Nitrite Uptake Research Articles

Characterization and functional analysis of Litopenaeus vannamei Na+/K+/2Cl− cotransporter 1 under nitrite stress

The function of Litopenaeus vannamei Na+/K+/2Cl− cotransporter 1 (NKCC1) under nitrite stress was investigated. The full-length cDNA sequence of the L. vannamei NKCC1 gene was cloned using the rapid amplification of cDNA ends (RACE) technique, and the sequence was analysed using bioinformatics tools. Expression and localisation of NKCC1 in tissues were assessed using real-time quantitative PCR and in situ hybridisation, respectively. The impact of nitrite stress on the survival, physiology, biochemistry and tissue structure of L. vannamei was investigated following silencing of NKCC1 by RNA interference. The 3143 bp cDNA sequence of L. vannamei NKCC1 encodes a polypeptide of 918 amino acids. It is evolutionarily conserved. NKCC1 expression was highest in gill tissue, particularly within cuticle and gill epithelial cells. After silencing NKCC1, an increase in shrimp survival was observed, accompanied by a significant reduction in nitrite entry into the body (P < 0.05). Moreover, the oxidative stress enzyme system remained unaffected and damage to gill tissue was alleviated. The results suggest that NKCC1 is involved in regulating nitrite uptake, and plays a crucial role in facilitating nitrite entry into the organism through gill tissue. The findings provide a vital experimental basis for addressing concerns related to nitrite toxicity.

Rapid transition from complete nitrification to partial nitrification-anammox at low temperatures via thermal inactivation of nitrite oxidoreductase

The stable and efficient biological nitrogen removal at low temperatures has always posed a challenge for the engineering application of the partial nitrification-anammox (PN/A) process. In this study, a complete nitrification system operating at 15 ± 1 °C was rapidly switched to PN/A mode and stably operated through thermal treatment of thickened sludge and anammox biofilm. Batch test results revealed that the ammonia uptake rate (AUR) and nitrite uptake rate (NUR) of activated sludge, after being treated at 35 °C for 2 days, decreased by 22.88 % and 96.10 %, respectively. Similarly, anammox biofilm exhibited no significant change in anammox activity (ram), but a significant decrease in NUR by 52.7 % after being treated at 40 °C for 2 days. Long-term coupling experiments demonstrated that the complete nitrification system at 15 °C was rapidly switched to PN/A mode with a TN removal rate (TNRR) of 87.91 ± 1.53 % through selective inactivation between ammonia monooxygenase (AMO) and nitrite oxidoreductase (NOR) at 35 °C for 2 days for activated sludge. Furthermore, the coexistence of Nitrospira in the seeding anammox biofilm and the proliferation of Nitrotoga in the biofilm led to the deterioration of the PN/A system. However, the collapsed TNRR could be rapidly restored to 96.42 % through selective inactivation between hydrazine synthase (HDH) and NOR at 40 °C for 2 days for anammox biofilm. The results of key enzymatic activity and Illumina MiSeq sequencing indicated a significant decrease in NOR activity but no significant change in community structure after thermal treatment for both thickened sludge and anammox biofilm. Therefore, the rapid transition of the PN/A system in a complete nitrification system at low temperatures was achieved through the selective inactivation of enzymes between NOR and AMO/HDH, rather than NOB washout.

Testing the influence of light on nitrite cycling in the eastern tropical North Pacific

Abstract. Light is considered a strong controlling factor of nitrification rates in the surface ocean. Previous work has shown that ammonia oxidation and nitrite oxidation may be inhibited by high light levels, yet active nitrification has been measured in the sunlit surface ocean. While it is known that photosynthetically active radiation (PAR) influences microbial nitrite production and consumption, the level of inhibition of nitrification is variable across datasets. Additionally, phytoplankton have light-dependent mechanisms for nitrite production and consumption that co-occur with nitrification around the depths of the primary nitrite maximum (PNM). In this work, we experimentally determined the direct influence of light level on net nitrite production, including all major nitrite cycling processes (ammonia oxidation, nitrite oxidation, nitrate reduction and nitrite uptake) in microbial communities collected from the base of the euphotic zone. We found that although ammonia oxidation was inhibited at the depth of the PNM and was further inhibited by increasing light at all stations, it remained the dominant nitrite production process at most stations and treatments, even up to 25 % surface PAR. Nitrate addition did not enhance ammonia oxidation in our experiments but may have increased nitrate and nitrite uptake at a coastal station. In contrast to ammonia oxidation, nitrite oxidation was not clearly inhibited by light and sometimes even increased at higher light levels. Thus, accumulation of nitrite at the PNM may be modulated by changes in light, but light perturbations did not exclude nitrification from the surface ocean. Nitrite uptake and nitrate reduction were both enhanced in high-light treatments relative to low light and in some cases showed high rates in the dark. Overall, net nitrite production rates of PNM communities were highest in the dark treatments.

