Role Of Nitrate Research Articles

Both AOA and AOB contribute to nitrification and show linear correlation with nitrate leaching in purple soils with a wide nitrogen gradient

Ammonia oxidizers play an important role in nitrification that forms nitrate, the main form of leaching nitrogen (N). However, little is known about how ammonia oxidizers bridge long-term N fertilization levels and soil nitrate leaching. We conducted a field experiment in purple soil, investigating the interactions among soil physico-chemical parameters, ammonia-oxidizing microbial communities, and N leaching under 0, 90, 180, 270, and 360 kg N ha−1 yr−1 fertilization levels. We found that soil inorganic N leaching increased exponentially with increasing N application rate. N fertilization enhanced the abundances of the amoA gene in ammonia-oxidizing archaea (AOA) and bacteria (AOB), while partial least squares regression analysis revealed that AOA and AOB abundances were correlated with pH and soil organic carbon (SOC). Compared with no N fertilization, N application reduced AOA alpha diversity and increased AOB alpha diversity. AOA alpha diversity was associated with pH and bulk density, whereas soil SOC and inorganic N content were more important in predicting changes in AOB alpha diversity. A linear relationship was established between soil NO3−-N leaching, the potential nitrification rate (PNR), and the abundances of AOA and AOB. The association of soil NO3−-N leaching and PNR with both AOA and AOB abundances were further corroborated by Mantel test, random forest regression, and partial least squares path modelling. Furthermore, alterations in the AOB alpha diversity, soil pH and NH4+-N content also contribute to the increasing soil NO3−-N leaching along the N application rate. Our results suggest that AOA, which previous studies have found to be active only under low N conditions, can also contribute to nitrification and support soil NO3−-N leaching at a wide range of N gradients. Overall, this finding advances the current understanding of the relationship between soil N leaching and microbial functional properties to some extent.

Extreme soil salinity reduces N and P metabolism and related microbial network complexity and community immigration rate.

Soil microbiomes are well known to suffer from the effects of rising salinity. There are, however, no current understandings regarding its specific effects on microbial metabolic functions associated with nitrogen (N) and phosphorus (P) cycling, particularly in the Yellow River Delta (YRD), one of the largest estuaries in the world. This research examined soil microbiomes at 50 sites in the YRD region to analyze their co-occurrence networks and their relationship with N (nitrification, denitrification, dissimilatory, assimilatory, fixation, and mineralization) and P (solubilization, mineralization, transportation, and regulation) metabolism processes. Our findings indicate a notable reduction in soil multifunctionality as salinity levels increase, with Halofilum-ochraceum playing a significant role in nitrification, whereas Bacteroidetes-SB0662-bin-6 helps solubilize inorganic P in highly saline areas. High soil salinity negatively affected the amoA gene involved in nitrification and increased the nosZ gene involved in denitrification in extreme salinity soil with 8.2g/kg salt content. Extreme salinity significantly reduced the expression of genes involved in inorganic P solubilization, such as ppa and ppx. Additionally, the alkaline P gene phoD exhibited significant decreases in extremely saline soils, thereby impeding the mineralization of organic P. The neutral community models indicated that microbial community immigration rate showed a linear negative relationship with soil EC in the six N and four P processes. Salinization, however, displayed a nonlinear pattern with clearly defined thresholds on the community of microbes involved in N and P cycling. Reduced microbial diversity and interactions are causing a decline in soil multifunctionality, and the soil multifunctionality and network edges jointly limited the microbial community immigration rate involved in N and P cycling. It is crucial to preserve soil microbial functions to support nutrient cycling and predict the ecological effects of soil salinization.

Fish production, water quality, and the role of nitrification as an ammonia removal process in intensively aerated hybrid catfish ponds

