Search Results (37)

In Northeast China’s degraded croplands, nitrate (NO₃⁻-N) leaching is the dominant pathway for fertilizer-nitrogen (N) loss, which presents an increasing threat to the quality of groundwater. Conservation tillage, defined as no-tillage (NT) and straw retention, is a widely adopted management strategy to maintain cropland fertility in the black soil (BS) regions. At present, however, the impact of shifting from conventional to conservation tillage on the vertical distribution and regulatory mechanisms of NO₃⁻-N derived from applied fertilizer-N (F_NO3) remains poorly understood. Based on a 12-year field experiment, we integrated ¹⁵N-tracing field monitoring with ¹⁵N-paired-labeling incubation to quantify the vertical migration of F_NO3 into deep soil profiles, and specify the dominant processes regulating N retention and supply. Across the tested BS croplands, total NO₃⁻-N production rates (4.06–6.58 mg N kg⁻¹ soil day⁻¹) were faster than their consumption rates (0.36–0.92 mg N kg⁻¹ soil day⁻¹), leading to a net accumulation of NO₃⁻-N, and implying a potential for leaching of NO₃⁻-N, from the perspective of substrate availability. The results of the field ¹⁵N micro-plot experiment also indicated that, by maize maturity in the first growing season, an average of 7.5% of F_NO3 had migrated to the 80–100 cm soil layer. During the following two growing seasons, the maximum accumulation of F_NO3 had shifted downward to 140–160 cm and 180–220 cm, respectively. Such a pattern, particularly in light of the increased extreme precipitation in the studied regions, raises clear concerns about NO₃⁻-N leaching losses. Compared with conventional management, no-tillage with full-rate straw mulching decreased net rates of NO₃⁻-N production from 6.22 to 3.14 mg N kg⁻¹ soil day⁻¹. This reduction resulted from a decline in the gross oxidation of NH₄⁺-N to NO₃⁻-N (from 6.39 to 3.70 mg N kg⁻¹ soil day⁻¹) and an increase in DNRA (from 0.35 to 0.85 mg N kg⁻¹ soil day⁻¹), which collectively delayed the downward transport of F_NO3. Conservation tillage also increased the gross rate of heterotrophic nitrification (from 0.19 to 0.36 mg N kg⁻¹ soil day⁻¹) and its proportion relative to total nitrification (from 2.8% to 8.9%). Despite this shift, autotrophic nitrification remained the dominant process for NO₃⁻-N production in the tested BS croplands, likely due to a pH constraint on heterotrophic nitrification. With the increasingly widespread promotion of conservation tillage for soil fertility improvement, heterotrophic nitrification warrants greater attention, particularly in BS regions where pH < 6.5 and C/N contents are relatively high. Collectively, our findings provide a scientific basis for tailoring tillage practices to maintain sustainable agriculture in Northeast China. Full article

The coal mining subsidence area constitutes a distinct ecotone in the transition from agricultural soil to sediment, yet the microbially mediated nitrogen cycle within it remains inadequately understood. This investigation comprehensively analyzed physicochemical properties, microbial communities, functional genes, and co-occurrence networks along a 0–6500 mm depth gradient. Results indicated that pH transitioned from acidic to alkaline, while TN, TP, OM, and NH₄⁺–N accumulated with depth. NO₃⁻–N decreased rapidly within 1000 mm and then stabilized. Alpha-diversity showed an S-shaped increase in richness, with Shannon index peaking at 1500 mm. Beta-diversity shifted along PC1, and the shallow subsidence area (SS) influenced by NO₃⁻–N; the transition zone (TZ) regulated by OM, TN, and NH₄⁺–N; deep subsidence area (DS) was constrained by TP and pH. Microbial communities transitioned from aerobic/facultative to strictly anaerobic phyla, yet Pseudomonadota remained dominant (24–32%) across depths. With increasing depth, gene abundances for denitrification, assimilatory nitrate reduction to ammonium (ANRA), and nitrate assimilation declined, while those for dissimilatory nitrate reduction to ammonium (DNRA) and nitrification increased; nitrogen fixation remained weak. Co-occurrence networks shifted from highly connected, short-pathlength, and clustered in TZ to highly modular and long-pathlength in DS, with Aminicenantes, Syntrophus, and Methanoregula as key taxa. Overall, the thick and stable reducing zone in the subsidence area restructured the nitrogen cycle, shifting terminal products from N₂ removal to NH₄⁺ retention. These findings advance the understanding of nitrogen transformation in soil-sediment ecotones and provide a mechanistic framework for nitrogen cycling in mining-affected ecosystems. Full article

