Nitrate Inhibition Research Articles

Characterization and inhibition of hydrogen sulfide-producing bacteria from petroleum reservoirs subjected to alkali-surfactant-polymer flooding.

Alkali-surfactant-polymer (ASP) flooding is an emerging and promising oil recovery technique. However, the methods for preventing hydrogen sulfide-producing bacteria (SPB), chief culprits to microbial souring, in such alkali reservoirs remains unknown. Here, four alkaline-tolerant SPB exhibiting versatile sulfur metabolism were identified. Representative strains DS3, DS5, DS8, and DS23 were affiliated with Sulfurospirillum alkalitolerans, Desulfonatronovibrio hydrogenovorans, Desulfobotulus sapovorans, and Desulfovibrio alkalitolerans, respectively. Pure culture experiments showed nitrite exerted partial inhibitory effects since DS3 preferred nitrite as an electron acceptor. And nitrate inhibition was feeble, as nitrate was dissimilated to ammonium by DS3 and DS5, and DS8 preferentially utilized sulfate compared with nitrate, and DS23 ignored nitrate respiration. Glutaraldehyde effectively prevented the production of H2S in pure culture and microcosmic simulation system, demonstrating its practical application potential in alkali reservoirs. This study enhances the understanding on physiological characteristics of SPB and bridges the gap in souring management in high alkaline ASP-flooded reservoirs.

Cerium nitrate microcapsules for coating application: characterization and corrosion study

Microcapsules show great potential in metal anticorrosive coating in recent years. In the following paper, first, urea-formaldehyde (UF) microcapsules containing cerium nitrate were synthesized under different parameter conditions. Three different quantities of the microcapsules were introduced to the epoxy coatings and applied on the AZ31B substrate to meet the increasing demands for anticorrosive coatings. An analysis of the scanning electron microscopy surface morphology of UF microcapsules synthesized by nine different parameter conditions shows that the ratio of formaldehyde to urea is 1.5:1, and 2 wt.% of emulsifier, 25 wt.% of cerium nitrate, and 150 r/min of rotation speed are the best choice for the synthesis of microcapsules, resulting in spherical particles with an average particle size of about 25 μm. The characteristics of microcapsules were studied by optical microscope, Fourier transform infrared, and thermogravimetric analysis. The result of electrochemical impedance spectroscopy indicated that the 2 wt.% microcapsule content in the defective coating shows better corrosion protection performance than neat epoxy coating and cerium nitrate inhibitor coating.

Soybean CEP6 Signaling Peptides Positively Regulate Nodulation

Nodulation is the most efficient nitrate assimilation system in the ecosystem, while excessive fertilization has an increased nitrate inhibition effect; deciphering the nitrate signal transduction mechanism in the process is of the utmost importance. In this study, genome-wide analyses of the GmCEP genes were applied to identify nodulation-related CEP genes; 22 GmCEP family members were identified, while GmCEP6 was mainly expressed in nodules and significantly responded to nitrate treatment and rhizobium infection, especially in later stages. Overexpression and CRISPR-Cas9 were used to validate its role in nodulation. We found that GmCEP6 overexpression significantly increased the nodule number, while GmCEP6 knock-out significantly decreased the nodule number, which suggests that GmCEP6 functions as a positive regulator in soybean nodulation. qRT-PCR showed that alterations in the expression of GmCEP6 affected the expression of marker genes in the Nod factor signaling pathway. Lastly, the function of GmCEP6 in nitrate inhibition of nodulation was analyzed; nodule numbers in the GmCEP6-overexpressed roots significantly increased under nitrogen treatments, which suggests that GmCEP6 functions in the resistance to nitrate inhibition. The study helps us understand that GmCEP6 promotes nodulation and participates in the regulation of nitrate inhibition of nodulation, which is of great significance for high efficiency utilization of nitrogen in soybeans.

GmNLP1 and GmNLP4 activate nitrate-induced CLE peptides NIC1a/b to mediate nitrate-regulated root nodulation.

