Microbial Nitrogen Metabolism in Chloraminated Drinking Water Reservoirs
Microbial Nitrogen Metabolism in Chloraminated Drinking Water Reservoirs
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DOI：
10.1128/msphere.00274-20
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发表时间：
2019-06
期刊：
影响因子：
4.8
通讯作者：
Sarah C. Potgieter;Zihan Dai;S. Venter;Makhosazana Sigudu;A. Pinto
中科院分区：
文献类型：
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作者：
Sarah C. Potgieter;Zihan Dai;S. Venter;Makhosazana Sigudu;A. Pinto
当游离氯残留难以维持时，氯胺常被用作辅助消毒剂。然而，氯胺化通常与硝化的不良影响相关，这会导致许多饮用水公用事业公司出现运营问题。在氯胺化过程中引入氨通过添加过量氨或通过氯胺衰变提供了潜在的氮源。这促进硝化微生物的生长，并为其他生物的生长提供氮源（即硝酸盐）。虽然典型的氨氧化细菌和亚硝酸盐氧化细菌在氯胺化饮用水系统中的作用已被广泛研究，但这些研究很大程度上采用了以基因为中心的目标方法。此外，人们对完全氨氧化（即comammox）细菌的潜在长期共存以及硝化生物与其能够反硝化和氮同化的异养对应物的潜在代谢协同作用知之甚少。这项研究利用基因组解析宏基因组学在一段时间内获得的数据表明，虽然硝化细菌占主导地位并且可能在硝化作用中发挥主要作用，但它们与异养生物的共存表明一氧化氮的产生和硝酸盐还原为氨也可能发生在氯胺化饮用水系统中。摘要 氯胺化产生的氨可促进硝化生物的生长，从而消耗氯胺残留物并导致饮用水公用事业公司的运行问题。在这项研究中，我们使用宏基因组方法来确定参与氯胺饮用水水库内氮生物转化的微生物的身份和功能潜力。氮形态的空间变化包括硝酸盐浓度增加，同时随着距氯胺化地点距离的增加，铵浓度降低。这种硝化活性可能是由典型的氨氧化细菌（即亚硝化单胞菌）和亚硝酸盐氧化细菌（即硝化螺菌）以及完全氨氧化（即comammox）硝化螺菌类细菌驱动的。通过功能注释来评估与氮代谢相关的基因，群落基因目录主要包含与硝化作用、硝酸盐和亚硝酸盐还原以及一氧化氮还原相关的基因。此外，我们组装了 47 个高质量的宏基因组组装基因组 (MAG)，代表高度多样化的细菌组合。其中，5 个 MAG 在所有样本中均表现出高覆盖度，其中包括两种亚硝化单胞菌、硝化螺菌、鞘氨醇单胞菌和类根瘤菌 MAG。对这些 MAG 与氮代谢相关的系统基因组水平分析表明，在氨限制条件下，硝酸盐也可能被还原回氨以进行同化。或者，硝酸盐可以还原为一氧化氮，并可能在调节生物膜形成中发挥作用。总体而言，这项研究提供了对微生物群落及其氮代谢的深入了解，并与水化学数据一起提高了我们对氯胺饮用水分配系统中氮生物转化的理解。重要性 当游离氯残留难以维持时，氯胺通常用作辅助消毒剂。然而，氯胺化通常与硝化的不良影响相关，这会导致许多饮用水公用事业公司出现运营问题。在氯胺化过程中引入氨通过添加过量氨或通过氯胺衰变提供了潜在的氮源。这促进硝化微生物的生长，并为其他生物的生长提供氮源（即硝酸盐）。虽然典型的氨氧化细菌和亚硝酸盐氧化细菌在氯胺化饮用水系统中的作用已被广泛研究，但这些研究很大程度上采用了以基因为中心的目标方法。此外，人们对完全氨氧化（即comammox）细菌的潜在长期共存以及硝化生物与其能够反硝化和氮同化的异养对应物的潜在代谢协同作用知之甚少。这项研究利用基因组解析宏基因组学在一段时间内获得的数据表明，虽然硝化细菌占主导地位并且可能在硝化作用中发挥主要作用，但它们与异养生物的共存表明一氧化氮的产生和硝酸盐还原为氨也可能发生在氯胺化饮用水系统中。
Chloramines are often used as a secondary disinfectant when free chlorine residuals are difficult to maintain. However, chloramination is often associated with the undesirable effect of nitrification, which results in operational problems for many drinking water utilities. The introduction of ammonia during chloramination provides a potential source of nitrogen either through the addition of excess ammonia or through chloramine decay. This promotes the growth of nitrifying microorganisms and provides a nitrogen source (i.e., nitrate) for the growth for other organisms. While the roles of canonical ammonia-oxidizing and nitrite-oxidizing bacteria in chloraminated drinking water systems have been extensively investigated, those studies have largely adopted a targeted gene-centered approach. Further, little is known about the potential long-term cooccurrence of complete-ammonia-oxidizing (i.e., comammox) bacteria and the potential metabolic synergies of nitrifying organisms with their heterotrophic counterparts that are capable of denitrification and nitrogen assimilation. This study leveraged data obtained for genome-resolved metagenomics over a time series to show that while nitrifying bacteria are dominant and likely to play a major role in nitrification, their cooccurrence with heterotrophic organisms suggests that nitric oxide production and nitrate reduction to ammonia may also occur in chloraminated drinking water systems. ABSTRACT