A Critical Review on Nitrous Oxide Production by Ammonia-Oxidizing Archaea

Tracing the electron transfer behavior driven by hydrophyte-derived carbon materials empowered autotrophic denitrification in iron-based constructed wetlands: Efficacy and enhancement mechanism

Iron-based constructed wetlands (ICWs) displayed great potential in deep nitrogen elimination for low-polluted wastewater. However, the unsatisfactory denitrification performance caused by the limited solubility and sluggish activity of iron substrates needs to be improved in an eco-effective manner. To fill this gap, the bioavailability of iron substrates (iron scraps) affected by wetland biomass-derived carbon materials with potential conductivity were explored. Results indicated that the cumulative removal of TN in biochar-added ICW (BC-ICW) and activated carbon-added ICW (AC-ICW) increased by 29.04 % and 22.96 %, respectively. The carbon matrix of AC played the geo-conductor role to facilitate the rapid release of iron ions, as indicated by the higher TN removal efficiency of AC-ICW (45.36 ± 1.45 %) at the early stage, while the reduced conductivity of AC negatively impacted the nitrogen removal. BC-ICW exhibited intensified denitrification potential, with higher TN removal capacity (52.08 ± 3.04 %) and effluent Fe2+ concentration. Electroactive bacteria (EB) (Geobacter, Desulfovibrio, Shewanella, etc.) associated with extracellular electron transfer were enriched in BC-ICW, as well as the expanded niches breadth and improved microbial community diversity. The electron-shuttling effect of BC was mainly attributed to its oxygenated functional groups (quinone/phenolic moieties), which supported the electron transfer from EB to extracellular iron oxides, as evidenced by the increased Fe(III)(hydro)oxides bioavailability. Besides, biochar concurrently up-regulated the gene expression of electron transport chains/mediators and denitrification reductases, suggesting that BC boosted the active iron cycle and iron-mediated autotrophic denitrification in ICWs by accelerating intracellular and extracellular electron transfer. This work explored the electron transfer behavior of biomass-derived carbon materials coupled with ICWs to enhance denitrification, providing insights into the sustainable application of biomass derived carbon-assisted ICWs in tertiary treatment.

Path to zero emission of nitrous oxide in sewage treatment: is nitrification controllable or avoidable?

Amid growing concerns over climate change, the need to reduce nitrous oxide (N2O) emissions from sewage treatment is more urgent than ever. Sewage treatment plants are significant sources of N2O due to its production as an intermediate in nitrification and its release into the air during aeration. Effective management of the nitrification process is therefore vital for controlling or eliminating these emissions. Despite substantial efforts to quantify and understand N2O emissions from sewage treatment, success in reducing them has been limited. This review discusses and proposes promising solutions for reducing N2O emissions in sewage treatment, evaluates the potential of various strategies, and identifies ways to accelerate their development and implementation.

The regulatory mechanism controlling nitrification inhibitors-induced mitigation of nitrification and NO3--N leaching in alkaline purple soil

Nitrification inhibitors (NIs) are critical to reduce nitrogen (N) leaching losses. However, the efficacy of different NIs can be highly variable across soils and crop types, and a deeper understanding of the mechanistic basis of this efficiency variation, especially in purple soil under vegetable production, is lacking. To enrich this knowledge gap, the impact of different NIs amendment (3,4-dimethylpyrazole phosphate, DMPP; dicyandiamide, DCD; nitrapyrin, NP) on nitrification and the microbial mechanistic basis of controlling nitrate (NO3--N) leaching of vegetable purple soil was explored in southwest China. The results showed that DCD and NP effect is dose-dependent, with 10% DCD, 1% DMPP and 1% NP were found to be optimal for nitrification inhibition in vegetable purple soil. When compared with the control treatment without NIs amendments, DCD, DMPP and NP reduced NO3--N leaching by 26.3%, 30.6% and 19.2%, respectively. It was noteworthy that NO3--N leaching inhibition was mediated predominantly by inhibiting ammonia-oxidizing bacteria (AOB) abundance. DCD, NP and DMPP incorporation decreased the AOB abundance by 39.8%, 73.2% and 51.4% and suppressed the ammonia monooxygenase (AMO) activity by 22.2%, 36.8% and 28.7%, respectively, in comparison with the control treatment without NIs amendments. DMPP inhibited AOB abundance and AMO activity much more than DCD and NP. DMPP also significantly decreased AOB alpha diversity and altered their community structure, whereas DCD and NP had no significant effect. The mantel test indicated that AOB abundance and AMO activity are strongly correlated with NO3--N leaching rate. These results show that soil application of 1% DMPP effectively mitigates NO3--N leaching from sub-tropical alkaline purple vegetable soil. This study also expanded our mechanistic understanding of NO3--N leaching and its regulators in an alkaline soil vegetable production system with N fertilizer and NI inputs.

Organic fertilizer significantly mitigates N2O emissions while increase contributed of comammox Nitrospira in paddy soils

Nitrification is the dominant process for nitrous oxide (N2O) production under aerobic conditions, but the relative contribution of the autotrophic nitrifiers (the ammonia-oxidising archaea (AOA), the ammonia-oxidising bacteria (AOB) and the comammox) to this process is still unclear in some soil types. This is particularly the case in paddy soils under different fertilization regimes. We investigated active nitrifiers and their contribution to nitrification and N2O production in a range of unfertilized and fertilized paddy soils, using 13CO2-DNA based stable isotope probing (SIP) technique combined with a series of specific nitrification inhibitors, including acetylene (C2H2), 3, 4-dimethylpyrazole phosphate (DMPP) and 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide (PTIO). The soils had a long-term history of fertilizer application, including chemical fertilizer only, a mixture of chemical fertilizers (70 %) and chicken manure (30 %) or a mixture of rice straw and chemical fertilizers. 13CO2-DNA-SIP and Illumina MiSeq sequencing demonstrated that comammox clades A.1 and B were active nitrifiers in all fertilized paddy soils. Inhibitor experiment showed that AOB largely contributed to nitrification activity and N2O emission in all paddy soils, while comammox contribution was more significant than AOA. Fertilization considerably altered nitrifiers' relative contribution to nitrification activity and N2O emissions. Applying organic fertilizers significantly decreased the N2O emissions but increased the contribution of comammox to the process. These findings expand the functional ecological niche of comammox, revealing their nitrification role and N2O production in other ecosystems than oligotrophic habitats.

