Nitrite Consumption Research Articles

Identification of a Repressor of a Truncated Denitrification Pathway in Moraxella catarrhalis

Growth of Moraxella catarrhalis in a biofilm resulted in marked upregulation of two open reading frames (ORFs), aniA and norB, predicted to encode a nitrite reductase and a nitric oxide reductase, respectively (W. Wang, L. Reitzer, D. A. Rasko, M. M. Pearson, R. J. Blick, C. Laurence, and E. J. Hansen, Infect. Immun. 75:4959-4971, 2007). An ORF designated nsrR, which was located between aniA and norB, was shown to encode a predicted transcriptional regulator. Inactivation of nsrR resulted in increased expression of aniA and norB in three different M. catarrhalis strains, as measured by both DNA microarray analysis and quantitative reverse transcriptase PCR. Provision of a wild-type nsrR gene in trans in an nsrR mutant resulted in decreased expression of the AniA protein. DNA microarray analysis revealed that two other ORFs (MC ORF 683 and MC ORF 1550) were also consistently upregulated in an nsrR mutant. Consumption of both nitrite and nitric oxide occurred more rapidly with cells of an nsrR mutant than with wild-type cells. However, growth of nsrR mutants was completely inhibited by a low level of sodium nitrite. This inhibition of growth by nitrite was significantly reversed by introduction of an aniA mutation into the nsrR mutant and was completely reversed by the presence of a wild-type nsrR gene in trans. NsrR regulation of the expression of aniA was sensitive to nitrite, whereas NsrR regulation of norB was sensitive to nitric oxide.

Nitric oxide synthesis in patients with advanced HIV infection.

The discovery that humans produce nitric oxide and that this molecule plays an important role in cell communication, host resistance to infection, and perhaps in host defence to neoplastic disease, has created much interest in further research on its function in the body. A cytokine-inducible high output L-arginine/nitric oxide pathway was recently detected in patients with advanced malignancy treated with IL-2. The production of nitric oxide was thus examined in patients with advanced HIV infection and in intensive care unit control patients. Extrinsic nitrate and nitrite consumption were carefully controlled in the diet or through the use of total parenteral nutrition. Seven of eight HIV+ patients were placed into positive nitrogen balance. Nitric oxide synthesis was found to be within the normal human range. In contrast, nitric oxide synthesis in extremely ill intensive care unit patients was low normal to depressed.

Inhibition of myeloperoxidase-mediated protein nitration by tempol: Kinetics, mechanism, and implications

Despite the therapeutic potential of tempol (4-hydroxy-2,2,6,6-tetra-methyl-1-piperidinyloxy) and related nitroxides as antioxidants, their effects on peroxidase-mediated protein tyrosine nitration remain unexplored. This posttranslational protein modification is a biomarker of nitric oxide-derived oxidants, and, relevantly, it parallels tissue injury in animal models of inflammation and is attenuated by tempol treatment. Here, we examine tempol effects on ribonuclease (RNase) nitration mediated by myeloperoxidase (MPO), a mammalian enzyme that plays a central role in various inflammatory processes. Some experiments were also performed with horseradish peroxidase (HRP). We show that tempol efficiently inhibits peroxidase-mediated RNase nitration. For instance, 10 muM tempol was able to inhibit by 90% the yield of 290 muM 3-nitrotyrosine produced from 370 muM RNase. The effect of tempol was not completely catalytic because part of it was consumed by recombination with RNase-tyrosyl radicals. The second-order rate constant of the reaction of tempol with MPO compound I and II were determined by stopped-flow kinetics as 3.3 x 10(6) and 2.6 x 10(4) M(-1) s(-1), respectively (pH 7.4, 25 degrees C); the corresponding HRP constants were orders of magnitude smaller. Time-dependent hydrogen peroxide and nitrite consumption and oxygen production in the incubations were quantified experimentally and modeled by kinetic simulations. The results indicate that tempol inhibits peroxidase-mediated RNase nitration mainly because of its reaction with nitrogen dioxide to produce the oxammonium cation, which, in turn, recycles back to tempol by reacting with hydrogen peroxide and superoxide radical to produce oxygen and regenerate nitrite. The implications for nitroxide antioxidant mechanisms are discussed.

