Temporal metagenomic characterization of microbial community structure and nitrogen modification genes within an activated sludge bioreactor system

The biological removal of nitrogen using natural microbial metabolic processes can be a valuable component of wastewater treatment that helps reduce downstream eutrophication of receiving water ecosystems. Biological nutrient removal (BNR) is a well-established component of wastewater treatment due to its recognized environmental benefits. The composition and diversity of these microbial communities are an important consideration, as disruptions to or instability in the microbial community can negatively impact N cycling and reduce treatment efficiency. To characterize the bacterial community and associated nitrogen cycling genes within a cold-acclimated BNR facility, metagenomic sequencing combined with a read-based quantification strategy and metagenomic assembled genome (MAG) generation was used on samples collected from a Canadian prairie wastewater treatment plant. Generally, this system had a high abundance of Proteobacteria and Actinobacteria throughout the year, including the genera Thiomonas, Tetrasphaera, Afipia, and Hyphomicrobium. Communities remained stable throughout the different bioreactors in this system, while diversity varied between sampling months, demonstrating seasonal effects on the population dynamics. Genes involved in the denitrification pathway were abundant and distributed widely across different MAGs, while genes involved in nitrification were absent. Additionally, these genes remained stable across all sampling months, suggesting that the efficacy and robustness of this system rely on more than the taxonomic composition of the microbial community.IMPORTANCEWastewater treatment plays an essential role in minimizing negative impacts on downstream aquatic environments. Microbial communities are known to play a vital role in the wastewater treatment process, particularly in the removal of nitrogen and phosphorus, which can be especially damaging to aquatic ecosystems. There is limited understanding of how these microbial communities may change in response to fluctuating temperatures or how seasonality may impact their ability to participate in the treatment process. The findings of this study indicate that the microbial communities of wastewater are relatively stable both compositionally and functionally across fluctuating temperatures. Wastewater treatment plays an essential role in minimizing negative impacts on downstream aquatic environments. Microbial communities are known to play a vital role in the wastewater treatment process, particularly in the removal of nitrogen and phosphorus, which can be especially damaging to aquatic ecosystems. There is limited understanding of how these microbial communities may change in response to fluctuating temperatures or how seasonality may impact their ability to participate in the treatment process. The findings of this study indicate that the microbial communities of wastewater are relatively stable both compositionally and functionally across fluctuating temperatures.