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1.
Enhancing mainstream nitrogen removal by employing nitrate/nitrite-dependent anaerobic methane oxidation processes.
Liu, T, Hu, S, Guo, J
Critical reviews in biotechnology. 2019;(5):732-745
Abstract
Due to serious eutrophication in water bodies, nitrogen removal has become a critical stage for wastewater treatment plants (WWTPs) over past decades. Conventional biological nitrogen removal processes are based on nitrification and denitrification (N/DN), and are suffering from several major drawbacks, including substantial aeration consumption, high fugitive greenhouse gas emissions, a requirement for external carbon sources, excessive sludge production and low energy recovery efficiency, and thus unable to satisfy the escalating public needs. Recently, the discovery of anaerobic ammonium oxidation (anammox) bacteria has promoted an update of conventional N/DN-based processes to autotrophic nitrogen removal. However, the application of anammox to treat domestic wastewater has been hindered mainly by unsatisfactory effluent quality with nitrogen removal efficiency below 80%. The discovery of nitrate/nitrite-dependent anaerobic methane oxidation (n-DAMO) during the last decade has provided new opportunities to remove this barrier and to achieve a robust system with high-level nitrogen removal from municipal wastewater, by utilizing methane as an alternative carbon source. In the present review, opportunities and challenges for nitrate/nitrite-dependent anaerobic methane oxidation are discussed. Particularly, the prospective technologies driven by the cooperation of anammox and n-DAMO microorganisms are put forward based on previous experimental and modeling studies. Finally, a novel WWTP system acting as an energy exporter is delineated.
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Influence of Hydrogen Electron Donor, Alkaline pH, and High Nitrate Concentrations on Microbial Denitrification: A Review.
Albina, P, Durban, N, Bertron, A, Albrecht, A, Robinet, JC, Erable, B
International journal of molecular sciences. 2019;(20)
Abstract
Bacterial respiration of nitrate is a natural process of nitrate reduction, which has been industrialized to treat anthropic nitrate pollution. This process, also known as "microbial denitrification", is widely documented from the fundamental and engineering points of view for the enhancement of the removal of nitrate in wastewater. For this purpose, experiments are generally conducted with heterotrophic microbial metabolism, neutral pH and moderate nitrate concentrations (<50 mM). The present review focuses on a different approach as it aims to understand the effects of hydrogenotrophy, alkaline pH and high nitrate concentration on microbial denitrification. Hydrogen has a high energy content but its low solubility, 0.74 mM (1 atm, 30 °C), in aqueous medium limits its bioavailability, putting it at a kinetic disadvantage compared to more soluble organic compounds. For most bacteria, the optimal pH varies between 7.5 and 9.5. Outside this range, denitrification is slowed down and nitrite (NO2-) accumulates. Some alkaliphilic bacteria are able to express denitrifying activity at pH levels close to 12 thanks to specific adaptation and resistance mechanisms detailed in this manuscript, and some bacterial populations support nitrate concentrations in the range of several hundred mM to 1 M. A high concentration of nitrate generally leads to an accumulation of nitrite. Nitrite accumulation can inhibit bacterial activity and may be a cause of cell death.
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3.
In-situ remediation of sediment by calcium nitrate combined with composite microorganisms under low-DO regulation.
Li, W, Zhang, S, Zhang, L, Li, X, Wang, F, Li, G, Li, J, Li, W
The Science of the total environment. 2019;:134109
Abstract
In this work, in-situ remediation of sediment was carried out by combining various methods. The results showed that the treatment effect of Calcium nitrate + composite functional microorganisms + Low-DO (dissolved oxygen) aeration (CN/CFM/LDA) was the best, in which 2.5 g calcium nitrate, 1 g functional bacteria and intermittent aeration (0.1 m3/h, 3 h per day) were utilized for the remediation of 500 g sediments within 40-day experimental period. The DO and oxidation reduction potential (ORP) in overlying water have been improved from 3.23 mg/L to 4.4 mg/L and 25.8 mV to 112.4 mV, respectively. The release fluxes of ammonia nitrogen (NH4+-N), nitrite nitrogen (NO2--N) and nitrate nitrogen (NO3--N) were respectively reduced by 30.51%, 13.11% and 77.45% compared with the control and the removal rate of the acid volatile sulfide (AVS) in sediments was 94.14% compared with the original sample. The results of high-throughput sequencing show that the dominant bacterial community in CN/CFM/LDA was transformed into Proteobacteria (relative abundance of 74.17%) at the phylum level and Thiobacillus (relative abundance of 38.52%) at the genus level. The results of 16S functional prediction indicated that the remediation method can enhance the numbers of microbial key enzymes (92360) in the nitrification and denitrification process, where Low-DO aeration can mediate the growth of denitrifying bacteria and promote the performance of key enzymes. In conclusion, the experimental results show that the use of calcium nitrate and composite functional microorganisms under low-DO regulation has a promising remediation effect on sediments of black-malodorous water.