Concentration and natural stable isotope profiles of nitrogen species in theBlack Sea

We measured natural abundance profiles of N 2, nitrate, ammonium, suspended particulate organic nitrogen (PON) and total organic nitrogen (TON) concentrations and nitrogen stable isotopes in the Black Sea during five research cruises: R/V Bilim September 1999, R/V Bilim September 2000, Voyage 162, Leg 17 of the R/V Knorr 2001, Voyage 172, Leg 7 of R/V Knorr 2003 and Cruise 403 of R/V Endeavor 2005. Excess N 2 of biogeochemical origin had maximum values that were centered at the lower part of the suboxic zone. The δ 15 N of this excess N 2 was highly depleted in 2000 and 2001 (− 30‰ to − 40‰) and was much less depleted in 1999, 2003 and 2005 (− 1‰). The variabilities of N 2/Ar ratios, excess N 2 and δ 15 N of excess N 2 cannot be explained by variability in the profiles of nitrate and ammonium. Using a nitrogen mass balance of NO 3 −, NH 4 + and N 2 we determined that a missing N flux was required to complete the nitrogen mass balance in some years, especially 2000 and 2001. We suggest that this missing flux is most likely from remineralization of sinking PON. The δ 15 N of the missing nitrogen flux was also highly depleted in 2001 and 2000. The concentration profiles of nitrate, nitrite and ammonium concentrations approached zero, indicating total consumption to form nitrogen gas. However, in 2000 and 2001 the δ 15 N of excess N 2 increased with increasingly excess N 2, which is consistent with partial consumption. We propose that there are different states for the nitrogen system in the Black Sea and the system varies between them due to climate oscillations and variations in the major nitrogen budget components. When the system is at a steady state, total consumption of nitrate and ammonium occurs in the suboxic zone and partial denitrification is of minor importance. This results in higher values of δ 15 N 2 and lower values of excess N 2 in the suboxic zone. The balance of nitrate and ammonium fluxes into the suboxic zone with N 2 gas fluxes out of the suboxic zone in 1999, 2003 and 2005 imply that the system allowed total consumption at steady state in those years. Remineralization of depleted organic matter, presumably from nitrogen fixation in the euphotic zone, is necessary to support N 2 production of − 1‰ during complete consumption of nitrate, nitrite and ammonium. Near surface (oxic region) values of δ 15 N–N 2 in 2000 and 2001 (0.9‰) are more enriched than for N 2 in equilibrium with the atmosphere (0.68‰). These enriched values can be explained by the consumption of N 2 during nitrogen fixation with a fractionation effect between − 1.3 to − 2.6‰. When the system is in a transitory state, like that observed in 2000 and 2001, sinking organic matter from a phytoplankton bloom may stimulate both partial denitrification and the anammox reaction which can produce depleted N 2 and support higher values of excess N 2 in the suboxic zone.

