Tracking composition and dynamics of nitrification and denitrification microbial community in a biofilm reactor by PCR-DGGE and combining FISH with flow cytometry

A compact suspended carrier biofilm reactor (SCBR) was operated at three different C/N ratios (C/N = 10:1, 5:1 and 3:1) with focus on reactor performance and microbial community composition of nitrifying and denitrifying bacteria. The process was capable of achieving over 90% removal of chemical oxygen demand (COD) and over 83.3% of simultaneous nitrification and denitrification (SND) efficiency. Denaturing gradient gel electrophoresis (DGGE) analysis showed that the diversity of ammonia-oxidizing bacteria (AOB) community decreased with inoculation sludge, C/N ratio 3:1, 10:1 and 5:1 in turn. Phylogenetics analysis indicated that there were three distinct groups of AOB in Betaproteobacteria subdivision, where Nitrosomonas were the dominant members in the biofilm. Fluorescence in situ hybridization-flow cytometry (FISH-FCM) results revealed that Alpha-, Beta- and Gamma-proteobacteria accounted for over 50% of all cells. Additionally, the clusters of Nitrosomonas, Nitrosospira, Nitrobacter, Nitrospira and AOB of Betaproteobacteria yielded a similar distribution pattern about 5–12% of all cells. Nested analysis of variance assay (ANOVA) demonstrated that the C/N ratio did not significantly affect the shift of populations in different groups of nitrifying and denitrifying bacteria detected by FISH-FCM.