Cast from the Past? Microbial Diversity of a Neolithic Stone Circle

We studied the microbial diversity colonizing limestone rock pools at a Neolithic Monument (Arbor Low, Derbyshire, England). Five pools were analyzed: four located at the megaliths of the stone circle and one pool placed at the megalith at the Gib Hill burial mound 300 m distant. Samples were taken from rock pool walls and sediments, and investigated through molecular metabarcoding. The microbiome consisted of 23 phyla of bacteria (831 OTUs), 4 phyla of archaea (19 OTUs), and 27 phyla of microbial eukarya (596 OTUs). For bacteria, there were statistically significant differences in wall versus sediment populations, but not between pools. For archaea and eukarya, significant differences were found only between pools. The most abundant bacterial phylum in walls was Cyanobacteriota, and Pseudomonadota in sediments. For archaea and microbial eukarya, the dominant phyla were Euryarcheota and Chlorophyta, respectively, in both wall and sediments. The distant pool (P5) showed a markedly different community structure in phyla and species, habitat discrimination, and CHN content. Species sorting and dispersal limitation are discussed as mechanisms structuring the microbiome assemblages and their spatial connectivity. The Arbor Low microbiome is composed of terrestrial representatives common in extreme environments. The high presence of Cyanobacteriota and Chlorophyta in the Arbor Low stones is troubling, as these microorganisms can induce mechanical disruption by penetrating the limestone matrix through endolithic/chasmoendolithic growth. Future research should focus on the metabolic traits of strains to ascertain their implication in bioweathering and/or biomineralization.

N2O recovery from wastewater and flue gas via microbial denitrification: Processes and mechanisms

Nitrous oxide (N2O) is increasingly regarded as a significant greenhouse gas implicated in global warming and the depletion of the ozone layer, yet it is also recognized as a valuable resource. This paper comprehensively reviews innovative microbial denitrification techniques for recovering N2O from nitrogenous wastewater and flue gas. Critical analysis is carried out on cutting-edge processes such as the coupled aerobic-anoxic nitrous decomposition operation (CANDO) process, semi-artificial photosynthesis, and the selective utilization of microbial strains, as well as flue gas absorption coupled with heterotrophic/autotrophic denitrification. These processes are highlighted for their potential to facilitate denitrification and enhance the recovery rate of N2O. The review integrates feasible methods for process control and optimization, and presents the underlying mechanisms for N2O recovery through denitrification, primarily achieved by suppressing nitrous oxide reductase (Nos) activity and intensifying competition for electron donors. The paper concludes by recognizing the shortcomings in existing technologies and proposing future research directions, with an emphasis on prioritizing the collection and utilization of N2O while considering environmental sustainability and economic feasibility. Through this review, we aim to inspire interest in the recovery and utilization of N2O, as well as the development and application of related technologies.

Nitrous oxide production and consumption by marine ammonia-oxidizing archaea under oxygen depletion

Ammonia-oxidizing archaea (AOA) are key players in the nitrogen cycle and among the most abundant microorganisms in the ocean, thriving even in oxygen-depleted ecosystems. AOA produce the greenhouse gas nitrous oxide (N2O) as a byproduct of ammonia oxidation. Additionally, the recent discovery of a nitric oxide dismutation pathway in the AOA isolate Nitrosopumilus maritimus points toward other N2O production and consumption pathways in AOA. AOA that perform NO dismutation when exposed to oxygen depletion, produce oxygen and dinitrogen as final products. Based on the transient accumulation of N2O coupled with oxygen accumulation, N2O has been proposed as an intermediate in this novel archaeal pathway. In this study, we spiked N2O to oxygen-depleted incubations with pure cultures of two marine AOA isolates that were performing NO dismutation. By using combinations of N compounds with different isotopic signatures (15NO2 - pool +44N2O spike and 14NO2 - pool +46N2O spike), we evaluated the N2O spike effects on the production of oxygen and the isotopic signature of N2 and N2O. The experiments confirmed that N2O is an intermediate in NO dismutation by AOA, distinguishing it from similar pathways in other microbial clades. Furthermore, we showed that AOA rapidly reduce high concentrations of spiked N2O to N2. These findings advance our understanding of microbial N2O production and consumption in oxygen-depleted settings and highlight AOA as potentially important key players in N2O turnover.

The Impact of Aboveground Epichloë Endophytic Fungi on the Rhizosphere Microbial Functions of the Host Melica transsilvanica

In nature, the symbiotic relationship between plants and microorganisms is crucial for ecosystem balance and plant growth. This study investigates the impact of Epichloë endophytic fungi, which are exclusively present aboveground, on the rhizosphere microbial functions of the host Melica transsilvanica. Using metagenomic methods, we analyzed the differences in microbial functional groups and functional genes in the rhizosphere soil between symbiotic (EI) and non-symbiotic (EF) plants. The results reveal that the presence of Epichloë altered the community structure of carbon and nitrogen cycling-related microbial populations in the host's rhizosphere, significantly increasing the abundance of the genes (porA, porG, IDH1) involved in the rTCA cycle of the carbon fixation pathway, as well as the abundance of nxrAB genes related to nitrification in the nitrogen-cycling pathway. Furthermore, the presence of Epichloë reduces the enrichment of virulence factors in the host rhizosphere microbiome, while significantly increasing the accumulation of resistance genes against heavy metals such as Zn, Sb, and Pb. This study provides new insights into the interactions among endophytic fungi, host plants, and rhizosphere microorganisms, and offers potential applications for utilizing endophytic fungi resources to improve plant growth and soil health.

The different responses of AOA and AOB communities to irrigation systems in the semi-arid region of Northeast China

Ammonia oxidation is the rate-limiting step in nitrification and the key step in the nitrogen (N) cycle. Most soil nutrients and biological indicators are extremely sensitive to irrigation systems, from the perspective of improving soil fertility and soil ecological environment, the evaluation of different irrigation systems and suitability of selection, promote crop production and soil quality, study the influence of the soil microenvironment contribute to accurate evaluation of irrigation farmland soil health. Based on the amoA gene, the abundance and community diversity of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) and their responses to soil physicochemical factors and enzyme activities were studied in semi-arid areas of Northeast China. The study consisted of three irrigation systems: flood irrigation (FP), shallow buried drip irrigation (DI), and mulched drip irrigation (MF). The results showed that DI and MF significantly increased the contents of alkaline hydrolyzed nitrogen (AN), nitrate nitrogen (NO3--N), soil moisture, and the activities of ammonia monooxygenase (AMO) and hydroxylamine oxidase (HAO). Compared with FP, DI significantly increased the abundance of soil AOA and AOB, while MF significantly increased the abundance of soil AOB. Irrigation systems significantly affected the community composition of ammonia-oxidizing microorganisms (AOM). Also, AN and soil moisture had the greatest influence on the community composition of AOA and AOB, respectively. The AOB community had better stability and stress resistance. Moreover, the symbiotic network of AOB in the three irrigation systems was more complex than that of AOA. Compared with FP, the AOA community under treatment DI had higher complexity and stability, maintaining the versatility and sustainability of the ecosystem, while the AOB community under treatment MF had higher transfer efficiency in terms of matter and energy. In conclusion, DI and MF were more conducive to the propagation of soil AOM in the semi-arid area of Northeast China, which can provide a scientific basis for rational irrigation and N regulation from the perspective of microbiology.