Response of Nitrosomonas, Nitrobacter and Escherichia coli to drilling fluids

Inhibition of ammonia oxidation by Nitrosomonas, nitrite oxidation by Nitrobacterand carbon IV oxide evolution by Escherichia coli were employed as indices to determine the effect of four drilling fluids (Paradril, IMC0-W, IMC0-O and Gel/KCL/polymer to these bacteria. The percentage survival (determined by aerobic spread plate count) of these bacteria when exposed to these fluids was also used as toxicity index. Ammonia oxidation (nitrite accumulation) and nitrite oxidation (consumption) were determined by coupling of diazotised sulfanilic acid with a-napthyl-ethylene diamine dihydrochloride. Carbon IV oxide evolution was monitored by passing air from inoculated lactose broth into calcium hydroxide solution and titration with sulphuric acid. Toxicity indices were determined throughout the following exposure period (0, 1, 2, 3, 4, 8, 12, 24, 36 and 48 h) in static shake flask systems. Percentage survival decreased with increasing concentration of the drilling fluids and increasing exposure period of the three bacteria especially at high concentrations (10.0, 100 and 1000 mg/l). At lower concentrations (0.01, 0.1 and 1.0 mg/l) some fluids stimulated bacterial growth. Controls revealed bacterial growth through out the exposure period. Nitrite accumulation by Nitrosomonas, nitrite consumption by Nitrobacter and carbon IV oxide evolution by E. coli decreased with increase in concentration and exposure time of the four fluids. Controls revealed an increase in these indices with increase in exposure period. Results showed that the drilling fluids inhibited the two stages of the nitrification in the nitrogen cycle and respiration (by E. coli). This may affect the agricultural productivity of ecosystems in the Niger Delta where they are employed by causing dislocations in the nitrogen cycle where nitrifying and aerobic bacteria participate. Key words: Nitrite accumulation, nitrite consumption, respiration, drilling fluids.

Evidence Mounts That Nitrite Contributes to Hypoxic Vasodilation in the Human Circulation

Hypoxic vasodilation is a conserved physiological response to hypoxia that matches blood flow and oxygen delivery to tissue metabolic demand. This fundamental physiological process has been characterized for >100 years since the initial description by Roy and Brown1 in 1880. Hypoxic vasodilation requires a sensor mechanism that can detect a divergence in the normal relationship between delivered blood oxygen and tissue oxygen consumption.2 This hypoxic sensor mechanism must be coupled to the feedback generation of vasodilatory effectors that increase blood flow to maintain adequate tissue oxygenation. In short, hypoxic vasodilation requires hypoxia and/or pH sensing coupled to the release of a vasodilating signal. In mammalian species, the set point for hypoxic vasodilation occurs as the hemoglobin desaturates from 60% to 40%, around a partial pressure of oxygen ranging from 40 to 20 mm Hg.3 Despite the fact that the hypoxic vasodilation response was discovered almost 150 years ago, the identities of the oxygen sensor mechanism and the specific feedback vasodilator effectors remain uncertain. Although a number of mediators have been considered, including adenosine, nitric oxide (NO), ATP-sensitive potassium (KATP) channels, endothelium-derived hyperpolarizing factor (candidates include CO, H2O2, or ONOO−), and prostacyclin,2,4 the specific blockade of many of these pathways fails to completely inhibit hypoxic vasodilation.2 Article p 670 The present study published by Maher and colleagues5 in this issue of Circulation provides compelling evidence in normal human volunteers that the circulating anion salt nitrite (NO2−) may be an effector of hypoxic vasodilation. They report that nitrite potently vasodilates the venous forearm circulation under resting conditions and potently vasodilates the arteriolar circulation during experimental hypoxia, achieved by systemic breathing of 11% oxygen. Their studies indicate that the vasodilatory effect of nitrite is maximal in the deoxygenated venous …

Nitrite consumption and production in the cardiopulmonary circulation during hemorrhagic shock and resuscitation

Nitrite (NO2-) is reduced to nitric oxide (NO) by deoxyhemoglobin, and resynthesized in blood by oxidation of NO in the presence of ceruloplasmin. The central circulation seems a probable site for nitrite consumption and repletion during periods of oxidative stress and recovery such as that seen in hemorrhagic shock and resuscitation (HSR). We asked whether NO2- is consumed in the central circulation during hemorrhage, and reconstituted during resuscitation.

