Low O2 Concentrations Research Articles

Consequences of perinatal hypoxia in developing brain: Changes in GABA transporter functioning in cortical, hippocampal and thalamic rat nerve terminals

Perinatal hypoxia leads to behavioral abnormalities, cognitive disabilities, and epilepsy resulting from alterations in neurodevelopment, maturation and construction of the network. Considering a particular role of γ-aminobutyric acid (GABA) for an immature brain, we analysed transporter-mediated [3H]GABA uptake in the cortical, hippocampal and thalamic nerve terminals isolated from rats of different age in the control and after perinatal hypoxia. The state of hypoxia was induced by exposure of rats at the age of 10 postnatal days (pd) (that corresponds approximately to the time of birth in humans) to a respiratory medium with low O2 content (4% O2 and 96%N2) for 12min (up to the initiation of clonico-tonic seizures). Here, we found that the initial rate of [3Н]GABA uptake was higher in the young rats (pd 17–19) as compared to the older ones (pd 24–26, 38–40 and 66–73) in both control and hypoxia groups. It decreased abruptly by 50% in the thalamus and by 25% in the cortex for the period from pd 17–19 to pd 66–73. In the hippocampus, a decrease in the rate during the same time interval was 25%. Exposure to hypoxia had no effect on the intensity of [3Н]GABA uptake by the cortical and thalamic nerve terminals, but caused a significant age-dependent attenuation (by 35%) of the uptake intensity in the hippocampal ones. Significant age-dependent hypoxia-independent decrease in [3Н]GABA uptake with step-like dynamics of changes was shown in the thalamus and cortex. Gradual age-dependent hypoxia-dependent decrease in [3Н]GABA uptake was revealed in the hippocampus, and so a particular vulnerability of the latest structure to hypoxia as compared to the cortex and thalamus was revealed.

Assessing oxygen depletion in the Northeastern Pacific Ocean during the last deglaciation using I/Ca ratios from multiple benthic foraminiferal species

AbstractPaleo‐redox proxies are crucial for reconstructing past bottom water oxygen concentration changes brought about by ocean circulation and marine productivity shifts in response to climate forcing. Carbonate I/Ca ratios of multiple benthic foraminifera species from Ocean Drilling Program Hole 1017E—a core drilled within the Californian oxygen minimum zone (OMZ), on the continental slope—are employed to reexamine the transition from the well‐oxygenated last glacial into poorly oxygenated modern conditions. The redox and export productivity history of this site is constrained by numerous proxies used to assess sensitivity of I/Ca ratios of benthic foraminifera to changes in bottom and pore water O2 concentrations. Reconstructed iodate (IO3−) availability is from the I/Ca ratio of epifaunal (Cibicidoides sp.), shallow infaunal (Uvigerina peregrina), and deep infaunal (Bolivina spissa) foraminifera. The reconstructed IO3− availability profile is used to determine the contribution of bottom water O2 relative to oxidant demand on pore water O2 concentrations. These results suggest that high export productivity on the California Margin drove low pore water O2 concentrations during the Bølling. In contrast, low bottom water O2 concentrations at 950 m water depth only contributed to reduced sediments during the Allerød. Increased contribution of modified North Pacific Intermediate Water to the California Current System ventilated the California OMZ during the late glacial and the Younger Dryas such that water overlying the site was oxygenated. These results highlight the promising potential of this new proxy for understanding the relative influence of bottom water O2 concentration and pore water oxidant demand on OMZs.

Trophoblast survival signaling during human placentation requires HSP70 activation of MMP2-mediated HBEGF shedding.