Effects of C/N ratio on N2O emissions and nitrogen functional genes during vegetable waste composting

Nitrous oxide (N2O) generation during composting not only leads to losses of nitrogen (N) but also reduces the agronomic values and environmental benefits of composting. This study aimed to investigate the effect of the C/N ratio on N2O emissions and its underlying mechanisms at the genetic level during the composting of vegetable waste. The experiment was set up with three treatments, including low C/N treatment (LT, C/N = 18), middle C/N treatment (MT, C/N = 30), and high C/N treatment (HT, C/N = 50). The results showed that N2O emission was mainly concentrated in the cooling and maturation periods, and the cumulative N2O emissions decreased as the C/N ratio increased. Specifically, the cumulative N2O emission was 57,401 mg in LT, significantly higher than 2155 mg in MT and 1353 mg in HT. Lowering the C/N ratio led to increasing TN, NH4+-N, and NO3--N contents throughout the composting process. All detected nitrification-related gene abundances in LT continued to increase during composting, significantly surpassing those in MT during the cooling period. By contrast, in HT, there was a slight increase in the abundance of detected nitrification-related genes but a significant decrease in the abundance of narG, napA, and norB genes in the thermophilic and cooling periods. The structural equation model revealed that hao and nosZ genes were vital in N2O emissions. In conclusion, increasing the C/N ratio effectively contributed to N2O reduction during vegetable waste composting.

The enrichment characterisation of Nitrospira under high DO conditions

Nitrite-oxidizing bacteria (NOB) are crucial to nitrification and nitrogen elimination in wastewater treatment. Mass reports exist on the links between NOB and other microorganisms, for instance, ammonia-oxidizing bacteria (AOB). However, a few studies exist on the enrichment characterisation of NOB under high dissolved oxygen (DO) conditions. In this study, NOB was designed to be enriched individually under high DO conditions in a continuous aeration sequencing batch reactor (SBR), and the kinetic characterisation of NOB was evaluated. The analysis revealed that the average NO2--N removal rate was steady above 98%, with DO and NO2--N being 3-5 mg L-1 and 50-450 mg L-1, respectively. The NO2--N removal efficiency of the system was significantly enhanced and better than in other studies. The high-throughput sequencing suggested that Parcubacteria_ genera_incertae_sedis was the first dominant genus (21.99%), which often appeared in the NOB biological community with Nitrospira. However, the dominant genus NOB was Nitrospira rather than Nitrobacter (8.49%). This result suggested that Nitrospira was capable of higher NO2--N removal. But lower relative abundance indicated that excessive NO2--N had an adverse effect on the enrichment and activity of Nitrospira. In addition, the nitrite half-saturation constant (KNO2) and the oxygen half-saturation constant (KO) were 1.71 ± 0.19 mg L-1 and 0.95 ± 0.10 mg L-1, respectively. These results showed that the enriched Nitrospira bacteria had different characteristics at the strain level, which can be used as a theoretical basis for wastewater treatment plant design and optimisation.

Boosting the denitrification efficiency of iron-based constructed wetlands in-situ via plant biomass-derived biochar: Intensified iron redox cycle and microbial responses

Considering the unsatisfied denitrification performance of carbon-limited wastewater in iron-based constructed wetlands (ICWs) caused by low electron transfer efficiency of iron substrates, utilization of plant-based conductive materials in-situ for improving the long-term reactivity of iron substrates was proposed to boost the Fe (III)/Fe (II) redox cycle thus enhance the nitrogen elimination. Here, we investigated the effects of withered Iris Pseudacorus biomass and its derived biochar on nitrogen removal for 165 days in ICWs. Results revealed that accumulate TN removal capacity in biochar-added ICW (BC-ICW) increased by 14.7 % compared to biomass-added ICW (BM-ICW), which was mainly attributed to the synergistic strengthening of iron scraps and biochar. The denitrification efficiency of BM-ICW improved by 11.6 % compared to ICWs, while its removal capacity declined with biomass consumption. Autotrophic and heterotrophic denitrifiers were enriched in BM-ICW and BC-ICW, especially biochar increased the abundance of electroactive species (Geobacter and Shewanella, etc.). An active iron cycle exhibited in BC-ICW, which can be confirmed by the presence of more liable iron minerals on iron scraps surface, the lowest Fe (III)/Fe (II) ratio (0.51), and the improved proportions of iron cycling genes (feoABC, korB, fhuF, TC.FEV.OM, etc.). The nitrate removal efficiency was positively correlated with the nitrogen, iron metabolism functional genes and the electron transfer capacity (ETC) of carbon materials (P < 0.05), indicating that redox-active carbon materials addition improved the iron scraps bioavailability by promoting electron transfer, thus enhancing the autotrophic nitrogen removal. Our findings provided a green perspective to better understand the redox properties of plant-based carbon materials in ICWs for deep bioremediation in-situ.

AOB Nitrosospira cluster 3a.2 (D11) dominates N2O emissions in fertilised agricultural soils

Ammonia-oxidation process directly contribute to soil nitrous oxide (N2O) emissions in agricultural soils. However, taxonomy of the key nitrifiers (within ammonia oxidising bacteria (AOB), archaea (AOA) and complete ammonia oxidisers (comammox Nitrospira)) responsible for substantial N2O emissions in agricultural soils is unknown, as is their regulation by soil biotic and abiotic factors. In this study, cumulative N2O emissions, nitrification rates, abundance and community structure of nitrifiers were investigated in 16 agricultural soils from major crop production regions of China using microcosm experiments with amended nitrogen (N) supplemented or not with a nitrification inhibitor (nitrapyrin). Key nitrifier groups involved in N2O emissions were identified by comparative analyses of the different treatments, combining sequencing and random forest analyses. Soil cumulative N2O emissions significantly increased with soil pH in all agricultural soils. However, they decreased with soil organic carbon (SOC) in alkaline soils. Nitrapyrin significantly inhibited soil cumulative N2O emissions and AOB growth, with a significant inhibition of the AOB Nitrosospira cluster 3a.2 (D11) abundance. One Nitrosospira multiformis-like OTU phylotype (OTU34), which was classified within the AOB Nitrosospira cluster 3a.2 (D11), had the greatest importance on cumulative N2O emissions and its growth significantly depended on soil pH and SOC contents, with higher growth at high pH and low SOC conditions. Collectively, our results demonstrate that alkaline soils with low SOC contents have high N2O emissions, which were mainly driven by AOB Nitrosospira cluster 3a.2 (D11). Nitrapyrin can efficiently reduce nitrification-related N2O emissions by inhibiting the activity of AOB Nitrosospira cluster 3a.2 (D11). This study advances our understanding of key nitrifiers responsible for high N2O emissions in agricultural soils and their controlling factors, and provides vital knowledge for N2O emission mitigation in agricultural ecosystems.