Symbiotic nitrogen fixation is an energy-intensive process, to maintain the balance between growth and nitrogen fixation, high concentrations of nitrate inhibit root nodulation. However, the precise mechanism underlying the nitrate inhibition of nodulation in soybean remains elusive. In this study, CRISPR-Cas9-mediated knockout of GmNLP1 and GmNLP4 unveiled a notable nitrate-tolerant nodulation phenotype. GmNLP1b and GmNLP4a play a significant role in the nitrate-triggered inhibition of nodulation, as the expression of nitrate-responsive genes was largely suppressed in Gmnlp1b and Gmnlp4a mutants. Furthermore, we demonstrated that GmNLP1b and GmNLP4a can bind to the promoters of GmNIC1a and GmNIC1b and activate their expression. Manipulations targeting GmNIC1a and GmNIC1b through knockdown or overexpression strategies resulted in either increased or decreased nodule number in response to nitrate. Additionally, transgenic roots that constitutively express GmNIC1a or GmNIC1b rely on both NARK and hydroxyproline O-arabinosyltransferase RDN1 to prevent the inhibitory effects imposed by nitrate on nodulation. In conclusion, this study highlights the crucial role of the GmNLP1/4-GmNIC1a/b module in mediating high nitrate-induced inhibition of nodulation.

Synergistic effect of oxide nanoparticles and inorganic inhibitor on anti-corrosion performance of epoxy coating

PurposeThis study aims to explore the synergistic effect of oxide nanoparticles (ZnO, Fe2O3, SiO2) and cerium nitrate inhibitor on anti-corrosion performance of epoxy coating. First, cerium nitrate inhibitors are absorbed on the surface of various oxide nanoparticles. Thereafter, epoxy nanocomposite coatings have been fabricated on carbon steel substrate using these oxide@Ce nanoparticles as both nano-fillers and nano-inhibitors.Design/methodology/approachTo evaluate the impact of oxides@Ce nanoparticles on mechanical properties of epoxy coating, the abrasion resistance and impact resistance of epoxy coatings have been examined. To study the impact of oxides@Ce nanoparticles on anti-corrosion performance of epoxy coating for steel, the electrochemical impedance spectroscopy has been carried out in 3% NaCl solution.FindingsZnO@Ce3+ and SiO2@Ce3+ nanoparticles provide more enhancement in the epoxy pore network than modification of the epoxy/steel interface. Whereas, Fe2O3@Ce3+ nanoparticles have more to do with modification of the epoxy/steel interface than to change the epoxy pore network.Originality/valueIncorporation of both oxide nanoparticles and inorganic inhibitor into the epoxy resin is a promising approach for enhancing the anti-corrosion performance of carbon steel.

Mitigated ammonium nitrate inhibition in SCR over Cu-SSZ-13 + Ce/Mn-oxide composite catalysts: insights from temperature-programmed desorption analysis

Ce/Mn-oxide reduces the quantity and stability of NH4NO3 deposits in Cu-SSZ-13.

Abstract 15796: Akt1 Y350f Mutation: A Protective Mechanism Against Pulmonary Hypertension, Suppressing Endothelial-to-Mesenchymal Transition in vivo and in vitro

Background: Pulmonary hypertension (PH) is a life-threatening condition characterized by elevated blood pressure in the lungs due to narrowed arteries. Endothelial-to-mesenchymal transition (EndMT) contributes to enhanced proliferation and metabolic changes in the pulmonary arteries of PH patients. Our previous reports have highlighted the role of Akt nitration at tyrosine 350 (Y350) residue in promoting proliferation and metabolic switch in PH models. To investigate the protective potential of inhibiting Akt nitration, we developed a mouse model with a mutation of Akt Y350 to phenylalanine (Y350F), preventing nitration and activation of Akt. Hypothesis: We hypothesized that Akt1 Y350F mutant mice would be protected in preclinical PH models due to inhibited EndMT. Methods: Both mutant Y350F and wild-type Akt1 mice were treated with Sugen5416 (20mg/kg/week i.p.)/hypoxia (10% O2) (Su/Hx) for four weeks to explore pathological mechanisms. Endothelial cells were isolated for in vitro evaluation under EndMT inducers, including Sin-1 chloride and TGF-β1. Results: The wild-type Su/Hx model exhibited vascular remodeling, increased right ventricular systolic pressure (RVSP) (p<0.001), and right ventricular hypertrophy. In contrast, the Akt Y350F mutant model displayed significant protection, with reduced vascular remodeling, pulmonary pressure, and right heart hypertrophy. Akt nitration-induced EndMT markers, TGF-β1 (p<0.05) and TWIST1 (p<0.01), were elevated in wild-type Su/Hx lung tissue. However, the Akt Y350F mutation prevented Akt activation and diminished EndMT markers in the Akt1 Y350F Su/Hx lungs. In isolated cells and lung tissue, induction of EndMT resulted in a progressive PH phenotype, while Akt inhibition exhibited a protective role against PH progression in the Akt Y350F mutant model. Conclusion: Inhibition of Akt nitration through the Y350F mutation restricts vascular remodeling and halts EndMT both in vivo and in vitro. Our findings suggest that strategies targeting Akt nitration could be effective in controlling PH.