Physiological and phylogenetic characterization of a novel lithoautotrophic nitrite-oxidizing bacterium, 'Candidatus Nitrospira bockiana'

A new isolate of a lithoautotrophic nitrite-oxidizing bacterium was obtained from internal corrosion deposits from a steel pipeline of the Moscow heating system. The organism oxidized nitrite as the sole energy source and fixed carbon dioxide as the only carbon source. The cells were extremely pleomorphic: loosely wound spirals, slightly curved and even straight rods were detected, as well as coccoid cells. The highest rate of nitrite consumption (1.5 mM nitrite as substrate) was measured at 42 degrees C, with a temperature range of 28-44 degrees C. In enrichment cultures with Nocardioides sp. as an accompanying organism, optimal oxidation of 5.8 mM nitrite occurred at 45 degrees C, with a range of 28-48 degrees C. Neither pyruvate nor yeast extract stimulated nitrification. Organotrophic growth was not observed. Phylogenetic analysis of 16S rRNA gene sequences revealed that the novel isolate represents a new sublineage of the genus Nitrospira. On the basis of physiological, chemotaxonomic and molecular characteristics, the name 'Candidatus Nitrospira bockiana' is proposed.

An evaluation of semi-quantitative test strips for the measurement of nitrate in drinking water in epidemiologic studies

Consumption of nitrate and nitrite is associated with a variety of health outcomes. Commercially available test strips that allow semi-quantitative estimation of these contaminants in drinking water are inexpensive relative to laboratory testing, and are simple to use. To examine the accuracy of a nitrate/nitrite test strip, we recruited Washington State residents to estimate levels of these contaminants in their tap water using these strips, and simultaneously provide a tap water sample for laboratory analysis. Paired results were available from 102 homes. On the basis of laboratory assay, nitrate levels as nitrogen ranged from no nitrate (27%) to 40.5 mg/l (median 0.4 mg/l). Spearman's correlation coefficient between test strip- and laboratory-measured nitrate indicated moderate precision overall (r=0.72). Correlation was similar for homes inside and outside city/town limits, but differed by primary source of water for the purveyor indicated by residents (r=0.72 for groundwater and r=0.34 for surface water). Seven (7%) participants reported difficulty in distinguishing colors (contaminant levels) when using the test strip; and among the samples with nitrate, the laboratory assay indicated higher nitrate levels than the test strip for 81%. Nitrite was not detected by laboratory assay; in comparison, five (5%) subjects reported any nitrite according to the test strip. Nitrate/nitrite test strips may be useful in some epidemiologic studies, but should be used with caution, preferably as a screening tool or when laboratory assays are not feasible.

Reactions of thiocyanate in the mixture of nitrite and hydrogen peroxide under acidic conditions: Investigation of the reactions simulating the mixture of saliva and gastric juice

Nitrite and SCN− in saliva can mixes with H2O2 in the stomach. The mixing can result in the formation of ONOOH. It is not yet known how salivary SCN− reacts with ONOOH. An objective of the present study was to elucidate the reaction between ONOOH and SCN− . In nitrite/H2O2 systems at pH 2, SCN− inhibited the consumption of nitrite and the formation of . SCN− enhanced the decomposition of ONOOH and H2O2 in HNO2/H2O2 systems. Accompanying the reactions, sulfate was formed, suggesting that ONOOH oxidized SCN− . SCN− inhibited the nitration of phenolics induced by HNO2/H2O2. The inhibition is discussed taking SCN− -dependent reduction of ONOOH to HNO2 into consideration. SCN− also inhibited H2O2-induced consumption of nitrite and nitration of phenolics in acidified saliva. The result obtained in this study suggests that salivary SCN− can reduce ONOOH to /HNO2 inhibiting nitrating reactions in the stomach.

Nitric oxide synthase reduces nitrite to NO under anoxia.