Microbial pathways of nitrous oxide emissions and mitigation approaches in drylands

Drylands refer to water scarcity and low nutrient levels, and their plant and biocrust distribution is highly diverse, making the microbial processes that shape dryland functionality particularly unique compared to other ecosystems. Drylands are constraint for sustainable agriculture and risk for food security, and expected to increase over time. Nitrous oxide (N2O), a potent greenhouse gas with ozone reduction potential, is significantly influenced by microbial communities in drylands. However, our understanding of the biological mechanisms and processes behind N2O emissions in these areas is limited, despite the fact that they highly account for total gaseous nitrogen (N) emissions on Earth. This review aims to illustrate the important biological pathways and microbial players that regulate N2O emissions in drylands, and explores how these pathways might be influenced by global changes for example N deposition, extreme weather events, and climate warming. Additionally, we propose a theoretical framework for manipulating the dryland microbial community to effectively reduce N2O emissions using evolving techniques that offer inordinate specificity and efficacy. By combining expertise from different disciplines, these exertions will facilitate the advancement of innovative and environmentally friendly microbiome-based solutions for future climate change vindication approaches.

Nitrogen removal characteristics of novel bacterium Klebsiella sp. TSH15 by assimilatory/dissimilatory nitrate reduction and ammonia assimilation

A novel strain with heterotrophic nitrification and aerobic denitrification was screened and identified as Klebsiella sp. TSH15 by 16S rRNA. The results demonstrated that the ammonia-N and nitrate-N removal rates were 2.99 mg/L/h and 2.53 mg/L/h under optimal conditions, respectively. The analysis of the whole genome indicated that strain TSH15 contained the key genes involved in assimilatory/dissimilatory nitrate reduction and ammonia assimilation, including nas, nar, nir, nor, glnA, gltB, gdhA, and amt. The relative expression levels of key nitrogen removal genes were further detected by RT-qPCR. The results indicated that the N metabolic pathways of strain TSH15 were the conversion of nitrate or nitrite to ammonia by assimilatory/dissimilatory nitrate reduction (NO3-→NO2-→NH4+) and further conversion of ammonia to glutamate (NH4+-N → Glutamate) by ammonia assimilation. These results indicated that the strain TSH15 had the potential to be applied to practical sewage treatment in the future.

Achieving partial nitrification: A strategy for washing NOB out under high DO condition

This study investigated the effect of high DO concentrations on PN. The experimental setup involved operating at high DO concentrations (1.5-2.5 mg/L) and environmental temperatures (15-20 °C) over a period of 180 days. Through a sludge enrichment process, the kinetic parameters of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) were determined. Surprisingly, contrary to conventional reports, it was observed that NOB exhibited a stronger affinity for DO compared to AOB. As a result, high DO concentrations were necessary to provide favorable conditions for the growth of AOB. In order to establish PN, strategies including intermittent aeration, free ammonia (FA), and controlled sludge retention time (SRT) were employed. The successful PN was achieved with a specific ammonia oxidation rate of 24 mg N/g MLVSS/h and a specific nitrite oxidation rate below 0.10 mg N/g MLVSS/h. The nitrite accumulation rate (NAR) was maintained at 100% during stable operation. The abundance of Nitrosomonas, a typical genus of AOB, was found to be 68.62%, which surpasses previous studies in similar research. A slightly higher DO concentrations may increase energy consumption, but achieve higher efficiency and stability in PN. This study provided new insights into the application of PN in wastewater treatment.

Discriminative Analysis of NOx Gases by Two-Dimensional Violet Phosphorus Field-Effect Transistors

Two-dimensional violet phosphorus (VP) has emerged as a new sensing material in various sensing applications due to its unique electrical properties and high stability among allotropes of phosphorus. Currently, the research of the VP-based analysis method is at the early stage. In this work, a VP nanosheet-based field-effect transistor (FET) sensor is reported for the detection of NO2 and N2O gases with extraordinary sensing performance. This sensor can achieve excellent sensitivity of up to ∼50% current change/ppm and a low detection limit of 5.9 ppb and enables the NO2 analysis in various mixed gases. Moreover, this sensor can effectively distinguish between NO2 and N2O gases, which is a big challenge for current FET or chemiresistor gas sensors. The different sensing behaviors of the VP sensor to NO2 and N2O gases have been investigated, and the mechanism study shows that the adsorption energy, bond length of the gas molecule on the VP surface, and the decomposition of N2O led to the differential responses. This work is one of the pioneer studies of VP gas sensors and presents a new sensing method for the discriminative analysis of NO2 and N2O for greenhouse gas emission monitoring and air quality control.

Ascription of nosZ gene, pH and copper for mitigating N2O emissions in acidic soils

Soil nitrous oxide (N2O) emissions are alarming for global warming and climate change. N2O reduction is carried out only by nosZ gene encoded N2O-reductase, which is highly sensitive to acidic pH and copper (Cu) contents. Therefore, a microcosm study was conducted to examine the attribution of soil pH management, Cu supply and nosZ gene abundance for N2O emission mitigation. Cu was applied at the dose of 0, 10, 25 and 50 mg kg-1 to three acidic soils (Soil 1, 2 and 3) without and with dolomite (0 and 5 g kg-1). Cu application and soil pH increment substantially enlarged the abundance of nosZ gene, and consequently mitigated soil N2O emissions; highest reduction with 25 Cu mg kg-1. Decline in NH4+ and subsequently accumulation of NO3-, and large contents of MBC and DOC in dolomite treated soils led to a substantial N2O reduction. The cumulative N2O emissions were lowest in the treatment of 25 Cu mg kg-1 with dolomite application for each soil. Results suggest that soil pH increment, an adequate Cu supply, and nosZ gene abundance can potentially lower soil N2O emissions in acidic soils.