AbstractSix 0.1‐ha earthen ponds with 45 kW/ha of aeration capacity were stocked with hybrid catfish (Ictalurus punctatus x I. furcatus) ranging from 15,000 to 90,000 fish ha−1 in 15,000 fish ha−1 increments to analyze the effect of nitrogen loading on ammonia accumulation and fish production. Minimum dissolved oxygen (DO) concentration was maintained above 3.0 mg O2 L−1 to prevent hypoxia‐induced appetite reduction. Stocking density did not impact survival but decreased average fish harvest weight and increased food conversion ratio (FCR). Gross production increased with stocking density and ranged from 7249 to 35,674 kg ha−1. Average total (TAN) and un‐ionized ammonia (NH3) were not different among stocking densities despite greater nitrogen inputs in ponds with higher feeding rates. Nitrite () and nitrate () concentrations were significantly higher in ponds with higher stocking densities, suggesting that nitrification increased with nitrogen loading. Phytoplankton assimilation of ammonia is the primary ammonia removal process in traditional catfish ponds with modest fish densities and feeding rates. However, in intensively aerated ponds with high feeding rates, nitrification can become an important process for ammonia removal. These data indicate that small earthen hybrid catfish ponds with high aeration capacities can increase catfish production without ammonia accumulating.

Protein nitration in the artery wall: A contributor to cardiovascular disease?

Nitration is a well-established post-translational modification of selected free amino acids, as well as proteins, lipids and nucleic acids. Considerable evidence is now available for the formation of long-lived species containing an added –NO2 function on the aromatic rings of tyrosine (Tyr) and tryptophan (Trp) residues (both free and on proteins), to purine nucleobases (and particularly guanine), and to unsaturated lipids within biological systems. Multiple potential mechanisms that give rise to these nitrated species have been identified including reactions of the potent oxidant and nitrating species peroxynitrous acid/peroxynitrite (ONOOH/ONOO−) and via oxidative reactions of heme proteins/enzymes (e.g. peroxidases) with the biologically-relevant anion nitrite (NO2−). •NO2 is likely to be a key intermediate, though involvement of HNO2, NO2+ and NO2Cl has also been proposed. The resulting nitrated products have been widely employed as qualitative or quantitative biomarkers of nitration events in vitro and in vivo. Increasing evidence suggests that at least some of these products are not benign species, with evidence for pro-inflammatory actions. In this article the mechanisms and role of nitration, and particularly that on proteins within the artery wall, in cardiovascular disease is discussed, together with emerging data suggesting that low levels of nitration occur within biological systems in the absence of added oxidants. Both stimulated and endogenous nitration may play a role in modulating cell signaling, alter the structure and function of both cellular- and extracellular proteins, and contribute to various inflammatory pathologies, including atherosclerosis.

Role of Nitrate in the Production of Iron-Modified Hydrochar for Arsenic Removal

Role of Nitrate in the Production of Iron-Modified Hydrochar for Arsenic Removal

Canonical ammonia oxidizers and comammox Clade A play active roles in nitrification in a black soil at different pH and ammonium concentrations

Canonical ammonia oxidizers and comammox Clade A play active roles in nitrification in a black soil at different pH and ammonium concentrations

Contrasting response of comammox Nitrospira, ammonia oxidising bacteria, and archaea to soil pH and nitrogen inputs

This study aimed to investigate the effect of soil pH change, and nitrogen amendment on ammonia oxidiser abundance and comammox Nitrospira community composition. The experimental design used soil mesocosms placed in a temperature-controlled incubator for 90 days. A Templeton silt loam was used as its physiochemical properties are typical of the region's dairy farms. The results showed that comammox Nitrospira clade B preferred the natural (pH 6.1–6.2) soil pH with no applied nitrogen. Furthermore, synthetic urine (N700) decreased the abundance of comammox Nitrospira clade B. This may have been because the large amounts of available ammonia in the N700 treatments inhibited the growth of comammox Nitrospira.These results suggest that while comammox Nitrospira clade B are present in New Zealand dairy farm soils, but their role in nitrification in the very high nitrogen environment under a urine patch in grazed pastures may be limited. Further research is needed to confirm this.In contrast to comammox, the AOB community (dominated by Nitrosospira) responded positively to the application of synthetic urine. The response was greatest in the high pH soil (7.1), followed by the natural and then the low pH (4.9) soils. This may be due to the difference in ammonia availability. At high pH, the ammonia/ammonium equilibrium favours ammonia production. Calculated ammonia availability in the N700 treatments accurately predicted the AOB amoA gene abundance.Interestingly, the AOA community abundance (which was predominantly made up of Thaumarchaeota group I.1b clade E) seemed to prefer the natural and high pH soils over the low pH. This may be due to the specific lineage of AOA present. AOA did not respond to the application of nitrogen.