Ammonia availability due to chloramination can promote the growth of nitrifying organisms, which can deplete chloramine residuals and result in operational problems for drinking water utilities. In this study, we used a metagenomic approach to determine the identity and functional potential of microorganisms involved in nitrogen biotransformation within chloraminated drinking water reservoirs. Spatial changes in the nitrogen species included an increase in nitrate concentrations accompanied by a decrease in ammonium concentrations with increasing distance from the site of chloramination. This nitrifying activity was likely driven by canonical ammonia-oxidizing bacteria (i.e., Nitrosomonas) and nitrite-oxidizing bacteria (i.e., Nitrospira) as well as by complete-ammonia-oxidizing (i.e., comammox) Nitrospira-like bacteria. Functional annotation was used to evaluate 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, we assembled 47 high-quality metagenome-assembled genomes (MAGs) representing a highly diverse assemblage of bacteria. Of these, five MAGs showed high coverage across all samples, which included two Nitrosomonas, Nitrospira, Sphingomonas, and Rhizobiales-like MAGs. Systematic genome-level analyses of these MAGs in relation to nitrogen metabolism suggest that under ammonia-limited conditions, nitrate may be also reduced back to ammonia for assimilation. Alternatively, nitrate may be reduced to nitric oxide and may potentially play a role in regulating biofilm formation. Overall, this study provides insight into the microbial communities and their nitrogen metabolism and, together with the water chemistry data, improves our understanding of nitrogen biotransformation in chloraminated drinking water distribution systems. IMPORTANCE Chloramines are often used as a secondary disinfectant when free chlorine residuals are difficult to maintain. However, chloramination is often associated with the undesirable effect of nitrification, which results in operational problems for many drinking water utilities. The introduction of ammonia during chloramination provides a potential source of nitrogen either through the addition of excess ammonia or through chloramine decay. This promotes the growth of nitrifying microorganisms and provides a nitrogen source (i.e., nitrate) for the growth for other organisms. While the roles of canonical ammonia-oxidizing and nitrite-oxidizing bacteria in chloraminated drinking water systems have been extensively investigated, those studies have largely adopted a targeted gene-centered approach. Further, little is known about the potential long-term cooccurrence of complete-ammonia-oxidizing (i.e., comammox) bacteria and the potential metabolic synergies of nitrifying organisms with their heterotrophic counterparts that are capable of denitrification and nitrogen assimilation. This study leveraged data obtained for genome-resolved metagenomics over a time series to show that while nitrifying bacteria are dominant and likely to play a major role in nitrification, their cooccurrence with heterotrophic organisms suggests that nitric oxide production and nitrate reduction to ammonia may also occur in chloraminated drinking water systems.