Cultured bEND.3 endothelial cells show a marked increase in NO production when subjected to anoxia, even though the normal arginine pathway of NO formation is blocked due to absence of oxygen. The rate of anoxic NO production exceeds basal unstimulated NO synthesis in normoxic cells. The anoxic release of NO is mediated by endothelial nitric oxide synthase (eNOS), can be abolished by inhibitors of NOS and is accompanied by consumption of intracellular nitrite. The anoxic NO release is unaffected by the xanthine oxidase inhibitor oxypurinol. The phenomenon is attributed to anoxic reduction of intracellular nitrite by eNOS, and its magnitude and duration suggests that the nitrite reductase activity of eNOS is relevant for fast NO delivery in hypoxic vascular tissues.

Effect of Storage on Levels of Nitric Oxide Derivatives in Blood Components.

The traditional view of the red blood cell (RBC) as only a carrier of oxygen and carbon monoxide has been changed by the current understanding of the erythrocyte's role in nitric oxide (NO) physiology. Nitrite is a primary oxidative NO metabolite and is considered a major intravascular storage pool for NO. In the vascular system, erythrocytes are the major storage sites of nitrite, which can be activated to NO by deoxyhemoglobin, but also are responsible for its rapid destruction after reaction with oxyhemoglobin. The purpose of this study was to quantify the NO metabolites, nitrite and nitrate, in whole blood and packed red blood cells and to evaluate their correlations with the time of storage. Whole blood, leukoreduced, and non-leukoreduced packed RBCs were obtained from 3 donors and were stored in polyvinyl chloride (PVC) bags up to 42 days at 4°C. Sequential aliquots were taken from the bags using a liquid transfer set to maintain sterile conditions. Nitrite and nitrate were measured in the whole blood and in RBC components using reductive gas phase chemiluminescence. We found that both nitrite and nitrate decreased during the storage in the three blood components analyzed. The nitrite concentration measured in whole blood was 180± 18 before storage, 45±4 on day 1 and 43±5 nM on day 42. The nitrite concentration in RBCs was 225±51 before storage. In the leukoreduced RBCs, 75±12 on day 1 and 57±9 nM on day 42. In the non-leukoreduced RBCs, 68±10 on day 1 and 38±13 nM on day 42. The concentration of nitrate in whole blood was 50±7 before storage, 36±9 on day 1 and 27±3 uM on day 42. The concentration of nitrate in RBCs before storage was 43±5 uM. In the leukoreduced RBCs, 30±14 on day 1 and 33±5 uM on day 42. In the non-leukoreduced RBCs, 20±3 on day 1 and 23±3 uM on day 42. The whole blood pH after phlebotomy was 7.4±0.025 and decreased from 7±0.005 on day 1 to 6.5±0 on day 42 of storage. In leukoreduced RBC bags, the pH was 6.7±0.05 on day 1 and 6.5±0 on day 42 of storage. Similar values of pH were measured in the non-leukoreduced RBC bags. The blood pO2 before storage was 40.5±1.5 and increased to 251±4 mmHg in the leukoreduced RBC bag on day 42 of storage. Similar results were found for the non-leukoreduced RBCs and whole blood. In control experiments, a PVC bag was filled with saline and stored up to 42 days at 4°C. Nitrite and nitrate concentrations increased during saline storage. Our results showed that nitrite and nitrate levels fall in hemocomponents during blood bank storage, while pH decreases and pO2 increases. The decrease in nitrite levels could be explained either by its reaction with oxyhemoglobin, resulting in nitrate and methemoglobin, or with deoxyhemoglobin. Surprisingly nitrate levels did not increase during storage as one might expect from consumption of NO and nitrite. We are now investigating mechanisms for the possible reduction of nitrate under these conditions. The physiology of NO may have implication for transfusion medicine, ranging from the adverse effects of RBC transfusion to optimizing the preservation of stored hemocomponents. In addition, as erythrocytes may contribute to the control of blood flow and oxygen delivery through reduction of nitrite to NO under hypoxic and acid conditions, our findings may provide insight into the vasodynamic effects of blood transfusion and transfusion-related disorders.