Effects of the nutrient inhibition on the yield of DBPFPs by Microcystis aeruginosa.

The yield of three disinfection byproduct formation potentials (DBPFPs), including trichloromethane, dichloroacetic acid and trichloroacetic acid formation potential (TCMFP, DCAAFP and TCAAFP), by Microcystis aeruginosa under the nitrate and phosphate inhibition conditions was investigated. The results showed that excessive nitrate could inhibit the growth of M. aeruginosa, but the concentration of DBPFPs in the five fractions of algal metabolites, including hydrophilic extracellular organic matter (EOM), hydrophobic EOM, hydrophilic intracellular organic matter, hydrophobic intracellular organic matter and cell debris, only decreased slightly. Accordingly, the productivity of DBPFPs by M. aeruginosa increased by approximately 40% under the nitrate inhibition condition and the increased productivity of DBPFPs mainly came from EOM. The phosphate inhibition also performed a similar pattern with a lesser extent. The nutrient inhibition did not change the proportion of these three DPBFPs, and TCMFP accounted for approximately 87% of the total DBPFPs. The inhibition could promote M. aeruginosa to secrete more metabolites. However, the cyanobacteria tended to secrete more DBPFPs under the nitrate inhibition condition, which resulted in an increased specific DBPFP, while they tended to secrete more non-DBPFPs under the phosphate inhibition condition, which resulted in a decreased specific DBPFP.

Analysis of corrosion rate, inhibition efficiency, and economic cost of XD3 reinforced concrete related to inhibitor and plasticiser types

The main problem in concrete structure is rebar corrosion, which is caused by the penetration and diffusion of chloride ions into reinforced concrete structures; therefore, it is essential to give the most attention to preventing or limiting the impact of this condition. So, in order to find a practical solution to the problem of corrosion of rebar, the current article focuses on demonstrating the beneficial effects of green and calcium nitrate inhibitors on chloride-induced corrosion. Thus, this paper presented an analytical procedure based on corrosion rates and the economic cost to evaluate the efficacy of such an inhibitor. Ten samples with various concrete mixtures were divided into two groups according to the type of plasticiser and inhibitor have been immersed in an aqueous solution of 3.5 wt% sodium chloride at room temperature for 18 months. The optimal results in which the corrosion rate was significantly reduced were for the two groups of concrete mixtures, first group was (C2), which contains 3 wt% orange peels extract inhibitor mixed with 2.4 wt% Oxydtron as water-resisting admixture, and the second group was (E2) included 3 wt% calcium nitrate inhibitor with 2.4 wt% Oxydtron as water-resisting admixture. These two groups samples have been showed more excellent corrosion resistance against the saline solution after the completed immersion period. The inhibition efficiency analysis showed that there is a direct relationship between the inhibitor concentration and the efficiency of corrosion inhibition. However, the inhibition efficiency in the case of samples containing calcium nitrate inhibitor was higher than their counterparts containing green inhibitor extract. Finally, the economic cost analysis showed that the cost of the green inhibitor extract-containing samples was lower than that of the calcium nitrate inhibitor-containing samples.

