Article pubs.acs.org/est
Biofilm Community Dynamics in Bench-Scale Annular Reactors Simulating Arrestment of Chloraminated Drinking Water Nitrification Vicente Gomez-Alvarez, Karen A. Schrantz, Jonathan G. Pressman, and David G. Wahman* U.S. Environmental Protection Agency, Office of Research and Development, 26 West Martin Luther King Drive, Cincinnati, Ohio 45268, United States S Supporting Information *
ABSTRACT: Annular reactors (ARs) were used to study biofilm community succession and provide ecological insight during nitrification arrestment through simultaneously increasing monochloramine (NH2Cl) and chlorine to nitrogen mass ratios, resulting in four operational periods (I−IV). Analysis of 16S rRNA-encoding gene sequence reads (454-pyrosequencing) examined viable and total biofilm communities and found total samples were representative of the underlying viable community. Bacterial community structure showed dynamic changes corresponding with AR operational parameters. Period I (complete nitrification and no NH2Cl residual) was dominated by Bradyrhizobium (total cumulative distribution: 38%), while environmental Legionella-like phylotypes peaked (19%) during Period II (complete nitrification and minimal NH2Cl residual). Nitrospira moscoviensis (nitriteoxidizing bacteria) was detected in early periods (2%) but decreased to 97% similarity into operational taxonomic units (OTUs). Taxonomic classification and identification of nearest neighbors were performed with tool Classifier in Ribosomal Database Project II release 10.28 and NCBI BLASTn, respectively.26,27 Using MEGA v5.03,28 a phylogenetic tree was constructed with the Maximum Likelihood (ML) method using the Tamura-Nei model29 with 1,000 bootstrap replicates. Diversity Estimates of Bacterial Communities. Normalized libraries were used to calculate rarefaction curves and diversity estimates (e.g., OTUs richness, ChaoI and SACE richness estimator, Shannon diversity, and evenness). Rarefaction curves result from repeated randomizations of the observed species accumulation curve, allowing observed richness comparisons among samples.30 Rarefaction and diversity estimates were calculated using MOTHUR.22 A paired t-test was used to test whether there was a significant difference between OTU richness and Shannon diversity estimates. Statistical Analysis of Community Assemblages. Nonmetric multidimensional scaling (nMDS) ordination plots and Cluster Analysis (CA) dendrograms based on Bray−Curtis similarity coefficient of transformed data (log[x+1]) were used to describe relationships among biofilm communities based on relative distribution of OTU groups. The nMDS robustness was evaluated using the Shepard diagram, which is used for calculating nMDS plot goodness of fit (e.g.,
