Electron-acceptor loadings affect chloroform dechlorination in a hydrogen-based membrane biofilm reactor

Chloroform (CF) can undergo reductive dechlorination to dichloromethane, chloromethane, and methane. However, competition for hydrogen (H₂), the electron-donor substrate, may cause poor dechlorination when multiple electron acceptors are present. Common acceptors in anaerobic environments are nitrate (NO₃⁻), sulfate (SO₄²⁻), and bicarbonate (HCO₃⁻). We evaluated CF dechlorination in the presence of HCO₃⁻ at 1.56 e⁻ Eq/m²-day, then NO₃⁻ at 0.04–0.15 e⁻ Eq/m²-day, and finally NO₃⁻ (0.04 e⁻ Eq/m²-day) along with SO₄²⁻ at 0.33 e⁻ Eq/m²-day in an H₂-based membrane biofilm reactor (MBfR). When the biofilm was initiated with CF-dechlorination conditions (no NO₃⁻ or SO₄²⁻), it yielded a CF flux of 0.14 e⁻ Eq/m²-day and acetate production via homoacetogenesis up to 0.26 e⁻ eq/m²-day. Subsequent addition of NO₃⁻ at 0.05 e⁻ Eq/m²-day maintained full CF dechlorination and homoacetogenesis, but NO₃⁻ input at 0.15 e⁻ Eq/m²-day caused CF to remain in the reactor's effluent and led to negligible acetate production. The addition of SO₄²⁻ did not affect CF reduction, but SO₄²⁻ reduction significantly altered the microbial community by introducing sulfate-reducing Desulfovibrio and more sulfur-oxidizing Arcobacter. Dechloromonas appeared to carry out CF dechlorination and denitrification, whereas Acetobacterium (homoacetogen) may have been involved with hydrolytic dechlorination. Modifications to the electron acceptors fed to the MBfR caused the microbial community to undergo changes in structure that reflected changes in the removal fluxes.     

Novel gaseous polyatomic binary and ternary lanthanide oxides

A variety of novel gaseous polyatomic binary and ternary oxides were observed at ambient temperature arising from lanthanide (Ln) nitrate Schiff base complexes, simple salts and sesquioxides, in an FAB mass spectrometer. The new binary oxides (as singly positive ions) detected are Ln₂O₃, Ln₃O₃, Ln₃O₄, Ln₄O₄, Ln₄O₅, Ln₄O₆, Ln₅O₆, Ln₅O₇, Ln₅O₈, Ln₆O₈, Ln₆O₉, Ln₇O₁₀, Ln₈O₁₁, Ln₈O₁₂ and Ln₉O₁₃; the ternary gaseous oxides are CeEuO₂, CeEu₂O₃ and Ce₂EuO₄, LaYbO₂, La₂YbO₄ and LaYb₂O₄; NdHoO₃, Nd₂HoO₄, and NdHo₂O₄; YTmO₃; Y_xTm_3−xO₄, x=1−2; Y_xTm_4−xO₆, x=1−3; Y_xTm_5−xO₇, x=1−4; Y_xTm_6−xO₉, x=1−5. Some of these oxides show the lanthanide cations in unusual oxidation states. Gadolinium-gallium ternary oxides, GdGaO₂, GdGaO₃ and Gd₂GaO₄ were also detected. The FAB MS environment is significantly reducing, yielding a homologous series Eu_nO_n where Eu²⁺ is dominant (E°(Eu³⁺/Eu²⁺)=−0.35 V) and no gallium or indium oxides (E°(M³⁺/M°=−0.34 V (In), −0.53 V (Ga)) were formed. The stoichiometry of the polylanthanide ternary oxides formed is determined largely by the chemistry of the major metallic component. The gaseous polyatomic oxides are probably formed through a reductive condensation process involving primary species Ln⁺ and LnO⁺ formed when the rare earth compounds are struck by fast Xe atoms. The demonstrated possibility of double component oxide formation broadens the number and types of gaseous lanthanide oxides which are accessible.     

