O2 Supply Research Articles

Muscle oxygen saturation rates coincide with lactate-based exercise thresholds.

Monitoring muscle metabolic activity via blood lactate is a useful tool for understanding the physiological response to a given exercise intensity. Recent indications suggest that skeletal muscle oxygen saturation (SmO2), an index of the balance between local O2 supply and demand, may describe and predict endurance performance outcomes. We tested the hypothesis that SmO2 rate is tightly related to blood lactate concentration across exercise intensities, and that deflections in SmO2 rate wouldcoincide with established blood lactate thresholds (i.e., lactate thresholds 1 and 2). Ten elite male soccer players completed an incremental running protocol to exhaustion using 3-min work to 30s rest intervals. Blood lactate samples were collected during rest and SmO2 was collected continuously via near-infrared spectroscopy from the right and left vastus lateralis, left biceps femoris and the left gastrocnemius. Muscle O2 saturation rate (%/min) was quantified after the initial 60s of each 3-min segment. The SmO2 rate was significantly correlated with blood lactate concentrations for all muscle sites; RVL, r = -0.974; LVL, r = -0.969; LG, r = -0.942; LHAM, r = -0.907. Breakpoints in SmO2 rate were not significantly different from LT1 or LT2 at any muscle sites (P > 0.05). Bland-Altman analysis showed speed threshold estimates via SmO2 rate and lactate are similar at LT2, but slightly greater for SmO2 rate at LT1. Muscle O2 saturation rate appears to provide actionable information about maximal metabolic steady state and is consistent with bioenergetic reliance on oxygen and its involvement in the attainment of metabolic steady state.

Hydrogenase-based oxidative biocatalysis without oxygen

Biocatalysis-based synthesis can provide a sustainable and clean platform for producing chemicals. Many oxidative biocatalytic routes require the cofactor NAD+ as an electron acceptor. To date, NADH oxidase (NOX) remains the most widely applied system for NAD+ regeneration. However, its dependence on O2 implies various technical challenges in terms of O2 supply, solubility, and mass transfer. Here, we present the suitability of a NAD+ regeneration system in vitro based on H2 evolution. The efficiency of the hydrogenase-based system is demonstrated by integrating it into a multi-enzymatic cascade to produce ketoacids from sugars. The total NAD+ recycled using the hydrogenase system outperforms NOX in all different setups reaching up to 44,000 mol per mol enzyme. This system proves to be scalable and superior to NOX in terms of technical simplicity, flexibility, and total output. Furthermore, the system produces only green H2 as a by-product even in the presence of O2.

Techno-Economic Assessment of PEM Electrolysis for O2 Supply in Activated Sludge Systems—A Simulation Study Based on the BSM2 Wastewater Treatment Plant

The conversion of renewable energy into hydrogen (H2) by power-to-gas technologies involving electrolysis is seen today as a key element in the transition to a sustainable energy sector. Wastewater treatment plants (WWTP) could be integrated into future green H2 networks as users of oxygen (O2) produced alongside H2 in water electrolysis. In WWTPs, O2 is required for biological treatment steps, e.g., in activated sludge (AS) systems. However, the production costs of electrolysis O2 should be competitive with those of conventional O2 production processes. In this study, mathematical models of a polymer electrolyte membrane electrolyser (PEME) plant and the WWTP of the Benchmark Simulation Model No. 2 (BSM2) were used to simulate electrolysis O2 supply to an AS system and estimate net costs of production (NCP) for produced O2 via a techno-economic assessment (TEA). Assuming that produced H2 is sold to a nearby industry, NCPs for O2 were calculated for two different PEME plant dimensions, four alternatives regarding electricity supply and costs, and three sets of assumptions regarding system performance and market conditions. The analyses were performed for 2020 as a reference year and 2030 based on forecasts of relevant data. Results of the dimensioning of the PEME show the O2 demand of a municipal WWTP with an installed capacity of 80,000 population equivalents (PE), such as the one of the BSM2, can be covered for more than 99% of the simulated period by either a 6.4 MW PEME operated for 4073 full load hours or a 4.8 MW PEME operated for 6259 full load hours. Investment costs for the PEME stacks and the operational costs for electricity make up most of the NCP of electrolysis O2. The projected decrease in PEME stack costs and renewable energy prices in favourable market conditions can result in a competitive NCP for electrolysis O2 in 2030. The approach described in this study can be applied to analyse O2 supply to biological wastewater treatment in WWTPs with different characteristics, in processes different from AS, and under different assumptions regarding economic conditions.