Survival of trophoblast cells in the low oxygen environment of human placentation requires metalloproteinase-mediated shedding of HBEGF and downstream signaling. A matrix metalloproteinase (MMP) antibody array and quantitative RT-PCR revealed upregulation of MMP2 post-transcriptionally in human first trimester HTR-8/SVneo trophoblast cells and placental villous explants exposed to 2% O2. Specific MMP inhibitors established the requirement for MMP2 in HBEGF shedding and upregulation. Because α-amanitin inhibited the upregulation of HBEGF, differentially expressed genes were identified by next-generation sequencing of RNA from trophoblast cells cultured at 2% O2 for 0, 1, 2 and 4 h. Nine genes, all containing HIF-response elements, were upregulated at 1 h, but only HSPA6 (HSP70B') remained elevated at 2-4 h. The HSP70 chaperone inhibitor VER 155008 blocked upregulation of both MMP2 and HBEGF at 2% O2, and increased apoptosis. However, both HBEGF upregulation and apoptosis were rescued by exogenous MMP2. Proximity ligation assays demonstrated interactions between HSP70 and MMP2, and between MMP2 and HBEGF, supporting the concept that MMP2-mediated shedding of HBEGF, initiated by HSP70, contributes to trophoblast survival at the low O2 concentrations encountered during the first trimester, and is essential for successful pregnancy outcomes. Trophoblast survival during human placentation, when oxygenation is minimal, required HSP70 activity, which mediated MMP2 accumulation and the transactivation of anti-apoptotic ERBB signaling by HBEGF shedding.

Abstract 4523: Agent-based models for prediction of tumor spheroid response to radiation and the hypoxia-activated prodrug SN30000

Abstract Introduction: Hypoxia-activated prodrugs (HAPs) are a promising strategy to specifically target radioresistant hypoxic cells in tumors. We have used multicellular layers (MCLs) and steady state Green’s function pharmacokinetic/pharmacodynamic (PK/PD) modelling in microvascular networks to select SN30000 as a tirapazamine analogue with optimal spatial complementarity with radiation. However these models have several limitations such as lack of time dependent PK. Multicellular tumor spheroids are a more tractable model than MCLs for investigating PD parameters. However, the challenges of interpreting spheroid experiments in terms of spatial complementarity limits their application. We have developed an in silico agent-based (AB) tumor spheroid model, in which cell fate can be tracked as a function of time and is determined by spatially-varying concentrations of oxygen, glucose and therapeutic agents (radiation and HAP). The hypothesis is that our AB model can predict tumor spheroid response to radiation and SN30000, both alone and in combination. Methods: In the AB model, spheroid growth is simulated as a function of oxygen, glucose and drug concentrations determined by solving diffusion equations using oxygen consumption measured in HCT116 monolayers and glucose and SN30000 diffusion and metabolism measured in HCT116 MCLs and stirred cell suspensions, linked with intracellular reaction equations. Cell fate is determined by oxygen, glucose and drug concentrations. Spheroid diameter, cell survival and hypoxic fraction of HCT116 spheroids grown at a range of oxygen and initial glucose concentrations were compared to model predictions, as was glucose depletion from the culture medium. Radiation (cobalt-60) and SN30000 induced clonogenic cell killing under oxia and anoxia was determined using HCT116 monolayers. Model simulations of HCT116 spheroid response to radiation and SN30000 were compared to experimental results. Results: The model reproduced known features of spheroids including oxygen and glucose gradients, rapid cell proliferation at the periphery and central hypoxia and necrosis. Measured HCT116 spheroid diameters increased linearly with time, at rates that decreased at lower ambient O2 concentrations. Spheroid growth and glucose depletion was well-fitted by the AB model. Good agreement was found between simulated and measured clonogenic cell killing by radiation and SN30000, while the model underestimated spheroid growth delay by radiation and SN30000 than experimental observation. Discussion: An oxygen and glucose dependent AB model for growth and PD response (cell killing and growth delay) of HCT116 spheroids has been developed and calibrated using experimentally determined parameters. Further development of this model will link cell fates (including cell cycle arrest) explicitly to DNA damage responses and O2 and glucose-dependence of cell proliferation and survival. Citation Format: Xinjian Mao, Gib Bogle, Sarah McManaway, William Wilson, Kevin Hicks. Agent-based models for prediction of tumor spheroid response to radiation and the hypoxia-activated prodrug SN30000 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4523. doi:10.1158/1538-7445.AM2017-4523

The In Vivo Potential-Regulated Protective Protein of Nitrogenase in Azotobacter vinelandii Supports Aerobic Bioelectrochemical Dinitrogen Reduction In Vitro.