Intake and food sources of nitrites and N-nitrosodimethylamine in Spain

To conduct a comprehensive assessment of dietary intakes of nitrites and N-nitrosodimethylamine (NDMA). A study was conducted within the Spanish cohort of the European Prospective Investigation in Cancer and Nutrition (EPIC) to assess the intake and food sources of these compounds in Spanish adults. The study included 41,446 health volunteers, aged 29-69 years, from Northern and Southern regions. Usual food intake was estimated by in-person interviews using a computerised dietary questionnaire. The estimated geometric mean was 0.994 mg day(-1) for nitrites and 0.114 microg day(-1) for NDMA. For both compounds a positive trend in consumption with increasing energy intake was observed. Dietary NDMA was related to age and sex after energy adjustment, while nitrite consumption increased with higher intakes of vitamin C (P < 0.001). The food groups that contributed most to intakes were meat products, cereals, vegetables and fruits for nitrites, and processed meat, beer, cheese and broiled fish for NDMA. Current and past smokers, who had high levels of NDMA from tobacco exposure, were also identified as the highest consumers of dietary NDMA. Furthermore, smokers had low intakes of vitamin C (an inhibitor of endogenous nitrosation). Intake levels of NDMA and nitrites in a Mediterranean cohort are currently relatively lower than those previously reported, although processed meat, beer and cured cheese still are the most important contributors to NDMA intake.

Salivary uric acid at the acidic pH of the stomach is the principal defense against nitrite-derived reactive species: Sparing effects of chlorogenic acid and serum albumin

A complex antioxidant system is present in human saliva, with uric acid being the most concentrated component. Ascorbic acid, present at low concentrations in saliva, is actively secreted into the gastric lumen. We report that ascorbic acid added to human saliva at pH 2 was consumed within a few minutes, regenerating HNO 2, whereas uric acid was consumed relatively slowly in a nitrite-dependent manner. The consumption of uric acid was (i) rapid under normoxic conditions and slower at low oxygen tensions, (ii) coupled to NO release, (iii) linked to the decrease in nitrite consumption and in nitrate formation, and (iv) unaffected by the nitrosation catalyst thiocyanate. Both chlorogenic acid and bovine serum albumin, representative of a phenol- and a protein-rich meal, respectively, were able to spare uric acid, although chlorogenic acid increased, whereas bovine serum albumin inhibited, NO release. We hypothesize that the major role of uric acid in saliva at pH 2 could be to preserve the stomach from the formation of toxic nitrogen species and that low levels of uric acid, together with ascorbic acid consumption, may contribute to the high occurrence of tumors at the gastroesophageal junction and cardia. The sparing effects of dietary compounds may therefore be an important not fully appreciated effect.

The Inhibitory Effects of Free Nitrous Acid on the Energy Generation and Growth Processes of an Enriched Nitrobacter Culture

The inhibitory effects of nitrite (NO2-)/free nitrous acid (HNO2-FNA) on the metabolism of Nitrobacter were investigated using a method allowing the decoupling of the growth and energy generation processes. A lab-scale sequencing batch reactor was operated forthe enrichment of a Nitrobacter culture. Fluorescent in situ hybridization (FISH) analysis showed that 73% of the bacterial population was Nitrobacter. Batch tests were carried out to assess the oxygen and nitrite consumption rates of the enriched culture at low and high nitrite levels, in the presence or absence of inorganic carbon. It was observed that in the absence of CO2, the Nitrobacter culture was able to oxidize nitrite at a rate that is 76% of that in the presence of CO2, with an oxygen consumption rate that is 85% of that measured in the presence of CO2. This enabled the impacts of nitrite/FNA on the catabolic and anabolic processes of Nitrobacter to be assessed separately. FNA rather than nitrite was likely the actual inhibitor to the Nitrobacter metabolism. It was revealed that FNA of up to 0.05 mg HNO2-N x L(-1) (3.4 microM), which was the highest FNA concentration used in this study, did not have any inhibitory effect on the catabolic processes of Nitrobacter. However, FNA initiated its inhibition to the anabolic processes of Nitrobacterat approximately 0.011 mg HNO2-N x L(-1) (0.8 microM), and completely stopped biomass synthesis at a concentration of approximately 0.023 mg HNO2-N x L(-1) (1.6 microM). The inhibitory effect could be described by an empirical inhibitory model proposed in this paper, but the underlying mechanisms remain to be revealed.

