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• Denitrification is predominant in surface coastal mangrove sediments, while DNRA becomes more advantageous at deeper depths. • Functional gene quantification and microbial profiles validate activity trends by depth. • C/N, salinity, and carbon quality regulate denitrification-DNRA competition across depths. Mangrove aquatic ecosystems receive substantial nitrogen (N) inputs from both land and sea, playing critical roles in modulating coastal N fluxes. The microbially-mediated competition between denitrification and dissimilatory nitrate reduction to ammonium (DNRA) in mangrove sediments significantly impacts the N fate and transformation processes. Despite their recognized role in N loss or retention in surface sediments, how these two processes vary with sediment depths and their influential factors remain elusive. Here, we employed a comprehensive approach combining 15N isotope tracer, quantitative PCR (qPCR) and metagenomics to verify the vertical dynamics of denitrification and DNRA across five 100-cm mangrove sediment cores. Our results revealed a clear vertical partitioning, with denitrification dominated in 0-30 cm sediments, while DNRA played a greater role with increasing depths. Quantification of denitrification and DNRA functional genes further explained this phenomenon. Taxonomic analysis identified Pseudomonadota as the primary denitrification group, while Planctomycetota and Pseudomonadota exhibited high proportion in DNRA group. Furthermore, genome-resolved metagenomics revealed multiple salt-tolerance strategies and aromatic compound utilization potential in denitrification assemblages. This allowed denitrification to dominate in oxygen-fluctuating and higher-salinity surface sediments. However, the elevated C/N in anaerobic deep sediments favored DNRA, tending to generate biologically available NH 4 +. Together, our results uncover the depth-related variations in the microbially-mediated competition between denitrification and DNRA, regulating N dynamics in mangrove ecosystems. [Display omitted] [ABSTRACT FROM AUTHOR]

• We summarized adaptive versatility of anammox bacteria associated with organics. • We re-evaluated the Krebs cycle in anammox bacteria for mixotrophic metabolism. • Brocadia exhibit remarkable organotrophic lifestyle in eutrophic surroundings. • Nitrate reduction to ammonium in anammox bacteria is associated with organotrophy. Anaerobic ammonium oxidizing (anammox) bacteria, which were first discovered nearly three decades ago, are crucial for treating ammonium-containing wastewater. Studies have reported on the biochemical nitrogen conversion process and the physiological, phylogenic, and ecological features of anammox bacteria. For a long time, anammox bacteria were assumed to have a lithoautotrophic lifestyle. However, recent studies have suggested the functional versatility of anammox bacteria. Genome-based analysis and experiments with enrichment cultures have demonstrated the association of the metabolic activities of anammox bacteria with different stress conditions, revealing the importance of utilizing specific organic substances, including organoautotrophy, for growth and adaptation to stress conditions. Our understanding regarding the utilization and metabolism of organic substances and their associations with anammox reactions in anammox bacteria is growing but still incomplete. In this review, we summarize the effect of the utilization of organic substances by anammox bacteria under environmental stress conditions, emphasizing their potential organoautotrophic activity and metabolic flexibility. Although most anammox bacteria may utilize specific organic substances, Ca. Brocadia exhibited the highest level of mixoautotrophic activity. The environmental factors that substantially affect the organoautotrophic activities of anammox bacteria were also examined. This review provides a new perspective on the organoautotrophic capacity of anammox bacteria. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract Stormwater control measures (SCMs) have the potential to mitigate negative effects of watershed development on hydrology and water quality. Stormwater regulations and scientific literature have assumed that SCMs are important sites for denitrification, the permanent removal of nitrogen, but this assumption has been informed mainly by short-term loading studies and measurements of potential rates of nitrogen cycling. Recent research concluded that SCM nitrogen removal can be dominated by plant and soil assimilation rather than by denitrification, and rates of nitrogen fixation can exceed rates of denitrification in SCM sediments, resulting in a net addition of nitrogen. Nitrogen cycling measurements from other human-impacted aquatic habitats have presented similar results, additionally suggesting