Europium(III) Functionalized Covalent Organic Framework as Sensitive and Selective Fluorescent Switch for Detection of Uranium

Uranium poses severe health risks due to its radioactivity and chemical toxicity if released into the environment. Therefore, there is an urgent demand to develop sensing materials in situ monitoring of uranium with high sensitivity and stability. In this work, a fluorescent Eu3+-TFPB-Bpy is synthesized by grafting Eu3+ cation onto TFPB-Bpy covalent organic framework (COF) synthesized through Schiff base condensation of monomers 1,3,5-tris(4-formylphenyl)benzene (TFPB) and 5,5'-diamino-2,2'-bipyridine (Bpy). The fluorescence of Eu3+-TFPB-Bpy is enhanced compared with that of TFPB-Bpy, which is originated from the intramolecular rotations of building blocks limited by the bipyridine units of TFPB-Bpy coordinated with Eu3+. More significantly, Eu3+-TFPB-Bpy is a highly efficient probe for sensing UO22+ in aqueous solution with the luminescence intensity efficiently amplified by complexation of UO22+ with Eu3+. The turn-on sensing capability was derived from the resonance energy transfer occurring from UO22+ to the Eu3+-TFPB-Bpy. The developed probe displayed desirable linear range from 5 nM to 5 μM with good selectivity and rapid response time (2 s) for UO22+ in mining wastewater. This strategy provides a vivid illustration for designing luminescence lanthanide COF hybrid materials with applications in environmental monitoring.

σ-Hole Effect-Induced Electroluminescence of Halogen Cocrystals for Determination of Iodide in Seawater

Developing new electrochemiluminescence (ECL) luminators with high stability, wide applicability, and strong designability is of great strategic significance to promote the ECL field to the frontier. Here, driven by the I···N bond, 1,3,5-trifluoro-2,4,6-triiodobenzene (TFTI) and 2,4,6-trimethyl-1,3,5-triazine (TMT) self-assembled into a novel halogen cocrystal (TFTI-TMT) through slow solution volatilization. Significant difference of charge density existed between the N atoms on TMT and the σ-hole of the I atoms on TFTI. Upon the induction of σ-hole effect, high-speed and spontaneous charge transferring from TMT to the σ-hole of TFTI occurred, stimulating exciting ECL signals. Besides, the σ-hole of the I atoms could capture iodine ions specifically, which blocked the original charge transfer from the N atoms to the σ-hole, causing the ECL signal of TFTI-TMT to undergo a quenching rate as high as 92.9%. Excitingly, the ECL sensing of TFTI-TMT toward I- possessed a wide linear range (10-5000 nM) and ultralow detection limit (3 nM) in a real water sample. The halogen cocrystal strategy makes σ-hole a remarkable new viewpoint of ECL luminator design and enables ECL analysis technology to contribute to addressing the environmental and health threats posed by iodide pollution.

Hydrogen-Bonded Cocrystals Encapsulating CsPbBr3 Perovskite Nanocrystals with Enhancement of Charge Transport for Photocatalytic Reduction of Uranium

At present, poor stability and carrier transfer efficiency are the main problems that limit the development of perovskite-based photoelectric technologies. In this work, hydrogen-bonded cocrystal-coated perovskite composite (PeNCs@NHS-M) is easily obtained by inducing rapid crystallization of melamine (M) and N-hydroxysuccinimide (NHS) with PeNCs as the nuclei. The outer NHS-M cocrystal passivates the undercoordinated lead atoms by forming covalent bonds, thereby greatly reducing the trap density while maintaining good structure stability for perovskite nanocrystals. Moreover, benefiting from the interfacial covalent band linkage and long-range ordered structures of cocrystals, the charge transfer efficiency is effectively enhanced and PeNCs@NHS-M displays superior photoelectric performance. Based on the excellent photoelectric performance and abundant active sites of PeNCs@NHS-M, photocatalytic reduction of uranium is realized. PeNCs@NHS-M exhibits U(VI) reduction removal capability of up to 810.1 mg g-1 in the presence of light. The strategy of cocrystals trapping perovskite nanocrystals provides a simple synthesis method for composites and opens up a new idea for simultaneously improving the stability and photovoltaic performance of perovskite.