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.

Synechococcus nitrogen gene loss in iron-limited ocean regions

Synechococcus are the most abundant cyanobacteria in high latitude regions and are responsible for an estimated 17% of annual marine net primary productivity. Despite their biogeochemical importance, Synechococcus populations have been unevenly sampled across the ocean, with most studies focused on low-latitude strains. In particular, the near absence of Synechococcus genomes from high-latitude, High Nutrient Low Chlorophyll (HNLC) regions leaves a gap in our knowledge of picocyanobacterial adaptations to iron limitation and their influence on carbon, nitrogen, and iron cycles. We examined Synechococcus populations from the subarctic North Pacific, a well-characterized HNLC region, with quantitative metagenomics. Assembly with short and long reads produced two near complete Synechococcus metagenome-assembled genomes (MAGs). Quantitative metagenome-derived abundances of these populations matched well with flow cytometry counts, and the Synechococcus MAGs were estimated to comprise >99% of the Synechococcus at Station P. Whereas the Station P Synechococcus MAGs contained multiple genes for adaptation to iron limitation, both genomes lacked genes for uptake and assimilation of nitrate and nitrite, suggesting a dependence on ammonium, urea, and other forms of recycled nitrogen leading to reduced iron requirements. A global analysis of Synechococcus nitrate reductase abundance in the TARA Oceans dataset found nitrate assimilation genes are also lower in other HNLC regions. We propose that nitrate and nitrite assimilation gene loss in Synechococcus may represent an adaptation to severe iron limitation in high-latitude regions where ammonium availability is higher. Our findings have implications for models that quantify the contribution of cyanobacteria to primary production and subsequent carbon export.

Integrating thermodynamics and mathematical modelling to investigate the stoichiometry and kinetics of sulphide oxidation-nitrate reduction with a special focus on partial autotrophic denitrification

In the present study, the stoichiometry of the Sulphur Oxidizing-Nitrate Reducing (SO-NR) process, with a focus on Partial Autotrophic Denitrification (PAD), has been evaluated through a thermodynamic-based study whereas a model-based approach has been adopted to assess process kinetics. Experimental data on process performance and biomass yields were available from a previous work achieving efficient PAD, where a biomass yield of 0.113 gVSS/gS was estimated. First, the free Gibbs energy dissipation method has been implemented, in order to provide a theoretical framework exploring the boundaries for sulphur oxidizing biomass yields. Second, a screening of available mathematical models describing SO-NR process was conducted and five published models were selected, in order to assess the most suitable model structure for describing the observed PAD kinetics. To the best of our knowledge, none of reported biomass yields are estimated in systems operating PAD as the main process and, analogously, none of the proposed models have been applied to case studies aiming at partial denitrification only. The work showed that the very low biomass yield of 0.117 ± 0.007 gVSS/gS, observed in a PAD system in our previous work, suggests that the conditions applied to achieve partial denitrification resulted in a high energy-dissipating metabolism compared to complete denitrification applications. Models’ analysis revealed that nitrite accumulation can be described by a classical Monod kinetics if different μmax are adopted for each intermediate reaction, with Theil Inequality Coefficient values lower than 0.21 for both NO3− and NO2−. Nonetheless, adopting Haldane-type kinetics for nitrite uptake inferred higher identifiability to the model structure, resulting in confidence intervals below ±10% for all the parametric estimations. The thermodynamic and modelling outcomes support the experimental results obtained in the reference study and the critical comparison of model suitability to represent PAD process is believed pivotal to pave the way to its real-scale implementation.