that dissimilatory nitrate reduction to ammonium (DNRA) and algal uptake could be important processes for recycling nitrogen in SCMs. Future research should directly measure a suite of nitrogen cycling processes in SCMs and reveal controlling mechanisms of individual rate processes. There is ample opportunity for research on SCM nitrogen cycling, including investigations of seasonal variation, differences between climatic regions, and trade-offs between nitrogen removal and phosphorus removal. Understanding nitrogen dynamics within SCMs will inform more efficient SCM design and management that promotes denitrification to help mitigate negative effects of urban stormwater on downstream ecosystems. Graphical abstract Image 1 Highlights • SCMs are considered important sites for denitrification. • Studies reporting high denitrification rates in SCMs mostly used indirect assays. • Direct denitrification measurements suggest temporary removal pathways may dominate in SCMs. • Nitrogen cycling within SCMs should be measured using direct methods. • Quantifying seasonal and spatial variability of SCM nitrogen cycling is critical. [ABSTRACT FROM AUTHOR]

Sediment microbes have a great potential to transform reactive N to harmless N 2 , thus decreasing wastewater nitrogen load into aquatic ecosystems. Here, we examined if spatial allocation of the wastewater discharge by a specially constructed sediment diffuser pipe system enhanced the microbial nitrate reduction processes. Full-scale experiments were set on two Finnish lake sites, Keuruu and Petäjävesi, and effects on the nitrate removal processes were studied using the stable isotope pairing technique. All nitrate reduction rates followed nitrate concentrations, being highest at the wastewater-influenced sampling points. Complete denitrification with N 2 as an end-product was the main nitrate reduction process, indicating that the high nitrate and organic matter concentrations of wastewater did not promote nitrous oxide (N 2 O) production (truncated denitrification) or ammonification (dissimilatory nitrate reduction to ammonium; DNRA). Using 3D simulation, we demonstrated that the sediment diffusion method enhanced the contact time and amount of wastewater near the sediment surface especially in spring and in autumn, altering organic matter concentration and oxygen levels, and increasing the denitrification capacity of the sediment. We estimated that natural denitrification potentially removed 3–10% of discharged wastewater nitrate in the 33 ha study area of Keuruu, and the sediment diffusion method increased this areal denitrification capacity on average 45%. Overall, our results indicate that sediment diffusion method can supplement wastewater treatment plant (WWTP) nitrate removal without enhancing alternative harmful processes. [ABSTRACT FROM AUTHOR]

• Denitrification and DNRA rates were modulated mainly by their gene abundances, followed by the environmental factors. • Denitrification rates significantly increased as further eutrophication, but DNRA rates were not. • Pseudomonas and Anaeromyxobacter was the dominant genus mediated denitrification and DNRA, respectively. Traditional views indicate that eutrophication and subsequent algal blooms favor denitrification and dissimilatory nitrate reduction to ammonium (DNRA) in lake ecosystems. However, lakes tend to show an increasing propensity for inorganic nitrogen (N) limitation as they become more eutrophic. Thus, the influence of further eutrophication on denitrification and DNRA in eutrophic lakes are unclear due to the uncertainty of N availability. To fill this gap, we investigated the genes abundance (AOA, AOB, nirS, nirK and nrfA) and the composition of N-cycling microbes through quantitative PCR and 16S rRNA sequencing analysis, respectively, in 15 shallow eutrophic lakes of the Yangtze-Huaihe River basin, China. The results indicated that denitrification and DNRA rates could be modulated mainly by their functional gene abundances (nirS, nirK and nrfA), followed by the environmental factors (sediment total organic carbon and nitrogen). Denitrification rates significantly increased from slightly to highly eutrophic lakes, but DNRA rates were not. An explanation is that nitrification provided ample nitrate for denitrification, and this cooperative interaction was indicated by the positive correlation of their gene abundances. In addition, Pseudomonas and Anaeromyxobacter was the dominant genus mediated denitrification and DNRA, showing the potential to perform facultative anaerobic and strict anaerobic nitrate reduction, respectively. High level of dissolved oxygen might favor the facultatively aerobic denitrifiers over the obligately anaerobic fermentative DNRA bacteria in these shallow lakes. Chlorophyll a had a weak but positive effect on the gene abundances for nitrification (AOA and AOB). Further eutrophication had an indirect effect on denitrification and DNRA rates through modulating the genes abundances of N-cycling microbes. [Display omitted] [ABSTRACT FROM AUTHOR]