Rapid Charge Transfer Enabled by Noncovalent Interaction through Guest Insertion in Supercapacitors based on Covalent Organic Frameworks

Covalent organic frameworks (COFs) have been proposed for electrochemical energy storage, although the poor conductivity resulted from covalent bonds limits their practical performance. Here, we propose to introduce noncovalent bonds in COFs through a molecular insertion strategy for improving the conductivity of the COFs as supercapacitor. The synthesized COFs (MI-COFs) establish equilibriums between covalent bonds and noncovalent bonds, which construct a continuous charge transfer channel to enhance the conductivity. The rapid charge transfer rate enables the COFs to activate the redox sites, bringing about excellent electrochemical energy storage behavior. The results show that the MI-COFs exhibit much better performance in specific capacitance and capacity retention rate than those of most COFs-based supercapacitors. Moreover, through simply altering inserted guests, the mode and strength of noncovalent bond can be adjusted to obtain different energy storage characteristics. The introduction of noncovalent bonds is an effective and flexible way to enhance and regulate the properties of COFs, providing a valuable direction for the development of novel COFs-based energy storage materials.

Molecular Insertion: A Master Key to Unlock Smart Photoelectric Responses of Covalent Organic Frameworks

Covalent organic frameworks (COFs) show potentials in prominent photoelectric responses by judicious structural design. However, from the selections of monomers and condensation reactions to the synthesis procedures, the acquisition of photoelectric COFs has to meet overmuch high conditions, limiting the breakthrough and modulation in photoelectric responses. Herein, the study reports a creative "lock-key model" based on molecular insertion strategy. A COF with suitable cavity size, TP-TBDA, is used as the host to load guests. Merely through the volatilization of mixed solution, TP-TBDA and guests can be spontaneously assembled via non-covalent interactions (NCIs) to produce molecular-inserted COFs (MI-COFs). The NCIs between TP-TBDA and guests acted as a bridge to facilitate charge transfer in MI-COFs, unlocking the photoelectric responses of TP-TBDA. By exploiting the controllability of NCIs, the MI-COFs can realize the smart modulation of photoelectric responses by simply changing the guest molecule, thus avoiding the arduous selection of monomers and condensation reactions required by conventional COFs. The construction of molecular-inserted COFs circumvents complicated procedures for achieving performance improvement and modulation, providing a promising direction to construct late-model photoelectric responsive materials.

Structural Isomerism of Covalent Organic Frameworks Causing Different Electrochemiluminescence Effects and Its Application for the Detection of Arsenic

The structural isomerism of the covalent organic framework (COF) has a significant effect on the electrochemiluminescence (ECL) performance. Herein, we report a pair of isomeric COFs, (TFPB-BD(OMe)₂-H and TAPB-BD(OMe)₂-H), based on the different directions of imine linkages and further conversion of the imine to the quinoline structure. The obtained two isomeric COFs with the same composition and similar structures exhibit dramatic differences in the photoelectrochemical and ECL fields. Indeed, TFPB-BD(OMe)₂-H demonstrates robust ECL emission superior to that of TAPB-BD(OMe)₂-H. The difference in ECL performance is due to the stronger polar interaction of TFPB-BD(OMe)₂-H than that of TAPB-BD(OMe)₂-H. The polarity is derived from the uneven charge distribution within the framework and enhances the electron interactions. In addition, the ordered conjugate skeleton provides high-speed charge transport channels for carrier transport. Therefore, the TFPB-BD(OMe)₂-H presents a smaller band gap energy and stronger polarization interaction, which are more favorable to charge migration to achieve stronger ECL signals. Furthermore, we describe a convenient ECL sensor for detecting toxic As(V) with an outstanding detection property and ultralow detection limit. This work provides a guiding principle for the design and development of ECL organic luminophores.

Guest Molecular Assembly Strategy in Covalent Organic Frameworks for Electrochemiluminescence Sensing of Uranyl

The application of covalent organic frameworks (COFs) in electrochemiluminescence (ECL) is promising in environmental monitoring. Developing an emerging design strategy to expand the class of COF-based ECL luminophores is highly desirable. Here, a COF-based host-guest system was constructed through guest molecular assembly to deal with nuclear contamination analysis. The efficient charge transport network was formed by inserting an electron-withdrawing guest tetracyanoquinodimethane (TCNQ) into the open space of the COF host (TP-TBDA; TP = 2,4,6-trihydroxy-1,3,5-benzenetricarbaldehyde and TBDA = 2,5-di(thiophen-2-yl)benzene-1,4-diamine) with an electron-donating property; the construction of the COF-based host-guest system (TP-TBDA@TCNQ) triggered the ECL emission of non-emitting TP-TBDA. Furthermore, the dense active sites in TP-TBDA were utilized to capture the target substance UO₂²⁺. The presence of UO₂²⁺ broke the charge-transfer effect in TP-TBDA@TCNQ, resulting in the weakening of the ECL signal, thus the established ECL system integrating the low detection limit with high selectivity monitors UO₂²⁺. This COF-based host-guest system provides a novel material platform for constructing late-model ECL luminophores and creates an opportunity for the vigorous ECL technology.

