Biodiversity and population dynamics of microorganisms in a full-scale membrane bioreactor for municipal wastewater treatment

The total, ammonia-oxidizing, and denitrifying Bacteria in a full-scale membrane bioreactor (MBR) were evaluated monthly for over one year. Microbial communities were analyzed by denaturing gradient gel electrophoresis (DGGE) and clone library analysis of the 16S rRNA and ammonia monooxygenase (amoA) and nitrous oxide reductase (nosZ) genes. The community fingerprints obtained were compared to those from a conventional activated sludge (CAS) process running in parallel treating the same domestic wastewater. Distinct DGGE profiles for all three molecular markers were observed between the two treatment systems, indicating the selection of specific bacterial populations by the contrasting environmental and operational conditions. Comparative 16S rRNA sequencing indicated a diverse bacterial community in the MBR, with phylotypes from the α- and β-Proteobacteria and Bacteroidetes dominating the gene library. The vast majority of sequences retrieved were not closely related to classified organisms or displayed relatively low levels of similarity with any known 16S rRNA gene sequences and thus represent organisms that constitute new taxa. Similarly, the majority of the recovered nosZ sequences were novel and only moderately related to known denitrifiers from the α- and β-Proteobacteria. In contrast, analysis of the amoA gene showed a remarkably simple ammonia-oxidizing community with the detected members almost exclusively affiliated with the Nitrosomonas oligotropha lineage. Major shifts in total bacteria and denitrifying community were detected and these were associated with change in the external carbon added for denitrification enhancement. In spite of this, the MBR was able to maintain a stable process performance during that period. These results significantly expand our knowledge of the biodiversity and population dynamics of microorganisms in MBRs for wastewater treatment.