Evaluation of the environmental benefits of constructed wetlands (CWs) requires an understanding of their impacts on the groundwater quality under the wetlands. Empirical mass-balance (nitrogen in/nitrogen out) approaches for estimating nitrogen (N) removal in CWs do not characterise the final fate of N; where nitrate (NO 3 − -N) could be reduced to either ammonium (NH 4 + -N) or N 2 with the potential for significant production of N 2 O. Herein, in situ denitrification and DNRA (dissimilatory nitrate reduction to ammonium) rates were measured in groundwater beneath cells of an earthen lined integrated constructed wetland (ICW, used to remove the nutrients from municipal wastewater) using the 15 N-enriched NO 3 − -N push-pull method. Experiments were conducted utilising replicated (n = 3) shallow (1 m depth) and deep (4 m depth) piezometers installed along two control planes. These control planes allowed for the assessment of groundwater underlying high (Cell 2, septic tank waste) and low (Cell 3) load cells of the ICW. Background piezometers were also installed off-site. Results showed that denitrification (N 2 O-N + N 2 -N) and DNRA were major NO 3 − -N consumption processes accounting together for 54–79% of the total biochemical consumption of the applied NO 3 − -N. Of which 14–16% and 40–63% were consumed by denitrification and DNRA, respectively. Both processes differed significantly across ICW cells indicating that N transformation depends on nutrient loading rates and were significantly higher in shallow compared to the deep groundwater. In such a reduced environment (low dissolved oxygen and low redox potential), higher DNRA over the denitrification rate can be attributed to the high C concentration and high TC/NO 3 − -N ratio. Low pH (6.5–7.1) in this system might have limited denitrification to some extent to an incomplete state, evidenced by a high N 2 O-N/(N 2 O-N+N 2 -N) ratio (0.35 ± 0.17, SE). A relatively higher N 2 O-N/(N 2 O-N+N 2 -N) ratio and higher DNRA rate over denitrification, suggest that the end products of N transformations are reactive. This N 2 O can be consumed to N 2 and/or emitted to the atmosphere. The DNRA rate and accumulation of NH 4 + -N indicated that the ICW created a suitable groundwater biogeochemical environment that enhanced NO 3 − -N reduction to NH 4 + -N. This study showed that CWs significantly influence NO 3 − -N attenuation to reactive forms of N in the groundwater beneath them and that solely focusing on within wetland NO 3 − -N attenuation can underestimate the environmental benefits of wetlands. [ABSTRACT FROM AUTHOR]

• Double-edged sword effects of DNRA bacteria on anammox performance were studied. • Overgrowth DNRA bacteria out competed anammox cell with toxic NO 2 −-N accumulation. • Predominant C. Kuenenia were replaced by C. Brocadia with high NO 2 −-N loading. • DNRA showed positive effects on anammox with low Ratio NH 4 +-N: NO 2 −-N (1.25). Dissimilatory nitrate reduction to ammonium (DNRA) bacteria imposing double-edged sword effects on anammox bacteria were investigated in an anammox-membrane bioreactor (MBR) experiencing an induced crash-recovery event. During the experiment, the anammox-MBR was loaded with NH 4 +-N:NO 2 −-N ratios (Ratio NH 4 +-N: NO 2 −-N) of 1.20–1.60. Initially, the anammox-MBR removed over 95% of 100 mg/L NH 4 +-N and 132 mg/L NO 2 −-N (Ratio NH 4 +-N: NO 2 −- N = 0.76, the well accepted stoichiometric Ratio NH 4 +-N: NO 2 −-N for anammox) in the influent (Stage 0). Then, we induced a system crash-recovery event via nitrite shock loadings to better understand responses from different guilds of bacteria in anammox-MBR, loaded with 1.60 Ratio NH 4 +-N: NO 2 −-N with 100 mg/L NO 2 −-N in the influent (Stage 1). Interestingly, the nitrogen removal by anammox bacteria was maintained for about 20 days before starting to decrease significantly. In Stage 2, we further increased influent nitrite concentration to 120 mg/L (1.33 Ratio NH 4 +-N: NO 2 −-N) to simulate a high nitrite toxicity scenario for a short period of time. As expected, nitrogen removal efficiency dropped to only 16.8%. After the induced system crash, anammox-MBR performance recovered steadily to 93.2% nitrogen removal with a 1.25 Ratio NH 4 +-N:NO 2 −-N and a low nitrite influent concentration of 80 mg/L NO 2 −-N. Metagenomics analysis revealed that a probable causality of the decreasing nitrogen removal efficiency in Stage 1 was the overgrowth of DNRA-capable bacteria. The results showed that the members within the Ignavibacteriales order (21.7%) out competed anammox bacteria (17.0%) in the anammox-MBR with elevated nitrite concentrations in the effluent. High NO 2 −-N