Nitrogenase, the only enzyme known to be able to reduce dinitrogen (N2) to ammonia (NH3), is irreversibly damaged upon exposure to molecular oxygen (O2). Several microbes, however, are able to grow aerobically and diazotrophically (fixing N2 to grow) while containing functional nitrogenase. The obligate aerobic diazotroph, Azotobacter vinelandii, employs a multitude of protective mechanisms to preserve nitrogenase activity, including a "conformational switch" protein (FeSII, or "Shethna") that reversibly locks nitrogenase into a multicomponent protective complex upon exposure to low concentrations of O2. We demonstrate in vitro that nitrogenase can be oxidatively damaged under anoxic conditions and that the aforementioned conformational switch can protect nitrogenase from such damage, confirming that the conformational change in the protecting protein can be achieved solely by regulating the potential of its [2Fe-2S] cluster. We further demonstrate that this protective complex preserves nitrogenase activity upon exposure to air. Finally, this protective FeSII protein was incorporated into an O2-tolerant bioelectrosynthetic cell whereby NH3 was produced using air as a substrate, marking a significant step forward in overcoming the crippling limitation of nitrogenase's sensitivity toward O2.

Effect of nano packaging on preservation quality of Nanjing 9108 rice variety at high temperature and humidity

A nano packaging material containing nano Ag, nano TiO2, nano attapulgite and SiO2 was prepared, and its impact on quality of Nanjing 9108 rice at 37°C and 85% relative humidity was studied. Effects of the packaging on ambient gases and chromatic aberration of rice were determined. Moreover, oxidation level, molds growth and flavor of rice were also analyzed. Results showed that nano packaging material had antimicrobial effects and maintained low O2 and high CO2 content in the packages. The packages thereby inhibited the growth of molds and the production of fatty acids, restrained the increase of lipase activity, and reduced the oxidation of fats and proteins. As a result, the production of yellow and white-belly rice were inhibited. Furthermore, the color and flavor of rice were maintained. Therefore, the nano-packing material could be applied for preservation of rice to improve preservation quality.

To harness stem cells by manipulation of energetic metabolism

The maintenance of the primitive Hematopoietic Stem Cells (HSC) in course of ex vivo expansion is a critical point to preserve the long-term reconstituting capacity of a hematopoietic graft. On the basis of the numerous experimental results, the maintenance of primitive HSC is related to their specific metabolic profile shifted towards the anaerobiosis. Hence, in addition to the exposition of the cultures to more appropriate, physiologically low O2 concentrations (usually misleadingly termed “hypoxia”), a specter of “hypoxia-mimicking” factors (cytokines, growth factors, receptor-ligands, antioxidants) can be applied to maintain this specific metabolic profile enabling an appropriate genetic and epigenetic regulation. Some factors already proved to be able to achieve this goal and “hypoxia-mimicking” ex vivo cultures were already used to produce cells for clinical trials. In this article we are discussing the approaches aimed to amplify and/or to condition the HSC, based on the manipulation of energetic metabolism properties.

Transcriptional and biochemical regulation of internal browning disorder in ‘Rocha’ pear as affected by O2 and CO2 concentrations

The biochemical basis of internal browning disorders (IBD) in ‘Rocha’ pear has been linked to alterations in the antioxidant and fermentative metabolism. In order to further elucidate the involvement of these metabolic pathways on IBD development, we investigated their regulation at a metabolic and transcriptional level in pears that were stored under four distinct conditions: i) cold air (−0.5°C); ii) standard controlled atmosphere (CA; 2kPa O2+0.5kPa CO2); iii) high CO2 (2kPa O2+10kPa CO2), and iv) high CO2+low O2 (O2-switch: 60 d under high CO2+80 d under high CO2 and 1kPa O2). Only the fruit stored under high CO2 were affected by IBD. The faster depletion of ascorbate in high CO2-stored fruit was associated with the down-regulation of glutathione reductase (PcGR) and ascorbate peroxidase (PcAPX) as well as a down-regulation of monodehydroascorbate reductase (PcMDHAR). The O2-switched fruit had the highest IBD incidence. Increased incidence in this sample was associated to a sharp increase in fermentation immediately after transfer to lower O2 atmosphere suggesting a synergistic effect between high CO2 and low O2 concentrations in IBD development. Overall, our results suggest that biochemical and transcriptional regulation of the antioxidant system affects IBD occurrence in ‘Rocha’ pear, and that fermentation, resulting from fruit exposure to low O2 concentrations, may further promote the browning process.

