Citation:

Gomez-Alvarez, V., S. Siponen, A. Kauppinen, A. Hokajarvi, A. Tiwari, A. Sarekoski, I. Miettinen, E. Torvinen, AND T. Pitkanen. A comparative analysis employing a gene- and genome-centric metagenomic approach reveals changes in composition, function, and activity in waterworks with different treatment processes and source water in Finland. WATER RESEARCH. Elsevier Science Ltd, New York, NY, 229:119495, (2023). https://doi.org/10.1016/j.watres.2022.119495

Impact/Purpose:

While disinfection strategies aim to mitigate the presence of microbes in drinking water distribution systems (DWDS), they do not completely eradicate their growth; therefore, a better understanding of the DWDS microbiome is needed to develop microbial control strategies. The information generated in this study improves our understanding of the drinking water ecosystem, particularly the potential sources of adverse exposure (unintended consequences of disinfectant switching practices) and how these sources may be monitored to ensure public and ecosystem health.

Description:

The emergence and development of next-generation sequencing technologies (NGS) has made the analysis of the water microbiome in the drinking water distribution systems (DWDSs) more accessible and opens new perspectives in microbial ecology studies. The current study focused on the characterization of the water microbiome of five waterworks in Finland with different raw water sources, treatment methods, and disinfectant. Metagenomes and 16S rRNA-based analysis indicate a highly dynamic and diverse microbial community. Changes in the microbial community structure may correspond to the presence or absence and type of disinfectant residual which indicates that these conditions exert selective pressure on the microbial community. The microbial communities exhibit a distribution pattern of a few dominant taxa and a large representation of low-abundance bacterial species. Most of the Bacterial domain diversity were associated with the phylum Proteobacteria followed by, Nitrospirota, Omnitrophota, Patescibacteria, Planctomycetota, Bacteroidota, Desulfobacterota, and Actinobacteriota. The Archaea domain represent a small fraction (up to 2.5%) and seemed to be effectively controlled by disinfection of water. Their role particularly in non-disinfected DWDS may be more important than previously considered. Results confirmed that non-disinfected DWDSs harbor higher microbial diversity. Maintaining disinfectant residual is significantly important for ensuring low microbial concentrations and diversity. Metagenomic binning yields with 139 bins (138 bacterial and 1 archaeal) representing metagenome-assembled genomes (MAGs) that had a >50% completeness and <10% contamination consisting of 20 class representatives in 12 phyla. The presence and occurrence of NOB-like microorganisms have significant implications for the nitrogen biotransformation in drinking water systems. Metabolic complexity and functional potential of the microbiome is evident in DWDS ecosystems. At the metagenomic and metatranscriptome level, comparative analysis found a set of differentially abundant taxonomic groups and functional genes. The wider set of genes expressed may indicate an active and diverse community regardless of the treatment methods applied to the water. DWDSs are considered pathogen-free but still contain waterborne pathogens. Our results indicate a highly dynamic and diverse microbial community and confirm that every DWDS is unique, and the community reflects the selection pressures exerted at the community structure, but also at the functional and metabolic potential level.

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