Nitrite Consumption Research Articles

Fe/Cl/N triply-doped bamboo-like structure wrapped with Fe3C nanoparticles for electrochemical selective nitrite detection

Nitrite is commonly found in the natural environment and in everyday human activities. However, excessive nitrite consumption can potentially harm human health. Consequently, it is crucial to develop a reliable and sensitive method for nitrite detection. In this work, trichloroacetic acid functionalized Cl-Fe-MIL-88B metal-organic framework is obtained through nucleophilic reaction between animated Fe-MIL-88B and trichloroacetic acid, which is then annealed with melamine in an N2 atmosphere to produce the Fe/Cl/N triply-doped bamboo-like carbon nanotubes (CNTs) wrapped with Fe3C nanoparticles. Owing to the effective doping of Fe/Cl/N elements, the charge distribution and chemical activity of the bamboo-like structure are tailored, greatly improving the conductivity and facilitating electron transfer of the composite for potential electrocatalytic reaction. The Fe3C nanoparticles wrapped inside the CNTs contribute to expose more active sites and provide effective surface area. Accordingly, the Fe/Cl/N doped bamboo-like structure modified glassy carbon electrode shows excellent electrochemical nitrite sensing properties with a high sensitivity of 1060µAcm-2 mM-1, a low detection limit of 0.61µM in a wide linear concentration range of 5-5000μM, as well as good anti-interference and long-term stability. Also, the electrochemical sensor has a satisfactory recovery rate for detecting nitrite ions in spiked milk samples. This work proposes a simple precursor chlorination and pyrolysis strategy to obtain metal-filled bamboo-like structure with high electrical conductivity and electrocatalytic properties, endowing great potential in food safety and environment monitoring.

Нитрозирование лигносульфонатов в условиях твердофазного катализа

Lignosulfonates are the most common commercial lignin-based product due to their unique properties. Various methods are known for modifying lignosulfonates and lignosulfonic acids. This article presents the results of the development of a new approach to the production of nitrosated lignosulfonic acids. The method is based on a reaction catalyzed by cation exchange resins in the H-form: KU-2-8 cation exchanger and wofatite. The influence of reagent consumption and reaction duration on the course of nitrosation has been studied. The dynamics of the proposed nitrosation practically coincides with the dynamics of a similar reaction using sulfuric acid by the known method. The optimal consumption of sodium nitrite equals 15 %, and the optimal consumption of cation exchanger equals 100 % by weight of lignosulfonates. During the nitrosation of lignosulfonates, significant changes in the electronic spectra occur in the region of 280...500 nm. Two overlapping absorption bands appear with maxima at 300 and 330 nm, as well as an intense absorption band at 430 nm, due to nitroso groups conjugated with the aromatic nuclei of phenylpropane units. To analyze the ionization spectra, they have been deconvoluted. The resulting spectra are well approximated by 5 Gaussians with an error of no more than 5 %. Two options for carrying out the nitrosation reaction of lignosulfonates have been proposed: under static and dynamic conditions. It has been established that under dynamic conditions, nitroso derivatives of lignosulfonic acids are formed that do not contain metal cations, and the pH of the resulting solutions does not exceed 1.4. The elemental compositions of the isolated initial and nitrosated lignosulfonic acids have been determined. The nitrogen content of lignosulfonic acids has increased from 0.32 (initial) to 2.17 % (nitrosated). In addition, under dynamic conditions, an additional stage of separating the cation exchanger from the reaction medium by filtration is not required. New bands have appeared in the IR spectrum of nitrosated lignosulfonic acids: at 1540 cm–1, which is due to the presence of nitroso groups, and a wide absorption band at 1700...1715 cm–1, which can be caused by vibrations of the carboxyl group or the quinone monooxime tautomeric form of the guaiacyl structures of lignosulfonic acids.

