Microbial biogeography across a full-scale wastewater treatment plant transect: evidence for immigration between coupled processes.

Wastewater treatment plants use a variety of bioreactor types and configurations to remove organic matter and nutrients. Little is known regarding the effects of different configurations and within-plant immigration on microbial community dynamics. Previously, we found that the structure of ammonia-oxidizing bacterial (AOB) communities in a full-scale dispersed growth activated sludge bioreactor correlated strongly with levels of NO2 (-) entering the reactor from an upstream trickling filter. Here, to further examine this puzzling association, we profile within-plant microbial biogeography (spatial variation) and test the hypothesis that substantial microbial immigration occurs along a transect (raw influent, trickling filter biofilm, trickling filter effluent, and activated sludge) at the same full-scale wastewater treatment plant. AOB amoA gene abundance increased >30-fold between influent and trickling filter effluent concomitant with NO2 (-) production, indicating unexpected growth and activity of AOB within the trickling filter. Nitrosomonas europaea was the dominant AOB phylotype in trickling filter biofilm and effluent, while a distinct "Nitrosomonas-like" lineage dominated in activated sludge. Prior time series indicated that this "Nitrosomonas-like" lineage was dominant when NO2 (-) levels in the trickling filter effluent (i.e., activated sludge influent) were low, while N. europaea became dominant in the activated sludge when NO2 (-) levels were high. This is consistent with the hypothesis that NO2 (-) production may cooccur with biofilm sloughing, releasing N. europaea from the trickling filter into the activated sludge bioreactor. Phylogenetic microarray (PhyloChip) analyses revealed significant spatial variation in taxonomic diversity, including a large excess of methanogens in the trickling filter relative to activated sludge and attenuation of Enterobacteriaceae across the transect, and demonstrated transport of a highly diverse microbial community via the trickling filter effluent to the activated sludge bioreactor. Our results provide compelling evidence that substantial immigration between coupled process units occurs and may exert significant influence over microbial community dynamics within staged bioreactors.

Fine-scale bacterial community dynamics and the taxa-time relationship within a full-scale activated sludge bioreactor.

In activated sludge bioreactors, aerobic heterotrophic communities efficiently remove organics, nutrients, toxic substances, and pathogens from wastewater, but the dynamics of these communities are as yet poorly understood. A macroecology metric used to quantify community shifts is the taxa-time relationship, a temporal analog of the species-area curve. To determine whether this metric can be applied to full-scale bioreactors, activated sludge samples were collected weekly over a one-year period at a local municipal wastewater treatment plant. Bacterial community dynamics were evaluated by monitoring 16S rRNA genes using Terminal Restriction Fragment Length Polymorphism (T-RFLP), corroborated by clone libraries. Observed taxa richness increased with time according to a power law model, as predicted by macroecological theory, with a power law exponent of w = 0.209. The results reveal strong long-term temporal dynamics during a period of stable performance (BOD removal and nitrification). Community dynamics followed a gradual succession away from initial conditions rather than periodicity around a mean "equilibrium", with greater within-month then among-month community similarities. Changes in community structure were significantly associated via multivariate statistical analyses with dissolved oxygen, temperature, influent silver, biomass (MLSS), flow rate, and influent nitrite, cadmium and chromium concentrations. Overall, our results suggest patterns of bacterial community dynamics likely regulated in part by operational parameters and provide evidence that the taxa-time relationship may be a fundamental ecological pattern in macro- and microbial systems.

Ammonia-oxidizing communities in a highly aerated full-scale activated sludge bioreactor: betaproteobacterial dynamics and low relative abundance of Crenarchaea.

Ammonia-oxidizing bacteria (AOB) have long been considered key to the removal of nitrogen in activated sludge bioreactors. Culture-independent molecular analyses have established that AOB lineages in bioreactors are dynamic, but the underlying operational or environmental factors are unclear. Furthermore, the contribution of ammonia-oxidizing archaea (AOA) to nitrogen removal in bioreactors has not been studied. To this end, we investigated the abundance of AOA and AOB as well as correlations between dynamics in AOB lineages and operational parameters at a municipal wastewater treatment plant sampled weekly over a 1 year period. Quantitative PCR measurements of bacterial and archaeal ammonia monooxygenase subunit A (amoA) genes revealed that the bacterial homologue predominated by at least three orders of magnitude in all samples. Archaeal amoA was only detectable in approximately 15% of these samples. Using terminal restriction fragment length polymorphism analysis, we monitored AOB lineages based on amoA genes. The Nitrosomonas europaea lineage and a novel Nitrosomonas-like cluster were the dominant AOB signatures, with a Nitrosospira lineage present at lower relative abundance. These lineages exhibited strong temporal oscillations, with one becoming sequentially dominant over the other. Using non-metric multidimensional scaling and redundancy analyses, we tested correlations between terminal restriction fragment length polymorphism profiles and 20 operational and environmental parameters. The redundancy analyses indicated that the dynamics of AOB lineages correlated most strongly with temperature, dissolved oxygen and influent nitrite and chromium. The Nitrosospira lineage signal had a strong negative correlation to dissolved oxygen and temperature, while the Nitrosomonas-like (negative correlations) and N. europaea lineages (positive correlations) were inversely linked (relative to one another) to influent nitrite and chromium. Overall, this study suggests that AOA may be minor contributors to ammonia oxidation in highly aerated activated sludge, and provides insight into parameters controlling the diversity and dominance of AOB lineages within bioreactors during periods of stable nitrification.