μM Nitrate Research Articles

P46: Low sodium nitrite (but not nitrate) concentrations attenuate MMP-9 production by endothelial cells

Reduced nitric oxide (NO) bioavailability and imbalanced matrix metalloproteinase (MMP) activity have important roles in the pathogenesis of cardiovascular diseases, and some NO donors were shown to downregulate MMP expression in some cell types. However, while nitrite and nitrate can be recycled back to NO by non enzymatic and enzymatic mechanisms as an alternative to NO formation from l -arginine, no previous study has examined whether sodium nitrite can downregulate stimulated MMP release by endothelial cells. We examined the effect of sodium nitrite and sodium nitrate on MMP-9 production by endothelial cells. Human umbilical vein endothelial cells were cultured in a modified DMEM (iron(III) nitrate is replaced by iron(III) sulfate) and treated for 24 h with 10 nM phorbol myristate acetate (PMA; a MMP-9 inducer) and sodium nitrite or sodium nitrate, or their vehicles. Conditioned medium were analyzed by gelatin zimography to assess MMP-9 activity. PMA increased MMP-9 activity from 0.02 ± 0.01 arbitrary units (AU) to 1.14 ± 0.34 AU ( P < 0.05). While low nitrite concentrations (0.2 or 2 μM) attenuated the increases in MMP-9 activity induced by PMA (0.77 ± 0.12 AU or 0.71 ± 0.14 AU, respectively; both P < 0.05 vs. PMA), high nitrite concentrations (10 or 20 μM) had no effects on PMA-induced increases in MMP-9 activity (0.88 ± 0.14 AU or 1.18 ± 0.36 AU, respectively; both P > 0.05 vs. PMA). Both low (10 or 100 μM) or high (200 or 400 μM) nitrate concentrations had no effects on PMA-induced increases in MMP-9 activity PMA ( P > 0.05 vs. PMA). Our results suggest that low nitrite (but not nitrate) concentrations attenuate MMP-9 production by endothelial cells. FAPESP, CNPq, FAEPA. Nothing to disclose.

Використання сульфату і нітрату сульфатвідновлювальними бактеріями Desulfomicrobium sp. CrR3 за наявності біхромату в середовищі

The usage of sodium sulfate and sodium nitrate in the presence of potassium biсhromate in the medium by sulfate-reducing bacteria Desulfomicrobium sp. CrR3 was studied. It was shown that 5 mM of nitrate, 5 mM of sulfate and 0.5 mM of bichromate were optimal conditions for the bacterial growth. The nitrate in concentration of 5 mM provides better growth of microorganisms than 5 mM sulfate. An increase of sulfate and nitrate concentrations to 15 mM and bichromate to 1 mM led to slower bacterial growth. In the presence of biсhromate and sulfate in the medium, the chromium was used first, herewith utilisation of sulfate was inhibited. Influence of bichromate on sulfate reduction depends on bichromate concentration in the medium. It was found that sulfate reduction and hydrogen sulfide formation in the presence of bichromate started after usage of bichromate. The presence of nitrate and bichromate in the medium led to the inhibition of Desulfomicrobium sp. CrR3 growth and nitrate reduction, compared to the bacteria growth and nitrate reduction in the medium that contains nitrate only. Keywords: sulfate-reducing bacteria, sulfate reduction, bichromate, nitrate, sulfate.

Lab-on-Chip Measurement of Nitrate and Nitrite for In Situ Analysis of Natural Waters

Microfluidic technology permits the miniaturization of chemical analytical methods that are traditionally undertaken using benchtop equipment in the laboratory environment. When applied to environmental monitoring, these "lab-on-chip" systems could allow high-performance chemical analysis methods to be performed in situ over distributed sensor networks with large numbers of measurement nodes. Here we present the first of a new generation of microfluidic chemical analysis systems with sufficient analytical performance and robustness for deployment in natural waters. The system detects nitrate and nitrite (up to 350 μM, 21.7 mg/L as NO(3)(-)) with a limit of detection (LOD) of 0.025 μM for nitrate (0.0016 mg/L as NO(3)(-)) and 0.02 μM for nitrite (0.00092 mg/L as NO(2)(-)). This performance is suitable for almost all natural waters (apart from the oligotrophic open ocean), and the device was deployed in an estuarine environment (Southampton Water) to monitor nitrate+nitrite concentrations in waters of varying salinity. The system was able to track changes in the nitrate-salinity relationship of estuarine waters due to increased river flow after a period of high rainfall. Laboratory characterization and deployment data are presented, demonstrating the ability of the system to acquire data with high temporal resolution.

