Correlating microbial community structure and composition with aeration intensity in submerged membrane bioreactors...

For understanding of the microbial community structure and composition under different aeration intensities, 454 high-throughput pyrosequencing was applied to analyze the 16S rRNA gene of bacteria in two submerged membrane bioreactors (MBRs) under low (R(L)) and high aeration (R(H)) conditions. In total, 7818 (R(L)) and 9353 (R(H)) high-quality reads were obtained, and 1230 (R(L)) and 924 (R(H)) operational taxonomic units (OTUs) were generated at 3% cutoff level, respectively. 454 pyrosequencing could also reveal the minority bacteria that were hardly detected by the conventional molecular methods. Although the core populations were shared with highly functional organization (>80%), clear differences between the samples in the two MBRs were revealed by richness-diversity indicators and Venn analyses. Notably, microbial diversity was decreased under high aeration condition, and the evolution of the populations was observed mainly in the shared OTUs. Moreover, specific comparison down to the class and genus level showed that the relative abundances of β-Proteobacteria and γ-Proteobacteria in the R(H) community were respectively decreased by 41.5% and 66.6%, consistent with the observed membrane fouling mitigation during the reactor operation. It was also found that Nitrospira and Nitrosomonas, being nitrite oxidizing bacteria (NOB) and ammonium oxidizing bacteria (AOB), were the dominant phylogenetic groups at the genus level of both reactors, and that the high ratio of NOB to AOB populations well supported the complete ammonium oxidation performance in the two reactors. Although some populations of NOB and AOB decreased with the increase of aeration intensity, the functional stability of the nitrification process was less affected, probably due to the low influent substrate concentration and the high level of functional organization.