Reservoirs are hotspots for the coupling of nutrients and heavy metals, and they substantially modify the compositions and spatiotemporal distributions of microorganisms in fluvial systems. However, relatively few studies have been performed that investigate the microbial mechanisms driving interactions among heavy metals and nutrients in reservoirs. The Goupitan Reservoir, a seasonal stratified reservoir located within the Wujiang River catchment, was chosen as the research subject. The temporal and spatial variations in heavy metals and nutrients, and the metagenomic composition of the reservoir water were analyzed in January, April, July, and October 2019. The results revealed that As, Ni, Co, and Mn were derived primarily from mine wastewater, whereas Zn, Pb, Cd, and Cr were related to domestic and agricultural wastewater discharge. The study area was dominated by Proteobacteria, Actinobacteria, Cyanobacteria, and Bacteroidetes, with the proportion of dominant phyla reaching 90%. Decreases in the dissolved oxygen (DO) concentration and pH in the bottom water during July and October were conducive to increases in the abundance of the anaerobic bacterial groups Planctomycetes and Acidobacteria. The functional genes norBC and nosZ associated with denitrification (DNF), the key gene nrfAH involved in the dissimilatory nitrate reduction to ammonium (DNRA) process, the functional genes aprAB and dsrAB responsible for sulfate reduction/sulfide oxidation, as well as the thiosulfate oxidation complex enzyme system SOX, all exhibit high abundance in hypoxic water bodies and peak in the redoxcline, highlighting the significance of related nitrogen (N) and sulfur (S) metabolic processes. In addition, the concentrations of heavy metals significantly affected the spatial differentiation of the planktonic bacterial community structure, with Mn, Co, Fe, Ni, As, and Cu making relatively high individual contributions (p < 0.01). This study is important for elucidating the sources and microbiological mechanisms influencing heavy metals and nutrients in seasonally stratified subtropical reservoirs. Full article

To clarify the role and mechanism of sod-seeding patterns in improving soil fertility and mitigating nitrous oxide (N₂O) emissions in peach orchards, we conducted a study since 2023. Taking clean tillage (CK) as the control, three sod-seeding patterns—Trifolium repens–Lolium perenne mixed sowing (TPr), T. repens single sowing (Tr), and L. perenne single sowing (Pr)—were tested to analyze soil physicochemical properties, nitrogen cycle functional genes, and N₂O emission-related genes, and to explore the driving mechanism of N₂O mitigation. Results showed that all three sod-seeding patterns significantly reduced soil pH and bulk density, increased soil electrical conductivity and mean aggregate size, and improved soil nutrient status compared with CK; TPr performed best, significantly enhancing soil enzyme activities related to carbon and nitrogen cycles. Sod-seeding patterns had no significant effect on genes involved in assimilatory nitrate reduction, denitrification, or nitrification, but significantly increased dissimilatory nitrate reduction (DNRA) and nitrogen degradation gene abundances, and reduced N₂O-producing gene (amoA + amoB, nirS + nirK) abundances. Field monitoring indicated TPr reduced N₂O emissions by 34.0%, 35.7%, and 41.0%, relative to CK, Pr, and Tr, respectively. Structural equation modeling revealed that sod-seeding reduced N₂O emissions mainly by decreasing soil NH₄⁺-N content and nirS + nirK abundance. In conclusion, sod-seeding patterns improve soil fertility and mitigate N₂O emissions in peach orchards, with TPr showing the best comprehensive benefits. Full article

