Effect of nitrate and thiosulfate concentration on the denitrification activity of bacterial isolates

The denitrification activity of five bacterial isolates was studied in samples of soil and freshwater sediments and from a wastewater treatment plant. The bacteria were exposed in a mineral medium supplied with Na₂S₂O₃·5H₂O (electron donor) and KNO₃ (electron acceptor). The effect of different concentrations of donor and/or acceptor of electrons was evaluated by the method of acetylene inhibition of N₂O-reductase. No positive influence on denitrification activity was observed with increased levels of individually added substrates. Three bacterial isolates exhibited a significant increase of denitrification activity when measured in the presence of both tested substances.