Potential Use of Nitrate Reductase as a Biomarker for the Identification of Active and Dormant Inhibitors of Mycobacterium tuberculosis in a THP1 Infection Model

The development of a macrophage-based, antitubercular high-throughput screening system could expedite discovery programs for identifying novel inhibitors. In this study, the kinetics of nitrate reduction (NR) by Mycobacterium tuberculosis during growth in Thp1 macrophages was found to be almost parallel to viable bacilli count. NR in the culture medium containing 50 mM of nitrate was found to be optimum on the fifth day after infection with M. tuberculosis. The signal-to-noise (S/N) ratio and Z-factor obtained from this macrophage-based assay were 5.4 and 0.965, respectively, which confirms the robustness of the assay protocol. The protocol was further validated by using standard antitubercular inhibitors such as rifampicin, isoniazid, streptomycin, ethambutol, and pyrazinamide, added at their IC90 value, on the day of infection. These inhibitors were not able to kill the bacilli when added to the culture on the fifth day after infection. Interestingly, pentachlorophenol and rifampicin killed the bacilli immediately after addition on the fifth day of infection. Altogether, this assay protocol using M. tuberculosis–infected Thp-1 macrophages provides a novel, cost-efficient, robust, and easy-to-perform screening platform for the identification of both active and hypoxic stage-specific inhibitors against tuberculosis.

A Simple and High Resolution Ion-Pair HPLC Method for Separation and Simultaneous Determination of Nitrate and Thiocyanate in Different Water Samples

An ion-pair reversed-phase high-performance liquid chromatography method with isocratic elution and ultraviolet detection was developed and validated for the separation and simultaneous determination of nitrate and thiocyanate. The separation was performed on a C18 analytical column with mobile phase containing 0.08 mM hexadecyltrimethylammonium bromide as an ion-pair reagent, 40 mM of acetate buffer and 30% methanol at pH 3.2. The detection was monitored at 206 nm. The response was linear from 1 to 10 mM for nitrate, with a detection limit of 0.05 mM, and 1 to 10 mM for thiocyanate, with a detection limit of 0.31 mM. Calibration curves were found to be linear in these concentration ranges with correlation coefficient better than 0.99.

Size distribution and chemical composition of secondary organic aerosol formed from Cl-initiated oxidation of toluene

Secondary organic aerosol (SOA) formed from Cl-initiated oxidation of toluene was investigated in a home-made smog chamber. The size distribution and chemical composition of SOA particles were measured using aerodynamic particle sizer spectrometer and the aerosol laser time-of-flight mass spectrometer (ALTOFMS), respectively. According to a large number of single aerosol diameter and mass spectra, the size distribution and chemical composition of SOA were obtained statistically. Experimental results showed that SOA particles created by Cl-initiated oxidation of toluene is predominantly in the form of fine particles, which have diameters less than 2.5 μm (i.e., PM2.5), and glyoxal, benzaldehyde, benzyl alcohol, benzoquinone, benzoic acid, benzyl hydroperoxide and benzyl methyl nitrate are the major products components in the SOA. The possible reaction mechanisms leading to these products are also proposed.

Growth characteristics of two bloom-forming synurophytes (Mallomonas elongata and Synura petersenii) at different nitrate and phosphate concentrations

Two dominant planktonic bloom-forming algal species in a small shallow eutrophic pond were identified as Mallomonas elongata and Synura petersenii by electron microscopy. Their growth requirements were investigated as uni-algal cultures in a laboratory study. The maximum population growth and maximum growth rate of M. elongata occurred at concentrations of 24 μM nitrate (NO3) and 5 μM phosphate (PO4) at a temperature of 15°C and a pH of 6. Synura petersenii grew maximally and exhibited the highest growth rate at a NO3 concentration of 24 μM and a PO4 concentration of 2 μM. Mallomonas elongata and S. petersenii had similar nutrient requirements for optimum growth, suggesting that the biomass of these two species can be controlled by nutrient gradients.