Long-term positioning tests can systematically reveal the evolution characteristics of soil fertility and crop productivity, and reflect the spatiotemporal changes in soil quality and their driving factors. While soil microorganisms mediating nutrient cycling are crucial for maintaining crop productivity and the long-term resilience of agricultural ecosystems, how prolonged use of different fertilization strategies affects their functional capacity remains insufficiently understood. In this study, we applied metagenomic sequencing to investigate how three fertilization treatments, namely (i) N0 receiving only phosphorus (P) and potassium (K) fertilizers, (ii) N250 receiving conventional urea + P and K, and (iii) F250 receiving humic acid urea + P and K, influence soil microbial communities, functional genes related to C and N cycling, and associated soil properties in a long-term field experiment. The F250 treatment significantly increased average annual yields of wheat and maize to 7166.21 kg hm⁻² and 8309.96 kg hm⁻², respectively. These values were 148.66% and 73.47% higher than those under N0, and 8.22% and 11.64% higher than those under N250. Compared with N0, both N250 and F250 signally augmented soil nitrate, ammonium, total nitrogen (TN), and soil organic carbon (SOC), altered microbial community composition, and enhanced the relative abundance of genes engaged in C fixation and methane oxidation. Both treatments also promoted denitrification and dissimilatory nitrate reduction to ammonium (DNRA). Relative to N250, F250 specifically enriched the beneficial bacterial genus Pedobacter, further increased the abundance of the C fixation gene pccA, and markedly upregulated the DNRA gene nrfA. Soil TN and SOC were identified as the key environmental factors regulating microbial community structure and the functional potential of C and N cycling pathways. Collectively, our findings provide a mechanistic understanding of how long-term application of humic acid urea enhances crop productivity by modulating the genetic potential of soil microorganisms in biogeochemical cycles, offering a biological foundation for optimizing fertilization strategies in sustainable agriculture. Full article

Spartina alterniflora invasion has posed severe ecological threats to coastal wetlands. Deep tillage is considered an effective physical method for ecological restoration in such wetlands; however, its effects on sediment nitrogen transformation processes remain unclear. In this study, we investigated the impacts of deep tillage on soil physicochemical properties and key nitrogen transformation pathways, including nitrification, denitrification, anammox, and DNRA, across different soil depths (0–10, 10–20, 20–30, 30–50, and 50–100 cm) in Spartina alterniflora-invaded coastal wetlands. Deep tillage significantly restructured the distribution of soil moisture (p < 0.05), pH (p > 0.05), electrical conductivity (p < 0.05), and nutrients, promoting NO₃⁻-N accumulation in deeper layers while reducing NH₄⁺-N concentrations in surface soils (p < 0.05). It markedly enhanced denitrification and DNRA rates (p < 0.05), suppressed surface nitrification (p < 0.05), and altered the vertical distribution of anammox activity. Correlation analysis revealed that NH₄⁺-N and NO₃⁻-N concentrations were the primary drivers of nitrogen transformation, with pH and electrical conductivity playing secondary roles. Overall, deep tillage stimulated nitrogen removal processes and affected net ammonium changes. These findings reveal that deep tillage can stimulate nitrogen removal processes by alleviating soil compaction and altering nitrogen transformation pathways, thus supporting biogeochemical recovery mechanisms after deep tillage. These insights provide scientific guidance for the ecological restoration of Spartina alterniflora-invaded coastal wetlands. Full article

Rice paddy fields are sustainable agricultural systems as soil microorganisms help maintain nitrogen fertility through generating ammonium. In these soils, dissimilatory nitrate reduction to ammonium (DNRA), nitrogen fixation, and denitrification are closely linked. DNRA and denitrification share the same initial steps and nitrogen gas, the end product of denitrification, can serve as a substrate for nitrogen fixation. However, the microorganisms responsible for these three reductive nitrogen transformations, particularly those focused on ammonium generation, have not been comprehensively characterized. In this study, we used stable isotope probing with ¹⁵NO₃⁻, ¹⁵N₂O, and ¹⁵N₂, combined with 16S rRNA high-throughput sequencing and metatranscriptomics, to identify ammonium-generating microbial consortia in paddy soils. Our results revealed that several bacterial families actively contribute to ammonium generation under different nitrogen substrate conditions. Specifically, Geobacteraceae (N₂O and +N₂), Bacillaceae (+NO₃⁻ and +N₂), Rhodocyclaceae (+N₂O and +N₂), Anaeromyxobacteraceae (+NO₃⁻ and +N₂O), and Clostridiaceae (+NO₃⁻ and +N₂) were involved. Many of these bacteria participate in key ecological processes typical of paddy environments, including iron or sulfate reduction and rice straw decomposition. This study revealed the ammonium-generating microbial consortia in paddy soil that contain several key bacterial drivers of multiple reductive nitrogen transformations and suggested their diverse functions in paddy soil metabolism. Full article