Organic substitution stimulates ammonia oxidation-driven N2O emissions by distinctively enriching keystone species of ammonia-oxidizing archaea and bacteria in tropical arable soils

Partial organic substitution (POS) is pivotal in enhancing soil productivity and changing nitrous oxide (N₂O) emissions by profoundly altering soil nitrogen (N) cycling, where ammonia oxidation is a fundamental core process. However, the regulatory mechanisms of N₂O production by ammonia oxidizers at the microbial community level under POS regimes remain unclear. This study explored soil ammonia oxidation and related N₂O production, further building an understanding of the correlations between ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) activity and community structure in tropical arable soils under four-year field management regimes (CK, without fertilizer N; N, with only inorganic N; M1N1, with 1/2 organic N + 1/2 inorganic N; M1N2, with 1/3 organic N + 2/3 inorganic N). AOA contributed more to potential ammonia oxidation (PAO) than AOB across all treatments. In comparison with CK, N treatment had no obvious effects on PAO and lowered related N₂O emissions by decreasing soil pH and downregulating the abundance of AOA- and AOB-amoA. POS regimes significantly enhanced PAO and N₂O emissions relative to N treatment by promoting the abundances and contributions of AOA and AOB. The stimulated AOA-dominated N₂O production under M1N1 was correlated with promoted development of Nitrososphaera. By contrast, the increased AOB-dominated N₂O production under M1N2 was linked to the enhanced development of Nitrosospira multiformis. Our study suggests organic substitutions with different proportions of inorganic and organic N distinctively regulate the development of specific species of ammonia oxidizers to increase associated N₂O emissions. Accordingly, appropriate options should be adopted to reduce environmental risks under POS regimes in tropical croplands.

Effects of acidification on nitrification and associated nitrous oxide emission in estuarine and coastal waters

In the context of an increasing atmospheric carbon dioxide (CO₂) level, acidification of estuarine and coastal waters is greatly exacerbated by land-derived nutrient inputs, coastal upwelling, and complex biogeochemical processes. A deeper understanding of how nitrifiers respond to intensifying acidification is thus crucial to predict the response of estuarine and coastal ecosystems and their contribution to global climate change. Here, we show that acidification can significantly decrease nitrification rate but stimulate generation of byproduct nitrous oxide (N₂O) in estuarine and coastal waters. By varying CO₂ concentration and pH independently, an expected beneficial effect of elevated CO₂ on activity of nitrifiers ("CO₂-fertilization" effect) is excluded under acidification. Metatranscriptome data further demonstrate that nitrifiers could significantly up-regulate gene expressions associated with intracellular pH homeostasis to cope with acidification stress. This study highlights the molecular underpinnings of acidification effects on nitrification and associated greenhouse gas N₂O emission, and helps predict the response and evolution of estuarine and coastal ecosystems under climate change and human activities.

Contribution of nitrous oxide to the carbon footprint of full-scale wastewater treatment plants and mitigation strategies- a critical review

Nitrous oxide (N₂O), a potent greenhouse gas, significantly contributes to the carbon footprint of wastewater treatment plants (WWTPs) and contributes significantly to global climate change and to the deterioration of the natural environment. Our understanding of N₂O generation mechanisms has significantly improved in the last decade, but the development of effective N₂O emission mitigation strategies has lagged owing to the complexity of parameter regulation, substandard monitoring activities, and inadequate policy criteria. Based on critically screened published studies on N₂O control in full-scale WWTPs, this review elucidates N₂O generation pathway identifications and emission mechanisms and summarizes the impact of N₂O on the total carbon footprint of WWTPs. In particular, a linear relationship was established between N₂O emission factors and total nitrogen removal efficiencies in WWTPs located in China. Promising N₂O mitigation options were proposed, which focus on optimizing operating conditions and implementation of innovative treatment processes. Furthermore, the sustainable operation of WWTPs has been anticipated to convert WWTPs into absolute greenhouse gas reducers as a result of the refinement and improvement of on-site monitoring activities, mitigation mechanisms, regulation of operational parameters, modeling, and policies.

Microplastics in urban waters and its effects on microbial communities: a critical review

Microplastic (MP) pollution is one of the emerging threats to the water and terrestrial environment, forcing a new environmental challenge due to the growing trend of plastic released into the environment. Synthetic and non-synthetic plastic components can be found in rivers, lakes/reservoirs, oceans, mountains, and even remote areas, such as the Arctic and Antarctic ice sheets. MPs' main challenge is identifying, measuring, and evaluating their impacts on environmental behaviors, such as carbon and nutrient cycles, water and wastewater microbiome, and the associated side effects. However, until now, no standardized methodical protocols have been proposed for comparing the results of studies in different environments, especially in urban water and wastewater. This review briefly discusses MPs' sources, fate, and transport in urban waters and explains methodological uncertainty. The effects of MPs on urban water microbiomes, including urban runoff, sewage wastewater, stagnant water in plumbing networks, etc., are also examined in depth. Furthermore, this study highlights the pathway of MPs and their transport vectors to different parts of ecosystems and human life, particularly through mediating microbial communities, antibiotic-resistant genes, and biogeochemical cycles. Overall, we have briefly highlighted the present research gaps, the lack of appropriate policy for evaluating microplastics and their interactions with urban water microbiomes, and possible future initiatives.

Integration of MFC reduces CH4, N2O and NH3 emissions in batch-fed wetland systems

The combination of microbial fuel cells (MFCs) with constructed wetlands (CWs) for enhancing water purification efficiency and generating bioelectricity has attracted extensive attention. However, the other benefits of MFC-CWs are seldom reported, especially the potential for controlling gaseous emissions. In this study, we have quantitatively compared the pollutant removal efficiency and the emission of multiple gases between MFC-CWs and batch-fed wetland systems (BF CWs). MFC-CWs exhibited significantly (p < 0.01) higher COD, NH₄⁺-N, TN, and TP removal efficiencies and significantly (p < 0.01) lower global warming potential (GWP) than BF CWs. The integration of MFC decreased GWP by 23.88% due to the reduction of CH₄ and N₂O fluxes, whereas the CO₂ fluxes were slightly promoted. The quantitative PCR results indicate that the reduced N₂O fluxes in MFC-CWs were driven by the reduced transcription of the nosZ gene and enhanced the ratio of nosZ/(nirS + nirK); the reduced CH₄ fluxes were related to pomA and mcrA. Additionally, the NH₃ fluxes were reduced by 52.20% in MFC-CWs compared to BF CWs. The integration of MFC promoted the diversity of microbial community, especially Anaerolineaceae, Saprospiraceae and Clostridiacea. This study highlights a further benefit of MFC-CWs and provides a new strategy for simultaneously removing pollutants and abating multiple gas emissions in BF CWs.