Stoichiometric and kinetic characterisation of Nitrobacter in mixed culture by decoupling the growth and energy generation processes

The growth, maintenance and lysis processes of Nitrobacter were characterised. A Nitrobacter culture was enriched in a sequencing batch reactor (SBR). Fluorescent in situ hybridisation showed that Nitrobacter constituted 73% of the bacterial population. Batch tests were carried out to measure the oxygen uptake rate and/or nitrite consumption rate when both nitrite and CO2 were in excess, and in the absence of either of these two substrates. The results obtained, along with the SBR performance data, allowed the determination of the maintenance coefficient and in situ cell lysis rate of Nitrobacter. Nitrobacter spends a significant amount of energy for maintenance, which varies considerably with the specific growth rate. At maximum growth, Nitrobacter consume nitrite at a rate of 0.042 mgN/mgCOD(biomass) . h for maintenance purposes, which increases more than threefold to 0.143 mgN/mgCOD(biomass) . h in the absence of growth. In the SBR, where Nitrobacter grew at 40% of its maximum growth rate, a maintenance coefficient of 0.113 mgN/mgCOD . h was found, resulting in 42% of the total amount of nitrite being consumed for maintenance. The above three maintenance coefficient values obtained at different growth rates appear to support the maintenance model proposed in Pirt (1982). The in situ lysis rate of Nitrobacter was determined to be 0.07/day under aerobic conditions at 22 degrees C and pH 7.3. Further, the maximum specific growth rate of Nitrobacter was estimated to be 0.02/h (0.48/day). The affinity constant of Nitrobacter with respect to nitrite was determined to be 1.50 mgNO2(-)-N/L, independent of the presence or absence of CO2.

Nitrite concentration influences the population structure of Nitrospira‐like bacteria

Chemolithoautotrophic nitrite oxidizers of the genus Nitrospira are a monophyletic but diverse group of organisms, are widely distributed in many natural habitats, and play a key role in nitrogen elimination during biological wastewater treatment. Phylogenetic analyses of cloned 16S rRNA genes and fluorescence in situ hybridization with newly developed rRNA-targeted oligonucleotide probes revealed coexistence of uncultured members of sublineages I and II of the genus Nitrospira in biofilm and activated sludge samples taken from nitrifying wastewater treatment plants. Quantitative microscopic analyses of their spatial arrangement relative to ammonia oxidizers in the biofilm and activated sludge flocs showed that members of the Nitrospira sublineage I occurred significantly more often in immediate vicinity to ammonia oxidizers than would be expected from random community assembly while such a relationship was not observed for Nitrospira sublineage II. This spatial distribution suggested a niche differentiation of these coexisting Nitrospira populations with respect to their preferred concentrations of nitrite. This hypothesis was tested by mathematical modelling of nitrite consumption and resulting nitrite gradients in nitrifying biofilms and by quantifying the abundance of sublineage I and II Nitrospira in activated sludge during incubations with nitrite in different concentrations. Consistent with the observed localization patterns, a higher nitrite concentration selected for sublineage I but suppressed sublineage II Nitrospira.