Effect of Environmental Factors on Nitrite Nitrogen Absorption in Microalgae–Bacteria Consortia of Oocystis borgei and Rhodopseudomonas palustris

The effects of temperature, salinity, and illumination on the nitrite uptake rate of the microalgae–bacteria consortia of Oocystis borgei and Rhodopseudomonas palustris were investigated. The absorption rates of nitrite and the contribution rate of each component in the consortia under different temperatures (15, 20, 25, 30, 35 °C), illuminations (0, 15, 25, 35, 45 μmol·m−2·s−1), and salinities (0, 5, 15, 25, 35‰) were determined by stable isotope labeling technique. The single and combined effects of three environmental factors on nitrite uptake by the microalgae–bacteria consortia were analyzed using single-factor and orthogonal experiments. The single-factor experiment showed that the microalgae–bacteria consortia could absorb nitrite efficiently when the temperature, salinity, and illumination were 20~30 °C, 0~15‰, and 25~45 μmol·m−2·s−1, respectively, with the highest absorption rates were 2.086, 3.058, and 2.319 μg∙g−1∙h−1, respectively. The orthogonal experiment showed that the most efficient environmental conditions for nitrite uptake were 30 °C, 5‰ salinity, 35 μmol·m−2·s−1 illumination, and the rate of nitrite uptake by the microalgae–bacteria consortia was 3.204 μg∙g−1∙h−1. The results showed that the nitrite uptake rate of the O. borgei–R. palustris consortia was most affected by temperature, followed by salinity, and least by illumination. Under the same conditions, the nitrite absorption capacity of the microalgae–bacteria consortia was greater than that of single bacteria or algae, and R. palustris played a major role in the nitrite absorption of the consortia. The O. borgei and R. palustris consortia still maintain high nitrite absorption efficiency when the environment changes greatly, which has broad application prospects in the regulation and improvement of water quality in shrimp culture.

Microbial Niche Differentiation during Nitrite-Dependent Anaerobic Methane Oxidation.

Nitrite-dependent anaerobic methane oxidation (n-DAMO) has been demonstrated to play important roles in the global methane and nitrogen cycle. However, despite diverse n-DAMO bacteria widely detected in environments, little is known about their physiology for microbial niche differentiation. Here, we show the microbial niche differentiation of n-DAMO bacteria through long-term reactor operations combining genome-centered omics and kinetic analysis. With the same inoculum dominated by both species "Candidatus Methylomirabilis oxyfera" and "Candidatus Methylomirabilis sinica", n-DAMO bacterial population was shifted to "Ca. M. oxyfera" in a reactor fed with low-strength nitrite, but shifted to "Ca. M. sinica" with high-strength nitrite. Metatranscriptomic analysis showed that "Ca. M. oxyfera" harbored more complete function in cell chemotaxis, flagellar assembly, and two-component system for better uptake of nitrite, while "Ca. M. sinica" had a more active ion transport and stress response system, and more redundant function in nitrite reduction to mitigate nitrite inhibition. Importantly, the half-saturation constant of nitrite (0.057 mM vs 0.334 mM NO2-) and inhibition thresholds (0.932 mM vs 2.450 mM NO2-) for "Ca. M. oxyfera" vs "Ca. M. sinica", respectively, were highly consistent with genomic results. Integrating these findings demonstrated biochemical characteristics, especially the kinetics of nitrite affinity and inhibition determine niche differentiation of n-DAMO bacteria.

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.