To date, the nitrogen metabolism pathways and salt-tolerance mechanisms of halophilic denitrifying bacteria have not been fully studied, and full-scale engineering trials with saline fly ash-washing wastewater have not been reported. In this study, we isolated and screened a halophilic denitrifying bacterium (Marinobacter sp.), GH-1, analyzed its nitrogen metabolism pathways and salt-tolerance mechanisms using whole-genome data, and explored its nitrogen removal characteristics under both aerobic and anaerobic conditions at different salinity levels. GH-1 was then applied in a full-scale engineering project to treat saline fly ash-washing leachate. The main results were as follows: (1) Based on the integration of whole-genome data, it is preliminarily hypothesized that the strain possesses complete nitrogen metabolism pathways, including denitrification, a dissimilatory nitrate reduction to ammonium (DNRA), and ammonium assimilation, as well as the following three synergistic strategies through which to counter hyperosmotic stress: inorganic ion homeostasis, organic osmolyte accumulation, and structural adaptations. (2) The strain demonstrated effective nitrogen removal under aerobic, anaerobic, and saline conditions (3–9%). (3) When applied in a full-scale engineering system treating saline fly ash-washing wastewater, it improved nitrate nitrogen (NO₃⁻-N), total nitrogen (TN), and chemical oxygen demand (COD) removal efficiencies by 31.92%, 25.19%, and 31.8%, respectively. The proportion of Marinobacter sp. increased from 0.73% to 3.41% (aerobic stage) and 2.86% (anoxic stage). Overall, halophilic denitrifying bacterium GH-1 can significantly enhance the nitrogen removal efficiency of saline wastewater systems, providing crucial guidance for biological nitrogen removal treatment. Full article

Nitrate is the most prevalent inorganic pollutant in aquatic environments, posing a significant threat to human health and the ecological environment, especially in lakes and groundwater, which are located in the high agricultural activity intensity areas. In order to reveal the sources of nitrogen pollution in lakes and groundwater, this study of the transformation mechanism of nitrogen in the interaction zone between lakes and groundwater has become an important foundation for pollution prevention and control. The coupling effect between the biogeochemical processes of nitrate and iron has been pointed out to be widely present in various water environments in recent years. However, the impact of iron minerals on nitrate reduction in the lake–groundwater interaction zone of a high-salinity environment still remains uncertain. Based on the sediment and water chemistry characteristics of the Chagan Lake–groundwater interaction zone in northeastern China (groundwater TDS: 420~530 mg/L, Na⁺: 180~200 mg/L, and Cl⁻: 15~20 mg/L and lake water TDS: 470~500 mg/L, Na⁺: 210~240 mg/L, and Cl⁻: 71.40~87.09 mg/L), this study simulated relative oxidizing open system conditions and relative reducing closed conditions to investigate hematite and siderite effects on nitrate reduction and microbial behavior. The results indicated that both hematite and siderite promoted nitrate reduction in the closed system, whereas only siderite promoted nitrate reduction in the open system. Microbial community analysis indicated that iron minerals significantly promoted functional bacterial proliferation and restructured community composition by serving as electron donors/acceptors. In closed systems, hematite addition preferentially enriched Geobacter (denitrification, +15% abundance) and Burkholderiales (DNRA, +12% abundance), while in open systems, siderite addition fostered a distinct iron-carbon coupled metabolic network through Sphingomonas enrichment (+48% abundance), which secretes organic acids to enhance iron dissolution. These microbial shifts accelerated Fe(II)/Fe(III) cycling rates by 37% and achieved efficient nitrogen removal via combined denitrification and DNRA pathways. Notably, the open system with siderite amendment demonstrated the highest nitrate removal efficiency (80.6%). This study reveals that iron minerals play a critical role in regulating microbial metabolic pathways within salinized lake–groundwater interfaces, thereby influencing nitrogen biogeochemical cycling through microbially mediated iron redox processes. Full article