Physiological and cognitive responses to hyperoxic exercise in full water submersion

ABSTRACT The positive effects of combined hyperoxia and physical exercise on physiological parameters and cognitive functioning are established for normobaric laboratory contexts. Still, increased practicability exists in hyperbaric settings like underwater activities and SCUBA diving, where environmental and sport-specific factors might moderate effects. Improved cognition, reduced ventilation (V̇E), and lower blood lactate concentrations [Lac-] are highly relevant, especially during high-stress and rescue scenarios. Fifteen participants performed 3 × 8 min of continuous underwater fin-swimming at 25 % (low), 45 % (moderate), and 75 % (vigorous) heart rate reserve (HRR) in each test. Three separate test days differed solely by the inspiratory oxygen partial pressure (PIO2: 29 kPa, 56 kPa, and 140 kPa). V̇E was measured continuously, whereas breathing gas analysis, blood sampling, and Eriksen Flanker tasks for inhibitory control (100 stimuli) were performed post-exercise. Two-way ANOVAs with repeated measures on the factors PIO2 and exercise intensity analyzed physiological outcome variables and reactions times (RT) and accuracy (ACC) of inhibitory control. V̇E was significantly reduced for 140 kPa during moderate and vigorous and for 56 kPa during vigorous compared to 29 kPa. 56 kPa and 140 kPa showed no differences. [Lac-], post-exercise V̇CO2, and velocity were unaffected by PIO2. Faster RTs but lower ACC of inhibitory control were observed following exercise at 75 % HRR compared to rest, 25 %, and 45 % HRR, while PIO2 produced no effects. Underwater performance in hyperoxia presents reduced V̇E, possible by dampened chemoreceptor sensitivity, and effects on cognition that differ from laboratory results and emphasise the moderating role of sport-specific factors.

Photosynthetic capacity in seagrass seeds and early-stage seedlings of Zostera marina.

In many terrestrial seeds, photosynthetic activity supplies O2 to the developing plant embryo to sustain aerobic metabolism and enhance biosynthetic activity. However, whether seagrass seeds possess similar photosynthetic capacity to alleviate intra-seed hypoxic stress conditions is unknown. We used a novel combination of microscale variable chlorophyll fluorescence imaging, a custom-made O2 optode microrespirometry system and planar optode O2 imaging, to determine the O2 microenvironment and photosynthetic activity in developing seeds and seedlings of seagrass (Zostera marina). Developing, sheath-covered seeds exhibited high O2 concentrations in the photosynthetic active seed sheath and low O2 concentrations in the centre of the seed at the position of the embryo. In light, photosynthesis in the seed sheath increased O2 availability in central parts of the seed enabling enhanced respiratory energy generation for biosynthetic activity. Early-stage seedlings also displayed photosynthetic capacity in hypocotyl and cotyledonary tissues, which may be beneficial for seedling establishment. Sheath O2 production is important for alleviating intra-seed hypoxic stress, which might increase endosperm storage activity, improving the conditions for successful seed maturation and germination.

Methanotrophic oxidation of organic micropollutants and nitrogen upcycling in a hybrid membrane biofilm reactor (hMBfR) for simultaneous O2 and CH4 supply

Pharmaceuticals and other organic micropollutants (OMPs) present in wastewater effluents are of growing concern, as they threaten environmental and human health. Conventional biological treatments lead to limited removal of OMPs. Methanotrophic bacteria can degrade a variety of OMPs. By employing a novel bubble-free hybrid membrane biofilm bioreactor (hMBfR), we grew methanotrophic bacteria at three CH4 loading rates. Biomass productivity and CH4 loading showed a linear correlation, with a maximum productivity of 372 mg-VSS·L−1·d−1, with corresponding biomass concentration of 1117.6 ± 56.4 mg-VSS·L−1. Furthermore, the biodegradation of sulfamethoxazole and 1H-benzotriazole positively correlated with CH4 oxidation rates, with highest biodegradation kinetic constants of 3.58 L·g−1·d−1 and 5.42 L·g−1·d−1, respectively. Additionally, the hMBfR recovered nutrients as microbial proteins, with an average content 39% DW. The biofilm community was dominated by Methylomonas, while the bulk was dominated by aerobic heterotrophic bacteria. The hMBfR removed OMPs, allowing for safer water reuse while valorising CH4 and nutrients.

Degradation of emerging pollutants on bifunctional ZnFeV LDH@graphite felt cathode through prominent catalytic activity in heterogeneous electrocatalytic processes

The heterogeneous Electro-Fenton (EF) process is a promising wastewater treatment technology that can generate onsite H2O2, and operate in a wide pH range without generating a metal sludge. However, the heterogeneous EF process needs bifunctional cathode electrodes that can have high activity in 2e− oxygen reduction reaction and H2O2 decomposition. Herein, ZnFeV layered double hydroxide (LDH), as a heterogeneous catalyst, was coated on the graphite felt (ZnFeV LDH@GF) cathode using the electrophoretic deposition method. ZnFeV LDH@GF cathode was able to generate 59.8 ± 5.9 mg L−1 H2O2 in 90 min under a constant supply of O2. EF process with ZnFeV LDH@GF cathode exhibited 89.8 ± 6.8% removal efficiency for pharmaceutical (ciprofloxacin) at neutral pH. Remarkably, the apparent reaction rate constant (kapp) of the ZnFeV LDH@GF-EF was 2.14 times that of the EF process with pristine GF. ZnFeV LDH coating increased the hydroxyl radical (•OH) production of the EF process from 1.74 mM to 3.65 mM. The pathway of •OH production is thought to be a single electron transfer from redox couples of Fe2+/Fe3+ and V4+/V5+ to H2O2. After 10 reuse cycles, the ZnFeV LDH@GF cathode retained 90.2% of its efficiency. Eight intermediate compounds were identified by GC-MS including cyclic compounds and aliphatic compounds.