High Potential Inhibition of the 17-4 PH Stainless Steel in the Presence of Nitrate and Evolution of Metastable Pitting

In the present investigation, the potential effect of nitrate ions’ inhibition on pitting corrosion of 17-4 precipitation hardening (PH) stainless steel in different chloride and nitrate concentrations was investigated using potentiostatic and potentiodynamic examinations. Furthermore, metastable pitting was examined in depth to clarify nitrate inhibition. The results demonstrate that adding nitrate as an inhibitor to the chloride-containing solution decreases the metastable pit peak current, stability products, and pit radius. In contrast, no significant difference between metastable pit lifetime was observed in the presence and absence of nitrate in the chloride solution. It was also shown that introducing 17-4 PH stainless steel to the high potential resulted in the repassivation of the surface, even if the nitrate/chloride concentration ratio was less than the critical value needed for nitrate inhibition. Overall, nitrate ions have an inhibition effect in the chloride solution. Especially at very high potential, whether the nitrate concentration was less than the critical value or not, nitrate forces the surface to get repassivated.

How anaerobic sludge microbiome respond to different concentrations of nitrite, nitrate, and ammonium ions: a comparative analysis.

High concentrations of ammonium, nitrite, and nitrate always induce inhibition in anaerobic wastewater treatment. Due to the complexity and vulnerability of the microbial community (especially methanogens) in anaerobic sludge, little is understood about its underlying microbial mechanism under such inhibition. In this study, the shifts of microbial communities in anaerobic sludge under increasing levels of nitrite, nitrate, and ammonium ions were compared. Results show that although half maximal inhibitory concentrations (methanogenesis) were different for nitrite, nitrate, and ammonium ions with EC50 values of 12, 30, and 3000mg N/L, respectively, bacteria genera Kosmotoga and Brooklawnia dominated in all of the three high-stress inhibitory systems. Network analysis and redundancy analysis (RDA) of the microbial community showed the treatments with nitrate and nitrite ions decreased the modularity of anaerobic microorganisms. RDA showed that specific methanogenic activity was positively related to coenzyme F420 under nitrite inhibition (rp = 0.833, p < 0.05) and closely correlated with viability under nitrate inhibition. Gram-positive and nonmotile Brooklawnia genus showed a negative correlation with physiological characteristics in the ammonia treatments, suggesting its high resistance to ammonia.

SPL12 Regulates AGL6 and AGL21 to Modulate Nodulation and Root Regeneration under Osmotic Stress and Nitrate Sufficiency Conditions in Medicago sativa.

The highly conserved plant microRNA, miR156, affects root architecture, nodulation, symbiotic nitrogen fixation, and stress response. In Medicago sativa, transcripts of eleven SQUAMOSA-PROMOTER BINDING PROTEIN-LIKE, SPLs, including SPL12, are targeted for cleavage by miR156. Our previous research revealed the role of SPL12 and its target gene, AGL6, in nodulation in alfalfa. Here, we investigated the involvement of SPL12, AGL6 and AGL21 in nodulation under osmotic stress and different nitrate availability conditions. Characterization of phenotypic and molecular parameters revealed that the SPL12/AGL6 module plays a negative role in maintaining nodulation under osmotic stress. While there was a decrease in the nodule numbers in WT plants under osmotic stress, the SPL12-RNAi and AGL6-RNAi genotypes maintained nodulation under osmotic stress. Moreover, the results showed that SPL12 regulates nodulation under a high concentration of nitrate by silencing AGL21. AGL21 transcript levels were increased under nitrate treatment in WT plants, but SPL12 was not affected throughout the treatment period. Given that AGL21 was significantly upregulated in SPL12-RNAi plants, we conclude that SPL12 may be involved in regulating nitrate inhibition of nodulation in alfalfa by targeting AGL21. Taken together, our results suggest that SPL12, AGL6, and AGL21 form a genetic module that regulates nodulation in alfalfa under osmotic stress and in response to nitrate.