Impact of organic carbon on sulfide-driven autotrophic denitrification: Insights from isotope fractionation and functional genes

Additional organics are generally supplemented in the sulfide-driven autotrophic denitrification system to accelerate the denitrification rate and reduce sulfate production. In this study, different concentrations of sodium acetate (NaAc) were added to the sulfide-driven autotrophic denitrification reactor, and the S0 accumulation increased from 7.8% to 100% over a 120-day operation period. Batch experiments revealed a threefold increase in total nitrogen (TN) removal rate at an Ac−-C/N ratio of 2.8 compared to a ratio of 0.5. Addition of organic carbon accelerated denitrification rate and nitrite consumption, which shortened the emission time of N2O, but increased the N2O production rate. The lowest N2O emissions were achieved at the Ac−-C/N ratio of 1.3. Stable isotope fractionation is a powerful tool for evaluating different reaction pathways, with the 18ε/15ε values in nitrate reduction ranging from 0.5 to 1.0. This study further confirmed that isotope fractionation can reveal denitrifying nutrient types, with the 18ε (isotopic enrichment factor of oxygen)/15ε (isotopic enrichment factor of nitrogen) value approaching 1.0 for autotrophic denitrification and 0.5 for heterotrophic denitrification. Additionally, the 18ε/15ε values can indicate changes in nitrate reductase. There is a positive correlation between the 18ε/15ε values and the abundance of the functional gene napA, and a negative correlation with the abundance of the gene narG. Moreover, 18ε and 15ε were associated with changes in kinetic parameters during nitrate reduction. In summary, the combination of functional gene analysis and isotope fractionation effectively revealed the complexities of mixotrophic denitrification systems, providing insights for optimizing denitrification processes.

The association of dietary nitrates/nitrites intake and the gut microbial metabolite trimethylamine N-oxide and kynurenine in adults: a population-based study.

Dietary nitrate and nitrite may affect the gut microbiota and its metabolites, such as trimethylamine N-oxide (TMAO) and kynurenine (KYN). However, this association and the exact mechanism are still unclear. Therefore, this study aimed to assess the association between dietary consumption of nitrite and nitrate on TMAO and KYN levels in adults. This cross-sectional study was employed on a subsample baseline phase of the Tehran University of Medical Sciences (TUMS) Employee's Cohort Study (TEC). A total of 250 adults aged 18 years or older were included in the current analysis. Data on the dietary intakes were collected using a validated dish-based food frequency questionnaire (FFQ), and dietary intakes of nitrite and nitrate were estimated using the FFQ with 144 items. Serum profiles and TMAO and KYN were measured using a standard protocol. The findings of this study demonstrate a significant association between the intake of animal sources of nitrate and nitrite and the likelihood of having elevated levels of TMAO and KYN. Specifically, after adjustment, individuals with the highest intake adherence to nitrates from animal sources exhibited increased odds of having the highest level of TMAO (≥51.02 pg/ml) (OR = 1.51, 95% CI = 0.59-3.88, P = 0.03) and KYN (≥417.41 pg/ml) (OR = 1.75, 95% CI = 0.73-4.17, P = 0.02). Additionally, subjects with the highest animal intake from nitrite sources have 1.73 and 1.45 times higher odds of having the highest levels of TMAO and KYN. These results emphasize the potential implications of animal-derived nitrate and nitrite consumption on the levels of TMAO and KYN. The present evidence indicates that a high level of nitrate and nitrite intake from animal sources can increase the odds of high levels of TMAO and KYN. Further studies suggest that we should better evaluate and understand this association.

Severe hypoxaemic hypercapnia compounds cerebral oxidative-nitrosative stress during extreme apnoea: Implications for cerebral bioenergetic function.