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4.
Reticulate evolution in eukaryotes: Origin and evolution of the nitrate assimilation pathway.
Ocaña-Pallarès, E, Najle, SR, Scazzocchio, C, Ruiz-Trillo, I
PLoS genetics. 2019;(2):e1007986
Abstract
Genes and genomes can evolve through interchanging genetic material, this leading to reticular evolutionary patterns. However, the importance of reticulate evolution in eukaryotes, and in particular of horizontal gene transfer (HGT), remains controversial. Given that metabolic pathways with taxonomically-patchy distributions can be indicative of HGT events, the eukaryotic nitrate assimilation pathway is an ideal object of investigation, as previous results revealed a patchy distribution and suggested that the nitrate assimilation cluster of dikaryotic fungi (Opisthokonta) could have been originated and transferred from a lineage leading to Oomycota (Stramenopiles). We studied the origin and evolution of this pathway through both multi-scale bioinformatic and experimental approaches. Our taxon-rich genomic screening shows that nitrate assimilation is present in more lineages than previously reported, although being restricted to autotrophs and osmotrophs. The phylogenies indicate a pervasive role of HGT, with three bacterial transfers contributing to the pathway origin, and at least seven well-supported transfers between eukaryotes. In particular, we propose a distinct and more complex HGT path between Opisthokonta and Stramenopiles than the one previously suggested, involving at least two transfers of a nitrate assimilation gene cluster. We also found that gene fusion played an essential role in this evolutionary history, underlying the origin of the canonical eukaryotic nitrate reductase, and of a chimeric nitrate reductase in Ichthyosporea (Opisthokonta). We show that the ichthyosporean pathway, including this novel nitrate reductase, is physiologically active and transcriptionally co-regulated, responding to different nitrogen sources; similarly to distant eukaryotes with independent HGT-acquisitions of the pathway. This indicates that this pattern of transcriptional control evolved convergently in eukaryotes, favoring the proper integration of the pathway in the metabolic landscape. Our results highlight the importance of reticulate evolution in eukaryotes, by showing the crucial contribution of HGT and gene fusion in the evolutionary history of the nitrate assimilation pathway.
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5.
Potential benefits of dietary nitrate ingestion in healthy and clinical populations: A brief review.
McDonagh, STJ, Wylie, LJ, Thompson, C, Vanhatalo, A, Jones, AM
European journal of sport science. 2019;(1):15-29
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Abstract
This article provides an overview of the current literature relating to the efficacy of dietary nitrate (NO3-) ingestion in altering aspects of cardiovascular and metabolic health and exercise capacity in healthy and diseased individuals. The consumption of NO3--rich vegetables, such as spinach and beetroot, have been variously shown to promote nitric oxide bioavailability, reduce systemic blood pressure, enhance tissue blood flow, modulate muscle O2 utilisation and improve exercise tolerance both in normoxia and in hypoxia, as is commonly observed in a number of disease states. NO3- ingestion may, therefore, act as a natural means for augmenting performance and attenuating complications associated with limited O2 availability or transport, hypertension and the metabolic syndrome. Recent studies indicate that dietary NO3- might also augment intrinsic skeletal muscle contractility and improve the speed and power of muscle contraction. Moreover, several investigations suggest that NO3- supplementation may improve aspects of cognitive performance both at rest and during exercise. Collectively, these observations position NO3- as more than a putative ergogenic aid and suggest that increasing natural dietary NO3- intake may act as a prophylactic in countering the predations of senescence and certain cardiovascular-metabolic diseases.
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Hydralazine and nitrates in the treatment of heart failure with reduced ejection fraction.