Effect of heat and mass transfer on corrosion of carbon steel in a crude oil medium using corrosion inhibitors sodium nitrate and castor oil under different circumstances

In the petroleum industry, corrosion is a fundamental problem that causes many operational and commercial problems, which require careful consideration and comprehensive studies in order to discover suitable solutions. Among these problems is the occurrence of corrosion in the crude oil production equipment as well as in the transportation pipelines of petroleum products, which leads to their failure; thus, increasing the cost as a result of maintenance or replacement. To protect them from corrosion, different types of inhibitors are commonly used, in which small amounts of inhibitor are continuously injected, slowly forming a thin layer of inhibitor between them and the corrosive materials to protect them from corrosion. In this study, the performance of the corrosion process was examined under varying temperatures, namely 20, 30, 40, 50 and 60 °C, at rotational speeds of 0, 500, 1250 and 2000 rpm. The concentrations of sodium nitrate (NaNO3) inhibitor were 0, 0.5, 1.0 and 1.5 g/l of crude oil, whereas the concentrations of castor oil inhibitor were 0, 0.5, 1.0 and 1.5 ml/l of crude oil. The results demonstrated that the corrosion rate of carbon steel in the crude oil decreases with the increase in the concentration of both types of inhibitors (NaNO3 and castor oil), while it increases with the rise in temperature and rotational speed. It was determined that the maximum efficiency of the green inhibitor (castor oil) in the crude oil was 93.7% at a concentration of 1.5 ml/l, temperature of 20 °C and a rotational speed of 0 rpm, while the maximum efficiency of the chemical inhibitor (NaNO3) in the crude oil was 98.6% at a concentration of 1.5 g/l, temperature of 20 ℃ and rotational speed of 0 rpm.

Myocardial Bridging, a Neglected Anomaly in Acute Coronary Syndrom

Background: Myocardial Bridging (MB) is an anomaly characterized by an intra-myocardial route of a segment of one of the major coronary arteries. Functional myocardial bridging is less commonly observed on angiography (0.5–16%) and can range from 4 to 80 mm in length. This case report elaborates about a case of a symptomatic MB occurrence in a patient manifesting as an acute coronary syndrome. Case presentation: A 66 years old female presented to ER with a typical angina gradually increasing since 1 week ago. Associated symptoms were episodic syncope, dyspnea, and dyspepsia. physical examination reveals, vital signs are within normal limits. The cardio-pulmonary examination was unremarkable. Electrocardiogram (ECG) showed inverted T waves on V1-V4, cardiac biomarker enzymes were not increased, chest X-ray revealed an enlarged heart, echocardiography showed a left ventricular hypertrophy (LVH) with normal left ventricle ejection fraction (LVEF). Nitrate, aspirin, and P2Y12 inhibitor were then administered in the ER, and the patient was then transferred to catheterization lab. CT-Angiography showed a MB in the middle left anterior descending (LAD), the patient was then treated with bisoprolol as a maintenance therapy. Conclusion: MB, if presenting symptomatically, especially as an acute coronary syndrome (ACS), may become lifeŧhreatening if not recognized and treated appropriately. Flow normalization and symptom management in such circumstances are best achieved through revascularisation via percutaneous coronary intervention (PCI) and drug therapy by using beta-blocker.

SIRT2 tyrosine nitration by peroxynitrite in response to renal ischaemia/reperfusion injury

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are the production of renal ischaemia/reperfusion (I/R). The current study is to elucidate a mechanism of SIRT2 tyrosine nitration to accelerate the cell apoptosis induced by peroxynitrite (ONOO‾), the most reactive and deleterious RNS type in renal ischaemia/reperfusion (I/R) injury. Our results demonstrate that there is a significant enhancement of the 3-nitrotyrosine levels in renal tissues of Acute Kidney Injury (AKI) patients and rats that underwent renal I/R, and a positive correlation between the 3-nitrotyrosine level and renal function impairment, indicative of an accumulation of peroxynitrite. Notably, peroxynitrite-evoked nitration of SIRT2 destroyed its enzymatic activity and the capability to deacetylate FOXO3a, and enhanced expression of Bim and caspase3, facilitating renal cell apoptosis in renal ischaemia/reperfusion and SIN-1(peroxynitrite donor) treatment in vitro, and these effects were reversed by FeTMPyP, a peroxynitrite decomposition scavenger. Importantly, we identified that the tyrosine 86 is responsible for SIRT2 nitration and inactivation using site-mutation assay and Mass Spectrography analysis. Altogether, these findings point to a novel protective mechanism that an inhibition of SIRT2 tyrosine nitration can be a promising strategy to prevent ischaemic renal diseases involving AKI.

