Combined Use of the Acetylene Inhibition Technique and Microsensors for Quantification of Denitrification in Sediments and Biofilms

Abstract

The introduction of the acetylene inhibition technique for quantification of denitrification (Balderston et al. 1976; Yoshinari and Knowles, 1976) supplied researchers of this reaction with a highly sensitive and relatively simple assay. Nitrous oxide is a free intermediary in the bacterial reduction of NO ⁻₃ to N₂, and the reduction of N₂O is inhibited by acetylene. The accumulation rate of N₂O in the inhibited sample is thus a measure of the denitrification activity. Gas chromatographs equipped with ECDs (Electron Capture Detectors) can be used to quantify the evolved N₂O with good accuracy and extremely high detection limits. A problem by use of gas chromatography is, however, the need to extract nitrous oxide from the sample before analysis. The procedures for extraction of sample segments may be elaborated to yield a reasonable spatial resolution of the assay (e.g., Sørensen et al, 1979), but the highest resolution by such an approach is still rather on a centimeter than on a millimeter scale while denitrifying microenvironments such as biofilms often have dimensions of less than 1 mm. The recent introduction of a microsensor for simultaneous detection of O₂ and N₂O has now made it possible to determine the activity within denitrifying microenvironments with a spatial resolution of less than 0.1 mm.