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

Because of a revival in the controversy surrounding 'aerobic denitrification', especially in relation to Thiosphaera pantotropha, activity in aerobic batch cultures was evaluated using gas chromatography and mass spectrometry after the addition of N-15-labelled NH4+ and NO2-. Aerobic denitrifying activity in T. pantotropha was present, but only at about 10% of the originally-reported levels. The activity of 'Pseudomonas denitrificans' was similar to previously-reported values. Alcaligenes faecalis showed significant aerobic denitrifying activity, producing almost equivalent amounts of N-2 and N2O. An unidentified pseudomonad, isolate G4, presumably requires anoxia for enzyme activity as it did not denitrify aerobically, even though it has a constitutive denitrifying pathway.