Effect of modified atmosphere packaging and temperature abuse on flavor related volatile compounds of rocket leaves (Diplotaxis tenuifolia L.).

The effect of storage conditions on flavor-related volatile composition of wild rocket (Diplotaxis tenuifolia) was investigated on Modified Atmosphere packed (MAP) leaves stored under isothermal and non-isothermal conditions. In a first experiment the effect of MAP was compared to the storage in air at 5°C; a second experiment aimed to study the effect of non isothermal conditions, with two temperature abuses (at 13°C for 24h) during a 5°C. Twenty-four volatiles were detected, including C6, C5, isothiocyanate, lipid-derived and sulfur compounds. In the first experiment, MAP-stored rocket showed a slower loss of typical flavour volatiles (thiocyanates and isothiocyanates) and a slower production of off-flavors until 6days of storage, compared to leaves stored in air. After this time, dimethyl sulfide and acetaldehyde dramatically increased in MAP-stored rocket samples. In the second experiment, samples stored under non-isothermal conditions showed lower O2 and higher CO2 concentrations than samples stored under isothermal conditions. Rocket leaves stored under non-isothermal conditions showed an increased production of volatiles responsible of off-flavors (acetaldehyde and dimethyl sulfide) following temperature abuse comparing to storage in isothermal condition. Thus, dimethyl sulfide and acetaldehyde could be effective markers for tracking the effect of temperature fluctuations on rocket during storage.

Study of a Cu-CuO chemical loop for the calcination of CaCO3 in a fixed bed reactor

The use of a Cu/CuO chemical loop to supply the heat required to carry out the calcination of CaCO3 in a fixed-bed reactor is experimentally evaluated. The effects of the fuel gas composition, the Cu/Ca molar ratio, the temperature of the solids bed and possible side reactions on the reduction/calcination stage are studied under pseudo-adiabatic conditions in a fixed-bed reactor (i.d.×L=0.038m×0.92m) using commercial Ca- and Cu-based materials. It was observed that initial temperatures in the solids bed of more than 650°C make it possible to achieve the complete calcination of CaCO3. Suitable Cu/Ca molar ratios, depending on the composition of the gaseous fuel used to reduce CuO, can moderate the increase in temperature in the reduction front and allow the simultaneous calcination of CaCO3. The multicycle operation at high temperature modifies the chemical composition of the functional materials and leads to the formation of mixed Ca-Cu oxides that are able to capture CO2, which affect the CO2 sorption capacity of these materials. Moreover, the influence of O2 dilution in the inlet gas upon the temperature profiles during the Cu oxidation stage was assessed. The recirculation of a large part of the product gas resulting from the oxidation stage moderates the temperature profile and the complete conversion of the Cu-based solids is achieved in a relatively sharp oxidation front despite the low O2 content in the feed (i.e., 3vol% O2). The experimental results are in close agreement with the predictions of a one-dimensional reactor model that incorporates existing information taken from the literature on the kinetics, fluid dynamics and heat transfer.

Influence of oxygen concentration on T cell proliferation and susceptibility to apoptosis in healthy men and women.