We examined the extent to which apnoea-induced extremes of oxygen demand/carbon dioxide production impact redox regulation of cerebral bioenergetic function. Ten ultra-elite apnoeists (sixmen and four women) performed two maximal dry apnoeas preceded by normoxic normoventilation, resulting in severe end-apnoea hypoxaemic hypercapnia, and hyperoxic hyperventilation designed to ablate hypoxaemia, resulting in hyperoxaemic hypercapnia. Transcerebral exchange of ascorbate radicals (by electron paramagnetic resonance spectroscopy) and nitric oxide metabolites (by tri-iodide chemiluminescence) were calculated as the product of global cerebral blood flow (by duplex ultrasound) and radial arterial (a) to internal jugular venous (v) concentration gradients. Apnoea duration increased from 306 ± 62s during hypoxaemic hypercapnia to 959 ± 201s in hyperoxaemic hypercapnia (P≤ 0.001). Apnoea generally increased global cerebral blood flow (all P≤ 0.001) but was insufficient to prevent a reduction in the cerebral metabolic rates of oxygen and glucose (P=0.015-0.044). This was associated with a general net cerebral output (v > a) of ascorbate radicals that was greater in hypoxaemic hypercapnia (P=0.046 vs. hyperoxaemic hypercapnia) and coincided with a selective suppression in plasma nitrite uptake (a > v) and global cerebral blood flow (P=0.034 to <0.001 vs. hyperoxaemic hypercapnia), implying reduced consumption and delivery of nitric oxide consistent with elevated cerebral oxidative-nitrosative stress. In contrast, we failed to observe equidirectional gradients consistent with S-nitrosohaemoglobin consumption and plasma S-nitrosothiol delivery during apnoea (all P≥ 0.05). Collectively, these findings highlight a key catalytic role for hypoxaemic hypercapnia in cerebral oxidative-nitrosative stress. KEY POINTS: Local sampling of blood across the cerebral circulation in ultra-elite apnoeists determined the extent to which severe end-apnoea hypoxaemic hypercapnia (prior normoxic normoventilation) and hyperoxaemic hypercapnia (prior hyperoxic hyperventilation) impact free radical-mediated nitric oxide bioavailability and global cerebral bioenergetic function. Apnoea generally increased the net cerebral output of free radicals and suppressed plasma nitrite consumption, thereby reducing delivery of nitric oxide consistent with elevated oxidative-nitrosative stress. The apnoea-induced elevation in global cerebral blood flow was insufficient to prevent a reduction in the cerebral metabolic rates of oxygen and glucose. Cerebral oxidative-nitrosative stress was greater during hypoxaemic hypercapnia compared with hyperoxaemic hypercapnia and coincided with a lower apnoea-induced elevation in global cerebral blood flow, highlighting a key catalytic role for hypoxaemia. This applied model of voluntary human asphyxia might have broader implications for the management and treatment of neurological diseases characterized by extremes of oxygen demand and carbon dioxide production.

Modern suicide trend from internet

IntroductionThe most common suicide methods vary slightly from country to country, partly related to the availability of effective means. Societal development over the years and especially the advent of the Internet has enabled the sudden spread of new suicide methods. Recently, especially since 2019, intentional sodium nitrite poisoning has appeared on many social networks as an increasingly popular method of suicide. Material and MethodsThere was performed a retrospective-prospective study of the autopsy protocols of the Medico-Legal Departments of the Healthcare Surveillance Authority in Slovakia, in a period of 15 years (2008–2022). We performed the analysis of cases of death due to nitrite poisoning, focusing on cases of intentional self-harm. In all selected cases, we present complete information, including photo documentation from the place of death, as well as the results of the performed autopsy and the results of additional laboratory examinations. ResultsWe did not record any fatal cases of unintentional, accidental consumption of sodium nitrite in Slovakia, nor any fatal cases of homicidal poisoning by this substance. However, there were three cases of intentional self-harm (completed suicide) by sodium nitrite poisoning (in 2019, 2020 and 2022). ConclusionsThe correct diagnosis of the cases of sodium nitrite poisoning deaths is possible only based on evaluating all the information obtained, a thorough examination of the body and the crime scene, and the correct interpretation of the findings found during a subsequent autopsy and the results of the toxicological analysis.