Cerebral O2 and CO2 transport in isovolumic haemodilution: Compensation of cerebral delivery of O2 and maintenance of cerebrovascular reactivity to CO2

This study investigated the influence of acute reductions in arterial O2 content (CaO2) via isovolumic haemodilution on global cerebral blood flow (gCBF) and cerebrovascular CO2 reactivity (CVR) in 11 healthy males (age; 28 ± 7 years: body mass index; 23 ± 2 kg/m2). Radial artery and internal jugular vein catheters provided measurement of blood pressure and gases, quantification of cerebral metabolism, cerebral CO2 washout, and trans-cerebral nitrite exchange (ozone based chemiluminescence). Prior to and following haemodilution, the partial pressure of arterial CO2 (PaCO2) was elevated with dynamic end-tidal forcing while gCBF was measured with duplex ultrasound. CVR was determined as the slope of the gCBF response and PaCO2. Replacement of ∼20% of blood volume with an equal volume of 5% human serum albumin (Alburex® 5%) reduced haemoglobin (13.8 ± 0.8 vs. 11.3 ± 0.6 g/dL; P < 0.001) and CaO2 (18.9 ± 1.0 vs 15.0 ± 0.8 mL/dL P < 0.001), elevated gCBF (+18 ± 11%; P = 0.002), preserved cerebral oxygen delivery (P = 0.49), and elevated CO2 washout (+11%; P = 0.01). The net cerebral uptake of nitrite (11.6 ± 14.0 nmol/min; P = 0.027) at baseline was abolished following haemodilution (−3.6 ± 17.9 nmol/min; P = 0.54), perhaps underpinning the conservation of CVR (61.7 ± 19.0 vs. 69.0 ± 19.2 mL/min/mmHg; P = 0.23). These findings demonstrate that the cerebrovascular responses to acute anaemia in healthy humans are sufficient to support the maintenance of CVR.

Diel change in inorganic nitrogenous nutrient dynamics and associated oxygen stoichiometry along the Pearl River Estuary

The reactive nitrogen (N) emitted from continents significantly perturbs the pristine N cycle around the land-ocean boundary resulting in eutrophication and hypoxia. As nutrients are transported downstream through an estuary, various types of biological processes co-occur to modulate nitrogen speciation to influence the biogeochemical habitats for downstream microorganisms. We surveyed the Pearl River Estuary to examine the N transfer dynamics among nitrogen species with considering process-specific oxygen production and consumption. By using 15N pulse-tracing techniques, we measured ammonia oxidation and uptakes of ammonium, nitrite, and nitrate simultaneously under dark and light conditions in parallel. Light strongly inhibited nitrification but enhanced N uptake, and such light effect was further considered in the calculation for nitrogen transformation rates over a diel cycle. We found both oxidation and uptake of ammonium decreased seaward as substrate decreased. The nitrifier and phytoplankton work in antiphase to draw down incoming ammonium rapidly. Contrary to ammonium uptake, uptake of nitrite and nitrate showed a seaward increasing pattern. Such an inverse spatial pattern implies a shift in N preference for phytoplankton. Such high ammonium preference inhibits nitrate/nitrite uptake allowing them to behave conservatively in the estuary and to travel farther to outer estuary. By integrating oxygen consumption and production induced by N transformation processes over the diel cycle, oxygen was produced although allochthonous ammonium input is high (∼250 μM). For most stations, ammonium was completely consumed within 2 days, some stations even less than 0.5 days, implying that although the water residence time is short (2-15 days), tremendous input of ammonium N from upstream was transformed into particulate organic or nitrate forms during traveling to modulate the biogeochemical niche, including substrate, organics and oxygen, of coastal microbes in water column and sediments.

Alleviating excess boron stress in tomato calli by applying benzoic acid to various biochemical strategies

Benzoic acid (BA) represents vital roles in plant activity and response to diverse unfavorable conditions. However, its participation in mitigating excess boron (EB) stress in plants is elusive. Herein, we have examined the impacts of BA (1 μM) in controlling boron (B) uptake in tomato (Solanum lycopersicum L.) calli exposed to various EB levels (0, 1, 2, and 3 mM). The free, semi-bound, and bound B forms were stimulated by EB, while these forms were reduced in B-stressed calli by BA supplementation (40.37%, 36.08%, and 66.91%, respectively, less than 3 mM B-stressed calli alone). EB caused a reduction in the uptake of potassium (K+), calcium (Ca2+), magnesium (Mg2+), and nitrite (NO2−) while increasing the concentration of phosphorus (P), nitrate (NO3−), sulfur (S), and sulfate (SO42−) in B-stressed calli. BA application induced the uptake of K+, Ca2+, Mg2+, NO3−, S, and SO42−; however, it reduced P and NO2− concentrations in B-stressed calli. EB reduced nitrate reductase activity (NR), while BA application did not alleviate this reduction. EB treatments significantly, in most cases, increased sulfite oxidase (SO) activity. Supplementation of BA along with EB further enhanced SO activity. Cell wall components (cellulose, hemicellulose, and pectin) were decreased under EB treatments but considerably increased in B-stressed calli by BA application. Fourier Transform Infrared Spectrometer (FT-IR) output showed that EB treatments with/without BA led to alterations in cell wall functional groups of calli. Our findings indicated that BA application enabled tomato callus to counteract the harmful effect of EB, leading to improved callus growth.