Straw addition promotes the nitrification process and the wheat yield linked to trophic interactions among microbes

AbstractStraw return with nitrogen (N) fertilizer can generally regulate soil N cycling by affecting the microbial community, thereby influencing crop productivity. Bacteria and fungi play a key role in nitrification, while the effects of soil microbial interactions that include protists under the condition of straw return and N fertilizer remain uncertain. Here, we evaluated the importance of the soil microbiome, particularly protists and ammonia‐oxidizing bacteria (AOB), in regulating the soil N transformation potential and wheat yields under different fertilization practices. The results showed that the activity of β‐1,4‐N‐acetylglucosaminidase (NAG) and the potential nitrification rate (PNR) increased significantly by 156.4% ~ 312.3% and 183.1% ~ 402.6% with the addition of N fertilizer and straw, respectively. The effect on PNR was greater for straw than fertilizer addition. The fertilization practices changed the microbial community structure, and there were stronger responses from the protists and AOB. The soil microbiome formed three closely co‐occurring modules (Modules 0, 1 and 2). Among them, Module 0 showed strong positive correlations with the soil total N, NAG, PNR and crop yield and may be the key ecological cluster. Moreover, the predatory protists Cercozoa, Conosa and Ochrophyta in Module 0 were significantly positively associated with the activity of NAG and the PNR, yields and AOB. The predatory protists in Module 0 may change the soil potential nitrification rate and enhance the yield of wheat by preying on the competitors of AOB. The results suggest that the incorporation of straw promotes the N transformation potential and wheat yields linked to trophic interactions between predatory protists and AOB in fluvo‐aquic soil.

Investigation on the role of nitrates in the microwave-assisted autoclave Pechini synthesis of aluminoborate phosphors

The different studies, with or without nitrate counterions, highlight their role enhancing the white photoluminescence properties of aluminoborate phosphors.

Changes in the activity and abundance of canonical nitrifiers and Comammox bacteria during stream switching: Shifting from a mainstream hybrid reactor for C, N, and P removal to a sidestream biofilm nitrification reactor

This study investigated how mainstream-sidestream switching affected the activity and abundance of canonical nitrifiers and Comammox bacteria. The experiment started in a mainstream hybrid reactor for C, N, and P removal with biomass in the form of activated sludge and biofilm. A highly effective nitrification sidestream reactor with pure moving bed technology was then obtained through gradual reduction of the reactor's organic loading rate (OLR), increase in the temperature (20–30 °C), and increase in the reactor's nitrogen loading rate (NLR). qPCR and kinetic batch test results suggest that Comammox bacteria could play an important role in nitrification in both the mainstream hybrid reactor and sidestream biofilm reactor, dominating even the canonical AOB. Biofilm provided a better environment for Comammox bacteria development, except when the system was transformed into a hybrid nitrifying reactor. In that case, the occurrence of Comammox bacteria in activated sludge was greater. Simultaneously with reduction of OLR an increase in ammonia oxidation rate was reported in both activated sludge and biofilm. An increase in NLR had a greater effect on the activity of NOB.

Structural and functional Analysis of novel 3‐Nitrotyrosine Aβ‐specific Antibodies

AbstractBackgroundPosttranslational modified (PTM) amyloid peptides are increasingly within the spotlight of Alzheimer’s drug research. Some of these modifications, such as the formation of pyroglutamate or isoaspartate, are associated with the deposition and increased toxicity of amyloid peptides. The role of nitration at Tyr10 of Aβ and its abundance in AD brain is less well understood. How 3NY10‐Aβ is formed is controversial, as well as the influence on aggregation behaviour. Hence, we here aimed at generation and characterization of monoclonal antibodies specific for 3NY10‐Aβ as research tool and potential therapeutic molecules.MethodMonoclonal antibodies were developed by immunizing mice with 3NY10‐Aβ(6‐14) and derivation of corresponding hybridoma cell lines. Characterisation of the antibodies was achieved by a variety of biochemical and kinetic analyses: isothermal titration calorimetry (ITC), dot blot analysis and ThioflavinT aggregation studies. X‐ray crystallography was used for structure determination. We used immunohistochemical (IHC) staining of brain tissue from 5xFAD mice and enzyme linked immune sorbent assay (ELISA) to assess the formation of 3NY10‐Aβ in transgenic mice.ResultTwo highly affine 3NY10‐Aβ antibodies 4C3 and 3B3 have been generated, both binding 3NY10‐Aβ(1‐16) in the nanomolar range (KD4C3 = 11 nM, KD3B3 = 88,5 nM) as determined by ITC. The specificity of the antibodies was confirmed by dot blot analysis, using several post‐translationally modified Aβ‐peptides. Aggregation studies of 3NY10‐Aβ(1‐40/42) peptides in presence of 3B3 or 4C3 showed an influence of fibril formation, as could be verified by means of transmission electron microscopy. Co‐crystallisation of 4C3 Fab‐fragment and 3NY10‐Aβ(1‐16) at a resolution of 2.5 Å revealed a binding of 3NY10. To investigate the role of 3NY10‐Aβ in AD, IHC‐staining of brain from mice with AD‐like pathology (5xFAD mice) was performed. The data support presence of 3NY10‐Aβ within amyloid deposits, although staining appeared weak. Likewise, a Sandwich‐ELISA of homogenized murine brain tissue displayed no significant proportion of 3NY10‐modified Aβ in relation to the total Aβ(1‐40/42).ConclusionIt has been demonstrated that the unique monoclonal 3NY10‐Aβ specific antibodies 4C3 and 3B3 are a suitable tool for investigating the role of 3NY10‐Aβ in AD. Future research aims to quantify the level of 3NY10‐Aβ in human brain tissue with AD‐pathology.