Assessment of the Nitrogen and Potassium Fertilizer in Green Bean Irrigated with Disinfected Urban Wastewater

Green bean Helda in autumn cycle (118 days) was grown under greenhouse conditions in sand-mulched sandy loam soil. The crop was irrigated with disinfected urban wastewater (DUW) obtained from ozone from the Almería Purifying Plant. The average nutrient parameters of DUW were 0.4 mM of nitrate (NO3 −), 2.1 mM of ammonium (NH4 +), 0.8 mM of potassium (K+), and electrical conductivity (EC) 1.6 dS m−1. Three different treatments were established: DUW without additional fertilization (FDUW), DUW with fertilization until the recommended rate was obtained (10.0 mM of N and 3.4 mM of K) (FNK), and DUW with fertilization until 1.5 FNK rate (15.0 mM of N and 5.1 mM of K) (F1.5NK) was obtained. The dry-matter production was not conditioned by the fertilizer level. Treatments FNK and F1.5NK showed the greatest yield and uptake of N and K independent of the fertilizer level. The most nitrogen (N), calcium (Ca), and magnesium (Mg) were in the leaf, phosphorus (P) was high in fruit, and K was similar in leaf and fruit. With regard to the macronutrient absorption efficiency, the F1.5NK treatment showed the least N and K efficiency and the greatest soil salinity.

Bioremediation potential of Chondrus crispus (Basin Head) and Palmaria palmata: effect of temperature and high nitrate on nutrient removal

To evaluate the nutrient removal capabilities of two red macroalgae, apical blades were cultured in the lab for 4 weeks at either 6, 10, or 17°C and nitrate at either 30 or 300 μM, typical of the seasonal range of conditions at a land-based Atlantic halibut farm. Stocking density was 2.0 g L−1, irradiance 125 μmol photons m−2 s−1, photoperiod 16:8 (L:D), and nitrogen to phosphorus ratio 10:1. For both species, the highest growth rate was at 300 μM NO3− with Palmaria palmata growing fastest at 6°C, 5.8% day−1, and Chondrus crispus growing best at 17°C, 5.5% day−1. Nitrogen and carbon removal by P. palmata was inversely related to temperature, the highest rate at 6°C and 300 μM NO3− of 0.47 mg N and 6.3 mg C per gram dry weight per day. In contrast, C. crispus removal of N was independent of temperature, with mean removal of 0.49 mgN gDW−1 day−1 at 300 μM NO3−. The highest carbon removal by C. crispus was 4.4 mgC gDW−1 day−1 at 10°C and 300 μM nitrate, though not significantly different from either 6 or 17°C and 300 μM nitrate. Tissue carbon:nitrogen ratios were >20 in both species at 30 μM nitrate, and all temperatures indicating nitrogen limitation in these treatments. Phycoerythrin content of P. palmata was independent of temperature, with means of 23.6 mg gFW−1 at 300 μM nitrate. In C. crispus, phycoerythrin was different only between 6°C and 17°C at 300 μM nitrate, with the highest phycoerythrin content of 12.6 mg gFW−1 at 17°C. Morphological changes were observed in P. palmata at high NO3− concentration as curling of the fronds, whilst C. crispus exhibited the formation of bladelets as an effect of high temperature.

