Micromolar sulfide concentrations alleviate acetylene blockage of nitrous oxide reduction by denitrifying Pseudomonas fluorescens

Abstract

The influence of low sulfide concentrations on nitrous oxide (N2O) reduction by resting cells of denitrifying Pseudomonas fluorescens was studied. Nitrous oxide reduction was inhibited by sulfide with an apparent Ki value of 1 .mu.M. The inhibition was immediate and was readily alleviated by a short treatment of the cells with O2. In the absence of sulfide, addition of acetylene (0.2 kPa C2H2 or more) caused an immediate and complete inhibition of N2O reduction. However, when the sulfide concentration was higher than 2 .mu.M, addition of C2H2 (range of 0.7-13 kPa tested) gave incomplete inhibition of the N2O reduction. Complete inhibition was in this case only obtained after prolonged exposure to the C2H2. The transition period with incomplete C2H2 blockage was shortest (about 20 min) for relatively high C2H2 applications (about 10 kPa). Incomplete C2H2 blockage was seen only when sulfide was added to the cell suspensions before C2H2. The data may relate to the low efficacy of the "acetylene blockage technique" when the assay is applied to NO3--deficient and reducing environments.