The start-up of anammox system inoculated with sludge overwhelmingly dominated by Candidatus Competibacter: System performance and microbial community succession

In situ start-up of the anaerobic ammonia oxidation (anammox) process using ordinary sludge is quite time-consuming, and the existing denitrifying bacteria can compete for nitrite during the initial start-up of the reactor, resulting in inadequacy of substrates. In this study, anaerobic sludge with the relative abundance of Candidatus Competibacter up to 40.27 % was used as a seed, and sufficient nitrite was provided to maintain the levels of electron acceptor for denitrifiers during the initial start-up of the reactor. After 176 days of operation, the anammox reactor achieved removal efficiencies of ammonia and nitrite at 93.75 % and 99.88 %, respectively, and the total nitrogen removal was 73.16 %. The refined ratios of influent nitrite to ammonia in the range of 1.33–2.66 were found to minimize the effect of the large consumption of nitrite by denitrifying bacteria. High-throughput sequencing results showed that Candidatus Brocadia was the only anammox genus obtained, which accounted for 20.31 % at the end of operation. Functional bacteria for denitrification, assumed to be the Candidatus Competibacter, were decreased to 0.88 %. The predicted functions confirmed the dominance of nitrate reductase gene napA, which was positively correlated with Candidatus Competibacter and Thermovirga (Spearman correlation, p < 0.05). Therefore, the speculated molecular mechanism was the Thermovirga-dominated syntrophic metabolism coupled with the endogenous denitrification process of Candidatus Competibacter. This study revealed the microbial ecology and evolution responsible for nitrogen removal during the rapid start-up of anammox, and provided an extra line of guidance for the start-up of anammox reactors inoculated with denitrifying sludge.

Brucella spp. are facultative anaerobic bacteria under denitrifying conditions.

Bacteria of the genus Brucella are responsible for human and animal brucellosis worldwide and comprise the well-characterized, so-called classical species belonging to the core clade, with a host range limited to mammals, and the novel atypical strains mainly considered as non-zoonotic to date, but able to colonize non-traditional hosts such as amphibians. Despite marked phenotypical differences between the two groups, Brucella species display a high degree of genome identity, including genes encoding reductases involved in the denitrification pathway, a respiratory process able to reduce nitrate to nitrogen under anoxic conditions. Brucella spp. have always been considered as strictly aerobic pathogens. Our study, however, describes for the first time that atypical Brucella spp. grow well under anoxia, but in a strictly nitrate-dependent manner, whereas classical species show a heterogeneous behavior. The rate of anaerobic growth of the atypical species Brucella microti was dependent on nitrate concentration, highlighting a more efficient denitrification pathway with rapid consumption of intermediate nitrite, whereas the classical species Brucella suis exhibited lower, nitrate concentration-independent growth coupled with nitrite accumulation. Transcriptional studies performed under anoxic conditions revealed a higher expression of genes participating in the last three denitrification steps in B. microti, as compared to B. suis, which correlates with the rapid and efficient consumption of nitrite in this atypical species and its rapid growth.IMPORTANCERespiration is a fundamental and complex process that bacteria use to produce energy. Despite aerobic respiration being the most common, some bacteria make use of a mode of respiration in the absence of oxygen, called anaerobic respiration, which can yield advantages in adaptation to various environmental conditions. Denitrification is part of this respiratory process ensuring higher respiratory flexibility under oxygen depletion. Here, we report for the first time the evidence of anaerobic growth of Brucella spp. under denitrifying conditions, which implies that this genus should be reconsidered as facultative anaerobic. Our study further describes that efficient denitrification is not equally found within the Brucella genus, with atypical species showing a greater ability to denitrify, correlated with higher expression of the genes involved, as compared to classical species.

Non-rhizosphere reinforces the contributions of Feammox and anammox to nitrogen loss than rhizosphere in riparian zones