Al-Mohammad, A
ESC heart failure. 2019;(4):878-883
Abstract
Hydralazine and nitrate combination was the first treatment that showed improved survival of patients with heart failure with reduced left ventricular ejection fraction (HFREF) in the Vasodilator Heart Failure Trial (V-HeFT trial) in 1986. This showed a 34% reduction of mortality at 2 years of follow-up in patients with advanced heart failure (New York Heart Association Class IV). The angiotensin-converting enzyme inhibitor (ACEi), beta-blockers, mineralocorticoid receptor antagonists, and most recently sacubitril-valsartan have superseded the combination of hydralazine and nitrates. However, the latter combination does have a place bridging the survival gap of Black patients with HFREF when added to their standard therapy. This was demonstrated in the African-American Heart Failure Trial (A-HeFT trial) in 2004 when the risk reduction in the Black patients was 43% compared with that in the placebo. This combination may have a potential use in patients with contraindications to the use of ACEi, angiotensin receptor blockers, and sacubitril-valsartan. This is suggested by both the European Society of Cardiology (ESC) Guidelines and the guidelines of the National Institute for Health and Care Excellence (NICE). In this perspective, the role of the combination of hydralazine and nitrates in the treatment of HFREF is reviewed through a synopsis of the evidence base consisting of three randomized controlled studies, several further analyses of subgroups within those trials, a systemic review, and two large observational studies of registry cohorts. The place of the combination in the treatment cascades proposed by heart failure guidelines of the ESC and NICE is explored. This perspective is to remind us of their appropriate roles, particularly given the findings of underuse of this combination in people of African ancestry in Europe.
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Occurrence and diversity of the oxidative hydroxyhydroquinone pathway for the anaerobic degradation of aromatic compounds in nitrate-reducing bacteria.
Pacheco-Sánchez, D, Rama-Garda, R, Marín, P, Martirani-Von Abercron, SM, Marqués, S
Environmental microbiology reports. 2019;(4):525-537
Abstract
The nitrate-reducing betaproteobacteria Azoarcus anaerobius and Thauera aromatica AR-1 use an oxidative mechanism to anaerobically degrade resorcinol and 3,5-dihydroxybenzoate (3,5-DHB), respectively, rendering hydroxyhydroquinone as intermediate. The first pathway step is performed by a dimethylsulphoxide-reductase family hydroxylase. The gene cluster coding for the pathway is homologous in these strains. Only these two Rhodocyclales are known to follow this anaerobic pathway, and nothing is known about its distribution in prokaryotes. To determine the relevance and diversity of this strategy in nature, we enriched for bacteria able to oxidize resorcinol or 3,5-DHB under denitrifying conditions. Nitrate-reducing bacteria able to degrade these compounds were present in soil, aquifer and marine sediments. We were able to isolate a number of strains with this capacity from soil and aquifer samples. Amplicon libraries of rehL, the gene encoding the first step of this pathway, showed an overall low diversity, most sequences clustering with either pathway enzyme. Isolates belonging to the Beta- and Gammaproteobacteria able to grow on these substrates revealed rehL homologues only in strains belonging to Thauera and Azoarcus. Analysis of sequenced genomes in the databases detected the presence of highly similar clusters in two additional betaproteobacteria and in the gammaproteobacterium Sedimenticola selenatireducens, although anaerobic growth on a dihydroxyaromatic could only be confirmed in Thauera chlorobenzoica 3CB-1. The presence of mobile elements in the flanking sequences of some of the clusters suggested events of horizontal gene transfer, probably contributing to expand the pathway to a broader host range within the Proteobacteria.
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High doses of sodium nitrate prior to exhaustive exercise increases plasma peroxynitrite levels in well-trained subjects: randomized, double-blinded, crossover study.