Denitrification of drinking water sources by advanced biological treatment using a membrane bioreactor

Nitrate often contaminates groundwater resources due to excessive use of fertilizers and uncontrolled on-land discharges of raw and treated wastewater and can therefore limit the direct use of groundwater for drinking water purposes. In order to investigate the possible application of a membrane bioreactor (MBR) for denitrification of groundwater, the performance of a pilot-scale MBR was tested as a function of hydraulic and biological parameters. For this purpose synthetic groundwater was prepared by taking lake water (Lago Maggiore, Italy) and adding known amounts of ethanol and sodium nitrate to study the nitrate removal capacity of the sludge, to search for an optimum C/N ratio and to measure filtering ability for micro-organisms through the membrane. The optimum C/N ratio was found at 2.2 gC/gN, resulting in an effluent nitrate concentration within the limits stated in EU Directive 98/83 and the US EPA for drinking water use. The effluent nitrite concentration was one order under the EU limit. The membrane module, Zenon ZW-10, was monitored and performed well except for a short stress episode due to low airflow, afterwards rapidly corrected and thus putting the membrane back to its previous stable behavior. Total bacterial count for the treated effluent was lower than influent water, and 100% removal was observed for both total coliforms and E. coli. Calorimetric thermograms related to heat dissipation due to biological denitrification (nitrate and nitrite consumption) and to substrate adaptation are discussed. A maximum nitrate removal rate close to 20 mgN-NO − 3 gVSS −1h −1 was measured in the calorimetric tests.

Modeling microbial-mediated reduction in batch reactors

The governing equations that depict microbially-mediated reduction of heavy metals in the subsurface include a system of coupled nonlinear partial differential equations (PDE’s) that describe physical (transport), chemical (sorption), and microbial (reduction/oxidation) processes. The existence of nonlinear reaction terms makes numerical simulations more challenging; however, with the advent of time-splitting solution algorithms, nonlinear reaction terms can be isolated from the convective–dispersive components of the governing transport equations and then solved as a coupled system of nonlinear ordinary differential equations (ODE’s). In this paper, four methods are evaluated for solving coupled systems of nonlinear ODE’s that describe microbially-mediated reduction/oxidation processes. The evaluation involves a series of comparisons of transient simulations of electron donor oxidation, electron acceptor reduction, and microbial biomass accumulation. The methods evaluation is initiated with a comparison of simulation results obtained with the four methods to those generated with an analytical model. Next, laboratory observations, of nitrite consumption by Nitrobacter winogradski in batch reactors are used in a comparison of batch system simulations generated using each of the four methods and BIOKEMOD (biogeochemical kinetic/equilibrium reaction model). The evaluation finds one of the four methods, the quasi-steady-state approximation (QSSA), to be among the most accurate and easiest to implement. Final validation of the QSSA is performed simulating experimental results of microbially-mediated chromium reductions in batch cultures.

Pancreatic Cancer and Drinking Water and Dietary Sources of Nitrate and Nitrite

N-Nitroso compounds, known animal carcinogens, are formed endogenously from drinking water and dietary sources of nitrate and nitrite. The authors conducted a population-based case-control study of pancreatic cancer in Iowa to determine whether increased consumption of nitrate and nitrite from drinking water and dietary sources was associated with risk. They linked detailed water source histories to nitrate measurements for Iowa community water supplies. After exclusions for insufficient data, 1,244 controls and 189 pancreatic cancer cases were available for analysis. Among controls, the median average nitrate level (1960-1987) was 1.27 (interquartile range, 0.6-2.8) mg of nitrate nitrogen per liter of water. No association was observed between pancreatic cancer risk and increasing quartiles of the community water supplies' nitrate level. Increasing intake of dietary nitrite from animal sources was associated with an elevated risk of pancreatic cancer among men and women (highest quartile odds ratios = 2.3, 95% confidence interval: 1.1, 5.1, for men and 3.2, 95% confidence interval: 1.6, 6.4, for women). In contrast, dietary nitrate intake showed an inverse association with risk among women and no association among men. This study suggests that long-term exposure to drinking water nitrate at levels below the maximum contaminant level of nitrate nitrogen (10 mg/liter) is not associated with pancreatic cancer; however, the consumption of dietary nitrite from animal products may increase risk.