loading (120 mg N/L) further caused the predominant Candidatus Kuenenia spp. were replaced by Candidatus Brocadia spp. Therefore, it was evident that DNRA bacteria posed negative effects on anammox with 1.60 Ratio NH 4 +-N: NO 2 −-N. Also, when 120 mg/L NO 2 −-N fed to anammox-MBR (Ratio NH 4 +-N: NO 2 −- N = 1.33), canonical denitrification became the primary nitrogen sink with both DNRA and anammox activities decreased. They probably fed on lysed microbial cells of anammox and DNRA. In Stage 3, a low Ratio NH 4 +-N: NO 2 −-N (1.25) with 80 mg/L NO 2 −-N was used to rescue the system, which effectively promoted DNRA-capable bacteria growth. Although anammox bacteria's abundance was only 7.7% during this stage, they could be responsible for about 90% of the total nitrogen removal during this stage. [Display omitted] [ABSTRACT FROM AUTHOR]

• Increased salinity inhibited denitrification rates in inland lakes. • Nitrogen retention capacity is relatively stronger in saline than freshwater lakes. • Climate change is expected to alter lake N fate via changing in salinity. Salinization caused by climate change and nitrogen (N) pollution are both important environmental threats for inland lakes. However, evaluating their interactive effects continues to be challenging. Here, field observation and microcosmic experiments were conducted in six lakes of East Asia with the different salinity and climate characteristics, to explore the response of the key N cycle processes related to N fate to the climate-induced change in salinity. The results indicated that increased salinity inhibited denitrification, which was the outcome of two cumulative effects: the long-term microbial adaptation effect and the direct salinity stress. Whereas increased salinity had unsignificant or positive effects on dissimilatory nitrate reduction to ammonium. It had caused that N retention capacity is relatively stronger in saline than freshwater lakes. Inland lakes are long-term basin-wide integrators of climatic conditions that drying (salinization) and wetting (desalination) with climate change. In semi-arid regions of East Asia, lake shrinkage, salinization and increasing temperature driven by climate warming and drying may exert a negative impact on N pollution through concentrating, decreasing denitrification and increasing ammonium release from sediment. The threat of climate change on these lakes is not just the quantity of water, but its quality. [Display omitted] [ABSTRACT FROM AUTHOR]

• Algal bloom caused high C/NO 3 −-N ratio in sediment;. • High C/NO 3 −-N ratio triggered DNRA over denitrification;. • Alkyl carbon-oxygen bond was responsible for DNRA induction;. • Less represented bacterial species were the main contributors for DNRA. Twelve sampling sites from two basins of Lake Chaohu were studied seasonally from June 2020 to April 2021 in Hefei City (China) to better understand the effect of organic carbon (C) quantity and composition on nitrate (NO 3 −-N) reduction pathways. Serious algal bloom in the west basin of Lake Chaohu (WLC) resulted in higher organic C accumulation and NO 3 −-N deficiency in interstitial water compared to the east basin of Lake Chaohu (ELC), jointly leading to a high C/NO 3 −-N ratio. This triggered dissimilatory nitrate reduction to ammonium (DNRA) over denitrification in terms of higher DNRA rate, nitrogen retaining index (NRI), and nrfA gene abundance mediating DNRA. Furthermore, high oxygen-alkyl C and abundance of functional genes mediating labile organic C decomposition and DNRA suggested that the alkyl carbon-oxygen bond was responsible for DNRA induction. Different bacterial community composition and diversity involved in C and nitrogen (N) metabolism in two basins indicated that bacteria in sediments of WLC were more active in NO 3 −-N reduction. Spearman correlation analysis showed that the less represented genera, such as Thiobacillus and Clostridium , were positively correlated with both organic C and NO 3 −-N reduction rates, respectively. Hence, organic C composition could affect NO 3 −-N reduction function by shaping the specific bacterial community. [Display omitted] [ABSTRACT FROM AUTHOR]