Interplay of hydrogen peroxide and nitric oxide: systemic regulation of photosynthetic performance and nitrogen metabolism in cadmium challenged cyanobacteria.

In the present study, thepotential role of hydrogen peroxide (H2O2) and nitric oxide (NO) has been well recorded in the induction of cadmium (Cd) stress tolerance in cyanobacteria. In this regard, H2O2 and SNP (sodium nitroprusside, NO donor), were applied to Nostoc muscorum and Anabaena sp. exposed to Cd (6µM) stress, to analyze different physiological and biochemical parameters. Results revealed that treatment of Cd reduced the growth, pigment contents, photosynthetic oxygen yield and performance of PS II photochemistry (decreased chlorophyll a fluorescence parameters, i.e., ФPo, Ψo, ФEo, PIABS along with Fv/Fo and increased the energy fluxparameters, i.e., ABS/RC, TRo/RC, ETo/RC, DIo/RC along with Fo/Fv. Similarly, uptake of nitrate (NO3 -) and nitrite (NO2 -), as well as the activities of nitrate and ammonia assimilating enzymes along with carbohydrate content, were severely affected by Cd toxicity and notwithstanding this, glutamate dehydrogenase (GDH) activity exhibited reverse trend. Exogenous application of a very low dose (1µM) of H2O2 (only for 3h) and NO (SNP; 10µM) notably counteracted Cd-induced toxicity. Nevertheless, the positive impact of H2O2 got reversed under the treatment of PTIO (NO scavenger) and LNAME (inhibitor of nitric oxide synthase; NOS) while NO could work efficiently even in the presence of NAC (H2O2 scavenger) and DPI (inhibitor of NADPH oxidase); hence indicated towards the H2O2 mediated NO signaling in averting Cd induced toxicity in test cyanobacteria. In conclusion, current finding demonstrated a positive cross-talk between H2O2 and NO for providing tolerance to cyanobacteria against Cd stress.

SiO2/Al2O3/C grafted 3-n propylpyridinium silsesquioxane chloride-based non-enzymatic electrochemical sensor for determination of carcinogenic nitrite in food products

The excessive uptake of nitrite is perilous and detrimental for human health that prone to cancer disease. Herein, described the synthesis of SiO2/Al2O3/C material through the sol–gel procedure followed by grafting with 3-n propylpyridinium silsesquioxane chloride organic ligand for enhancing electrochemical activity. H-NMR, 13C NMR, and 29Si studies were performed for confirmation of surface functionalization through the grafting technique. The surface morphology was evaluated through SEM and TEM techniques. The material showed an irregular and flakes-like structure that exhibited more compactness and conglomerate structure with no segregation in phase was observed after grafting. The elemental composition was confirmed from EDX analysis. The electrochemical measurements were performed with cyclic voltammetry, electrochemical impedance spectroscopy (EIS), and chronoamperometry. The prepared hybrid inorganic–organic composite Si/C/Al/SiPy+Cl- was applied for the modification of the glassy carbon (GC) electrode and assessed as a sensor for nitrite determination. The sensor showed the low limit of detection (0.01 μM), low limit of quantification (0.08 μM), wide linear response range (0.2–280 μM), and high sensitivity (410 μA·μM−1). It gave a quick response time of <1 s in the presence of 70 μM nitrite. The fabricated sensor showed high sensitivity, chemical stability, and insignificant interference from co-existing species present in sausage meat and food industry discharges. The repeatability of the sensor was evaluated as 2.5 % R.S.D.; for n = 10 at 50 μM nitrite.