The high-affinity binding site for manganese on the oxidizing side of Photosystem II

Electron donation to Photosystem II (PS II) by diphenylcarbazide (DPC) is interrupted by the presence of endogenous Mn in PS II particles. Removal of this Mn by Tris treatment greatly stimulates the electron transport with DPC as donor. Binding of low concentration of exogenous Mn(II) to Tris-treated PS II particles inhibits DPC photooxidation competitively with DPC. This phenomenon was used to locate a highly specific Mn(II) binding site on the oxidizing side of Photosystem II with dissociation constant about 0.15 μM. The binding of Mn(II) is electrostatic in nature. Its affinity depends not only on the ionic strength, but also on the anion species of the salt in the medium. The effectiveness in decreasing the affinity follows the order F⁻ > SO²⁻₄ > CH₃COO⁻ > CI⁻ > Br⁻ > NO₃⁻. This observation is interpreted as follows: smaller ions, like F⁻, CH₃COO⁻, and larger ions, like SO²⁻₄, have inhibitory effects on Mn(II) binding, whereas ions with optimal size, like Cl⁻, Br⁻ and NO₃⁻, can stabilize the binding, resembling the anion requirement for reactivation of Cl⁻-depleted chloroplasts. We suggest that the binding site for Mn(II) we observed is the site for the endogenous Mn in the O₂-evolving complex of PS II. This site remains after Tris treatment, which removes all the endogenous Mn as well as the three extrinsic proteins, indicating that it is on the intrinsic component(s) of PS II reaction centers. Furthermore, the Cl⁻ requirement for O₂ evolution may be attributed, at least partly to its stabilizing effect on Mn binding.     

The significance of stemflow chemistry for epiphytic lichen diversity in a dieback-affected spruce forest on Mt Brocken,northern Germany

Epiphytic lichen diversity in a boggy stand of Norway spruce (Picea abies) was studied in the eastern Harz Mountains, northern Germany. Spruce trees at wet sites were affected by forest dieback, whereas trees on drier sites remained unaffected. Lichen diversity was higher on dieback-affected trees than on healthy ones. The foliose lichen Hypogymnia physodes was significantly more frequent on dead trees, whereas the crustose, extremely toxitolerant Lecanora conizaeoides occurred more frequently on healthy trees. Stemflow concentrations of NH₄⁺, NO₃⁻, PO₃⁻, and SO₄²⁻ were lower on affected trees. This is attributed to reduced interception from the atmosphere due to needle loss. Cover of H. physodes decreased with increasing mean SO₄²⁻ concentration in stemflow. The total of lichen species per sample tree also decreased with increasing SO₄²⁻ concentration in stemflow, indicating that most species reacted in a similar way as H. physodes. Cover of L. conizaeoides increased with increasing SO₄²⁻ concentration, but decreased at higher SO₄²⁻ concentrations. Bark chemistry had a minor influence on lichen diversity.     

An integrated network analysis reveals that nitric oxide reductase prevents metabolic cycling of nitric oxide by Pseudomonas aeruginosa

Nitric oxide (NO) is a chemical weapon within the arsenal of immune cells, but is also generated endogenously by different bacteria. Pseudomonas aeruginosa are pathogens that contain an NO-generating nitrite (NO₂⁻) reductase (NirS), and NO has been shown to influence their virulence. Interestingly, P. aeruginosa also contain NO dioxygenase (Fhp) and nitrate (NO₃⁻) reductases, which together with NirS provide the potential for NO to be metabolically cycled (NO→NO₃⁻→NO₂⁻→NO). Deeper understanding of NO metabolism in P. aeruginosa will increase knowledge of its pathogenesis, and computational models have proven to be useful tools for the quantitative dissection of NO biochemical networks. Here we developed such a model for P. aeruginosa and confirmed its predictive accuracy with measurements of NO, O₂, NO₂⁻, and NO₃⁻ in mutant cultures devoid of Fhp or NorCB (NO reductase) activity. Using the model, we assessed whether NO was metabolically cycled in aerobic P. aeruginosa cultures. Calculated fluxes indicated a bottleneck at NO₃⁻, which was relieved upon O₂ depletion. As cell growth depleted dissolved O₂ levels, NO₃⁻ was converted to NO₂⁻ at near-stoichiometric levels, whereas NO₂⁻ consumption did not coincide with NO or NO₃⁻ accumulation. Assimilatory NO₂⁻ reductase (NirBD) or NorCB activity could have prevented NO cycling, and experiments with ΔnirB, ΔnirS, and ΔnorC showed that NorCB was responsible for loss of flux from the cycle. Collectively, this work provides a computational tool to analyze NO metabolism in P. aeruginosa, and establishes that P. aeruginosa use NorCB to prevent metabolic cycling of NO.     

