Fig. 6. Maximum biomass specific nitrification rate as a function of the fraction of nitrifying bacteria within the biofilm of R3 (Runs 11–14). The arrow indicates the data of Run 14, in which inhibition by free ammonium and free nitrous YK-4-279 took place (see Bassin et al. (2012b) for more details). This analysis was not conducted for R1 and R2 since in these continuously-fed reactors the nitrification rate was governed by the ammonium loading rate (substrate limiting condition).Figure optionsDownload full-size imageDownload as PowerPoint slide
In a more refined analysis, genus-specific FISH probes were employed to detect specific ammonium- and nitrite-oxidizing bacterial groups among the nitrifying community. According to FISH analysis, displayed in Fig. S3, bacteria of the genus Nitrosomonas were the only AOB in R2 and R3. This is in accordance with the DGGE analysis with both 16S rRNA and amoA genes, which also indicated that all AOB were members of the Nitrosomonas genus in these systems. Although bacteria belonging to Nitrosomonas were also dominant in R1, as evidenced by PCR-DGGE approach, FISH analysis have shown that few cells of Nitrosococcus mobilis were also detected in this autotrophic reactor. However, this specific genus was not detected in the PCR-DGGE analysis, which is likely due to their low cell number in comparison to other dominant bacteria.