its ability to oxidize sulfide with NO3 as an alternative electron acceptor. The gradient tubes contained different NO3 concentrations, and the chemotactic response of the Beggiatoa mats was observed. The effects of the Beggiatoa sp. on vertical gradients of O2, H2S, pH, and NO3 were determined with microsensors. The more NO3 that was added to the agar, the deeper the Beggiatoa filaments glided into anoxic agar layers, suggesting that the Beggiatoa sp. used NO3 to oxidize sulfide at depths below the depth that O2 penetrated. In the presence of NO3 Beggiatoa formed thick mats (>8 mm), compared to the thin mats (ca. 0.4 mm) that were formed when no NO3 was added. These thick mats spatially separated O2 and sulfide but not NO3 and sulfide, and therefore NO3 must have served as the electron acceptor for sulfide oxidation. This interpretation is consistent with a fourfold-lower O2 flux and a twofold-higher sulfide flux into the NO3-exposed mats compared to the fluxes for controls without NO3. Additionally, a pronounced pH maximum was observed within the Beggiatoa mat; such a pH maximum is known to occur when sulfide is oxidized to S0 with NO3 as the electron acceptor.
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