Synthesis and spectroscopic studies of platinum(II) complexes of N,N′-dicyclohexylethylenediamine

The platinum(II) complexes of the formula [Pt(DCHEDA)X₂], where DCHEDA is N,N′-dicyclohexylethylenediamine and X⁻ is CL⁻, Br⁻, I⁻, 0.5C₂O₄²⁻ (oxalate), 0.5C₃H₂O₄²⁻ (malonate), 0.5C₉H₄O₆²⁻ (4-carboxyphthalate), 0.5S₂O₃²⁻ or 0.5SO₄²⁻, have been synthesized and characterized by UVVis, IR, and ¹H NMR spectral techniques. All the above complexes are non-electrolytes in DMF/H₂O, except the sulphate complex which becomes a 1:1 electrolyte after incubation for 24 h at 28 °C. The halide complexes were also studied by X-ray photoelectron spectroscopy and these data suggest that there is π-bonding from platinum to halide in these complexes. The oxalate, malonate and sulphate bind in their complexes as bidentate ligands to platinum through two oxygen atoms whereas the thiosulphate in its complex binds as a bidentate ligand to platinum through one oxygen atom and one sulphur atom.     

Isotopic composition and concentration of total nitrogen and nitrate in xylem sap under near steady-state hydroponics

After root uptake, nitrate is effluxed back to the medium, assimilated locally, or translocated to shoots. Rooted black cottonwood (Populus trichocarpa) scions were supplied with a NO₃⁻-based (0.5 mM) nutrient medium of known isotopic composition (δ¹⁵N), and xylem sap was collected by pressure bombing. To establish a sampling protocol, sap was collected from lower and upper stem sections at 0.1–0.2 MPa above the balancing pressure, and after increasing the pressure by a further 0.5 MPa. Xylem sap from upper stem sections was partially diluted at higher pressure. Further analysis was restricted to sap obtained from intact shoots at low pressure. Total-, NO₃⁻-N and, by difference, organic-N concentrations ranged from 6.1–11.0, 1.2–2.4, and 4.6–9.4 mM, while discrimination relative to the nutrient medium was −6.3 to 0.5‰, −23.3 to −11.5‰ and − 1.3 to 4.9‰, respectively. There was diurnal variation in δ¹⁵N of total- and organic-N, but not NO₃⁻. The difference in δ¹⁵N between xylem NO₃⁻ and organic-N suggests that discrimination by nitrate reductase is near 25.1 ± 1.6‰. When this value was used in an isotope mass balance model, the predicted xylem sap NO₃⁻-N to total-N ratio closely matched direct measurement.     

Long distance nitrogen air pollution effects on lichens in Europe

The epiphytic lichen flora of 25 European ICP-IM monitoring sites, all situated in areas remote from air pollution sources, was statistically related to measured levels of SO₂in air, NH₄⁺, NO₃⁻ and SO₄²⁻ in precipitation, annual bulk precipitation, and annual average temperature. Significant regression models were calculated for eleven acidophytic species. Several species show a strong negative correlation with nitrogen compounds. At concentrations as low as 0·3 mg N l⁻¹in precipitation, a decrease of the probability of occurrence is observed for Bryoria capillaris, B. fuscescens, Cetraria pinastri, Imshaugia aleurites and Usnea hirta. The observed pattern of correlations strongly suggests a key role of NH₄⁺ in determining the species occurrence, but an additional role of NO₃⁻ cannot be ruled out. Some species show a distinct response to current levels of SO₂as well. It may be concluded that long distance nitrogen air pollution has strong influence on the occurrence of acidophytic lichen species.     

