Anaerobic Sulfide Oxidation with Nitrate by a Freshwater

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 o