Nitrate restricts nodule organogenesis through inhibition of cytokinin biosynthesis in Lotus japonicus

Legumes balance nitrogen acquisition from soil nitrate with symbiotic nitrogen fixation. Nitrogen fixation requires establishment of a new organ, which is a cytokinin dependent developmental process in the root. We found cytokinin biosynthesis is a central integrator, balancing nitrate signalling with symbiotic acquired nitrogen. Low nitrate conditions provide a permissive state for induction of cytokinin by symbiotic signalling and thus nodule development. In contrast, high nitrate is inhibitory to cytokinin accumulation and nodule establishment in the root zone susceptible to nodule formation. This reduction of symbiotic cytokinin accumulation was further exacerbated in cytokinin biosynthesis mutants, which display hypersensitivity to nitrate inhibition of nodule development, maturation and nitrogen fixation. Consistent with this, cytokinin application rescues nodulation and nitrogen fixation of biosynthesis mutants in a concentration dependent manner. These inhibitory impacts of nitrate on symbiosis occur in a Nlp1 and Nlp4 dependent manner and contrast with the positive influence of nitrate on cytokinin biosynthesis that occurs in species that do not form symbiotic root nodules. Altogether this shows that legumes, as exemplified by Lotus japonicus, have evolved a different cytokinin response to nitrate compared to non-legumes.

Nitric Oxide Mediation in Hydroxyurea and Nitric Oxide Metabolites' Inhibition of Erythroid Progenitor Growth.

In several systems, hydroxyurea has been shown to trigger nitric oxide (NO) release or activation of NO synthase (NOS). To elucidate this duality in its pharmacological effects, during myelosuppression, we individually examined hydroxyurea’s (NO releasing agent) and NO metabolites’ (stable NO degradation products) effects on erythroid colony growth and NOS/NO levels in mice using NO scavenger 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO). Hydroxyurea and nitrite/nitrate decreased the bone marrow cellularity that was blocked by PTIO only for the NO metabolites. Hydroxyurea inhibition of colony-forming unit-erythroid (CFU-E) formation and reticulocytes was reversed by PTIO. Moreover, hydroxyurea, through a negative feedback mechanism, reduced inducible NOS (iNOS) expressing cells in CFU-E, also prevented by PTIO. Nitrate inhibition of burst-forming units-erythroid (BFU-E) colony growth was blocked by PTIO, but not in mature CFU-E. The presented results reveal that NO release and/or production mediates the hydroxyurea inhibition of mature erythroid colony growth and the frequency of iNOS immunoreactive CFU-E.

Nitrite and nitrate inhibition thresholds for a glutamate-fed bio-P sludge

Enhanced biological phosphorus removal (EBPR) is an efficient and sustainable technology to remove phosphorus from wastewater. A widely known cause of EBPR deterioration in wastewater treatment plants (WWTPs) is the presence of nitrate/nitrite or oxygen in the anaerobic reactor. Moreover, most existing studies on the effect of either permanent aerobic conditions or inhibition of EBPR by nitrate or free nitrous acid (FNA) have been conducted with a “Candidatus Accumulibacter” or Tetrasphaera-enriched sludge, which are the two major reported groups of polyphosphate accumulating organisms (PAO) with key roles in full-scale EBPR WWTPs. This work reports the denitrification capabilities of a bio-P microbial community developed using glutamate as the sole source of carbon and nitrogen. This bio-P sludge exhibited a high denitrifying PAO (DPAO) activity, in fact, 56% of the phosphorus was uptaken under anoxic conditions. Furthermore, this mixed culture was able to use nitrite and nitrate as electron acceptor for P-uptake, being 1.8 μg HNO2–N·L−1 the maximum FNA concentration at which P-uptake can occur. Net P-removal was observed under permanent aerobic conditions. However, this microbial culture was more sensitive to FNA and permanent aerobic conditions compared to “Ca. Accumulibacter”-enriched sludge.