• DNRA-driven SOB enhances the durability of nitrate-mediated souring control. • Heterotrophic DN reduces the durability of nitrate-mediated souring control. • Autotrophic and heterotrophic nitrate reduction make SRB adaptable to nitrate. • Bio-augmented souring control combined with bio-demulsification is achieved. Biological souring (producing sulfide) is a global challenge facing anaerobic water bodies, especially the oil reservoir fluids. Nitrate injection has demonstrated great potential in souring control, and dissimilatory nitrate reduction to ammonium (DNRA) bacteria was proposed to play crucial roles in the process. How to durably control souring with nitrate amendment, however, remains undiscovered. Herein, Gordonia sp. TD-4, a DNRA-driven sulfide-oxidizing bacterium, was used to elucidate the effects of bio-augmentation with DNRA bacteria on the durability of nitrate-mediated souring control. The results revealed that nitrate amendment combined with bio-augmentation with TD-4 after souring could effectively control souring and enhance the durability of nitrate-mediated souring control, while nitrate amendment before souring failed to persistently control souring. Nitrate amendment before and after souring resulted in different evolution dynamics of nitrate-reducing bacteria. Denitrifying bacteria were enriched in reactors amended with nitrate before souring or in dissolved sulfide exhausted reactors amended with nitrate after souring. The heterotrophic denitrifying activity of denitrifying bacteria, however, decreased the durability of nitrate-mediated souring control. Comparative and functional genomics analysis identified potential niche adaptation mechanisms (autotrophic and heterotrophic nitrate/nitrite reduction, including DNRA and denitrification) of predominant SRB in nitrate-amended environments, which were responsible for the rapid resumption of sulfide accumulation after the depletion of nitrate and nitrite. Pulsed injection of nitrate combined with bio-augmentation with DNRA-driven sulfide-oxidizing bacteria was proposed as a potential method to enhance the durability of nitrate-mediated souring control. The findings were innovatively applied to simultaneous bio-demulsification and souring control of emulsified and sour produced water from the petroleum industry. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: The relative magnitudes of, and factors controlling, denitrification and dissimilatory nitrate reduction to ammonium (DNRA) were measured in the soil of a re-connected temperate floodplain divided into four different land management zones (grazing grassland, hay meadow, fritillary meadow and a buffer zone). Soil samples were collected from each zone to measure their respective potentials for nitrate attenuation using 15N both at the surface and at depth in the soil column and additional samples were collected to measure the lability of the organic carbon. Denitrification capacity ranged between 0.4 and 4.2 (μmol N g−1 dry soil d−1) across the floodplain topsoil and DNRA capacity was an order of magnitude lower (0.01–0.71 μmol N g−1 d−1). Land management practice had a significant effect on denitrification but no significant effects were apparent for DNRA. In this nitrogen-rich landscape, spatial heterogeneity in denitrification was explained by differences in lability and the magnitude of organic carbon associated with different management practices (mowing and grazing). The lability of organic carbon was significantly higher in grazing grassland in comparison to other ungrazed areas of the floodplain, and consequently denitrification capacity was also highest in this area. Our results indicate that bacteria capable of DNRA do survive in frequently flooded riparian zones, and to a limited extent, compete with denitrification for nitrate, acting to retain and recycle nitrogen in the floodplain. Exponential declines in both denitrification and DNRA capacity with depth in the floodplain soils of a hay meadow and buffer zone were controlled primarily by the organic carbon content of the soils. Furthermore, grazing could be employed in re-connected, temperate floodplains to enhance the potential for nitrate removal from floodwaters via denitrification. [Copyright &y& Elsevier]

Abstract: We analyzed benthic fluxes of inorganic nitrogen, denitrification and dissimilatory nitrate reduction to ammonium (DNRA) rates in hypolimnetic sediments of lowland lakes. Two neighbouring mesotrophic (Ca'' Stanga; CS) and hypertrophic (Lago Verde; LV) lakes, which originated from sand and gravel mining, were considered. Lakes are affected by high nitrate loads (0.2–0.7mM) and different organic loads. Oxygen consumption, dissolved inorganic carbon, methane and nitrogen fluxes, denitrification and DNRA were measured under summer thermal stratification and late winter overturn. Hypolimnetic sediments of CS were a net sink of dissolved inorganic nitrogen (−3.5 to −4.7mmolm−2 d−1) in both seasons due to high nitrate consumption. On the contrary, LV sediments turned from being a net sink during winter overturn (−3.5mmolm−2 d−1) to a net source of dissolved inorganic nitrogen under summer conditions (8.1mmolm−2 d−1), when significant ammonium regeneration was measured at the water–sediment interface. Benthic denitrification (0.7–4.1mmolm−2 d−1) accounted for up to 84–97% of total NO3 − reduction and from 2 to 30% of carbon mineralization. It was mainly fuelled by water column nitrate. In CS, denitrification rates were similar in winter and in summer, while in LV summer