Contrasting denitrifier communities relate to contrasting N2O emission patterns from acidic peat soils in arctic tundra

Cryoturbated peat circles (that is, bare surface soil mixed by frost action; pH 3-4) in the Russian discontinuous permafrost tundra are nitrate-rich 'hotspots' of nitrous oxide (N(2)O) emissions in arctic ecosystems, whereas adjacent unturbated peat areas are not. N(2)O was produced and subsequently consumed at pH 4 in unsupplemented anoxic microcosms with cryoturbated but not in those with unturbated peat soil. Nitrate, nitrite and acetylene stimulated net N(2)O production of both soils in anoxic microcosms, indicating denitrification as the source of N(2)O. Up to 500 and 10 μM nitrate stimulated denitrification in cryoturbated and unturbated peat soils, respectively. Apparent maximal reaction velocities of nitrite-dependent denitrification were 28 and 18 nmol N(2)O g(DW)(-1) h(-1), for cryoturbated and unturbated peat soils, respectively. Barcoded amplicon pyrosequencing of narG, nirK/nirS and nosZ (encoding nitrate, nitrite and N(2)O reductases, respectively) yielded ≈49 000 quality-filtered sequences with an average sequence length of 444 bp. Up to 19 species-level operational taxonomic units were detected per soil and gene, many of which were distantly related to cultured denitrifiers or environmental sequences. Denitrification-associated gene diversity in cryoturbated and in unturbated peat soils differed. Quantitative PCR (inhibition-corrected per DNA extract) revealed higher copy numbers of narG in cryoturbated than in unturbated peat soil. Copy numbers of nirS were up to 1000 × higher than those of nirK in both soils, and nirS nirK(-1) copy number ratios in cryoturbated and unturbated peat soils differed. The collective data indicate that the contrasting N(2)O emission patterns of cryoturbated and unturbated peat soils are associated with contrasting denitrifier communities.

Quasi-Lagrangian drifter studies of iron speciation and cycling off Point Conception, California

The distribution and speciation of dissolved Fe (dFe) were measured during four quasi-Lagrangian drogued drifter studies (~ 4 d duration each) that were conducted in the southern California Current System in May 2006 and April 2007. Three of the four drifter studies were within the coastal upwelling regime and one drifter study was in a warm-core anticyclonic eddy. Incubation bottle experiments were also conducted to determine the degree of phytoplankton Fe limitation and to assess changes in the concentration of Fe-binding ligands. In the coastal upwelling drifter studies, in situ dFe (1.4–1.8 nM) and macronutrients were initially high and declined over time. Fe addition incubation experiments indicated that the phytoplankton community was not Fe limited at the beginning of the coastal upwelling drifter experiments (when μM nitrate:nM dFe ratios were ~ 7–8). By the end of two of the three drifter studies (when μM nitrate:nM dFe ratios were ~ 12–19), Fe addition resulted in larger nitrate and silicic acid drawdown, and larger accumulations in chlorophyll a, particulate organic carbon and nitrogen, and diatom and dinoflagellate-specific carotenoid pigments. Fe speciation was measured in situ in three of the four drifter studies with stronger L 1-type ligands found to be present in excess of dFe in all samples. In Fe speciation incubation experiments, L 1-type ligand production was observed in conjunction with phytoplankton growth under Fe-limiting conditions. The results presented here support and add a quasi-Lagrangian perspective to previous observations of dFe and macronutrient cycling over space and time within the California coastal upwelling regime, including Fe limitation within the phytoplankton community in this region and the biological production of Fe-binding ligands concomitant with Fe limitation.

Electrochemical Conversion of Copper‐Based Hierarchical Micro/Nanostructures to Copper Metal Nanoparticles and Their Testing in Nitrate Sensing

AbstractMetallic copper nanoparticles (CuNP) are formed from the reduction of hierarchical copper‐based micro/nanostructures previously electrodeposited on polypyrrole‐polystyrene sulfonate (PPy‐PSS) thin films. The application of a high reduction potential causes the erosion of the micro/nanostructures nanosheets and the formation of CuNP. The CuNP are used in a series of preliminary tests in order to assess their performance in the sensing of nitrate. The sensing performance is improved with the introduction of polyethyleneimine‐functionalized multiwall carbon nanotubes (MWNT‐PEI) to the PPy‐PSS films. Electrochemical impedance spectroscopy studies show that the nanotubes increased the electronic conductivity of the reduced films. The limit of detection of the PPy‐PSS‐MWNT‐PEI‐CuNP nanocomposite is 30 µM nitrate. The materials need further development and optimization work in order to be applied as sensors.