Carbonate rock dissolution (CRD) in karst areas generates abundant ions, which contribute significantly to nitrogen (N) transformation in paddy ecosystems. However, little is known about the microbial mechanisms by which CRD ions (Ca²⁺, Mg²⁺, HCO₃⁻/CO₃²⁻, and OH-) regulate N balance. In this experiment, rice pot studies were conducted using karst soil (S1), karst soil with removed carbonate minerals (S2), non-karst soil (S3), and non-karst soil with additional carbonate minerals (S4). The effects of CRD on N-metabolizing microorganisms and functional genes in N metabolism were investigated using metagenomic sequencing technology. Six N metabolism pathways, including N fixation, nitrification, denitrification, dissimilatory nitrate reduction to ammonia (DNRA), assimilatory nitrate reduction to ammonia (ANRA), and complete nitrification (comammox) were revealed. Compared with S3, the relative abundance of the denitrification module (M00529) in S1 clearly increased by 1.52%. Additionally, compared to S3, the relative abundance of the complete nitrification (comammox) module (M00804) in S4 decreased by 0.66%. Proteobacteria and Anaeromyxobacter were significant contributors to variations in N metabolism. Key factors that influenced variations in N metabolism included Ca²⁺, Mg²⁺, and pH. This study explored the effects of CRD on N-metabolizing microorganisms and functions, which was of great significance to the N cycle in karst paddy ecosystems. Full article

Riverbank filtration (RBF) technology has been applied and investigated worldwide for water supplies due to its sustainable water quantity guarantee and reliable quality improvement. In this work, the development history, application status, research progress, and technical overview of RBF are reviewed and summarized. RBF usually uses rivers, lakes, and groundwater as raw water, with a few cases using seawater. Nitrogen removal in RBF systems primarily occurs through key geochemical processes such as adsorption, denitrification, organic nitrogen mineralization, and dissimilatory nitrate reduction to ammonium (DNRA). For the attenuation of emerging contaminants in groundwater environments, key processes such as filtration, adsorption, and biotransformation play a crucial role, and microorganisms are essential. Based on a discussion of the advantages and disadvantages, we proposed the research prospects of RBF. To further enhance the water-supply safety and security with RBF, the mechanisms of surface water and groundwater interaction, pollutant removal, and blockage; the impact of capturing surface water on the stability of river ecosystems; and the coupling and synergistic effect of RBF with other water treatment technologies should be deeply investigated. Full article

Urban landscape lakes are increasingly at risk of nitrogen-induced eutrophication. Microbial nitrogen transformation plays a crucial role in reducing nitrogen levels in these lakes. However, the relationships between microbial communities, nitrogen functional genes, and nitrogen dynamics in water and sediment, along with their underlying mechanisms, remain unclear. In this study, we systemically investigated the spatial distributions of physicochemical indicators in the overlying water and sediment in a typical urban landscape lake, Zizhuyuan Park, and the microbial communities and nitrogen cycling genes in the surface sediments of the lake connection (CO), side (SI), and center (CE) were evaluated via macrogenetic sequencing technology to analyze their relationships with environmental factors. The results revealed that the concentrations of TN, NO₃⁻, and NH₄⁺ in the lake water were within the ranges of 1.36~2.84, 0.98~1.92, and 0.01~0.29 mg·L⁻¹, respectively. The concentrations of TN, NO₃⁻, and NH₄⁺ in the sediments ranged from 1.17~3.47 g·kg⁻¹, 0.88~1.94 mg·kg⁻¹, and 5.61~10.09 mg·kg⁻¹, respectively. The contents of NH₄⁺ in water, TN and NO₃⁻ in sediments were significantly different in spatial distribution (p < 0.05). At the CE site, the Shannon diversity index was the highest and differed significantly from the values at the SI and CO sites (p < 0.01).The sediments of Central Lake contained a total of 36 phyla and 1303 genera of microorganisms. Proteobacteria (62.88–64.83%) and Actinobacteria (24.84–26.62%) accounted for more than 85% of the microorganisms. Nitrospirae, Ignavibacteriae, and Bacteroidetes were significantly different (p < 0.05) at the CE, and Planctomycetes were significantly different (p < 0.05) at the CO. The functional gene nrfA exhibited the highest abundance, followed by napA, nosZ, nirS, hao, ureC, norB, nifH, nirK, hdhA, nifB, and amoA. The abundances of hao and nifH differed significantly at various locations in Central Lake (p < 0.05). The key nitrogen transformation processes in the sediments, ranked by contribution rate, were DNRA, denitrification, nitrification, ammoniation, nitrogen fixation, and anammox. The six nitrogen processes showed significant differences (p < 0.01) in spatial distribution. The pH, TN, NO₃⁻, NH₄⁺, C/N ratio of the sediment, and NH₄⁺ in the lake water impact the microbial community and nitrogen conversion process. The sediment should be cleaned regularly, and the water cycle should be strengthened in urban landscape lakes to regulate microorganisms and genes and ultimately reduce nitrogen and control eutrophic water. This study can provide a reference for improving and managing lake water environments in urban landscapes. Full article