Much of what we know about the functioning of human T lymphocytes is based on the experiments carried out in atmospheric oxygen (O₂) concentrations, which are significantly higher than those maintained in blood. Interestingly, the gender differences in the activity of T cells and their susceptibility to apoptosis under different O₂ conditions have not yet been described. The aim of the study was to compare two main markers of lymphocyte function: proliferation capacity and ability to produce cytokines as well as their susceptibility to apoptosis under two different O₂ concentrations, between men and women. 25 healthy volunteers, both males (13) and females (12) were recruited to the study (mean age 25.48 ± 5.51). By using cytometry proliferation parameters of human CD4+ CD28+ cells or CD8+CD28+ cells in response to polyclonal stimulation of the TCR/CD3 complex at atmospheric (21%) and physiological (10%) O₂ concentrations using our modified dividing cell tracking technique (DCT) were analyzed as well as the percentages of apoptotic cells. We also determined the levels of IFN-γ, IL-2, IL-10 and IL-17A using Cytometric Bead Array Flex system in cell culture supernatants. CD4+CD28+ and CD8+CD28+ cells from the whole study group were characterized by shorter time required to enter the first (G1) phase of the first cell cycle at 21% compared to 10% O₂. Both T cell populations performed significantly more divisions at 21% O₂. The percentages of dividing cells were also significantly higher at atmospheric O₂. Interestingly, data analysis by gender showed that male lymphocytes had similar proliferative parameters at both O₂ concentrations while female lymphocytes proliferate more efficiently (note from the author: we cannot say that lymphocytes proliferate faster, rather more effectively, because cells perform more divisions, which gives more percentage of offspring cells) at 21% oxygen. Compared to males, the female CD4+ cells showed increased susceptibility to apoptosis at both O₂ concentrations. No differences in the levels of cytokines regardless of gender and oxygen conditions were found. We showed that in vitro female T cells (both CD4+ and CD8+ cells) are more sensitive than male lymphocytes to low O2 concentration as demonstrated by the decrease in their proliferation dynamics. The effect does not depend on increased apoptosis of female T cells under low O₂ because percentage of apoptotic cells was similar at both O₂ concentrations.

The effect of O2 concentration on the reaction mechanism in Li-O2 batteries

The promising lithium-oxygen battery chemistry presents a set of challenges that need to be solved if commercialization is ever to be realized. This study focuses on how the O2 reaction path is effected by the O2 concentration in the electrolyte. An electrochemical quartz crystal microbalance system was used to measure current, potential, and change in electrode mass simultaneously. It is concluded that the mass reversibility is O2 concentration dependent while the coulombic efficiency is not. The mass reversibility is higher at low O2 concentration meaning that more of the deposited Li2O2 is removed during oxidation in relation to the amount deposited during reduction. The first step of the reduction is the formation of soluble LiO2, which is then either reacting further at the electrode or being transported away from the electrode resulting in low current efficiency and low deposited mass per electrons transferred. During the oxidation, the first step involves de-lithiation of Li2O2 at low potential followed by bulk oxidation. The oxidation behavior is O2 concentration dependent, and this dependence is likely indirect as the O2 concentration effects the amount of discharge product formed during the reduction. The O2 concentration at different saturation pressures was determined using a mass spectrometer. It was found that the electrolyte follows Henry's law at the pressures used in the study. In conclusion, this study provides insight to the O2 concentration dependence and the preferred path of the O2 electrochemical reactions in lithium-oxygen batteries.

Effects of Additional Layer(s) on the Mobility of Arsenic from Hydrothermally Altered Rock in Laboratory Column Experiments

Hydrothermally altered rocks are frequently encountered when tunnels are constructed in Hokkaido, Japan. High concentraions of hazardous elements, such as arsenic (As), are often released from these rocks into the surrounding environments. Therefore, the rocks are considered potentially hazardous waste. This article describes the effects of water content and oxygen (O2) concentration in relation to additional layer(s), i.e., surface covering and bottom adsorption layers, on As leaching by using laboratory columns with water content and O2 concentration sensors. The results show that the use of additional layer(s) has a significant effect on lowering As migration. This was due not only to the adsorption capacity of As by the adsorption layer but also to the water content and O2 concentration inside the rock layer. The accumulation of pore water was increased in the rock layer in cases with additional layer(s), which resulted in lower O2 concentration in the rock layer. Consequently, the leaching of As by the oxidation of As-bearing minerals in the rock layer was reduced. Moreover, a longer water-resident time in the rock layer may induce precipitation of Fe oxy-hydroxide/oxide. These results suggest that the geochemical conditions of the rock layer affect As leaching and migration.