The emergence of anaerobic ammonium oxidation (anammox) coupled to iron reduction (named Feammox) refreshes the microbial pathways for nitrogen (N) loss. However, the ecological role of Feammox, compared with conventional denitrification and anammox, in microbial N attenuation in ecosystems remains unclear. Here, the specific contribution of Feammox to N loss and the underlying microbiome interactive characteristics in a riparian ecosystem were investigated through 15N isotope tracing and molecular analysis. Feammox was highlighted in the riparian interface soils and maximally contributed 14.2% of N loss. Denitrification remained the dominant contributor to N loss (68.0%–95.3%), followed by anammox (5.7%–19.1%) and Feammox (0–14.2%). The rates of Feammox and anammox significantly decreased in rhizosphere soils (0.15 ± 0.08 μg N g−1 d −1 for Feammox, 0.80 ± 0.39 μg N g−1 d −1 for anammox) compared with those in non-rhizosphere soils; however, the activities of denitrification remarkably increased in the rhizosphere (13.17 ± 3.71 μg N g−1 d −1). In rhizosphere soils, the competition between bioavailable organic matter (e.g., amino acids and carbohydrates) and ammonium for electron acceptor [i.e., Fe(III)] was the vital inducement for restricted Feammox, while the nitrite consumption boosted by heterotrophic denitrifiers was responsible for weakened anammox. The functional gene of autotrophic Acidimicrobiaceae bacterium A6, instead of heterotrophic Geobacteraceae spp., was significantly positively correlated with Feammox activity. Rare iron-reducing bacteria showed higher node degrees in the non-rhizosphere network than in the rhizosphere network. A syntrophic relationship was found between iron-reducing bacteria (e.g., Anaeromyxobacter, Geobacter) and iron-oxidizing bacteria (e.g., Sideroxydans) in the non-rhizosphere network and facilitated the Feammox pathway. This study provides an in-depth exploration of microbial driven N loss in a riparian ecosystem and introduces new insights into riparian management practices toward high-efficient N pollution alleviation.

Morpho-histological Study of the Rat Spleen Post-Induction of Sodium Nitrite and Acorus calamus L. Rhizome Ethanolic Extract

Sodium nitrite (NaNO2) is one of the most inorganic salts and is often used in processed meat products. Long-term consumption of sodium nitrite has been reported to cause of oxidative stress and spleen histological changes. Therefore, anti-oxidative effects are needed from natural ingredients such as Acorus calamus L. The study aims to determine the effect of A.calamus L. rhizome extract on anatomical structure and histological changes in the rat spleen induced with NaNO2. We used a completely randomized design with twenty-five male rats divided into 5 groups. Negative control (NC) was given 0.5% CMC for 40 days; positive control (PC) on days 1-15 was given NaNO2 (50 mg/kg BW); on days 16-30 given (50 mg/kg BW) NaNO2 + 0.5% CMC and on days 31-40 given 0,5% carboxy methyl cellulose (CMC). Treatment 1 (T1), Treatment 2 (T2), and Treatment 3 (T3) on days 1-15 were given NaNO2 doses of 50 mg; and; on days 16-30, groups T1, T2, and T3 were given NaNO2 + extract with each predetermined dose (250 mg/kg BW for T1, 500 mg/kg BW for T2, and 750 mg/kg BW for T3). For days 31-40 groups T1, T2, and T3 were given extracts with each predetermined dose. Results revealed that the extract of the A. calamus L. rhizome affects weight, length, and width of the spleen (P&lt;0.05); and bleeding lesions; while having no noticeable effect (P&lt;0.05) and having a noticeable effect on the area of the white pulp (P&lt;0.05). Administration of ethanol extract of A. calamus L. at a dose of 250 mg/kg BW has an impact on improving spleen length; a dose of 500 mg/kg BW has an impact on the weight and length of the spleen; and a dose of 750 mg / kg BW has an impact on improving spleen length, but the size variation is still in the normal category. While extracts at doses of 250 and 500 mg/kg BW have a repair impact on tissue shrinkage in damaged white pulp.

Assessment of dietary exposure to food additives used in Polish processed meat products

Dietary exposure assessments have been performed for nitrites, phosphates, erythorbic acid, and sodium erythorbate in processed meat in Poland. The exposure has been estimated based on the maximum level of use of additives contained in Regulation - tier 2 and the concentration of additives in processed meat - tier 3, additionally for nitrites. Daily intake was estimated using 24-h recall, repeated three times. Exposure analyses were correlated with the frequency of occurrence of food additives based on label analysis (tiers 2a and 3a). The mean nitrite intake from processed meat at tier 2 was 0.1 mg/kg bw (143% ADI), 0.08 mg/kg bw (118% - ADI) at tier 2a, 0.03 mg/kg bw (43% - ADI) at tier 3, and 0.026 mg/kg bw (37% - ADI) at tier 3a. The mean intakes of phosphate and erythorbic acid/sodium erythorbate from processed meat were 3.26 and 0.54 mg/kg bw (8.2% and 9% - ADI), respectively at tier 2. None of the respondents exceeded the ADIs for phosphates or erythorbic acid/sodium erythorbate. In contrast, nitrite consumption is of great concern because of significant ADI exceedances, particularly among young children.