[A cross-sectional survey and analysis of influencing factors of humanistic of the current status of humanistic care ability of burn specialist nurses]

Objective: To investigate the current status of humanistic care ability of burn specialist nurses and to analyze the influencing factors. Methods: A single-center cross-sectional research method was conducted. From May to August 2020, 63 burn specialist nurses who met the inclusion criteria in Ruijin Hospital affiliated to Shanghai Jiao Tong University School of Medicine were selected. Self-made general data questionnaire was used to investigate 17 indexes, including gender, age, professional title, working years, whether received humanistic care training, academic qualification, and caring ability inventory (CAI) was used to evaluate their humanistic care ability. After the nurses were classified by the general data, independent sample t test and one-way analysis of variance were performed on the data to analyze the total score of CAI. The CAI total scores and scores of cognition, courage, and patience of the nurses were compared with the international norm. The factors with statistically significant differences in unvariate analysis were selected for multiple linear regression analysis to screen the independent influencing factors of humanistic care ability of burn specialist nurses. Results: A total of 63 questionnaires were collected in this survey, all of which were valid. Among the 63 nurses, there were 4 males and 59 females, with the age mainly ranging from 20 to 30 years (30 nurses, 47.62%), the professional titles mainly being nurse practitioner (36 nurses, 57.14%), the working years mainly being more than 10 years (28 nurses, 44.44%), 32 nurses not receiving humanistic care training, and academic qualifications mostly being junior college (37 nurses, 58.73%). There were significant differences in the total scores of CAI among nurses with different ages, professional titles, working years, whether received humanistic care training, and academic qualifications (with F values of 53.95, 49.14, and 75.42, t values of 6.08 and -2.82, respectively, P<0.01). The scores of cognition, courage, and patience and the total scores of CAI of nurses in this group were significantly lower than those of international norm (with t values of -2.02, -2.04, -6.19, and -3.89, respectively, P<0.05 or P<0.01). Multiple linear regression analysis showed that age, working years, professional title, and whether received humanistic care training were the independent influencing factors of humanistic care ability of burn specialist nurses (with 95% confidence intervals of 1.91-23.23, 16.25-31.48, 1.05-19.09, and 6.72-31.82, unstandardized coefficient values of 12.57, 23.86, 10.07, and 19.27, respectively, P<0.05 or P<0.01). Conclusions: The humanistic care ability of burn specialist nurses is relatively weak. Age, professional title, working years, and whether received humanistic care training are the independent influencing factors of humanistic care ability of burn specialist nurses.

[Some HBeAg-negative chronic hepatitis B patients treated with nucleos(t)ide analogue can achieve HBsAg loss after drug withdrawal: stop-to-cure may be coming]

Nucleoside/Nucleotide analogues (NAs) are widely used for the antiviral treatment of chronic hepatitis B (CHB), however, it is difficult to achieve serum hepatitis B surface antigen (HBsAg) loss with NAs therapy. In recent years, several prospective trails have reported that HBsAg loss (functional cure or clinical cure) also occurs in a small number of hepatitis B e antigen (HBeAg) negative CHB patients who discontinued long-term treatment with NAs. Accordingly, the "stop-to-cure" strategy is proposed. Although the mechanism has not been fully elucidated, the known factors related to serum HBsAg loss with NAs withdrawal include HBV genotype, duration of NAs treatment, serum HBsAg and HBV RNA levels at end-of-treatment, and ethnic differences. In the review, we discuss the best time to stop NAs therapy, the potential markers for predicting relapse after cessation of NAs and the possible mechanism of "stop-to-cure" in HBeAg-negative CHB patients, and propose some suggestions on the time of retreatment.