Gholami, F, Rahmani, L, Amirnezhad, F, Cheraghi, K
Applied physiology, nutrition, and metabolism = Physiologie appliquee, nutrition et metabolisme. 2019;(12):1305-1310
Abstract
The aim of this study was to investigate the effect of different doses of pre-workout sodium nitrate supplementation on nitric oxide, peroxynitrite levels, and performance parameters. Ten well-trained male subjects participated in a randomized, double-blinded, crossover study. They ingested 8, 16, and 24 mmol sodium nitrate or placebo (NaCl) dissolved in water at 2.5 h before an incremental exercise test. Respiratory gases (oxygen consumption, carbon dioxide production, respiratory exchange ratio) were measured throughout the exercise trials and 3 blood samples (pre-ingestion, 2.5 h post-ingestion and postexercise) were taken to analyze nitrate/nitrite (NOx) and peroxynitrite levels. Data were analyzed using repeated-measures ANOVA at significance level of P < 0.05. NOx levels significantly increased following sodium nitrate ingestion compared with placebo (placebo: 40.86 ± 10.7 μmol/L, 8 mmol: 203.69 ± 25.1 μmol/L, 16 mmol: 289.41 ± 30.1 μmol/L, and 24 mmol: 300.95 ± 42.4 μmol/L, respectively) (P = 0.0001). However, this did not induce any significant change in oxygen consumption (P = 0.351), blood lactate concentration (P = 0.245), and time-to-exhaustion (P = 0.147). Peroxynitrite levels were similar compared with placebo when participants ingested 8 and 16 mmol of inorganic nitrate but a significant increase was observed after exercise at maximal intensity when participants were supplemented with 24 mmol (mean = 14.60 ± 1.3 μmol/L, P = 0.001). Pre-workout ingestion of high dose of sodium nitrate (24 mmol) induced peroxynitrate formation, a marker of oxidative stress. Caution must be taken regarding administration of higher doses before benefits or adverse effects are established in this population.
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Effects of acute nitric oxide precursor intake on peripheral and central fatigue during knee extensions in healthy men.
Le Roux-Mallouf, T, Laurent, J, Besset, D, Marillier, M, Larribaut, J, Belaidi, E, Corne, C, Doutreleau, S, Verges, S
Experimental physiology. 2019;(7):1100-1114
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Abstract
NEW FINDINGS What is the central question of this study? What is the effect of acute NO precursor intake on vascular function, muscle and cerebral oxygenation and peripheral and central neuromuscular fatigue during knee-extension exercise? What is the main finding and its importance? Acute NO precursor ingestion increases the plasma concentrations of NO precursors (nitrate, arginine and citrulline) and enhances post-ischaemic vasodilatation, but has no significant effect on muscle and cerebral oxygenation, peripheral and central mechanisms of neuromuscular fatigue and, consequently, does not improve exercise performance. ABSTRACT Nitric oxide (NO) plays an important role in matching blood flow to oxygen demand in the brain and contracting muscles during exercise. Previous studies have shown that increasing NO bioavailability can improve muscle function. The aim of this study was to assess the effect of acute NO precursor intake on muscle and cerebral oxygenation and on peripheral and central neuromuscular fatigue during exercise. In four experimental sessions, 15 healthy men performed a thigh ischaemia-reperfusion test followed by submaximal isometric knee extensions (5 s on-4 s off; 45% of maximal voluntary contraction) until task failure. In each session, subjects drank a nitrate-rich beetroot juice containing 520 mg nitrate (N), N and citrulline (6 g; N+C), N and arginine (6 g; N+A) or a placebo (PLA). Prefrontal cortex and quadriceps near-infrared spectroscopy parameters were monitored continuously. Transcranial magnetic stimulation and femoral nerve electrical stimulation were used to assess central and peripheral determinants of fatigue. The post-ischaemic increase in thigh blood total haemoglobin concentration was larger in N (10.1 ± 3.7 mmol) and N+C (10.9 ± 3.3 mmol) compared with PLA (8.2 ± 2.7 mmol; P < 0.05). Nitric oxide precursors had no significant effect on muscle and cerebral oxygenation or on peripheral and central mechanisms of neuromuscular fatigue during exercise. The total number of knee extensions did not differ between sessions (N, 71.9 ± 33.2; N+A, 73.3 ± 39.4; N+C, 74.6 ± 34.0; PLA, 71.8 ± 39.9; P > 0.05). In contrast to the post-ischaemic hyperaemic response, NO bioavailability in healthy subjects might not be the limiting factor for tissue perfusion and oxygenation during submaximal knee extensions to task failure.
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When the Heart Is Not in It: Breastfeeding with Cardiovascular Disease.
Anderson, PO
Breastfeeding medicine : the official journal of the Academy of Breastfeeding Medicine. 2019;(2):80-82