Blue-light-induced pH changes associated with NO3−, NO2− and Cl− uptake by the green alga Monoraphidium braunii

In M. braunii, the uptake of NO₃⁻ and NO₂⁻ is blue-light-dependent and is associated with alkalinization of the medium. In unbuffered cell suspensions irradiated with red light under a CO₂-free atmosphere, the pH started to rise 10s after the exposure to blue light. When the cellular NO₃⁻ and NO₂⁻ reductases were active, the pH increased to values of around 10, since the NH₄⁺ generated was released to the medium. When the blue light was switched off, the pH stopped increasing within 60 to 90s and remained unchanged under background red illumination. Titration with H₂SO₄ of NO₃⁻ or NO₂⁻ uptake and reduction showed that two protons were consumed for every one NH₄⁺ released. The uptake of Cl⁻ was also triggered by blue light with a similar 10 s time response. However, the Cl⁻ -dependent alkalinization ceased after about 3 min of blue light irradiation. When the blue light was turned off, the pH immediately (15 to 30 s) started to decline to the pre-adjusted value, indicating that the protons (and presumably the Cl⁻) taken up by the cells were released to the medium. When the cells lacked NO₃⁻ and NO₂⁻ reductases, the shape of the alkalinization traces in the presence of NO₃⁻ and NO₂⁻ was similar to that in the presence of Cl⁻, suggesting that NO₃⁻ or NO₂⁻ was also released to the medium. Both the NO₃⁻ and Cl⁻-dependent rates of alkalinization were independent of mono- and divalent cations.     

Trends in cation, nitrogen, sulfate and hydrogen ion concentrations in precipitation in the United States and Europe from 1978 to 2010: a new look at an old problem

Industrial emissions of SO₂ and NO_x, resulting in the formation and deposition of sulfuric and nitric acids, affect the health of both terrestrial and aquatic ecosystems. Since the mid-late 20th century, legislation to control acid rain precursors in both Europe and the US has led to significant declines in both SO₄–S and H⁺ in precipitation and streams. However, several authors noted that declines in streamwater SO₄–S did not result in stoichiometric reductions in stream H⁺, and suggested that observed reductions in base cation inputs in precipitation could lessen the effect of air pollution control on improving stream pH. We examined long-term precipitation chemistry (1978–2010) from nearly 30 sites in the US and Europe that are variably affected by acid deposition and that have a variety of industrial and land-use histories to (1) quantify trends in SO₄–S, H⁺, NH₄–N, Ca, and NO₃–N, (2) assess stoichiometry between H⁺ and SO₄–S before and after 1990, and (3) examine regional synchrony of trends. We expected that although the overall efforts of developed countries to reduce air pollution and acid rain by the mid-late 20th century would tend to synchronize precipitation chemistry among regions, geographically varied patterns of fossil fuel use and pollution control measures would produce important asynchronies among European countries and the United States. We also expected that control of particulate versus gaseous emission, along with trends in NH₃ emissions, would be the two most significant factors affecting the stoichiometry between SO₄–S and H⁺. Relationships among H⁺, SO₄–S, NH₄–N, and cations differed markedly between the US and Europe. Controlling for SO₄–S levels, H⁺ in precipitation was significantly lower in Europe than in the US, because (1) alkaline dust loading from the Sahara/Sahel was greater in Europe than the US, and (2) emission of NH₃, which neutralizes acidity upon conversion to NH₄ ⁺, is generally significantly higher in Europe than in the US. Trends in SO₄–S and H⁺ in precipitation were close to stoichometric in the US throughout the period of record, but not in Europe, especially eastern Europe. Ca in precipitation declined significantly before, but not after 1990 in most of the US, but Ca declined in eastern Europe even after 1990. SO₄–S in precipitation was only weakly related to fossil fuel consumption. The stoichiometry of SO₄–S and H⁺ may be explained in part by emission controls, which varied over time and among regions. Control of particulate emissions reduces alkaline particles that neutralize acid precursors as well as S-containing particulates, reducing SO₄–S and Ca more steeply than H⁺, consistent with trends in the northeastern US and Europe before 1990. In contrast, control of gaseous SO₂ emissions results in a stoichiometric relationship between SO₄–S and H⁺, consistent with trends in the US and many western European countries, especially after 1991. However, in many European countries, declining NH₃ emissions contributed to the lack of stoichiometry between SO₄–S and H⁺.Recent reductions in NO_x emissions have also contributed to declines in H⁺ in precipitation. Future changes in precipitation acidity are likely to depend on multiple factors including trends in NO_x and NH₃ emission controls, naturally occurring dust, and fossil fuel use, with significant implications for the health of both terrestrial and aquatic ecosystems.     