Effects of Nitrogen Fertilizer on Nitrospira- and Nitrobacter-like Nitrite-Oxidizing Bacterial Microbial Communities under Mulched Fertigation System in Semi-Arid Area of Northeast China

The accumulation of nitrite is frequently overlooked, despite the fact that nitrification is the most essential phase of the entire nitrogen (N) cycle and that nitrifying bacteria play a significant role in nitrification. At present, the effects of different N application rates on soil nitrite-oxidizing bacteria (NOB) abundance, community composition, diversity, and its main influencing factors are still unclear. In this study, five N fertilizer application rates under film mulching and a drip irrigation system were studied in the semi-arid area of Northeast China. The treatments were 0 kg ha−1 (N0), 90 kg ha−1 (N1), 150 kg ha−1 (N2), 210 kg ha−1 (N3), and 270 kg ha−1 (N4). Fluorescent quantitative PCR and Illumina Miseq sequencing were used to analyze the abundance and community structure of NOB under different amounts of N application. The results showed that the increase in amounts of N application was strongly accompanied by an increase in the content of soil organic matter (SOM), total nitrogen (TN), nitrate nitrogen (NO3−-N), and ammonium nitrogen (NH4+-N), while the pH significantly reduced with an increase in N fertilization. N fertilization significantly increased soil nitrite oxidoreductase (NXR) activity, soil nitrification potential (PNR), and soil nitrite oxidation potential (PNO). A high N application rate significantly heightened the abundance of Nitrospira- and Nitrobacter-like NOB. N fertilizer considerably raised the Shannon index of Nitrospira-like NOB. The N application amount was the key factor affecting the community structure of Nitrospira-like NOB, and available nitrogen (AN) had the dominant influence on the community structure of Nitrospira-like NOB. N fertilizer can cause soil acidification, which affects NOB abundance and diversity. Nitrospira-like NOB may promote nitrite oxidation in different N application rates under a mulched fertigation system. The findings offered a crucial scientific foundation for further investigation into how nitrite-oxidizing bacteria respond to N fertilizer management strategies in farmland soil under film mulching drip irrigation in Northeast China.

Effects of Vegetation Types and Seasonal Dynamics on the Diversity and Function of Soil Bacterial Communities in the Upper Reaches of the Heihe River