[Characteristics and regulatory mechanisms of lipid metabolism remodeling after malignant transformation of glioma-associated macrophages]

Objective: To observe the lipid metabolism characteristics of tumor-associated macrophages (TAM) after malignant transformation in the glioma micro-environment, and analyze the biological phenotype changes and regulatory mechanisms after inhibiting the lipid metabolism remodeling. Methods: Twelve male Balb/c mice of 6-8 weeks were used in the study. Macrophages (Mφ) were derived from mouse bone marrow, and malignantly transformed macrophages (tMφ₁ and tMφ₂) were cloned from the model of glioma stem cell (GSC) through interaction with Mφ in vivo and in vitro. Intracellular lipid droplet formation and cellular cholesterol content were measured respectively in Mφ, tMφ₁ and tMφ₂. qRT-PCR was performed to detect the genes expression level related with lipid metabolism, including sterol regulatory element binding protein (SREBP), fatty acid synthase (FASN), and 3-hydroxy-3-methylglutarate monoacyl coenzyme A reductase (HMG-CoA). Simvastatin (SIM) was used to analyze the proliferation, immigration and invasiveness ability in tMφ₁ and tMφ₂ after inhibition of the lipid metabolism. Differential expression profiles of miRNAs after SIM treatment were constructed in t-Mφ₁ and bio-informatics analysis was screened and verified for miR449a and its target gene sorting micro-tubule connectin 17 (SNX17) associated with lipid metabolism remodeling. The effect on SNX17 by up-regulated miR-449a were analyzed by qRT-PCR and Western blot, meanwhile, the biological phenotype and cholesterol content were observed after up-regulation of miR449a. Low-density lipoprotein receptor (LDLR) protein levels after SNX17 knockdown and intracellular cholesterol content after LDLR knockdown were detected respectively. Results: The numbers of intracellular lipid droplet formation in tMφ₁ and tMφ₂ were more than that in Mφ (P<0.001). Likewise, the relative contents of cholesterol (3.89±0.68 and 3.56±0.53), SREBP (4.78±0.60 and 2.84±0.41), FASN (4.65±0.70 and 3.01±0.45), and HMG-CoA (5.74±0.55 and 2.97±0.34) were significantly higher in tMφ₁ and tMφ₂ than those of Mφ (1.01 wel, 1.02 wel and 0.99 wel, respectively) (all P<0.001). The proliferation rates of tMφ₁ and tMφ₂ decreased from (47.06±5.88) % and (45.29±5.64)% to (23.53±4.70)% and (18.74±5.76)%, respectively after treatment with SIM (both P<0.05). The numbers of migrated cells decreased from 1 025±138 and 350±47 to 205±63 and 99±25, respectively (both P<0.001). And the numbers of invasiveness cells decreased from 919±45 and 527±34 to 220±23 and 114±21, respectively (both P<0.001). While the relative intracellular cholesterol content decreased to 0.52±0.08 and 0.58±0.07 (both P<0.05), respectively. MiR-449a was screened from tMφ₁ by SIM, and the target gene was analyzed and verified to be SNX17. SNX17 expression was down-regulated, and the proliferation rate, the number of migration and invasiveness was significantly decreased after miR-449a over-expression (all P<0.05). Low-density lipoprotein receptor (LDLR) expression was down-regulated after knock-down of SNX17, while the cholesterol content was decreased after knock-down of LDLR in tMφ₁ and tMφ₂ (all P<0.05). Conclusions: Malignantly transformed TAMs undergo lipid metabolism remodeling characterized with enhanced lipid metabolism. MiR-449a regulates the LDLR by targeting SNX17, thereby affecting the lipid metabolism of malignantly transformed macrophages, and subsequently inhibiting its proliferation, migration, and invasion ability. Precise intervention with miR-449a/SNX17/LDLR axis could provide an experimental basis for reversing its tumor-promoting micro-environment remodeled by GSC through metabolic intervention.

[Associations between adverse childhood experiences and adulthood substance use among lesbians]