rates were 4 times lower. DNRA rates were generally low in both lakes (0.07–0.12mmolm−2 d−1). An appreciable contribution of DNRA was only detected in the more reducing sediments of LV in summer (15% of total NO3 − reduction), while during the same period only 3% of reduced NO3 − was recycled into ammonium in CS. Under summer stratification benthic denitrification was mainly nitrate-limited due to nitrate depletion in hypolimnetic waters and parallel oxygen depletion, hampering nitrification. Organic enrichment and reducing conditions in the hypolimnetic sediment shifted nitrate reduction towards more pronounced DNRA, which resulted in the inorganic nitrogen recycling and retention within the bottom waters. The prevalence of DNRA could favour the accumulation of mineral nitrogen with detrimental effects on ecosystem processes and water quality. [Copyright &y& Elsevier]

• Biochar stimulated DNRA and enhanced the NRE of anammox system at low COD/N (0.1–0.5). • Ca. Jettenia caeni was the main bacteria responsible for DNRA metabolism. • The improved ETC by biochar was the reason for the improved anammox SAA and NRE. • Biochar increased the anammox-related (hzs) and complete DNRA-related genes abundance. Coupling dissimilatory nitrate reduction to ammonium (DNRA) pathway with anammox process has a prominent advantage in enhancement of nitrogen removal. However, the anammox bacteria driven-DNRA is difficult to proceed at normal autotrophic circumstance. Herein, for the first time, biochar (prepared by bamboo) was used as a mediator to stimulate the DNRA pathway of anammox bacteria under varying chemical oxygen demand (COD) to nitrogen (COD/N) ratios (0.1–0.7), and the underlying stimulation mechanism was elucidated by metagenomics sequencing analysis. Results showed that biochar addition (10 g/L) stimulated DNRA pathway of anammox bacteria at low COD/N ratios (0.1–0.5), thus enhancing the nitrogen removal efficiency (NRE) of the anammox system by 7.2%–16.4% and 0.9%–3.0%, respectively, compared to that of tests without sodium acetate and biochar (p <0.05). This enhancement was attributed to the improved extracellular electron accepting capacity of anammox biomass by biochar. The easily obtained electrons (from sodium acetate) further increased the relative abundances of anammox-related (hzs) and complete DNRA-related (nap AB and nrf AH) genes (p <0.05), which catalyze electron-consuming reactions. The stimulated anammox pathway and DNRA pathway further increased the specific anammox activity and the relative abundance of anammox bacteria (especially Ca. Jettenia) by 15.5%–23.0% and 11.3%–82.6% compared with that without biochar, respectively. Metagenomics sequencing also revealed that anammox bacteria, Ca. Jettenia caeni , was the main bacteria for DNRA metabolism in this system. Our findings reveal that biochar could selectively stimulate DNRA pathway of anammox bacteria affiliated by a low amount of carbon, which provides a novel strategy to improve the nitrogen removal of anammox-based processes. [Display omitted]. [ABSTRACT FROM AUTHOR]

• A novel iGB-A/PD reactor was developed for treating mainstream wastewaters. • An effluent TN of ∼3 mg•L−1 was achieved at a NRR of 0.8 ± 0.1 kg-N•m−3•d−1. • Multilevel A/PD is responsible for the exceptional performance in the single reactor. • PD and DNRA were responsible for 50% and 25% of nitrate reduction, respectively. This study describes an integrated granular sludge and fixed-biofilm (iGB) reactor innovatively designed to carry out the anammox/partial-denitrification (A/PD) process for nitrogen removal with mainstream municipal wastewater. The iGB-A/PD reactor consists of anammox granules inoculated in the lower region of reactor and an acclimated fixed-biofilm positioned in the upper region. Compared to the other reported A/PD systems for mainstream wastewater treatment, this iGB-A/PD reactor is notable due to its higher quality effluent with a total inorganic nitrogen (TIN) of ∼3 mg•L−1 and operation at a high nitrogen removal rate (NRR) of 0.8 ± 0.1 kg-N•m−3•d−1. Reads-based metatranscriptomic analysis found that the expression values of hzsA and hdh , key genes associated with anammox, were much higher than other functional genes on nitrogen conversion, confirming the major roles of the anammox bacteria in nitrogen bio-removal. In both regions of the reactor, the nitrate reduction genes (napA / narG) had expression values of 56–99 RPM, which were similar to that of the nitrite reduction genes (nirS / nirK). The expression reads from genes for dissimilatory nitrate reduction to ammonium (DNRA), nrfA and nirB , were unexpectedly high, and were over the half of the levels of reads from genes required for nitrate reduction. Kinetic assays confirmed that the granules had an anammox activity of 16.2 g-NH 4 +-N•kg−1-VSS•d−1 and a nitrate reduction activity of 4.1 g-N•kg−1-VSS•d−1. While these values were changed to be 4.9 g- NH 4 +-N•kg−1-VSS•d−1and 4.3 g-N•kg−1-VSS•d−1 respectively in the fixed-biofilm. Mass flux determination found that PD and DNRA was responsible for ∼50% and ∼25% of nitrate reduction, respectively, in the whole reactor, consistent with high effluent quality and treatment efficiency via a nitrite loop. Metagenomic binning analysis revealed that new and unidentified anammox species, affiliated with Candidatus Brocadia, were the dominant anammox organisms. Myxococcota and Planctomycetota were the principal organisms associated with the PD and DNRA processes, respectively. [Display omitted] [ABSTRACT FROM AUTHOR]