The process of interaction between the plant and soil microbial communities holds the key to understanding the biogeochemical cycle and preserving the stability of vegetation ecosystems. Owing to this significance, the primary goal of this research was to give a starting point and reference methods to restore local vegetation. The vegetation distribution in the mountainous area of the upper reaches of the Heihe River Basin had notable vertical zonality, which was characterized by five typical vegetation types, including cushion vegetation(CV), herbage meadow(HM), forest steppe(FS), mountainous steppe(MS), and desert grassland(DG). The organization and diversity of soil bacterial communities in various vegetation types were examined using high-throughput sequencing techniques in both the winter and summer seasons. Sampling sites were chosen in each of the five common vegetation types in turn. Additionally, based on the FAPROTAX database, the predicted functions of microbial communities were evaluated for different vegetation types and seasons. The redundancy analysis and structural equation model were also used to investigate the primary environmental elements and uncover the mechanisms affecting the soil bacterial populations. The findings revealed that:① the physical and chemical properties of soil differed significantly among vegetation types and seasons, and the property indices varied dissimilarly with depth. In particular, the soil water content(SWC) and nutrient content of total organic carbon(TOC) and total nitrogen(TN) were significantly higher in forest grassland(FS). ② The divergences of α-diversity indices among seasons(P<0.05) were greater than that of vegetation types(P>0.05). The Chao1 index measuring the abundance of the bacterial community was higher in winter. According to the Shannon index, the species of the bacterial community were dispersed in a "W" shape in the summer and a "hump" form in the winter with altitude. ③ The predominant phyla of the bacterial community, composed of Acidobacteria, Proteobacteria, and Actinobacteria, did not significantly differ from one another. However, the organization of the bacterial community presented a significant variation seasonally at the genus level. ④ The primary functions of the soil bacterial population, which largely consisted of chemoheterotrophy, nitrification, and aerobic ammonia oxidation, were not significantly different among vegetation types and seasons. ⑤ The key factors affecting soil bacterial communities at the genus level varied significantly among seasons, with soil temperature(ST), total organic carbon(TOC), and pH in winter and soil water content(SWC), carbon-nitrogen ratio(C/N), and pH in summer. ⑥ Synergized by interrelated environmental factors, soil physical and chemical features exerted a more direct impact on the diversity and functionality of bacterial communities compared with vegetation types, including significantly changing the abundance of Acidobacteria and Bacteroidetes, as well as the role of nitrification and ammonia oxidation. Hence, improving the carbon and nitrogen contents in soil nutrients would help to enhance the diversity and function of bacterial communities. The findings of this study provided a model for determining the mechanism of regional vegetation degradation and preserving the stability of alpine ecosystems in this area by revealing the seasonal distribution pattern of bacterial communities and the key biological processes beneath the typical vertical vegetation band in the upper reaches of the Heihe River.

Mitigation of ammonia emissions during food waste composting through acetic acid addition: A promising strategy for sustainable waste management

This research investigates using acetic acid to reduce ammonia emissions during composting while also evaluating its impact on microbial activity, compost quality, and nitrogen content. Composting is essential for recycling food waste and achieving renewable resource targets, but ammonia emissions pose environmental and health concerns. Addressing these issues is crucial for advancing composting technology and promoting sustainable waste management practices. The study reveals that adjusting the pH of compost piles to pH5, pH6, and pH7 reduced ammonia odor production by 65%, 40%, and 20%, respectively, compared to the control pile without acetic acid. The dominant bacteria, including Lactobacillus, Bacillus, and Aneurinibacillus species, played a crucial role in nitrification, leading to significant ammonia reduction during thermophilic and mesophilic phases. Additionally, nitrogen assimilation during composting enriches the nutrient content of the mature compost, as evidenced by seed germination indexes more significant than 80% in the treated piles. These findings contribute to optimizing composting processes and promoting sustainable agricultural circular economies.

Comammox Nitrospira dominates the nitrification in artificial coniferous forest soils of the Qilian Mountains

Complete ammonia oxidizers (Comammox, CMX) are a newly discovered and important component of the nitrogen cycle. While CMX Nitrospira has been detected in various ecosystems, few studies so far have focused on the relative contribution and co-occurrence network of ammonia oxidizing archaea (AOA), bacteria (AOB), and CMX Nitrospira in artificial forest ecosystems (tree plantations). We evaluated the dynamics of composition, co-occurrence patterns and contribution of soil microbial nitrifiers to nitrification in soil of various tree species with different ages in the Qilian Mountains employing the space for time substitution approach, quantitative PCR and high-throughput sequencing technology. Generally, plantation development significantly reduced soil potential nitrification rates. Inhibition experiments and modular analysis showed that AOA played leading roles in nitrification of abandoned farmland and 17-year-old Hippophae rhamnoides, whereas CMX Nitrospira dominated in 36-year-old Picea crassifolia, 36-year-old Picea crassifolia and Larix gmelinii mixed plantation, and 50-year-old Picea crassifolia. The dominant AOA and CMX Nitrospira lineages in all samples were Group I.1b and Clade B, respectively. The assembly of nitrifier community was governed by stochastic processes, in which dispersal limitation made a significant contribution. The nitrifiers coexist in a mutualistic manner, albeit with possible functional redundancy, while the modular analysis revealed the aggregation pattern of the four modules in different artificial forests' soil. The Mantel test showed that modular formation is mainly affected by NH4+ and SOM. These results broaden our current understanding of the relation between CMX Nitrospira and canonical ammonia oxidizers in terrestrial ecosystems, and provide empirical evidence for not only niche differentiation, but also the relative contribution and co-occurrence patterns of nitrifying communities in an artificial forest ecosystem.