Mechanism of nitrate uptake into Chara corallina cells: lack of evidence for obligatory coupling to proton pump and a new NO3−/NO3− exchange model

Abstract. Nitrate uptake into Chara corallina cells at different external pH (pH_o) after different NO₃⁻ pretreatment conditions has been investigated. Following NO₃⁻ pretreatment (0.2 mol m⁻³ NO₃⁻) there was little effect of pH_o on subsequent net NO₃⁻ uptake into Chara cells. After N deprivation (2 mmol m⁻³ NO₃⁻) there was a pronounced effect of pH_o on nitrate uptake, the maximum rate occurring at pH_o 4.7. There was no consistent relationship between OH⁻ efflux and NO₃⁻ uptake in short term experiments (< 1 h). NO₃⁻ efflux was also sensitive to pH_o, the maximum rate occurring at ∼ pH_o 5.0. An inhibitor of the proton pump, DES, immediately stimulated NO₃⁻ uptake into cells pretreated with NO₃⁻ and prevented the time-dependent decrease in NO₃⁻, uptake into Chara cells that had been previously treated with low N (2 mmol m⁻³ NO₃⁻). NO₃⁻ efflux was found to be very sensitive to DES with K_i= 0.7 mmol m⁻³. At the optimum pH_o for NO₃⁻ uptake the effect of DES on membrane potential (ψ_m) were slight, and only apparent after 30 min. The results are interpreted in context of current models relating NO₃⁻ uptake and H⁺ pump activity. A new model for NO₃⁻ uptake is proposed which involves NO₃⁻/NO₃⁻ exchange at steady state.     

Characterization of a proton pump from pea stem microsomes

Abstract The present work deals with the characterization of an ATP-dependent proton translocation monitored by the ΔpH probe acridine orange. The ATP-dependent proton translocation has an optimum activity at pH 6.5 and is substrate specific for ATP. It is stimulated by Cl⁻, HCO₃⁻ and Br⁻, but is insensitive to several monovalent cations. Divalent cations (Mg²⁺ or Mn²⁺) are required for proton translocation, while in the presence of Ca²⁺ no uptake is observed. NO₃⁻, NO₂⁻ and citrate strongly inhibit proton uptake. On the contrary, F⁻, SO₄²⁻, malate, pyruvate, succinate, oxalate and acetate have no inhibitory effect. Proton uptake is stimulated by valinomycin and unaffected by molybdate. Two thiols, dithioerythritol and dithiothreitol, are able partially to prevent the FCCP-abolished proton uptake or partially restore the ATP-dependent proton translocation in FCCP-collapsed vesicles. It is suggested that pea stem microsomes possess an electrogenic ATPase, acting as a proton pump, which, on the basis of its characteristics, can be tentatively associated with membranes of tonoplast origin.     

Effects of Anions on Swelling, Respiration, and Phosphorylation of Isolated Corn Mitochondria

The effects of a series of anions on swelling, respiration, and oxidative phosphorylation of corn mitochondria were studied. Active mitochondrial swelling similar to that found with HPO₄⁻² was demonstrated in the presence of IO₃⁻, NO₂⁻, MoO₄⁻², SO₄⁻², HAsO₄⁻², acetate, S₂O₃⁻², SeO₄⁻², CrO₄⁻², and WoO₄⁻². In general, those anions which caused active swelling also released respiration and reduced the efficiency of oxidative phosphorylation with exogenous NADH as substrate. The degree of passive swelling in the presence of certain of the monovalent anions was found to approximate the order of the lyotropic series (SCN⁻ > CIO₄⁻ > I⁻ > NO₃⁻ > CI⁻).     