Objective: To investigate the associations between adverse childhood experiences (ACE) and substance use behaviors among lesbians to provide a scientific basis for high-risk population identification and formulation of targeted intervention measures. Methods: Lesbians who participated in routine AIDS voluntary counseling, testing services, activities, and peer recommendations were recruited from July to December 2018, with the help of LesPark in Beijing. Convenient sampling method was used. Demographic characteristics, ACE, and substance use behaviors of subjects were investigated using an online platform powered by www.wjx.cn. Subsequently, the associations between ACE and adulthood substance use behaviors were evaluated using the logistic regression model. The SPSS 22.0 was used for statistical analysis. Results: A total of 294 lesbians were recruited in the study, 81.3% (239/294) of them were lesbians, and 18.7% (55/294) were bisexuals. Besides, 55.8% (164/294) of subjects reported they had had ACE, with proportions of lesbians experiencing abuse, neglect, and family dysfunction as 33.3% (98/294), 24.5% (72/294), and 32.7% (96/294), respectively. 55.1% (162/294) of the lesbians reported they had smoked in the past 30 days, 11.2% (33/294) reported having drug-use behavior in the past three months, and 22.8% (67/294) claimed drinking alcohol weekly. Multivariate logistic regression analysis showed that lesbians with ACE were at high risks to smoke (OR=1.87, 95%CI: 1.13-3.08), drink (OR=2.13, 95%CI: 1.18-3.84), and use drugs (OR=3.33, 95%CI: 1.29-8.61) in adulthood. Moreover, lesbians with childhood family dysfunction were at higher risk of smoking cigarettes (OR=2.60, 95%CI: 1.46-4.62) and drinking alcohol (OR=2.65, 95%CI: 1.44-4.87). At the same time, those with abuse experience were at higher risk of drug use (OR=3.17, 95%CI: 1.26-7.96). Conclusions: Substance use behaviors, including cigarette smoking, drinking alcohol, and drugs use, were common among lesbians. Positive associations were found between ACE and adulthood substance use behaviors.

Covalent Organic Frameworks as Advanced Uranyl Electrochemiluminescence Monitoring Platforms

Electrochemiluminescence (ECL), as an advanced sensing process, can selectively control the generation of excited states by changing the potential. However, most of the existing ECL systems rely on poisonous coreactants to provide radicals for luminescence; although the ECL efficiency was improved, the athematic coreactants will cause unpredictable interference to the accurate analysis of trace targets. Herein, we realized the ECL of nonemitting molecules by performing intramolecular electron transfer in the olefin-linked covalent organic frameworks (COFs), with a high efficiency of 63.7%. Employing internal dissolved oxygen as the coreactant, it is well suitable for the analysis of various complex samples in the environment. Taking nuclear contamination analysis as the goal orientation, we further illustrated a design of a "turn-on" uranyl ion monitoring system integrating fast response, low detection limit, and high selectivity, showing that new ECL-COFs are promising to facilitate environment-related sensing analysis and structure-feature correlation mechanism exploration.

Arousing Electrochemiluminescence Out of Non-Electroluminescent Monomers within Covalent Organic Frameworks

Covalent organic frameworks (COFs) with stable long-range ordered arrangements are promising materials for organic optoelectronics. However, their electrochemiluminescence (ECL) from non-ECL active monomers has not been realized. Here, we report a design strategy for ECL-emitting COF family. The donors and acceptors co-crystallized and stacked into the highly aligned array of olefin-linked COFs, so that electrons can be transported freely. By this means, a tunable ECL is activated from non-ECL molecules with the maximum efficiency of 32.1% in water with the dissolved oxygen as an inner coreactant, and no additional noxious co-reactant is needed any more. Quantum chemistry calculations further demonstrate that this design reduces the COFs' band gaps and the overlap of electrons and holes in the excited state for better photoelectric properties and stronger ECL signals. This work exploits a basis to envisage the broad application potential of ECL-COFs for various biosensors and light-emitting display.

A general design approach toward covalent organic frameworks for highly efficient electrochemiluminescence

Electrochemiluminescence (ECL) plays a key role in analysis and sensing because of its high sensitivity and low background. Its wide applications are however limited by a lack of highly tunable ECL luminophores. Here we develop a scalable method to design ECL emitters of covalent organic frameworks (COFs) in aqueous medium by simultaneously restricting the donor and acceptor to the COFs' tight electron configurations and constructing high-speed charge transport networks through olefin linkages. This design allows efficient intramolecular charge transfer for strong ECL, and no exogenous poisonous co-reactants are needed. Olefin-linked donor-acceptor conjugated COFs, systematically synthesized by combining non-ECL active monomers with C_2v or C_3v symmetry, exhibit strong ECL signals, which can be boosted by increasing the chain length and conjugation of monomers. The present concept demonstrates that the highly efficient COF-based ECL luminophores can be precisely designed, providing a promising direction toward COF-based ECL phosphors.