Community assembly of comammox Nitrospira in coastal wetlands across southeastern China.

Complete ammonia oxidizers (comammox Nitrospira) are ubiquitous in coastal wetland sediments and play an important role in nitrification. Our study examined the impact of habitat modifications on comammox Nitrospira communities in coastal wetland sediments across tropical and subtropical regions of southeastern China. Samples were collected from 21 coastal wetlands in five provinces where native mudflats were invaded by Spartina alterniflora and subsequently converted to aquaculture ponds. The results showed that comammox Nitrospira abundances were mainly influenced by sediment grain size rather than by habitat modifications. Compared to S. alterniflora marshes and native mudflats, aquaculture pond sediments had lower comammox Nitrospira diversity, lower clade A.1 abundance, and higher clade A.2 abundance. Sulfate concentration was the most important factor controlling the diversity of comammox Nitrospira. The response of comammox Nitrospira community to habitat change varied significantly by location, and environmental variables accounted for only 11.2% of the variations in community structure across all sites. In all three habitat types, dispersal limitation largely controlled the comammox Nitrospira community assembly process, indicating the stochastic nature of these sediment communities in coastal wetlands. IMPORTANCE Comammox Nitrospira have recently gained attention for their potential role in nitrification and nitrous oxide (N2O) emissions in soil and sediment. However, their distribution and assembly in impacted coastal wetland are poorly understood, particularly on a large spatial scale. Our study provides novel evidence that the effects of habitat modification on comammox Nitrospira communities are dependent on the location of the wetland. We also found that the assembly of comammox Nitrospira communities in coastal wetlands was mainly governed by stochastic processes. Nevertheless, sediment grain size and sulfate concentration were identified as key variables affecting comammox Nitrospira abundance and diversity in coastal sediments. These findings are significant as they advance our understanding of the environmental adaptation of comammox Nitrospira and how future landscape modifications may impact their abundance and diversity in coastal wetlands.

Novel Sulfate Reduction Coupled to Simultaneous Nitrification and Autotrophic Denitrification Process for Removing Nitrogen and Organics from Saline Wastewater.

Highly efficient sulfate reduction coupled to autotrophic denitrification plus nitrification is demonstrated by integrating an anaerobic membrane bioreactor (AnMBR) with a membrane aerated biofilm reactor (MABR). Concurrent chemical oxygen demand (COD) removal and sulfate reduction were accomplished in the AnMBR, while simultaneous nitrification and autotrophic denitrification were carried out in the MABR. Separate operation of the MABR achieved >90% total nitrogen (TN) removal when the N/S ratio was controlled at 0.4 gN/gS. The integrated AnMBR-MABR system efficiently resisted influent variability, realizing >95% COD removal in the AnMBR and >75% TN removal in the MABR when the influent COD/N ratio was above 4 gCOD/gN. Membrane fouling did not happen during ∼170 days of operation. Due to sulfide oxidation, a large amount of elemental sulfur (S0) accumulated in the MABR biofilm, where it served as an electron donor for denitrification. Microbial community analysis indicated that Nitrospira and Thiobacillus played key roles in nitrification and sulfide-driven denitrification, respectively, and that they occurred in different layers of the biofilm. This novel process offers advantages of a small land-area footprint, modular operation, and high efficiency electron-donor and oxygen utilizations, particularly for wastewater with a low COD/N ratio.

Analysis of biomass productivity and physiology of Nitrososphaera viennensis grown in continuous culture.