Manganese-cerium oxide catalysts prepared by non-thermal plasma for NO oxidation: Effect of O2 in discharge atmosphere

Non-thermal plasma with different O2 concentration in discharge atmosphere was applied to synthesize manganese and cerium mixed-oxides catalysts, which were compared in NO oxidation activity. Discharge atmosphere displayed a crucial influence on the performance of the catalysts prepared by plasma. Relatively low O2 concentration in discharge atmosphere allows synthesizing manganese-cerium oxides catalysts in a moderate environment and therefore is favorable for better physicochemical properties which lead to superior catalytic behavior. The best catalyst was obtained by treatment with 10% O2/N2 plasma and presented over 80% NO conversion in the temperature range of 275–325°C, whereas catalyst prepared in pure O2 discharge atmosphere had the same activity with a catalyst prepared by calcinations. A correlation between the surface properties of the plasma prepared catalysts and its catalytic activity in NO oxidation is proposed. The amount of the surface adsorbed oxygen has an obvious linear correlation with the amount of Ce3+, the H2 consumption at low temperatures and the catalytic performance. The superior catalytic performance is mainly attributed to the stronger interaction between manganese oxides and ceria, and the formation of poorly crystallized Mn-O-Ce phase in the catalyst which resulted from the slow decomposition of nitrates and organics during plasma treatment. Catalysts prepared in relatively low O2 concentration have large specific surface area and is abundant in Ce3+ species and active oxygen species. The study suggests that plasma treatment with proper discharge gas components is a promising method to prepare effective manganese- cerium oxides catalyst for NO oxidation.

Hypoxic Preconditioning Improves Respiratory Muscle Function during Hypoxia by Regulating Mitochondria in COPD Mice

Diaphragm weakness has been observed in patients with chronic obstructive pulmonary disease (COPD), which may be associated with the prolonged hypoxic conditions in the disease. We found that hypoxic preconditioning (HPC) can strengthen diaphragm under hypoxic conditions in COPD mice by treating the muscle with alternating low and high O2 concentrations. In this study, we tested the hypothesis that the protective effects offered by HPC are linked with the opening of mitochondrial ATP‐sensitive potassium channel (KATP) and the closing of the mitochondrial permeability transition pore (mPTP) in COPD mice. Adult C57BL6 mice were smoked for three months to develop COPD symptoms. Following the completion of smoking, diaphragms of the mice were isolated and mounted in a contractile chamber. Each muscle strip was treated (n = 6) or non‐treated with HPC (n = 6), or pre‐incubated with a combination of KATP channel inhibitor (glibenclamide; 100 μM) and mPTP opener (carboxyatractyloside; 50 μM; n = 6) for 30 min prior to HPC. Another two groups of muscles were treated either with KATP channel activator (diazoxide; 100 μM; n = 6) or mPTP inhibitor (cyclosporine A; 100 μM; n = 6) in the absence of HPC. The muscles were then consecutively stimulated for five minutes (0.5 Hz) during a 30‐min hypoxic period. Fatigue tolerance was determined as the ratio of residual force at the end of the five‐min contraction to the initial force. Data were expressed as means ± SE, and analyzed using multi‐way ANOVA. P < 0.05 was considered statistically different. Our results show that HPC significantly improved diaphragm function during hypoxia (29 ± 2.8% for HPC vs. 6 ± 1.3% for control, p < 0.05). However, such protective effects were eliminated via the simultaneous inhibition of KATP channel and the opening of mPTP (5 ± 2.1%, p < 0.05 vs. HPC). On the other hand, either the activation of KATP channel (27 ± 2.6%) or the inhibition of mPTP (24 ± 3.6%) significantly mitigates diaphragm fatigue (p < 0.05 vs. control) to an extent similar to that of HPC. These data collectively indicate that the mechanisms of HPC protection on diaphragm under hypoxia may involve the opening of mitochondrial KATP channel and inhibition of mPTP in COPD mice.Support or Funding InformationAmerican Physiological Society (APS) 2016 S&R Foundation Ryuji Ueno Award

Microaerophilic Fe(II)-Oxidizing Zetaproteobacteria Isolated from Low-Fe Marine Coastal Sediments: Physiology and Composition of Their Twisted Stalks.