Importance of groundwater and macrophytes for the nutrient balance at oligotrophic Lake Hampen, Denmark

ABSTRACTAn ecohydrological study was carried out at an oligotrophic seepage lake, Lake Hampen, Denmark, to determine the seepage in and out of the lake and determine the mass budgets for nutrients. The lake is primarily surrounded by forest, although there are agricultural fields bordering a small portion of the lake perimeter. The water and mass balances indicate that there is a groundwater input of 1643 × 103 m3 year−1 into the lake (∼70% of total input) and a groundwater output of 1997 × 103 m3 year−1. The groundwater input carries with it 2253 kg N year−1 (∼67% of total input) and 40 kg P year−1 (∼85% of total input). The majority of the nitrogen is leached from the agricultural fields bordering the lake. Concentrations as high as 1750 µM nitrate were measured in the rhizosphere of the littoral zone at this location. It is estimated that the macrophytes are able to take up 1695 kg N year−1 (∼50% of the input). The phosphorus uptake by plants was 310% of the input, indicating that plants are highly dependent on accumulated and remineralized phosphorus in the lake. The nutrients lost through recharge was much lower than input through groundwater discharge entailing a high retention of nutrients in the lake (92–96%). A significant part of the retained nitrogen may be lost through denitrification. Although the plant uptake may have slowed the eutrophication of the lake, the excess nutrients may over time give rise to eutrophication and a shift towards pelagic production. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Effect of nutrient enrichment on naturally occurring macroalgal species in six cave pools in Bermuda

Maloney B., Iliffe T.M., Gelwick F. and Quigg A. 2011. Effect of nutrient enrichment on naturally occurring macroalgal species in six cave pools in Bermuda. Phycologia 50: 132–143. DOI: 10.2216/09-83.1Bermuda has one of the highest concentrations of cave systems of any country in the world. As the island's resident human population and tourism expand, its unique subterranean habitats are becoming increasingly threatened by development and eutrophication. The response to nutrient enrichment of six macroalgal species found in Bermuda's anchialine cave pools (landlocked body with a subterranean connection to the ocean) was examined during summer of 2007. We used a combination of nutrient bioassays, productivity measurements, and water quality analysis. Ulva sp. (Chlorophyta) responded similarly across all nutrient treatments (+N as 30 µM nitrate, +P as 2 µM phosphate, and +NP as 30 µM nitrate + 2 µM phosphate) at Calabash, which had dissolved inorganic N (DIN):soluble reactive P (SRP) ratios of 13–16, whereas at Harbour Pool, Ulva sp. responded best to the +N addition alone. The latter was consistent with very low DIN:SRP (5.8) ratios indicative of potential N limitation in this pool. P limitation was only detected in nutrient assays conducted with Caulerpa mexicana (Chlorophyta) collected from Cliff Pool, which had DIN:SRP ratios of 110. Halymenia floresia (Rhodophyta) was found to be light rather than nutrient limited in the Emerald cave pool. In some combinations of cave pools (e.g. Grenadier and Deep Blue) and for some macroalgae [e.g. Caulerpa racemosa (Chlorophyta), Caulerpia sertularioides (Chlorophyta), and Cryptonemia sp. (Rhodophyta)], findings were not easily characterized with measured parameters. Our findings illustrate the importance of evaluating individual cave pools as well as individual macroalgal species in each cave pool. Of the six macroalgae examined, Ulva sp. and H. floresia showed the greatest potential as bioindicators for groundwater quality in Bermudian caves.

