Denitrification in dental plaque. Dental plaque of three individuals was suspended in aerobic mineral medium buffered at pH 7.2 containing 2% sucrose and 50 μM Na15NO3. Formation of (a) 30N2 (in μM/mg protein) and (b) apparent O2 concentrations (in μM) were measured in a time series experiment. Each symbol type represents 30N2 and O2 measurements of dental plaque incubations from one individual. Control measurements were done in the absence of Na15NO3 (open symbols).