Microaerophilic Fe(II) oxidizers are commonly found in habitats containing elevated Fe(II) and low O2 concentrations and often produce characteristic Fe mineral structures, so-called twisted stalks or tubular sheaths. Isolates originating from freshwater habitats are all members of the Betaproteobacteria, while isolates from marine habitats belong almost exclusively to the Zetaproteobacteria So far, only a few isolates of marine microaerophilic Fe(II) oxidizers have been described, all of which are obligate microaerophilic Fe(II) oxidizers and have been thought to be restricted to Fe-rich systems. Here, we present two new isolates of marine microaerophilic Fe(II)-oxidizing Zetaproteobacteria that originate from typical coastal marine sediments containing only low Fe concentrations (2 to 11 mg of total Fe/g of sediment [dry weight]; 70 to 100 μM dissolved Fe2+ in the porewater). The two novel Zetaproteobacteria share characteristic physiological properties of the Zetaproteobacteria group, even though they come from low-Fe environments: the isolates are obligate microaerophilic Fe(II) oxidizers and, like most isolated Zetaproteobacteria, they produce twisted stalks. We found a low organic carbon content in the stalks (∼0.3 wt%), with mostly polysaccharides and saturated aliphatic chains (most likely lipids). The Fe minerals in the stalks were identified as lepidocrocite and possibly ferrihydrite. Immobilization experiments with Ni2+ showed that the stalks can function as a sink for trace metals. Our findings show that obligate microaerophilic Fe(II) oxidizers belonging to the Zetaproteobacteria group are not restricted to Fe-rich environments but can also be found in low-Fe marine environments, which increases their overall importance for the global biogeochemical Fe cycle.IMPORTANCE So far, only a few isolates of benthic marine microaerophilic Fe(II) oxidizers belonging to the Zetaproteobacteria exist, and most isolates were obtained from habitats containing elevated Fe concentrations. Consequently, it was thought that these microorganisms are important mainly in habitats with high Fe concentrations. The two novel isolates of Zetaproteobacteria that are presented in the present study were isolated from typical coastal marine sediments that do not contain elevated Fe concentrations. This increases the knowledge about possible habitats in which Zetaproteobacteria can exist. Furthermore, we show that the physiology and the typical organo-mineral structures (twisted stalks) that are produced by the isolates do not notably differ from the physiology and the cell-mineral structures of isolates from environments with high Fe concentrations. We also showed that the organo-mineral structures can function as a sink for trace metals.

The influence of O2 availability and Fe(III) mineralogy on Fe metabolism by an acidophilic bacterial culture

Microbiological Fe(II) oxidation in emergent acid mine drainage (AMD) at the terrestrial surface, and continued precipitation of biogenic Fe(III) can lead to massive deposits of Fe(III) phases. Fe(II) oxidizing bacteria that mediate Fe(III) deposition are challenged to continue to metabolize despite burial in these Fe(III) phases, which increases the distance from the sediment-water interface where O2 is most readily available to support Fe(II) oxidation. Microbial communities associated with such deposits vary little with depth, indicating that the associated organisms can adapt to the physicochemical changes associated with Fe(III) deposition. A stable Alicyclobacillacea bacterium-containing culture (A06) was obtained under Fe(III) reducing conditions, and was also capable of aerobic growth with Fe(II) or glucose as electron donors. To evaluate the influence of Fe(III) mineralogy and O2 availability on microbial activities in an iron mound setting, we incubated the A06 culture in agarose-solidified suspensions of Fe(III) phases that mimicked the Fe(III) deposits. During the incubations, we measured O2 and Fe(II) concentrations at various depth intervals within these “artificial cores.” In incubations that included goethite, an Fe(II) oxidation front preceded maximal O2 diffusion into the incubations, indicating that Fe(II) oxidation could occur at extremely low O2 concentrations. This finding is consistent with previous field measurements. Computational modeling of activities in the incubations indicated that Fe(II) oxidation is partially controlled by diffusive O2 availability as well as Fe(II) diffusion, which may be influenced by the mineralogy of Fe(III) phases where Fe(II) oxidation is occurring. In incubations amended with glucose, schwertmannite-Fe(III) reduction occurred despite available O2, which is also consistent with previous field measurements. Our results indicate that Fe metabolism may be more heavily influenced by the mineralogical context in which activity occurs than the availability of O2.