Rapid Method for Simultaneous Determination of Nitrite and Nitrate in Water Samples Using Short-Column Ion-Pair Chromatographic Separation, Photochemical Reaction, and Chemiluminescence Detection

A rapid method has been developed for the simultaneous determination of nitrite and nitrate. The separation of nitrite and nitrate was achieved using an octadecylsilane (ODS) short column (5 µm, 20 × 4.6 mm) with 10 mM of borate buffer-methanol (99.5:0.5, v/v; pH 10.0), containing 5 mM of lauryltrimethylammonium chloride and 50 mM of NaBr. These ions were detected by luminol chemiluminescence following online UV irradiation. The calibration curves of nitrite and nitrate were linear in the range of 1.0 × 10(-7) to 2.0 × 10(-5) M and 1.0 × 10(-6) to 2.0 × 10(-4) M, respectively. The detection limits for nitrite and nitrate were 0.05 and 0.4 µM, respectively (with a signal-to-noise ratio of 3). The precisions of peak heights for 7 identical injections of a standard mixture of 0.50 µM of nitrite and 5.0 µM of nitrate were 2.7 and 2.1%, respectively. Analysis time per sample was less than 2 min, and system pressure was low (2.1 MPa). The proposed method was successfully applied to water samples from various sources.

A suite of sensitive chemical methods to determine the δ15N of ammonium, nitrate and total dissolved N in soil extracts

Natural (15) N abundances (δ(15) N values) of different soil nitrogen pools deliver crucial information on the soil N cycle for the analysis of biogeochemical processes. Here we report on a complete suite of methods for sensitive δ(15) N analysis in soil extracts. A combined chemical reaction of vanadium(III) chloride (VCl(3) ) and sodium azide under acidic conditions is used to convert nitrate into N(2) O, which is subsequently analyzed by purge-and-trap isotope ratio mass spectrometry (PTIRMS) with a cryo-focusing unit. Coupled with preparation steps (microdiffusion for collection of ammonium, alkaline persulfate oxidation to convert total dissolved N (TDN) or ammonium into nitrate) this allows the determination of the δ(15) N values of nitrate, ammonium and total dissolved N (dissolved organic N, microbial biomass N) in soil extracts with the same basic protocol. The limits of quantification for δ(15) N analysis with a precision of 0.5‰ were 12.4 µM for ammonium, 23.7 µM for TDN, 16.5 µM for nitrate and 22.7 µM for nitrite.

Simultaneous electrochemical determination of nitrate and nitrite in aqueous solution using Ag-doped zeolite-expanded graphite-epoxy electrode

In this work a new electrochemical sensor based on an Ag-doped zeolite-expanded graphite-epoxy composite electrode (AgZEGE) was evaluated as a novel alternative for the simultaneous quantitative determination of nitrate and nitrite in aqueous solutions. Cyclic voltammetry was used to characterize the electrochemical behavior of the electrode in the presence of individual or mixtures of nitrate and nitrite anions in 0.1 M Na 2SO 4 supporting electrolyte. Linear dependences of current versus nitrate and nitrite concentrations were obtained for the concentration ranges of 1–10 mM for nitrate and 0.1–1 mM for nitrite using cyclic voltammetry (CV), chronoamperometry (CA), and multiple-pulsed amperometry (MPA) procedures. The comparative assessment of the electrochemical behavior of the individual anions and mixtures of anions on this modified electrode allowed determining the working conditions for the simultaneous detection of the nitrite and nitrate anions. Applying MPA allowed enhancement of the sensitivity for direct and indirect nitrate detection and also for nitrite detection. The proposed sensor was applied in tap water samples spiked with known nitrate and nitrite concentrations and the results were in agreement with those obtained by a comparative spectrophotometric method. This work demonstrates that using multiple-pulse amperometry with the Ag-doped zeolite-expanded graphite-epoxy composite electrode provides a real opportunity for the simultaneous detection of nitrite and nitrate in aqueous solutions.

CARBOHYDRATE RELEASE BY A SUBTROPICAL STRAIN OF SPONDYLOSIUM PYGMAEUM (ZYGNEMATOPHYCEAE): INFLUENCE OF NITRATE AVAILABILITY AND CULTURE AGING1

