Fig. 3. Correlation of the activity-based fluorescent labeling signal intensity and staining efficiency with the growth stage of ammonia-oxidizing bacteria.

Ammonium consumption and nitrite production activity by a Nitrosomonas europaea and b Nitrosospira multiformis during the incubation period. Growth of c N. europaea and d N. multiformis as indicated by protein content, and its relation to the relative fluorescent signal intensity observed, as well as the biovolume fraction of the culture stained by the activity-based labeling protocol. Bacterial growth data are fitted to a Hill equation. Error bars represent standard deviation of technical triplicates of protein measurements.