The high affinity of Paracoccus denitrificans cells for nitrate as an electron acceptor. Analysis of possible mechanisms of nitrate and nitrite movement across the plasma membrane and the basis for inhibition by added nitrite of oxidase activity in permeabilised cells

(1) The apparent K_m for nitrate of the electron-transport system in intact cells of Paracoccus denitrificans was less than 5 μM. In contrast the apparent K_m for nitrate of inverted membrane vesicles oxidising NADH was greater than 50 μM. When azide, a competitive inhibitor, was present, the apparent K_m observed with the vesicles was raised to 0.64 mM, consistent with values previously reported for purified preparations of the reductase. In membrane vesicles the nitrate reductase is probably not rate-limiting for NADH-nitrate oxido-reductase activity, and thus a lower limit for K_m (NO₃⁻) is obtained. It is suggested that the very low K_m (NO₃⁻) in intact cells must arise from either a transport process or a nitrate-specific pore that allows access of nitrate directly to the active site of its reductase from the periplasm. (2) The swelling of spheroplasts has been studied under both aerobic and anaerobic conditions to probe possible mechanisms of nitrate and nitrite transport across the plasma membrane of P. denitrificans. Nitrate reductase was inhibited by azide to prevent reduction of internal nitrate. No evidence for operation of either nitrate-nitrite antiport or proton-nitrate symport was obtained. (3) Measurements from the fluorescence intensity of 8-anilino-naphthalene-1-sulphonate of the rates of decay of diffusion potentials generated by addition of potassium salts to valinomycin-treated plasma membrane vesicles from P. denitrificans showed that the permeability of the membrane to anions is SCN⁻ > NO₃⁻, NO₂⁻, pyruvate, acetate > CI⁻ > SO₄²⁻. In the presence of a protonophore the rate of decay of the diffusion potential was considerably enhanced with potassium acetate or potassium nitrite, but not with potassium salts of nitrate, chloride or pyruvate. This result indicates that HNO₂ and CH₃COOH can rapidly and passively diffuse across the cell membrane. This finding suggests that transport systems for nitrite are in general probably not required in bacteria. The failure of a protonophore to enhance the dissipation of the diffusion potential generated by potassium nitrate is evidence against the operation of a proton-nitrate symporter. (4) Low concentrations of added nitrite very strongly inhibit electron flow to oxygen in anaerobically grown cells, provided that they have been treated with Triton X-100 or an uncoupler. This inhibition is not observed with aerobically grown cells. It is concluded that the inhibitory species is a reaction product or an intermediate of the nitrite reductase reaction. The requirement for collapse of protonomotive force by uncoupler or permeabilising the plasma membrane suggests that any such species could be negatively charged. Nitroxyl anion (NO⁻) can be considered, as its conjugate acid is a postulated intermediate between nitrite and nitrous oxide; nitroxyl anion can bind to heme centres to give nitrosyl derivatives. (5) The basis for the ability of permeabilised, but not intact, cells of P. denitrificans to reduce oxygen and nitrate simultaneously is discussed.     

Mechanistic Elucidation of Salicylic Acid and Sulphur-Induced Defence Systems,Nitrogen Metabolism,Photosynthetic, and Growth Potential of Mungbean (Vigna radiata) Under Salt Stress

The potential of plant nutrients (such as sulphur, S) and phytohormones (such as salicylic acid, SA) has been explored in isolated studies by researchers in controlling the impact of abiotic stresses such as salinity in plants. However, information is scanty on the major mechanisms underlying the role of S and/or SA in modulation of enzymes involved in nitrogen (N) assimilation, GOGAT cycle, and antioxidant defence system; the cellular status of N-containing osmolyte proline, glucose, S-containing compounds; and their cumulative role in photosynthesis functions and growth in crop plants. The present study aimed to assess the role of cumulative effect of SA and S (SO₄²⁻) mediated induction of N assimilatory enzymes, GOGAT cycle, N-osmolyte proline and its metabolizing enzymes, glyoxylase enzymes, and antioxidant capacity in mungbean (Vigna radiata L.) exposed to NaCl with or without SO₄²⁻ and SA. Salt-exposed V. radiate showed differential elevations in damage (O^.₂⁻, H₂O₂, lipid peroxidation; glucose) and defence (ascorbate peroxidase, APX; glutathione reductase, GR; superoxide dismutase, SOD; reduced GSH; proline) and inhibitions in the activities of NR and NiR; N content, photosynthesis, photosynthetic N-use-efficiency (NUE), and growth. The separate supplementation of SA and SO₄²⁻ to 50 mM NaCl almost equally strengthened the antioxidant machinery and diminished NaCl-accrued damages. However, combined supply of SA and SO₄²⁻ to NaCl-exposed cultivars led to significant improvements in NR and NiR activities, the accumulation of N, GSH, proline, enhanced activity of APX, GR, and reduced activity of SOD, and also decreases in O^.₂⁻, H₂O₂, lipid peroxidation and glucose. These observations were corroborated with SA, SO₄²⁻ and NaCl-mediated changes in the traits of photosynthesis and growth, stomatal behaviour, and the polypeptide patterns of Rubisco in V. radiata. Overall, in V. radiata, SA-mediated higher enhancements in the activity of N assimilatory enzymes (NR, NiR, and GS), increase in the N and proline, and GSH; and decreases in the contents of Na⁺ and Cl⁻ ions, and glucose (a photosynthesis repressor); maintenance of a fine tuning among SOD, APX, and GR enzymes; and higher minimization of ROS (O^.₂⁻, H₂O₂) and lipid peroxidation finally led to a higher promotion in photosynthesis and growth.