[Early physical growth and disease analysis among children born delivered by HBsAg-positive mothers]

Objective: To estimate the early physical growth and disease in children born to HBsAg-positive mothers. Methods: This was a retrospective cohort study. Three areas as Xihu in Hangzhou, Lanxi in Jinhua, and Haiyan in Jiaxing in Zhejiang province were selected by cluster sampling. The growth outcomes of children born to HBsAg-positive mothers (exposure group) and matched 1∶1 women uninfected with HBV (control group) in 2014 were investigated and compared at birth, 6, 9, 12, and 18 months, respectively. There were totally 342 children in each group. Results: The incidences of low birth weight (LBW) for children born to exposure and control group were 1.8% (6/342), and 2.6% (9/342), respectively (P=0.433); and, rates of preterm birth were 2.3% (8/342), and 2.0% (7/342), respectively (P=0.794). The mean birth weight of children born to mothers without HBV infection (3.4±0.4) kg was dramatically higher than children in exposure group (3.3±0.4) kg (P=0.019). At 18 months, the average head circumference was significantly greater among children in control group (47.3±1.3) cm than children in exposure group (47.0±2.0) cm (P=0.038). Additional, mean birth weeks, height, weight, increases in height/weight/head circumference each month, weight/height/head circumference for age Z scores, proportion of growth retardation and low weight, disease prevalence were not observed statistically differences between two groups (P>0.05). All children born to HBsAg-positive mothers were received three-dose HBV vaccination. The rate of hepatitis B immunoglobulin for births born to HBsAg-positive was 98.8% (338/342). Mother to children transmission of HBV at 18 months was 1.0% (1/97). Conclusion: No significant differences in growth development and disease prevalence were found among children born to HBsAg-positive women and women without HBV infection.

Comparison of Nitrosospira strains isolated from terrestrial environments

Most of our knowledge about the physiology of ammonia-oxidizing bacteria is based on experiments with Nitrosomonas europaea, which appears to be less ubiquitous than Nitrosospira. We have isolated Nitrosospiras from widely different environments and compared their specific growth rate, substrate affinity, urease activity, temperature response, pH tolerance and cell morphology. Two of the strains had a variable morphology: the spirals were less tightly coiled than the classical Nitrosospira type and a fraction of the culture had a vibrioid appearance. These vibrioid strains were also peculiar in having a much higher apparent activation energy for ammonia monooxygenase (AMO) (129 and 151 kJ mol(-1)) than that of the more classical Nitrosospiras (78 and 79 kJ mol(-1)). The differences in morphology and activation energy were congruent with the phylogeny of the genes for 16S rRNA (Utåker et al., System. Appl. Microbiol. 18) and AMO. The response to pH in the medium was investigated for four strains. The oxidation rate at the onset of the pH exposure experiment was found to obey classical steady state enzyme kinetics, assuming that NH(3) (not NH(4)(+)) is the rate-limiting substrate. The calculated half saturation constants (K(s)) for AMO were 6-11 µM NH(3). Growth had a narrower pH range than oxidation activity and appeared to be restricted by pH-dependent factors other than NH(3). All the isolated strains were urease positive, with a specific urease activity ranging from 60 to 158% of their specific AMO activity. The urease activity was unaffected by acetylene inhibition of the energy metabolism. The substrate affinity for one strain was found to be around 670 µM.

Nitrous oxide production and methane oxidation by different ammonia-oxidizing bacteria

Ammonia-oxidizing bacteria (AOB) are thought to contribute significantly to N2O production and methane oxidation in soils. Most of our knowledge derives from experiments with Nitrosomonas europaea, which appears to be of minor importance in most soils compared to Nitrosospira spp. We have conducted a comparative study of levels of aerobic N2O production in six phylogenetically different Nitrosospira strains newly isolated from soils and in two N. europaea and Nitrosospira multiformis type strains. The fraction of oxidized ammonium released as N2O during aerobic growth was remarkably constant (0.07 to 0.1%) for all the Nitrosospira strains, irrespective of the substrate supply (urea versus ammonium), the pH, or substrate limitation. N. europaea and Nitrosospira multiformis released similar fractions of N2O when they were supplied with ample amounts of substrates, but the fractions rose sharply (to 1 to 5%) when they were restricted by a low pH or substrate limitation. Phosphate buffer (versus HEPES) doubled the N2O release for all types of AOB. No detectable oxidation of atmospheric methane was detected. Calculations based on detection limits as well as data in the literature on CH4 oxidation by AOB bacteria prove that none of the tested strains contribute significantly to the oxidation of atmospheric CH4 in soils.