Microbial ammonia oxidation is the first and usually rate limiting step in nitrification and is therefore an important step in the global nitrogen cycle. Ammonia-oxidizing archaea (AOA) play an important role in nitrification. Here, we report a comprehensive analysis of biomass productivity and the physiological response of Nitrososphaera viennensis to different ammonium and carbon dioxide (CO2) concentrations aiming to understand the interplay between ammonia oxidation and CO2 fixation of N. viennensis. The experiments were performed in closed batch in serum bottles as well as in batch, fed-batch, and continuous culture in bioreactors. A reduced specific growth rate (μ) of N. viennensis was observed in batch systems in bioreactors. By increasing CO2 gassing μ could be increased to rates comparable to that of closed batch systems. Furthermore, at a high dilution rate (D) in continuous culture (≥ 0.7 of μmax) the biomass to ammonium yield (Y(X/NH3)) increased up to 81.7% compared to batch cultures. In continuous culture, biofilm formation at higher D prevented the determination of D crit. Due to changes in Y(X/NH3) and due to biofilm, nitrite concentration becomes an unreliable proxy for the cell number in continuous cultures at D towards μmax. Furthermore, the obscure nature of the archaeal ammonia oxidation prevents an interpretation in the context of Monod kinetics and thus the determination of K S. Our findings indicate that the physiological response of N. viennensis might be regulated with different enzymatic make-ups, according to the ammonium catalysis rate. We reveal novel insights into the physiology of N. viennensis that are important for biomass production and the biomass yield of AOA. Moreover, our study has implications to the field of archaea biology and microbial ecology by showing that bioprocess technology and quantitative analysis can be applied to decipher environmental factors affecting the physiology and productivity of AOA.

Auxin efflux carrier ZmPIN1a modulates auxin reallocation involved in nitrate-mediated root formation

BackgroundAuxin plays a crucial role in nitrate (NO3–)-mediated root architecture, and it is still unclear that if NO3– supply modulates auxin reallocation for regulating root formation in maize (Zea mays L.). This study was conducted to investigate the role of auxin efflux carrier ZmPIN1a in the root formation in response to NO3– supply.ResultsLow NO3– (LN) promoted primary root (PR) elongation, while repressed the development of lateral root primordia (LRP) and total root length. LN modulated auxin levels and polar transport and regulated the expression of auxin-responsive and -signaling genes in roots. Moreover, LN up-regulated the expression level of ZmPIN1a, and overexpression of ZmPIN1a enhanced IAA efflux and accumulation in PR tip, while repressed IAA accumulation in LRP initiation zone, which consequently induced LN-mediated PR elongation and LR inhibition. The inhibition rate of PR length, LRP density and number of ZmPIN1a-OE plants was higher than that of wild-type plants after auxin transport inhibitor NPA treatment under NN and LN conditions, and the degree of inhibition of root growth in ZmPIN1a-OE plants was more obvious under LN condition.ConclusionThese findings suggest that ZmPIN1a was involved in modulating auxin levels and transport to alter NO3–-mediated root formation in maize.

A novel two-stage anoxic/oxic-moving bed biofilm reactor process for biological nitrogen removal in a full-scale municipal WWTP: Performance and bacterial community analysis

The application of a novel two-stage anoxic/oxic-moving bed biofilm reactor (TS-A/O-MBBR) was validated in a full-scale municipal wastewater treatment plant (WWTP), and its working mechanism was analysed for biological nitrogen removal in this study. Over one year, at a hydraulic residence time of only 9.8 h, the effluent chemical oxygen demand, ammonia nitrogen and total nitrogen (TN) concentrations remained below 40, 2 and 15 mg/L, which met strict emission standards. The seven compartments in this unit performed different functions, and together accomplished organics and nitrogen removal. TN removal could be controlled by the external carbon sources dosage added to the postanoxic compartments to cost effectively meet the standard with the lowest cost. The maximum TN removal efficiency and minimum effluent TN concentration reached 91.76 % and 4.12 mg/L, respectively. The bacterial communities differed in the suspended solids and preoxic, postanoxic and oxic biofilms (r = 0.87 and P = 0.001). The top 30 most abundant identified bacterial genera in biofilms included 24 denitrifying genera and 2 nitrifying genera. The most abundant biofilm genus was Methylotenera, which played important roles in denitrification in the anoxic compartments. 1 and 24 denitrifying genera were only abundant in the postanoxic and preanoxic compartments, respectively. Nitrosomonas and Nitrospira were abundant in the oxic compartments, and played roles in nitrification. This study verified the feasibility of the TS-A/O-MBBR process in a full-scale WWTP, and investigated its working mechanism.