CONFIRMATION OF AEROBIC DENITRIFICATION IN BATCH CULTURES, USING GAS-CHROMATOGRAPHY AND N-15 MASS-SPECTROMETRY

Because of a revival in the controversy surrounding 'aerobic denitrifi cation', especially in relation to Thiosphaera pantotropha, activity i n aerobic batch cultures was evaluated using gas chromatography and ma ss spectrometry after the addition of N-15-labelled NH4+ and NO2-. Aer obic denitrifying activity in T. pantotropha was present, but only at about 10% of the originally-reported levels. The activity of 'Pseudomo nas denitrificans' was similar to previously-reported values. Alcalige nes faecalis showed significant aerobic denitrifying activity, produci ng almost equivalent amounts of N-2 and N2O. An unidentified pseudomon ad, isolate G4, presumably requires anoxia for enzyme activity as it d id not denitrify aerobically, even though it has a constitutive denitr ifying pathway.