Anaerobic sulfide oxidation with nitrate by a freshwater Beggiatoa enrichment culture.
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.
Kamp
Anja
A
Institute for Microbiology, University of Hannover, Schneiderberg 50, 30167 Hannover, Germany. anja.kamp@ifmb.uni-hannover.de
Stief
Peter
P
Schulz-Vogt
Heide N
HN
D000693:Anaerobiosis; D003470:Culture Media; D005618:Fresh Water / Q000382:microbiology*; D006863:Hydrogen-Ion Concentration; D009566:Nitrates / Q000378:metabolism*; D010084:Oxidation-Reduction; D013440:Sulfides / Q000378:metabolism*; D041962:Thiotrichaceae / Q000254:growth & development* / Q000378:metabolism*
D003470:Culture Media; D009566:Nitrates; D013440:Sulfides