Haloalkaliphilic denitrifiers-dependent sulfate-reducing bacteria thrive in nitrate-enriched environments

As bridge in global cycles of carbon, nitrogen, and sulfur, sulfate-reducing bacteria (SRB) play more and more important role under various environments, especially the saline-alkali environments with significant increase in area caused by human activities. Sulfate reduction can be inhibited by environmental nitrate. However, how SRB cope with environmental nitrate stress in these extreme environments still remain unclear. Here, after a long-term enrichment of sediment from saline-alkali Qinghai Lake of China using anaerobic filter reactors, nitrate was added to evaluate the response of SRB. With the increase in nitrate concentrations, the inhibition on sulfate reduction was gradually observed. Interestingly, extension of hydraulic retention time can relieve the inhibition caused by high nitrate concentration. Mass balance analysis showed that nitrate reduction is prior to sulfate reduction. Further metatranscriptomic analysis shows that, genes of nitrite reductase (periplasmic cytochrome c nitrite reductase gene) and energy metabolisms (lactate dehydrogenase, formate dehydrogenase, pyruvate:ferredoxin-oxidoreductase, and fumarate reductase genes) in SRB was down-regulated, challenging the long-held opinion that up-regulation of these genes can relieve the nitrate inhibition. Most importantly, the nitrate addition activated the denitrification pathway in denitrifying bacteria (DB) via significantly up-regulating the expression of the corresponding genes (nitrite reductase, nitric oxide reductase c subunit, nitric oxide reductase activation protein and nitrous oxide reductase genes), quickly reducing the environmental nitrate and relieving the nitrate inhibition on SRB. Our findings unravel that in response to environmental nitrate stress, haloalkaliphilic SRB show dependency on DB, and expand our knowledge of microbial relationship during sulfur and nitrogen cycles.

Polyamine-Conjugated Nitroxides Are Efficacious Inhibitors of Oxidative Reactions Catalyzed by Endothelial-Localized Myeloperoxidase.

The heme enzyme myeloperoxidase (MPO) is a key mediator of endothelial dysfunction and a therapeutic target in cardiovascular disease. During inflammation, MPO released by circulating leukocytes is internalized by endothelial cells and transcytosed into the subendothelial extracellular matrix of diseased vessels. At this site, MPO mediates endothelial dysfunction by catalytically consuming nitric oxide (NO) and producing reactive oxidants, hypochlorous acid (HOCl) and the nitrogen dioxide radical (•NO2). Accordingly, there is interest in developing MPO inhibitors that effectively target endothelial-localized MPO. Here we studied a series of piperidine nitroxides conjugated to polyamine moieties as novel endothelial-targeted MPO inhibitors. Electron paramagnetic resonance analysis of cell lysates showed that polyamine conjugated nitroxides were efficiently internalized into endothelial cells in a heparan sulfate dependent manner. Nitroxides effectively inhibited the consumption of MPO's substrate hydrogen peroxide (H2O2) and formation of HOCl catalyzed by endothelial-localized MPO, with their efficacy dependent on both nitroxide and conjugated-polyamine structure. Nitroxides also differentially inhibited protein nitration catalyzed by both purified and endothelial-localized MPO, which was dependent on •NO2 scavenging rather than MPO inhibition. Finally, nitroxides uniformly inhibited the catalytic consumption of NO by MPO in human plasma. These studies show for the first time that nitroxides effectively inhibit local oxidative reactions catalyzed by endothelial-localized MPO. Novel polyamine-conjugated nitroxides, ethylenediamine-TEMPO and putrescine-TEMPO, emerged as efficacious nitroxides uniquely exhibiting high endothelial cell uptake and efficient inhibition of MPO-catalyzed HOCl production, protein nitration, and NO oxidation. Polyamine-conjugated nitroxides represent a versatile class of antioxidant drugs capable of targeting endothelial-localized MPO during vascular inflammation.