This paper describes the influence of nitrate availability on growth and release of dissolved free and combined carbohydrates (DFCHOs and DCCHOs) produced by Spondylosium pygmaeum (Cooke) W. West (Zygnematophyceae). This strain was isolated from a subtropical shallow pond, located at the extreme south of Brazil (Rio Grande, RS). Experiments were carried out in batch culture, comparing two initial nitrate levels (10/100 μM) in the medium. Growth was monitored by direct microscopic cell counts and chl a content. Nitrate consumption was determined by ion chromatography, while the production of extracellular carbohydrates was monitored by the phenol‐sulfuric method. The monosaccharide compositions of DFCHOs and DCCHOs were determined in each growth phase by HPLC with pulse amperometric detection (HPLC‐PAD). At the end of the experiment, the total composition of extracellular polysaccharide (EPS) molecules &gt;12 kDa was determined by gas chromatography. Nitrate availability had no influence on S. pygmaeum cell density at any phase. On the other hand, chl a content decreased after a few days growth when the availability of nitrate was restricted, but continued to rise when nitrate was plentiful. Also, nitrate depletion was faster at 10 μM nitrate. No influence of the growth phase or nitrate availability on the total carbohydrates (TDCHOs) released per cell was observed. Only DCCHOs were released by S. pygmaeum, and the composition varied between growth phases, especially at lower nitrate availability. EPS molecules &gt;12 kDa were composed mainly of xylose, fucose, and galactose, as for other desmids. However, a high N‐acetyl‐glucosamine content was found, uniquely among desmid EPSs.

Effect of nutrients and light intensity on growth of Mallomonascaudata (Synurophyceae)

We used batch cultures of three strains of the unicellular synurophyte Mallomonascaudata to investigate the effects of nitrate, phosphate, silicate and light intensity on population growth and growth rate. The three strains were isolated from three different reservoirs in Kyungpook Province, Korea. For all three strains, we observed high population growth under all nutrient concentrations studied, except at nitrate concentration below 0.8 μM. The maximum growth rate (μmax) occurred at 8.2 μM or 16.5 μM nitrate, depending on the strain, and at 11.5 μM phosphate. Silicate concentration had no effect on growth rate. With respect to light intensity, the maximum population growth and maximum growth rates (μmax) occured between 42 and 104 μmol m−2 s−1 depending on strain and culture temperature. Population growth of these three strains under batch culture occurred over a wide range of nutrient and light intensities, but there seemed to be strain‐specific differences that may represent adaptations to local environments.

Dietary nitrate supplementation reduces the O2cost of low-intensity exercise and enhances tolerance to high-intensity exercise in humans

Pharmacological sodium nitrate supplementation has been reported to reduce the O2 cost of submaximal exercise in humans. In this study, we hypothesized that dietary supplementation with inorganic nitrate in the form of beetroot juice (BR) would reduce the O2 cost of submaximal exercise and enhance the tolerance to high-intensity exercise. In a double-blind, placebo (PL)-controlled, crossover study, eight men (aged 19-38 yr) consumed 500 ml/day of either BR (containing 11.2 +/- 0.6 mM of nitrate) or blackcurrant cordial (as a PL, with negligible nitrate content) for 6 consecutive days and completed a series of "step" moderate-intensity and severe-intensity exercise tests on the last 3 days. On days 4-6, plasma nitrite concentration was significantly greater following dietary nitrate supplementation compared with PL (BR: 273 +/- 44 vs. PL: 140 +/- 50 nM; P < 0.05), and systolic blood pressure was significantly reduced (BR: 124 +/- 2 vs. PL: 132 +/- 5 mmHg; P < 0.01). During moderate exercise, nitrate supplementation reduced muscle fractional O2 extraction (as estimated using near-infrared spectroscopy). The gain of the increase in pulmonary O2 uptake following the onset of moderate exercise was reduced by 19% in the BR condition (BR: 8.6 +/- 0.7 vs. PL: 10.8 +/- 1.6 ml.min(-1).W(-1); P < 0.05). During severe exercise, the O2 uptake slow component was reduced (BR: 0.57 +/- 0.20 vs. PL: 0.74 +/- 0.24 l/min; P < 0.05), and the time-to-exhaustion was extended (BR: 675 +/- 203 vs. PL: 583 +/- 145 s; P < 0.05). The reduced O2 cost of exercise following increased dietary nitrate intake has important implications for our understanding of the factors that regulate mitochondrial respiration and muscle contractile energetics in humans.