• A new genus of anammox bacteria Ca. Loosdrechtii was retrieved from the biofilm. • High activities of core metabolisms and high metabolic versatility of anammox bacteria. • Anammox bacteria survive unfavorable conditions by coupling nitrate reduction to VFAs oxidation. • A new Ca. Brocadia species distributed in anoxic tank and the biofilm simultaneously. Anaerobic ammonium oxidation (anammox) is a key N 2 -producing process in the global nitrogen cycle. Major progress in understanding the core mechanism of anammox bacteria has been made, but our knowledge of the survival strategies of anammox bacteria in complex ecosystems, such as full-scale wastewater treatment plants (WWTPs), remains limited. Here, by combining metagenomics with in situ metatranscriptomics, complex anammox-driven nitrogen cycles in an anoxic tank and a granular activated carbon (GAC) biofilm module of a full-scale WWTP treating landfill leachate were constructed. Four distinct anammox metagenome-assembled genomes (MAGs), representing a new genus named Ca. Loosdrechtii, a new species in Ca. Kuenenia, a new species in Ca. Brocadia, and a new strain in " Ca. Kuenenia stuttgartiensis", were simultaneously retrieved from the GAC biofilm. Metabolic reconstruction revealed that all anammox organisms highly expressed the core metabolic enzymes and showed a high metabolic versatility. Pathways for dissimilatory nitrate reduction to ammonium (DNRA) coupled to volatile fatty acids (VFAs) oxidation likely assist anammox bacteria to survive unfavorable conditions and facilitate switches between lifestyles in oxygen fluctuating environments. The new Ca. Kuenenia species dominated the anammox community of the GAC biofilm, specifically may be enhanced by the uniquely encoded flexible ammonium and iron acquisition strategies. The new Ca. Brocadia species likely has an extensive niche distribution that is simultaneously established in the anoxic tank and the GAC biofilm, the two distinct niches. The highly diverse and impressive metabolic versatility of anammox bacteria revealed in this study advance our understanding of the survival and application of anammox bacteria in the full-scale wastewater treatment system. [Display omitted] [ABSTRACT FROM AUTHOR]

• Prokaryotic microbiomes of surface seawater were interrogated during a HAB event • Genes encoding key DNRA enzymes were highly enriched in HAB-affected regions • Taxonomic affiliations of DNRA genes were disproportionally biased towards Vibrio • Co-occurrence relationship suggests causal association of Vibrio and Prorocentrum Coastal harmful algal blooms (HABs), commonly termed 'red tides', have severe undesirable consequences to the marine ecosystems and local fishery and tourism industries. Increase in nitrogen and/or phosphorus loading is often regarded as the major culprits of increasing frequency and intensity of the coastal HAB; however, fundamental understanding is lacking as to the causes and mechanism of bloom formation despite decades of intensive investigation. In this study, we interrogated the prokaryotic microbiomes of surface water samples collected at two neighboring segments of East China Sea that contrast greatly in terms of the intensity and frequency of Prorocentrum -dominated HAB. Mantel tests identified significant correlations between the structural and functional composition of the microbiomes and the physicochemical state and the algal biomass density of the surface seawater, implying the possibility that prokaryotic microbiota may play key roles in the coastal HAB. A conspicuous feature of the microbiomes at the sites characterized with high trophic state index and eukaryotic algal cell counts was disproportionate proliferation of Vibrio spp., and their complete domination of the functional genes attributable to the dissimilatory nitrate reduction to ammonia (DNRA) pathway substantially enriched at these sites. The genes attributed to phosphorus uptake function were significantly enriched at these sites, presumably due to the P i -deficiency induced by algal growth; however, the profiles of the phosphorus mineralization genes lacked consistency, barring any conclusive evidence with regard