     

Impact of novel coronavirus disease (COVID-19) lockdown on ambient air quality of Saudi Arabia

The outbreak of COVID-19 has spread globally affecting human activities but with improvement in ambient air quality. The first case of the virus in the Kingdom of Saudi Arabia was on the 2nd of March 2020. The impact of COVID-19 lockdown on the ambient air quality of the Kingdom of Saudi Arabia for the first time using data from nine cities was determined in this study. Hourly air quality data, based on concentrations of carbon monoxide (CO), particulate matter (PM₁₀), sulfur dioxide (SO₂), nitrogen dioxide (NO₂) and ozone (O₃), and meteorological conditions (atmospheric temperature, relative humidity, and wind speed) of the nine cities studied were obtained from Saudi Arabian General Authority of Meteorology and Environmental Protection (GAMEP), for the period between January 2019 to May 2020. Significant variation (p < 0.05) was recorded for the five atmospheric pollutants across the cities before and during the lockdown, with lower concentrations during the lockdown except for the concentration of O₃ in Tabuk, Al Qasim, and Haql. This can be a result of NO and O₃ reaction, causing the inability of effective O₃ depletion. The percentage changes in concentrations of CO (33.60%) and SO₂ (44.16%) were higher in Jeddah; PM₁₀ (91.12%) in Riyadh, while NO₂ (44.35%) and O₃ (18.98%) were highest in Makkah. However, even though there was a decrease in pollutants concentrations during the lockdown, the concentrations for CO, PM₁₀, SO₂, NO_2, and O₃ were still above WHO 24 h and annual mean limit levels. The COVID-19 lockdown in the Kingdom of Saudi Arabia revealed the possibility of significant atmospheric pollutant reduction by controlling traffic, activities by industries, and environmentally friendly transportation programs such as green commuting programs.     

Assessing the sources and magnitude of diurnal nitrate variability in the San Joaquin River (California) with an in situ optical nitrate sensor and dual nitrate isotopes

1. We investigated diurnal nitrate (NO₃⁻) concentration variability in the San Joaquin River using an in situ optical NO₃⁻ sensor and discrete sampling during a 5‐day summer period characterized by high algal productivity. Dual NO₃⁻ isotopes (δ¹⁵N_NO3 and δ¹⁸O_NO3) and dissolved oxygen isotopes (δ¹⁸O_DO) were measured over 2 days to assess NO₃⁻ sources and biogeochemical controls over diurnal time‐scales. 2. Concerted temporal patterns of dissolved oxygen (DO) concentrations and δ¹⁸O_DO were consistent with photosynthesis, respiration and atmospheric O₂ exchange, providing evidence of diurnal biological processes independent of river discharge. 3. Surface water NO₃⁻ concentrations varied by up to 22% over a single diurnal cycle and up to 31% over the 5‐day study, but did not reveal concerted diurnal patterns at a frequency comparable to DO concentrations. The decoupling of δ¹⁵N_NO3 and δ¹⁸O_NO3 isotopes suggests that algal assimilation and denitrification are not major processes controlling diurnal NO₃⁻ variability in the San Joaquin River during the study. The lack of a clear explanation for NO₃⁻ variability likely reflects a combination of riverine biological processes and time‐varying physical transport of NO₃⁻ from upstream agricultural drains to the mainstem San Joaquin River. 4. The application of an in situ optical NO₃⁻ sensor along with discrete samples provides a view into the fine temporal structure of hydrochemical data and may allow for greater accuracy in pollution assessment.     