Interactive effects of aquatic nitrogen and plant biomass on nitrous oxide emission from constructed wetlands

Understanding of mechanisms in nitrous oxide (N₂O) emission from constructed wetland (CW) is particularly important for the establishment of related strategies to reduce greenhouse gas (GHG) production during its wastewater treatment. However, plant biomass accumulation, microbial communities and nitrogen transformation genes distribution and their effects on N₂O emission from CW as affected by different nitrogen forms in aquatic environment have not been reported. This study investigated the interactive effects of aquatic nitrogen and plant biomass on N₂O emission from subsurface CW with NH₄⁺-N (CW-A) or NO₃^--N (CW-B) wastewater. The experimental results show that NH₄⁺-N and NO₃^--N removal efficiencies from CW mesocosms were 49.4% and 87.6%, which indirectly lead to N₂O emission fluxes of CW-A and CW-B maintained at 213 ± 67 and 462 ± 71 μg-N/(m²·h), respectively. Correlation analysis of nitrogen conversion dynamic indicated that NO₂^--N accumulation closely related to N₂O emission from CW. Aquatic NH₄⁺-N could up-regulate plant biomass accumulation by intensifying citric acid cycle, glycine-serine-threonine metabolism etc., resulting in more nitrogen uptake and lower N₂O emission/total nitrogen (TN) removal ratio of CW-A compared to CW-B. Although the abundance of denitrifying bacteria and N₂O reductase nosZ in CW-B were significantly higher than that of CW-A, after fed with mixed NH₄⁺-N and NO₃^--N influent, N₂O fluxes and N₂O emission/TN removal ratio in CW-A were extremely close to that of CW-B, suggesting that nitrogen form rather than nitrogen transformation microbial communities and N₂O reductase nosZ determines N₂O emission from CW. Hence, the selection of nitrate-loving plants will play an important role in inhibiting N₂O emission from CW.

Carbon and N conservation during composting: A review

Composting, as a conventional solid waste treatment method, plays an essential role in carbon and nitrogen conservation, thereby reducing the loss of nutrients and energy. However, some carbon- and nitrogen-containing gases are inevitably released during the process of composting due to the different operating conditions, resulting in carbon and nitrogen losses. To overcome this obstacle, many researchers have been trying to optimize the adjustment parameters and add some amendments (i.e., pHysical amendments, chemical amendments and microbial amendments) to reduce the losses and enhance carbon and nitrogen conservation. However, investigation regarding mechanisms for the conservation of carbon and nitrogen are limited. Therefore, this review summarizes the studies on physical amendments, chemical amendments and microbial amendments and proposes underlying mechanisms for the enhancement of carbon and nitrogen conservation: adsorption or conversion, and also evaluates their contribution to the mitigation of the greenhouse effect, providing a theoretical basis for subsequent composting-related researchers to better improve carbon and nitrogen conservation measures. This paper also suggests that: assessing the contribution of composting as a process to global greenhouse gas mitigation requires a complete life cycle evaluation of composting. The current lack of compost clinker impact on carbon and nitrogen sequestration capacity of the application site needs to be explored by more research workers.

Antibiotics sulfamethoxazole alter nitrous oxide production and pathways in estuarine sediments: Evidenced by the N15-O18 isotopes tracing

Estuarine antibiotic residues are profoundly impacting microbial nitrogen (N) cycling and associated N₂O production, but the response of N₂O production pathways to antibiotics remains poorly understood. Here, ¹⁵N-¹⁸O labeling technique combined with molecular methods were used to investigate the impacts of sulfamethoxazole on the contribution of ammonia oxidation (nitrifier nitrification, nitrifier denitrification, and nitrification-coupled denitrification) and heterotrophic denitrification (HD) to N₂O production in estuarine sediments. Results showed that environmental concentration of sulfamethoxazole (4 ng/g) promoted the total N₂O production by 17.1% through nitrifier denitrification. Environmentally relevant (40-4000 ng/g) and irrelevant (40,000 ng/g) concentration of sulfamethoxazole drove nitrification denitrification to gradually lose the dominant role in total N₂O production and ammonia oxidation-derived N₂O, replaced by HD and nitrifier nitrification, while total N₂O production were inhibited. Furthermore, when HD dominated the total N₂O production, the HD-derived N₂O increased by 63.6% with sulfamethoxazole concentration reaching 40,000 ng/g. The mechanistic investigation further showed that nitrifying bacteria were more susceptible to sulfamethoxazole than nitrifying archaea and denitrifiers. The increased expression of nirS gene carried by non-dominant denitrifiers improved the ratio of nirS:nosZ and hence increased HD-derived N₂O under high sulfamethoxazole stresses. Overall, our results provide a comprehensive view into how antibiotics regulate N₂O production and its pathways in estuarine sediments.

Periphytic biofilms-mediated microbial interactions and their impact on the nitrogen cycle in rice paddies

Rice paddies are unique waterlogged wetlands artificially constructed for agricultural production. Periphytic biofilms (PBs) at the soil-water interface play an important role in rice paddies characterized by high nutrient input but low utilization efficiency. PBs are composed of microbial aggregates, including a wide variety of microorganisms (algae, bacteria, fungi, protozoa, and metazoa), extracellular polymeric substances and minerals (iron, aluminum, and calcium), which form an integrated food web and energy flux within a relatively stable micro-ecosystem. PBs are crucial to regulate and streamline the nitrogen cycle by neutralizing nitrogen losses and improving rice production since PBs can serve as both a sink by capturing surplus nitrogen and a source by slowly re-releasing this nitrogen for reutilization. Here the ecological advantages of PBs in regulating the nitrogen cycle in rice paddies are illustrated. We summarize the key functional importance of PBs, including the intricate and delicate community structure, microbial interactions among individual phylotypes, a wide diversity of self-produced organics, the active adaptation of PBs to constantly changing environments, and the intricate mechanisms by which PBs regulate the nitrogen cycle. We also identify the future challenges of microbial interspecific cooperation in PBs and their quantitative contributions to agricultural sustainability, optimizing nitrogen utilization and crop yields in rice paddies.

