Diversity and dynamics of dominant and rare bacterial taxa in replicate sequencing batch reactors operated under different solids retention time and seeded with either acclimated or non-acclimated sludge

In this study, 16S rRNA gene pyrosequencing was applied in order to provide a better insight on the effect of solids retention time (SRT) on the diversity and dynamics of total, dominant and rare bacterial taxa in eight replicate lab-scale sequencing batch reactors (SBRs) operated for a period of 78 days and seeded with either acclimated or non-acclimated sludge. Rank-abundance curves showed strong abundance of few dominant operational taxonomic units (OTUs) and a long tail of rare OTUs in all reactors. Results revealed that there was no detectable effect of SRT (2d vs. 10d) on Shannon diversity index and OTU richness of both dominant and rate taxa. Nonmetric Multidimensional Scaling (NMDS) analysis showed that the total, dominant and rare bacterial taxa were highly dynamic during entire period of stable reactor performance. Also, the rare taxa were more dynamic than the dominant taxa despite expected low invasion rates because of the use of sterile synthetic media. Moving-window analysis, Global ANOSIM and NMDS analysis revealed that the bacterial community structure in replicate SBRs seeded with acclimated or non-acclimated sludge was reproducible. Overall 16S rRNA gene pyrosequencing could reveal the dynamics of rare bacterial taxa that are normally left out using conventional molecular biology methods.