Transport of nitrite from large arteries modulates regional blood flow during stress and exercise.

Acute cardiovascular stress increases systemic wall shear stress (WSS)-a frictional force exerted by the flow of blood on vessel walls-which raises plasma nitrite concentration due to enhanced endothelial nitric oxide synthase (eNOS) activity. Upstream eNOS inhibition modulates distal perfusion, and autonomic stress increases both the consumption and vasodilatory effects of endogenous nitrite. Plasma nitrite maintains vascular homeostasis during exercise and disruption of nitrite bioavailability can lead to intermittent claudication. During acute cardiovascular stress or strenuous exercise, we hypothesize enhanced production of nitric oxide (NO) by vascular endothelial cells raises nitrite concentrations in near-wall layers of flowing blood, resulting in cumulative NO concentrations in downstream arterioles sufficient for vasodilation. Utilizing a multiscale model of nitrite transport in bifurcating arteries, we tested the hypothesis for femoral artery flow under resting and exercised states of cardiovascular stress. Results indicate intravascular transport of nitrite from upstream endothelium could result in vasodilator-active levels of nitrite in downstream resistance vessels. The hypothesis could be confirmed utilizing artery-on-a-chip technology to measure NO production rates directly and help validate numerical model predictions. Further characterization of this mechanism may improve our understanding of symptomatic peripheral artery occlusive disease and exercise physiology.

Spatial and temporal conversion of nitrogen using Arthrobacter sp. 24S4-2, a strain obtained from Antarctica.

According to average nucleotide identity (ANI) analysis of the complete genomes, strain 24S4-2 isolated from Antarctica is considered as a potential novel Arthrobacter species. Arthrobacter sp. 24S4-2 could grow and produce ammonium in nitrate or nitrite or even nitrogen free medium. Strain 24S4-2 was discovered to accumulate nitrate/nitrite and subsequently convert nitrate to nitrite intracellularly when incubated in a nitrate/nitrite medium. In nitrogen-free medium, strain 24S4-2 not only reduced the accumulated nitrite for growth, but also secreted ammonia to the extracellular under aerobic condition, which was thought to be linked to nitrite reductase genes nirB, nirD, and nasA by the transcriptome and RT-qPCR analysis. A membrane-like vesicle structure was detected in the cell of strain 24S4-2 by transmission electron microscopy, which was thought to be the site of intracellular nitrogen supply accumulation and conversion. This spatial and temporal conversion process of nitrogen source helps the strain maintain development in the absence of nitrogen supply or a harsh environment, which is part of its adaption strategy to the Antarctic environment. This process may also play an important ecological role, that other bacteria in the environment would benefit from its extracellular nitrogen source secretion and nitrite consumption characteristics.

Fe(OH)3 induced the Anammox system to perform extracellular electron transfer for enhancement of NH4+ removal

It is widely found that the ratio of nitrite consumption to ammonia consumption (ΔNO2--N/ΔNH4+-N) in Anammox systems is lower than its stoichiometry of 1.32, but the reason is unclear. In this study, ΔNO2--N/ΔNH4+-N of an Anammox system decreased to 0.80 with the addition of Fe(OH)3, which was significantly lower than a control system without the addition of Fe(OH)3. The lower ratio or more NH4+ removal was likely related to the reduction of Fe(OH)3 that served as extracellular electron acceptor to anaerobically oxidize NH4+, namely Feammox. Chemical or biological oxidation of the produced Fe2+ formed the Fe(III)/Fe(II) cycle to likely cause the continuous Feammox in the Anammox system. Isotopic analysis verified that the Anammox sludge collected from the Fe(OH)3-added reactor produced more 30N2 by Feammox. Raman analysis showed that the outer membrane cytochrome c of Fe(OH)3-added Anammox sludge could participate in the extracellular electron transfer during Feammox. Metagenomic analysis further confirmed that the gene encoding redox enzymes of cytochrome c of Candidatus Brocadia were enriched with adding Fe(OH)3. The results suggested that the Fe(OH)3 induced Anammox bacteria to perform extracellular electron transfer, allowing the Anammox system to effectively remove NH4+ via the Feammox pathway.