The nitrogen cycle and mitigation strategies for nitrogen loss during organic waste composting: A review

Composting is a promising technology to decompose organic waste into humus-like high-quality compost, which can be used as organic fertilizer. However, greenhouse gases (N₂O, CO₂, CH₄) and odorous emissions (H₂S, NH₃) are major concerns as secondary pollutants, which may pose adverse environmental and health effects. During the composting process, nitrogen cycle plays an important role to the compost quality. This review aimed to (1) summarizes the nitrogen cycle of the composting, (2) examine the operational parameters, microbial activities, functions of enzymes and genes affecting the nitrogen cycle, and (3) discuss mitigation strategies for nitrogen loss. Operational parameters such as moisture, oxygen content, temperature, C/N ratio and pH play an essential role in the nitrogen cycle, and adjusting them is the most straightforward method to reduce nitrogen loss. Also, nitrification and denitrification are the most crucial processes of the nitrogen cycle, which strongly affect microbial community dynamics. The ammonia-oxidizing bacteria or archaea (AOB/AOA) and the nitrite-oxidizing bacteria (NOB), and heterotrophic and autotrophic denitrifiers play a vital role in nitrification and denitrification with the involvement of ammonia monooxygenase (amoA) gene, nitrate reductase genes (narG), and nitrous oxide reductase (nosZ). Furthermore, adding additives such as struvite salts (MgNH₄PO₄·6H₂O), biochar, and zeolites (clinoptilolite), and microbial inoculation, namely Bacillus cereus (ammonium strain), Pseudomonas donghuensis (nitrite strain), and Bacillus licheniformis (nitrogen fixer) can help control nitrogen loss. This review summarized critical issues of the nitrogen cycle and nitrogen loss in order to help future composting research with regard to compost quality and air pollution/odor control.

Genome-resolved metagenomics reveals novel archaeal and bacterial genomes from Amazonian forest and pasture soils

Amazonian soil microbial communities are known to be affected by the forest-to-pasture conversion, but the identity and metabolic potential of most of their organisms remain poorly characterized. To contribute to the understanding of these communities, here we describe metagenome-assembled genomes (MAGs) recovered from 12 forest and pasture soil metagenomes of the Brazilian Eastern Amazon. We obtained 11 forest and 30 pasture MAGs (≥50% of completeness and ≤10 % of contamination), distributed among two archaeal and 11 bacterial phyla. The taxonomic classification results suggest that most MAGs may represent potential novel microbial taxa. MAGs selected for further evaluation included members of Acidobacteriota, Actinobacteriota, Desulfobacterota_B, Desulfobacterota_F, Dormibacterota, Eremiobacterota, Halobacteriota, Proteobacteria, and Thermoproteota, thus revealing their roles in carbohydrate degradation and mercury detoxification as well as in the sulphur, nitrogen, and methane cycles. A methane-producing Archaea of the genus Methanosarcina was almost exclusively recovered from pasture soils, which can be linked to a sink-to-source shift after the forest-to-pasture conversion. The novel MAGs constitute an important resource to help us unravel the yet-unknown microbial diversity in Amazonian soils and its functional potential and, consequently, the responses of these microorganisms to land-use change.

Soils and sediments host Thermoplasmata archaea encoding novel copper membrane monooxygenases (CuMMOs)

Copper membrane monooxygenases (CuMMOs) play critical roles in the global carbon and nitrogen cycles. Organisms harboring these enzymes perform the first, and rate limiting, step in aerobic oxidation of ammonia, methane, or other simple hydrocarbons. Within archaea, only organisms in the order Nitrososphaerales (Thaumarchaeota) encode CuMMOs, which function exclusively as ammonia monooxygenases. From grassland and hillslope soils and aquifer sediments, we identified 20 genomes from distinct archaeal species encoding divergent CuMMO sequences. These archaea are phylogenetically clustered in a previously unnamed Thermoplasmatota order, herein named the Ca. Angelarchaeales. The CuMMO proteins in Ca. Angelarchaeales are more similar in structure to those in Nitrososphaerales than those of bacteria, and contain all functional residues required for general monooxygenase activity. Ca. Angelarchaeales genomes are significantly enriched in blue copper proteins (BCPs) relative to sibling lineages, including plastocyanin-like electron carriers and divergent nitrite reductase-like (nirK) 2-domain cupredoxin proteins co-located with electron transport machinery. Ca. Angelarchaeales also encode significant capacity for peptide/amino acid uptake and degradation and share numerous electron transport mechanisms with the Nitrososphaerales. Ca. Angelarchaeales are detected at high relative abundance in some of the environments where their genomes originated from. While the exact substrate specificities of the novel CuMMOs identified here have yet to be determined, activity on ammonia is possible given their metabolic and ecological context. The identification of an archaeal CuMMO outside of the Nitrososphaerales significantly expands the known diversity of CuMMO enzymes in archaea and suggests previously unaccounted organisms contribute to critical global nitrogen and/or carbon cycling functions.

Digital Twins of the Soil Microbiome for Climate Mitigation

Recent advances in computation power have enabled the creation of digital twins of the microbiome (DTM) to substantially curb soil greenhouse gases (GHG) emissions under global change conditions [...]

The marine nitrogen cycle: new developments and global change

The ocean is home to a diverse and metabolically versatile microbial community that performs the complex biochemical transformations that drive the nitrogen cycle, including nitrogen fixation, assimilation, nitrification and nitrogen loss processes. In this Review, we discuss the wealth of new ocean nitrogen cycle research in disciplines from metaproteomics to global biogeochemical modelling and in environments from productive estuaries to the abyssal deep sea. Influential recent discoveries include new microbial functional groups, novel metabolic pathways, original conceptual perspectives and ground-breaking analytical capabilities. These emerging research directions are already contributing to urgent efforts to address the primary challenge facing marine microbiologists today: the unprecedented onslaught of anthropogenic environmental change on marine ecosystems. Ocean warming, acidification, nutrient enrichment and seawater stratification have major effects on the microbial nitrogen cycle, but widespread ocean deoxygenation is perhaps the most consequential for the microorganisms involved in both aerobic and anaerobic nitrogen transformation pathways. In turn, these changes feed back to the global cycles of greenhouse gases such as carbon dioxide and nitrous oxide. At a time when our species casts a lengthening shadow across all marine ecosystems, timely new advances offer us unique opportunities to understand and better predict human impacts on nitrogen biogeochemistry in the changing ocean of the Anthropocene.

Nitrous oxide and methane in a changing Arctic Ocean

Human activities are changing the Arctic environment at an unprecedented rate resulting in rapid warming, freshening, sea ice retreat and ocean acidification of the Arctic Ocean. Trace gases such as nitrous oxide (N₂O) and methane (CH₄) play important roles in both the atmospheric reactivity and radiative budget of the Arctic and thus have a high potential to influence the region's climate. However, little is known about how these rapid physical and chemical changes will impact the emissions of major climate-relevant trace gases from the Arctic Ocean. The combined consequences of these stressors present a complex combination of environmental changes which might impact on trace gas production and their subsequent release to the Arctic atmosphere. Here we present our current understanding of nitrous oxide and methane cycling in the Arctic Ocean and its relevance for regional and global atmosphere and climate and offer our thoughts on how this might change over coming decades.