During the process of managed aquifer recharge (MAR), when the aerobic surface water is recharged into the reductive aquifer, the redox environment changes along the water pathway. MAR practice can reshape the initial groundwater bacterial community, and further induce variations in the bacteria-mediated hydrochemical reactions. In this study, laboratory-scale column experiments were conducted to simulate the processes of aerobic/anaerobic recharge to aquifer. The results showed that the concentration of DO during the aerobic recharge was higher than that of the anaerobic recharge, and ORP showed a similar trend. Active nitrogen transformation was observed during the simulated MAR processes. In the early stages of both the aerobic and anaerobic recharges, nitrate reduction occurred due to denitrification and DNRA. However, in the late stages, nitrification might happen in the aerobic column, and nitrate reduction remained the major process in the anaerobic column. For the bacterial community, Massilia, Ralstonia, Legionella, and Curvibacter predominated under the aerobic recharge. Comparatively, Cedecea, Cupriavidus, and Ralstonia maintained high relative abundances under the anaerobic recharge. Our study provides essential information about the characteristics of bacterial-mediated hydrochemical reactions during the MAR process. The result would enhance understanding of MAR activities and provide valuable insights into the groundwater resources’ sustainable development and management. Full article

Background/Objectives: Chemical fumigation can effectively inhibit the occurrence of soil-borne diseases; however, this approach can negatively affect the structure of the soil microbial community. The combination of soil fumigant and organic fertilizer application thus represents a widely adopted strategy in agricultural practice. Traditional Chinese medicine residue (TCMR) is a high-quality organic fertilizer; however, the impact of post-fumigation TCMR application on keystone taxa and their functional traits remains uncertain. Methods: This study examined the effects of five fertilization treatments on the diversity, key species, and related functional genes of microbial communities in rhizosphere soil of continuous cropping pepper. Results: Chemical fumigation followed by TCMR application markedly enhanced soil nutrient content in the rhizosphere and significantly influenced microbial community composition as well as functional gene patterns associated with microbial nitrogen cycling. It was also strongly correlated with soil bioavailable nitrogen content. The abundance of keystone bacterial species (Pseudomonadota, Actinomycetota, and Bacillota) substantially increased following TCMR application, alongside a notable rise in Ascomycota abundance within the fungal community. This shift contributed to an increase in beneficial bacterial abundance while reducing that of harmful bacteria. Additionally, TCMR addition affected the abundance of denitrification and DNRA genes involved in nitrogen cycling; specifically, nirB and nirK were strongly associated with soil organic nitrogen content. Conclusions: The combined application of chemical fumigants and TCMR modified the composition of keystone microbial community species by influencing rhizosphere soil TN and other nutrients, and these alterations were linked to multiple nitrogen-cycling functional genes. Full article

The investigation of metabolic pathways and regulatory mechanisms in newly discovered species can offer valuable insights into the nitrogen removal function of heterotrophic nitrification–aerobic denitrification (HN-AD) bacteria. To investigate the nitrogen removal mechanism of a new genus, Delftia, we analyzed the complete genome, metabolic pathways, and the related genes of Delftia sp. B7. We further examined the nitrogen removal capacity of Delftia sp. B7 under various nitrogen sources and real wastewater. Our results demonstrate the presence of several genes in Delftia sp. B7, including narGHI, nasAB, nirK, nirS, nirBD, norBC, nosZ, nxrAB, gdhA, glnA, gltBD, amt, and nrt. These genes encode enzymes that facilitate ammonia assimilation, assimilatory nitrate reduction to nitrite, HN-AD, and dissimilatory nitrate reduction (DNRA) in Delftia sp. B7. Specifically, we propose an HN-AD pathway in Delftia sp. B7, NH₄⁺-N → NH₂OH → NO₂⁻-N → NO₃⁻-N → NO₂⁻-N → NO → N₂O → N₂, which accounts for the majority of nitrogen removal. Here, the transformation of NH₄⁺-N to NO₂⁻-N was achieved by unknown enzymes or by another pathway. When treating municipal wastewater, Delftia sp. B7 was able to remove 45.62 ± 1.29% of TN. These findings provide a theoretical basis for utilizing microbial resources to mitigate nitrogen contamination. Full article