Nitrite and Nitrate Residue in Non-Heat Treated Meat Products Marketed in East Azerbaijan Province

Background: Nitrite and nitrate salts are used as preservatives in meat products to prevent the growth of pathogen organisms such as Clostridium botulinum. Nitrogen salts additives create the desired color in meat products. However, the use of these salts accelerates nitrosamine production and increases the risk of carcinogenesis. Hence, nitrate and nitrite consumption rate should be according to the approved standards. This analytical study is designed to determine nitrate and nitrite residue of non-heat-treated meat products including hamburger and kebab in East Azerbaijan Province, Iran during 2015-2020. Methods: 120 samples of non-heat-treated meat products from different brands were randomly collected. They consisted of 60 products manufactured in East Azerbaijan province and 60 products imported from other provinces. Nitrate and Nitrite residues in non-heat-treated meat products including hamburger and kebab were determined by spectrophotometric method. Results: Results showed that the residue levels of nitrate and nitrite content regarding non-heat- treated meat products were less than maximum residual limits (MRLs) of national standards. The study also indicated that frozen non-heated meat products did not have any nitrogenous additive. Conclusion: The results of this research revealed that the frozen non-heat treated meat products including hamburger and kebab, produced or consumed in East Azerbaijan province during 2015-2020 did not have nitrate and nitrite additives. Continuous monitoring to ensure the compliance of meat products with the standards is necessary.

Nitrite cycling in the primary nitrite maxima of the eastern tropical North Pacific

Abstract. The primary nitrite maximum (PNM) is a ubiquitous feature of the upper ocean, where nitrite accumulates in a sharp peak at the base of the euphotic zone. This feature is situated where many chemical and hydrographic properties have strong gradients and the activities of several microbial processes overlap. Near the PNM, four major microbial processes are active in nitrite cycling: ammonia oxidation, nitrite oxidation, nitrate reduction and nitrite uptake. The first two processes are mediated by the nitrifying archaeal/bacterial community, while the second two processes are primarily conducted by phytoplankton. The overlapping spatial habitats and substrate requirements for these microbes have made understanding the formation and maintenance of the PNM difficult. In this work, we leverage high-resolution nutrient and hydrographic data and direct rate measurements of the four microbial processes to assess the controls on the PNM in the eastern tropical North Pacific (ETNP). The depths of the nitrite maxima showed strong correlations with several water column features (e.g., top of the nitracline, top of the oxycline, depth of the chlorophyll maximum), whereas the maximum concentration of nitrite correlated weakly with only a few water column features (e.g., nitrate concentration at the nitrite maximum). The balance between microbial production and consumption of nitrite was a poor predictor of the concentration of the nitrite maximum, but rate measurements showed that nitrification was a major source of nitrite in the ETNP, while phytoplankton release occasionally accounted for large nitrite contributions near the coast. The temporal mismatch between rate measurements and nitrite standing stocks suggests that studies of the PNM across multiple timescales are necessary.