Direct comparison of inorganic nitrite and nitrate on vascular dysfunction and oxidative damage in experimental arterial hypertension

Arterial hypertension is one of the major health risk factors leading to coronary artery disease, stroke or peripheral artery disease. Dietary uptake of inorganic nitrite (NO2−) and nitrate (NO3−) via vegetables leads to enhanced vascular NO bioavailability and provides antihypertensive effects. The present study aims to understand the underlying vasoprotective effects of nutritional NO2− and NO3− co-therapy in mice with angiotensin-II (AT-II)-induced arterial hypertension. High-dose AT-II (1 mg/kg/d, 1w, s. c.) was used to induce arterial hypertension in male C57BL/6 mice. Additional inorganic nitrite (7.5 mg/kg/d, p. o.) or nitrate (150 mg/kg/d, p. o.) were administered via the drinking water. Blood pressure (tail-cuff method) and endothelial function (isometric tension) were determined. Oxidative stress and inflammation markers were quantified in aorta, heart, kidney and blood. Co-treatment with inorganic nitrite, but not with nitrate, normalized vascular function, oxidative stress markers and inflammatory pathways in AT-II treated mice. Of note, the highly beneficial effects of nitrite on all parameters and the less pronounced protection by nitrate, as seen by improvement of some parameters, were observed despite no significant increase in plasma nitrite levels by both therapies. Methemoglobin levels tended to be higher upon nitrite/nitrate treatment. Nutritional nitric oxide precursors represent a non-pharmacological treatment option for hypertension that could be applied to the general population (e.g. by eating certain vegetables). The more beneficial effects of inorganic nitrite may rely on superior NO bioactivation and stronger blood pressure lowering effects. Future large-scale clinical studies should investigate whether hypertension and cardiovascular outcome in general can be influenced by dietary inorganic nitrite therapy.

Stable partial nitrification at low temperature via selective inactivation of enzymes by intermittent thermal treatment of thickened sludge

• Thermal treatment (35 °C/2 days) could expand the difference between SAUR and SNUR. • A stable NAR of 90.18 ± 5.74% was rapidly achieved in the long-term experiment. • NOR selective inactivation is the main reason for nitrite accumulation. • Cold-adapted Nitrotoga is the dominant NOB throughout the experiment. • A novel method of intermittent thickened sludge thermal treatment is proposed. Achieving stable nitrite accumulation at low temperature continues to be a challenging problem in partial nitrification (PN). This study proposes a strategy to achieve stable PN of thickened sludge at low temperatures through selective inactivation of enzymes by intermittent thermal treatment. This method was verified using a sequencing batch reactor (SBR) operated at 9 ± 1 °C in full nitrification mode. After thermally treating the activated sludge at 35 °C for 2 days, which was the optimal condition for selective inactivation of enzymes determined by batch tests, an average nitrite accumulation rate (NAR) of 90.18 ± 5.74% was rapidly achieved and the SBR was stably operated at 9 ± 1 °C for 80 days. This was consistent with a significant decrease of the specific nitrite uptake rate (SNUR), but no a reduction, or even an increase, of the specific ammonia uptake rate (SAUR). Also, there was no remarkable change in the nitrifying bacterial community except for a slight increase in both ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB). In addition, after thermal treatment at 35 °C for 2 days, the nitrite oxidoreductase (NOR) activity was significantly decreased, while those of ammonia monooxygenase (AMO) and hydroxylamine oxidoreductase (HAO) showed an increasing trend. Thus, the achievement of stable PN at low temperatures with this strategy may be due to the selective inactivation of NOR, rather than NOB washout.