Low pH (6, 5 and 4) sulfate reduction during the acidification of sucrose under thermophilic (55 °C) conditions

The effect of a low pH (6, 5 and 4) and different COD/SO₄²⁻ ratios (9 and 3.5) on thermophilic (55 °C) sulfate reduction and acidification of sucrose was investigated using three upflow anaerobic sludge bed reactors fed with sucrose at an organic loading rate of 3.5 gCOD (l_reactor d)⁻¹. The three reactors showed nearly 100% acidification of sucrose for all pH values and COD/SO₄²⁻ ratios investigated. Sulfate reduction was complete at pH 6 and a COD/SO₄²⁻ ratio of 9. At pH 5, sulfate reduction efficiencies were 80–95% for both COD/SO₄²⁻ ratios (9 and 3.5). At pH 4, sulfate reduction efficiencies further dropped to 55–65% at a COD/SO₄²⁻ ratio of 9 and 30–40% at a COD/SO₄²⁻ ratio of 3.5. The pH decrease from 6 to 5 or 4 caused a shift in the acidification products from mainly acetate to butyrate, as well as a higher production of ethanol, especially at pH 4. At pH 4, propionate and methane were not formed and hydrogen concentrations in the biogas reached 50%, equivalent to a hydrogen yield of 1.3 mol H₂ (mol glucose)⁻¹. This study shows that sulfate reduction is possible in the acidification phase of anaerobic wastewater treatment at pH values as low as 6 till 4 and that the pH strongly affects both the acidification pathways and the sulfate reduction efficiencies.     

Electrocatalytic Co-Upcycling of Nitrite and Ethylene Glycol over Cobalt–Copper Oxides

Electrocatalytic nitrite (NO₂⁻) reduction reaction (NO₂⁻RR) for ammonia (NH₃) synthesis is a promising alternative for NO₂⁻ resource utilization. Herein, a dual-site copper-cobalt oxide catalyst is reported for the efficient electrocatalytic reduction of NO₂⁻ to NH₃, exhibiting NH₃ Faradaic efficiency that remained above 95% (0.1 m NaNO₂) over a wide potential window (−0.1 to −0.6 V vs reversible hydrogen electrode, vs RHE). More importantly, the high NH₃ Faradaic efficiency maintains an over 85% (−0.1 to −0.3 V vs RHE) at a low concentration of NaNO₂ (0.01 m ). Theoretical calculations demonstrate that CuO serves the ^*NO₂ to ^*NO and is subsequently converted to NH₃ on Co₃O₄. Coupled anodic ethylene glycol (EG) oxidation reaction endows low cell voltage (ΔU = 480 mV, 10 mA cm⁻²) and energy consumption saving (>23%) in a two-electrode system. This work provides a reference for a co-upcycling electrolyzer for NO₂⁻ and EG.     

Microsensor Measurements of Sulfate Reduction and Sulfide Oxidation in Compact Microbial Communities of Aerobic Biofilms

The microzonation of O₂ respiration, H₂S oxidation, and SO₄^2- reduction in aerobic trickling-filter biofilms was studied by measuring concentration profiles at high spatial resolution (25 to 100 μm) with microsensors for O₂, S^2-, and pH. Specific reaction rates were calculated from measured concentration profiles by using a simple one-dimensional diffusion reaction model. The importance of electron acceptor and electron donor availability for the microzonation of respiratory processes and their reaction rates was investigated. Oxygen respiration was found in the upper 0.2 to 0.4 mm of the biofilm, whereas sulfate reduction occurred in deeper, anoxic parts of the biofilm. Sulfate reduction accounted for up to 50% of the total mineralization of organic carbon in the biofilms. All H₂S produced from sulfate reduction was reoxidized by O₂ in a narrow reaction zone, and no H₂S escaped to the overlying water. Turnover times of H₂S and O₂ in the reaction zone were only a few seconds owing to rapid bacterial H₂S oxidation. Anaerobic H₂S oxidation with NO₃^- could be induced by addition of nitrate to the medium. Total sulfate reduction rates increased when the availability of SO₄^2- or organic substrate increased as a result of deepening of the sulfate reduction zone or an increase in the sulfate reduction intensity, respectively.