Revisiting process-based simulations of soil nitrite dynamics: Tighter cycling between nitrite and nitrate than considered previously

Nitrite is an important precursor of many environmentally hazardous compounds (e.g., nitrate, nitrous oxide, and nitrous acid). However, its dynamics in the soil environment are not yet fully understood. The NtraceNitrite tool has been successful in analyzing 15N tracing data. Here, based on a 15N tracing experiment (under aerobic condition) where either the nitrite, the nitrate, or the ammonium pool was labelled, we developed an extended model (NO2Trace), which was featured by the addition of coupled nitrate reduction and nitrite re-oxidation and the separation of the nitrate pool in two sub-pools. With 5 additional parameters optimized, NO2Trace was able to achieve a superior fit to the data, as compared to the NtraceNitrite tool. The additional features might offer a suitable explanation for the isotopic composition of nitrate produced via nitrification in terrestrial ecosystems. Our results carry two important implications: (i) a key assumption of the classical isotope pool dilution technique (i.e., no reflux of tracer) for estimating gross nitrate fluxes is violated, leading to considerable underestimations (22–99% in the datasets tested); (ii) re-oxidation can dominate the consumption (∼75%) of nitrite derived from nitrate reduction, indicating the potential of this process as a target for nitrogen retention mechanism against gaseous nitrogen losses (through nitrite reduction). The additional features of the extended model show a tighter cycle between soil nitrite and nitrate than considered previously and provide a more comprehensive description of soil nitrite transformations. This study also highlights that more work is needed to develop methods capable of separating process- and pathways-specific nitrate and nitrite pools.

Effects of Co-existing Heterotrophs on Physiology of and Nitrogen Metabolism in Autotrophic Nitrite-oxidizing Candidatus Nitrotoga.

Interactions between autotrophic nitrifiers and heterotrophs have attracted considerable attention in microbial ecology. However, the mechanisms by which heterotrophs affect the physiological activity of and nitrogen metabolism in autotrophic nitrite oxidizers remain unclear. We herein focused on nitrite-oxidizing Candidatus Nitrotoga and compared an axenic culture including only Ca. Nitrotoga with a co-culture of both Ca. Nitrotoga and Acidovorax in physiological experiments and transcriptomics. In the co-culture with Acidovorax, nitrite consumption by Ca. Nitrotoga was promoted, and some genes relevant to nitrogen metabolism in Ca. Nitrotoga were highly expressed. These results provide insights into the mechanisms by which co-existing heterotrophs affect autotrophic nitrifiers.

The Summary of Nitritation Process in Mainstream Wastewater Treatment

The application of the mainstream partial nitritation/anammox (PN/A) process is promising due to the huge cost reduction compared to traditional biological nitrogen removal. However, the nitrite production rate (NPR) of a biological nitritation pre-treatment process is relatively lower than the nitrite consumption rate in a pure anammox reactor with a high nitrogen loading rate (NLR). Thus, the NPR is the rate-limiting step for operating the PN/A process with a higher NLR. Various studies have attempted to improve mainstream NPR. A comprehensive review of these processes is needed for the actual application of the PN/A process. This study focuses on: (1) various nitrite production processes that have emerged in recent years; (2) the main microbial species and characteristics involved in biological nitritation; (3) the existing problems and the N2O emission problem of these processes; and (4) a proposed novel and promising PN/A process facilitated with photocatalyst oxidation. This review is expected to provide references and a basis for the research on the nitritation step of the application of the mainstream PN/A process.

Effects of solid-state fermentation with Bacillus subtilis Y4 on the quality of Yibin Yacai

Bacillus spp. has been proven to be critical for the quality of many fermented foods, but as one of the domain bacteria, its effect on the quality of Yibin Yacai has not been fully addressed. Herein, the effects of inoculation of Bacillus subtilis Y4 on the physicochemical properties, flavor metabolism and microbial community changes of Yibin Yacai for three-month solid-state fermentation were investigated. The results showed that inoculation of B. subtilis Y4 could reduce the pH and salinity of Yibin Yacai, accelerate the consumption of nitrite, promote the growth of Lactobacillus and the production of sweet amino acid, and inhibit pathogenic microorganisms at the late fermentation stage. During solid-state fermentation, the dominant fungus Cystofilobasidium was positively correlated with most volatile flavor substances, which were indirectly affected by B. subtilis Y4. Furthermore, compared to spontaneous fermented Yibin Yacai, inoculation of B. subtilis Y4 promoted the production of alkenes and made the peak of ester content appear earlier. These results indicated that inoculation of B. subtilis Y4 for solid-state fermentation could improve the quality and taste of Yibin Yacai, and shorten the fermentation time.