to contribution of prokaryotic microbiota to phosphorus bioavailability. The results of the co-occurrence network analysis performed with the core prokaryotic microbiome supported that the observed proliferation of Vibrio and HAB may be causally associated. The findings of this study suggest a previously unidentified association between Vibrio proliferation and the Prorocentrum -dominated HAB in the subtropical East China Sea, and opens a discussion regarding a theoretically unlikely, but still possible, involvement of Vibrio -mediated DNRA in Vibrio - Prorocentrum symbiosis. Further experimental substantiation of this supposed symbiotic mechanism may prove crucial in understanding the dynamics of explosive local algal growth in the region during spring algal blooms. [Display omitted] [ABSTRACT FROM AUTHOR]

• Novel and diverse anammox genera were found in tropical wetland ecosystems. • Anammox accounted for up to 57.4% of nitrogen loss in ex situ batch experiments. • Sulfide-driven DNRA supports anammox by supplying nitrite and/or ammonium. • Anammox activity was inferred from sulfate concentrations and dsr and nrf abundance. • Combining sulfide-driven DNRA and anammox could reduce N 2 O emissions from WWTPs. Wetland ecosystems play an important role in nitrogen cycling, yet the role of anaerobic ammonium oxidation (anammox) in tropical wetlands remains unclear. In the current study the anammox process accounted for 29.8 ~ 57.3% of nitrogen loss in ex situ activity batch tests of microcosms established from anoxic sediments of different tropical wetlands, with the highest activity being 17.95±0.51 nmol-N/g dry sediment/h. This activity was most likely driven by sulfide oxidation with dissimilatory nitrate reduction to ammonium (sulfide-driven DNRA). Microbial community analyses revealed a variety of anammox bacteria related to several known lineages, including Candidatus Anammoximicrobium, Candidatus Brocadia and Candidatus Kuenenia , at different wetlands. Metagenome predictions, batch tests, and isotope-tracing suggested that the high level of anammox activity was due to sulfide-driven DNRA. This was corroborated by a strong correlation (through Pearson's analysis) between the abundance of anammox bacteria and the nrfA (a dissimilatory nitrate reduction to ammonium gene) and dsrA (a sulfate reductase gene) genes, as well as sulfate, ammonium and nitrate concentrations. These correlations suggest syntrophic interactions among sulfate-reducing, sulfide-driven DNRA, and anammox bacterial populations. A better understanding of the role of sulfur in nitrogen loss via the anammox reaction in natural systems could inform development of a viable wastewater treatment strategy that utilizes sulfate to minimize the activity of denitrifying bacteria and thus to reduce nitrous oxide emissions from wastewater treatment plants. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Cyanobacterial blooms change benthic nitrogen (N) cycling in eutrophic lake ecosystems by affecting organic carbon (OC) delivery and changing in nutrients availability. Denitrification, anaerobic ammonium oxidation (anammox), and dissimilatory nitrate reduction to ammonium (DNRA) are critical dissimilatory nitrate reduction pathways that determine N removal and N recycling in aquatic environments. A mechanistic understanding of the influence of algal accumulations on partitioning among these pathways is currently lacking. In the present study, a manipulative experiment in aquarium tanks was conducted to determine the response of dissimilatory nitrate reduction pathways to changes in algal biomass, and the interactive effects of OC and nitrate. Potential dinitrogen (N 2) production and DNRA rates, and related functional gene abundances were determined during incubation of 3–4 weeks. The results indicated that high algal biomass promoted DNRA but not N 2 production. The concentrations of dissolved organic carbon were the primary factor affecting DNRA rates. Low nitrate availability limited N 2 production rates in treatments with algal pellets and without nitrate addition. Meanwhile, the AOAamoA gene abundance was significantly correlated with the nrfA and nirS gene abundances, suggesting that coupled nitrification-denitrification/DNRA was prevalent. Partitioning between N 2 production and DNRA was positively correlated with the ratios of dissolved organic carbon to nitrate. Correspondingly, in Lake Taihu during summer to fall, the relatively high organic carbon/nitrate might favorably facilitate DNRA over denitrification, subsequently sustaining cyanobacterial blooms. Image 1 • Algal accumulations promoted potential DNRA rates, but N 2 production were not. • Low NO 3 − availability limited N 2 production during bloom periods. • The ratios of DOC to NO 3 − drive the partitioning between N 2 production and DNRA. [ABSTRACT FROM AUTHOR]