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bioRxiv · 10.1101/655316

Microbial Nitrogen Metabolism in Chloraminated Drinking Water Reservoirs

Potgieter, S. C.·Dai, Z.·Venter, S. N.·Sigudu, M.·Pinto, A. J.
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Abstract

Nitrification is a common concern in chloraminated drinking water distribution systems. The addition of ammonia promotes the growth of nitrifying organisms, causing the depletion of chloramine residuals and resulting in operational problems for many drinking water utilities. Therefore, a comprehensive understanding of the microbially mediated processes behind nitrogen metabolism together with chemical water quality data, may allow water utilities to better address the undesirable effects caused by nitrification. In this study, a metagenomic approach was applied to characterise the microbial nitrogen metabolism within chloraminated drinking water reservoirs. Samples from two geographically separated but connected chloraminated reservoirs within the same drinking water distribution system (DWDS) were collected within a 2-year sampling campaign. Spatial changes in the nitrogen compounds (ammonium (NH4+), nitrites (NO2-) and nitrates (NO3-)) across the DWDS were observed, where nitrate concentrations increased as the distance from the site of chloramination increased. The observed dominance of Nitrosomonas and Nitrospira-like bacteria, together with the changes in the concentration of nitrogen species, suggests that these bacteria play a significant role in contributing to varying stages of nitrification in both reservoirs. Functionally annotated protein sequences were mined for the genes associated with nitrogen metabolism and the community gene catalogue contained mostly genes involved in nitrification, nitrate and nitrite reduction and nitric oxide reduction. Furthermore, based on the construction of Metagenome Assembled Genomes (MAGs), a highly diverse assemblage of bacteria (i.e., predominately Alpha- and Betaproteobacteria in this study) was observed among the draft genomes. Specifically, 5 MAGs showed high coverage across all samples including two Nitrosomonas, Nitrospira, Sphingomonas and a Rhizobiales-like MAGs. The role of these MAGs in nitrogen metabolism revealed that the fate nitrate may be linked to changes in ammonia concentrations, that is, when ammonia concentrations are low, nitrate may be assimilated back to ammonia for growth. Alternatively, nitrate may be reduced to nitric oxide and potentially used in the regulation of biofilm formation. Therefore, this study provides insight into the genetic network behind microbially mediated nitrogen metabolism and together with the water chemistry data improves our understanding nitrification in chloraminated DWDSs.

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Potgieter, S. C., Dai, Z., Venter, S. N., Sigudu, M., Pinto, A. J.. 2019-06-13. Microbial Nitrogen Metabolism in Chloraminated Drinking Water Reservoirs. https://doi.org/10.1101/655316

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