Assessing the influence of environmental niche segregation in ammonia oxidizers on N2O fluxes from soil and sediments

Understanding the environmental niche segregation of ammonia-oxidizing archaea (AOA) and bacteria (AOB) and its impact on their relative contributions to nitrification and nitrous oxide (N₂O) production is essential for predicting N₂O dynamics within an ecosystem. Here, we used ammonia oxidizer-specific inhibitors to measure the differential contributions of AOA and AOB to potential ammonia oxidization (PAO) and N₂O fluxes over pH (4.0-9.0) and temperature (10-45 °C) gradients in five soils and three wetland sediments. AOA and AOB activities were differentiated using PTIO (2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide), 1-octyne, and acetylene. We used square root growth (SQRT) and macromolecular rate theory (MMRT) models to estimate cardinal temperatures and thermodynamic characteristics for AOA- and AOB-dominated PAO and N₂O fluxes. We found that AOA and AOB occupied different niches for PAO, and soil temperature was the major determinant of niche specialization. SQRT and MMRT models predicted a higher optimum temperature for AOA-dominated PAO and N₂O fluxes compared with those of AOB. Additionally, PAO was dominated by AOA in acidic conditions, whereas both AOA- and AOB-dominated N₂O fluxes decreased with increasing pH. Consequently, net N₂O fluxes (AOA and AOB) under acidic conditions were approximately one to three-fold higher than those observed in alkaline conditions. Moreover, structural equation and linear regression modeling confirmed a significant positive correlation (R² = 0.45, p < 0.01) between PAO and N₂O fluxes. Collectively, these results show the influence of ammonia oxidizer responses to temperature and pH on nitrification-driven N₂O fluxes, highlighting the potential for mitigating N₂O emissions via pH manipulation.

Long-Term Low Dissolved Oxygen Operation Decreases N2O Emissions in the Activated Sludge Process

Nitrous oxide (N₂O) is an important greenhouse gas and a dominant ozone-depleting substance. Nitrification in the activated sludge process (ASP) is an important N₂O emission source. This study demonstrated that a short-term low dissolved oxygen (DO) increased the N₂O emissions by six times, while long-term low DO operation decreased the N₂O emissions by 54% (P < 0.01). Under long-term low DO, the ammonia oxidizer abundance in the ASP increased significantly, and thus, complete nitrification was recovered and no NH₃ or nitrite accumulated. Moreover, long-term low DO decreased the abundance of ammonia-oxidizing bacteria (AOB) by 28%, while increased the abundance of ammonia-oxidizing archaea (AOA) by 507%, mainly due to their higher oxygen affinity. As a result, AOA outnumbered AOB with the AOA/AOB amoA gene ratio increasing to 19.5 under long-term low DO. The efficient nitrification and decreased AOB abundance might not increase N₂O production via AOB under long-term low DO conditions. The enriched AOA could decrease the N₂O emissions because they were reported to lack canonical nitric oxide (NO) reductase genes that convert NO to N₂O. Probably because of AOA enrichment, the positive and significant (P = 0.02) correlation of N₂O emission and nitrite concentration became insignificant (P = 0.332) after 80 days of low DO operation. Therefore, ASPs can be operated with low DO and extended sludge age to synchronously reduce N₂O production and carbon dioxide emissions owing to lower aeration energy without compromising the nitrification efficiency.

Exploring the Composition and Functions of Plastic Microbiome Using Whole-Genome Sequencing

Besides the ecotoxicological consequences of microplastics and associated chemicals, the association of microbes on plastics has greater environmental implications as microplastics may select for unique microbiome participating in environmentally significant functions. Despite this, the functional potential of the microbiome associated with different types of plastics is understudied. Here, we investigate the interaction between plastic and marine biofilm-forming microorganisms through a whole-genome sequencing approach on four types of microplastics incubated in the marine environment. Taxonomic analysis suggested that the microplastic surfaces exhibit unique microbial profiles and niche partitioning among the substrates. In particular, the abundance of Vibrio alginolyticus and Vibrio campbellii suggested that microplastic pollution may pose a potential risk to the marine food chain and negatively impact aquaculture industries. Microbial genera involved in xenobiotic compound degradation, carbon cycling, and genes associated with the type IV secretion system, conjugal transfer protein TraG, plant-pathogen interaction, CusA/CzcA family heavy metal efflux transfer proteins, and TolC family proteins were significantly enriched on all the substrates, indicating the variety of processes operated by the plastic-microbiome. The present study gives a detailed characterization of the rapidly altering microbial composition and gene pools on plastics and adds new knowledge surrounding the environmental ramifications of marine plastic pollution.

Use of additives in composting informed by experience from agriculture: Effects of nitrogen fertilizer synergists on gaseous nitrogen emissions and corresponding genes (amoA and nirS)

The effects of two nitrogen fertilizer synergists (urease inhibitor, UI; nitrification inhibitor, NI) on NH₃ and N₂O emissions and the successions of the amoA and nirS genes during composting were assessed. Results showed that the UI and UI + NI treatments reduced NH₃ emissions by 26.3% and 24.3%, respectively, and N₂O emissions were reduced by 63.9% for UI + NI treatment but were not reduced by UI. The addition of UI and NI significantly reduced the abundance of the nirS gene during thermophilic stage, while significantly increased that of the amoA gene during maturation stage. Crenarchaeota was the principal nitrifying archaeal phylum and was significantly affected by pH. Proteobacteria was the main denitrifying bacterial phylum, whose relative abundance was higher for UI + NI treatment than the other treatments. PICRUSt analysis showed that the addition of UI and NI inhibited enzymatic activity related to N transformation during thermophilic stage while enriching enzymatic activity during maturation phase.

Copper Aluminum Spinels Doped with Cerium as Catalysts for NO Removal

Cu-Ce(Mn)-Al oxide catalysts to NO removal in the broad temperature range were synthesized and tested. The precursor of copper aluminium spinel was obtained with the coprecipitation method. By this method, Cu–Al spinels with various amounts of manganese and cerium were synthesized as well. These oxides crystallized in the structure of inverse spinel; however, Ce doping caused the appearance of additional CeO2 phase as determined by XRD. The samples were mesoporous solids with moderate surface area and porosity measured by low temperature sorption of nitrogen. The addition of another metal to Cu–Al spinel caused an increase of activity in selective catalytic reduction of nitrogen oxide with ammonia. The presence of manganese caused the formation of a higher amount of N2O by-product. The catalytic activity increased with the cerium concentration. For the sample with the atomic ratio Ce0.15Cu0.18, ca. 90% of NO conversion was registered between 200 and 350 °C. As examined with XPS spectroscopy, such conversion was attained due to the good dispersion of copper on the catalyst surface. This copper was placed mainly in spinel octahedral positions which enable its easier reduction. The spinel structure causes the presence of cerium as the trivalent cation important in redox cycles with the participation of copper.