Influence of oxygen availability on the activities of ammonia-oxidizing archaea.

Recent studies point to the importance of oxygen (O2 ) in controlling the distribution and activity of marine ammonia-oxidizing archaea (AOA), one of the most abundant prokaryotes in the ocean. The AOA are associated with regions of low O2 tension in oceanic oxygen minimum zones (OMZs), and O2 availability is suggested to influence their production of the ozone-depleting greenhouse gas nitrous oxide (N2 O). We show that marine AOA available in pure culture sustain high ammonia oxidation activity at low μM O2 concentrations, characteristic of suboxic regions of OMZs (<10 µM O2 ), and that atmospheric concentrations of O2 may inhibit the growth of some environmental populations. We quantify the increasing N2 O production by marine AOA with decreasing O2 tensions, consistent with the plausibility of an AOA contribution to the accumulation of N2 O at the oxic-anoxic redox boundaries of OMZs. Variable sensitivity to peroxide also suggests that endogenous or exogenous reactive oxygen species are of importance in determining the environmental distribution of some populations.

Oxygen and temperature effects on the electrochemical and electrochromic properties of rf-sputtered V2O5 thin films

Vanadium pentoxide (V2O5) thin films grown by rf-sputtering have been studied as a function of two growth parameters, O2 content and substrate temperature, which influence importantly their structural, as well as their electrochemical and electrochromic properties. The increase in O2 content appears to result in an increase of the grain size of the films, while the increase in substrate temperature leads in platelets perpendicular to the substrate, which enhance the porosity of the films. Films with low O2 content (3%) and films grown at a substrate temperature of 300°C, present enhanced charge storage properties of 553mA h g−1 and large transmittance modulation ability. On the contrary, high O2 content (11%) and a substrate temperature of 150°C lead to improved coloration efficiency (at λ=400nm), reaching values of 84.5 and ∼132cm2C−1, respectively. These findings are discussed in terms of structural and morphological changes occurring during the two parameters studied.

Emission reduction through internal and low-pressure loop exhaust gas recirculation configuration with negative valve overlap and late intake valve closing strategy in a compression ignition engine

An investigation was carried out to examine the feasibility of replacing the conventional high-pressure loop/low-pressure loop exhaust gas recirculation with a combination of internal and low-pressure loop exhaust gas recirculation. The main objective of this alternative exhaust gas recirculation path configuration is to extend the limits of the late intake valve closing strategy, without the concern of backpressure caused by the high-pressure loop exhaust gas recirculation. The late intake valve closing strategy improved the conventional trade-off relation between nitrogen oxides and smoke emissions. The gross indicated mean effective pressure was maintained at a similar level, as long as the intake boosting pressure kept changing with respect to the intake valve closing timing. Applying the high-pressure loop exhaust gas recirculation in the boosted conditions yielded concern of the exhaust backpressure increase. The presence of high-pressure loop exhaust gas recirculation limited further intake valve closing retardation when the negative effect of increased pumping work cancelled out the positive effect of improving the emissions’ trade-off. Replacing high-pressure loop exhaust gas recirculation with internal exhaust gas recirculation reduced the burden of such exhaust backpressure and the pumping loss. However, a simple feasibility analysis indicated that a high-efficiency turbocharger was required to make the pumping work close to zero. The internal exhaust gas recirculation strategy was able to control the nitrogen oxides emissions at a low level with much lower O2 concentration, even though the initial in-cylinder temperature was high due to hot residual gas. Retardation of intake valve closing timing and intake boosting contributed to increasing the charge density; therefore, the smoke emission reduced due to the higher air–fuel ratio value exceeding 25. The combination of internal and low pressure loop loop exhaust gas recirculation with late intake valve closing strategy exhibited an improvement on the trade-off relation between nitrogen oxides and smoke emissions, while maintaining the gross indicated mean effective pressure at a comparable level with that of the high-pressure loop exhaust gas recirculation configuration.