Nitrate and nitrite as mixed source of nitrogen for Chlorella vulgaris: Growth, nitrogen uptake and pigment contents

Chlorella vulgaris was grown using mixed sources of nitrogen (nitrate and nitrite). Starting from B3N as basal medium, nitrate was substituted by nitrite keeping total nitrogen constant over 7 conditions: 0, 20, 40, 50, 60, 80 and 100% NO2–. Growth rate, nitrogen uptake, photosynthetic apparatus status and pigment contents were monitored. Nitrite addition triggered a growth rate inhibition from early introduction (20% NO2–, 81 mgNO2-/l). Nitrate uptake rate increased with nitrate content in the culture medium (maximum at 5.87 mg/l/Nd, 100% NO3–), while nitrite uptake remained constant around 2.93 mgN/l/d. Photosynthetic apparatus was not impacted by the nitrogen source substitution. Pigments profiles (chlorophyll a, b and total carotenoids) were not statistically different for all the tested conditions. From a biotechnological perspective, this finding rules out the use of nitrite substitution as a pigment manipulating stress strategy.

Porous hollow carbon nanospheres as a novel sensing platform for sensitive detection of nitrite in pickle directly

Excessive uptake of nitrite will damage the human health. Hence, there is a rising requirement to construction a highly sensitive electrochemical sensor for detecting the level of nitrite in food precisely. In this work, an electrochemical nitrite sensor was successfully constructed with the porous hollow carbon nanoparticles as the electrode material. The morphology and structure of the synthesized material were characterized by scanning electron microscopy, transmission electron microscope, Brunauer–Emmett–Teller, and Fourier transform infrared spectroscopy. Meanwhile, the electrochemical behavior of nitrite was studied by cyclic voltammetry and amperometry (i − t). As a result, the as-constructed sensor exhibited high electrocatalytic activity, high sensitivity (275.7 µA mM−1 cm−2), wider linear range (0.037–6950 μM), and lower limit of detection (10.41 nM) toward nitrite oxidation. Finally, the sensor was successfully applied to the detection of nitrite in pickle directly, indicating its feasibility for practical applications. The results showed that the porous hollow carbon nanospheres hold great prospect in sensitive detection of nitrite.

Development of an innovative nitrite sensing platform based on the construction of carbon-layer-coated In2O3 porous tubes

Excessive uptake of nitrite has been proven to be harmful for human health and ecological systems, so it is vital to develop a reliable methodology for nitrite analysis. In this work, we have synthesized innovative carbon-layer-coated In2O3 porous tubes (C@In2O3 PTs) to electrochemically detect nitrite in industrial wastewater samples. C@In2O3 PTs were prepared through the thermal decomposition of metal organic frameworks (MOFs, MIL-68-In) based on the two-step synthetic processes. The obtained C@In2O3 PTs displayed obviously increased catalytic activity to the electrochemical oxidation of nitrite, which benefited from the enhanced surface area and electron transfer based on the porous and hollow structure, and the maximized synergistic effect due to the intimate contact between In2O3 core and carbon layer. Thus, the sensitive determination of nitrite with a detection limit of 0.08 μM was realized, which was promising for sensitive determination of nitrite in the environmental analysis and food industry.

Toxicological effect of pendimethalin on some physiological parameters of the diazotrophic cyanobacterium Desmonostoc muscorum PUPCCC 405.10

Application of herbicides for the control of weeds in agri-ecosystem poses a great threat to natural inhabiting beneficial microbes. Toxicological impact of herbicides on the survivability of cyanobacteria has recently gained much attention. Thus, the present study was undertaken to understand the mode of action of pendimethalin on assimilation of carbon and nitrogen in diazotrophic cyanobacterium Desmonostoc muscorum PUPCCC 405.10. The lethal dose of pendimethalin for the test organism was 20 mg/l. Pendimethalin (4–12 mg/l) exhibits negative effect on the growth, photosynthetic pigments (8%–85%), photosynthesis (29%–58%), photochemical activities (16%–64%), and respiration (25%–62%). Nitrogen assimilation parameters such as nitrate (39%– 65%), nitrite (37%–83%), and ammonium (11%–37%) uptake and its enzymes such as nitrate reductase (27%– 40%), nitrite reductase (3%–18%), and glutamine synthetase (15%–39%) were also negatively affected by herbicide. Kinetic studies further revealed that the affinity of nitrate and nitrite uptake was unaffected by the herbicide, but the affinity of ammonium uptake was affected. Pendimethalin interacted non-competitively with activities of nitrogen assimilation enzymes.