The “Oxygen Sink” of Bamboo Shoots Regulates and Guarantees the Oxygen Supply for Aerobic Respiration

The amazingly rapid growth of bamboo shoots requires strong respiration and provides a large amount of energy and intermediate metabolites. Strong aerobic respiration requires a large amount of O2. This raises the following question: What is the source and mechanism of O2 supply to meet aerobic respiration? However, currently, this remains unknown. The underground buds (US), the 2-m-high overground buds (AS), and the 8-m-high growth arrest buds (HS) of bamboo (Phyllostachys prominens) were collected to represent their different stages of growth and development. The fifth bamboo shoot node at each stage was sealed by two membranes, and treated in a polyethylene zip-lock bag filled with air (21% O2 + 79% N2) and nitrogen (100% N2) for 1.5 h. The concentrations of free O2 and CO2 in the shoot cavities in polyethylene zip-lock bags, and the ethanol content in the shoot body before and after treatment were determined. In addition, the photosynthetic rates of the fifth bamboo internodes of 1 y/o, 2 y/o and 3 y/o bamboo in the field were measured. The results indicated that: (1) When treated with air and nitrogen, US, AS and HS mainly exhibited aerobic respiration, and there was almost no anaerobic respiration; (2) When treated with air, 59.66%, 54.47% and 45.84% of the O2 in the aerobic respiration of US, AS and HS came from the polyethylene zip-lock bag, 0.06%, 0.57% and 0.650% came from the shoot cavity, but 40.28%, 44.96% and 53.51% of the O2 was of an unknown source; (3) Treated by nitrogen, 0.19%, 4.71% and 4.79% of O2 in aerobic respiration of US, AS and HS came from shoot cavity, while the other 99.808%, 95.290% and 95.21% of O2 came from unknown sources; and (4) The photosynthesis of the fifth internodes of 1 y/o, 2 y/o and 3 y/o bamboo generated little oxygen that could not absolutely meet the huge O2 supply for aerobic respiration. It was concluded that the respiration of P. prominens shoots in its different growth and development stages was dominated by aerobic respiration. O2 supply pathways were mainly via the sheath stomata; however, there was little absorption from dissolved O2 in the soil water and little supply produced by shoot/stem photosynthesis. It was found that the large supply of oxygen in the aerobic respiration of bamboo shoots and young bamboo was of an unknown source under air treatment and nitrogen treatment, i.e., 40.28%–53.51% and 95.21%–99.81% of oxygen in the aerobic respiration of bamboo shoots and young bamboo was of unknown origin, respectively. Therefore, we proposed that bamboo shoots may exhibit the phenomenon of acting as an “oxygen sink”, which can provide a large amount of O2 from unknown sources to ensure the rapid growth of bamboo shoots and young bamboo.

In-vivo Estimation of Intramuscular and Diffusive Limitations to O2 Flow Limitations in Resistance and Endurance Trained Individuals by Near Infra-red Spectroscopy

Introduction: Compared with resistance training (RT), endurance training (ET) induces structural changes within skeletal muscles that include increased capillary density and increased oxidative enzyme activity. The adaptations in ET of oxidative capacity are thought to be greater than those of capillary density, causing the location of O2 flow limitation to move from the intramuscular (O2 utilization limited) to the extramuscular (O2supply limited) compartment. We recently proposed a new approach to estimate oxidative capacity and O2diffusion limitation in vivo by near-infrared spectroscopy (NIRS), using the premise that diffusion limitation is exposed by an experimentally-imposed reduction in O2 supply. We therefore evaluated whether this technique could distinguish muscular adaptations between ET and RT individuals. We hypothesized that both muscle oxidative capacity and diffusion limitation would be greater in ET than RT. Methods: Twenty-one young male resistance (RT, n=9, 26±4 yrs) and endurance (ET, n=12, 27±7 yrs) trained individuals volunteered. RT or ET status was characterized using: maximal isometric voluntary torque (MVT) of knee extensors; incremental cycle-ergometry to the limit of tolerance for peak oxygen uptake (V̇O2peak); vastus lateralis fractional O2extraction at V̇O2peak (ΔHHbMbpeak), expressed as percentage of ΔHHbMb during sustained occlusion; and by V̇O2 kinetics (τV̇O2) during moderate intensity constant work-rate exercise. Vastus lateralis muscle V̇O2recovery rate constant ( k) following brief knee extensor exercise was assessed using NIRS and repeated transient arterial occlusions. k was assessed twice, with arterial occlusions manipulated to maintain tissue saturation index within a 10% range in either LOW or HIGH conditions. Results: MVT was greater in RT than ET (328±43 vs. 255±40N, P<0.001). V̇O2peak was lower in RT than ET (38.8±4.6 vs. 55.6±3.8ml∙kg-1∙min-1, P<0.001). ΔHHbMbpeak was lower in RT than ET (57±11 vs. 91±6%, P<0.001). τV̇O2 was lower in RT than ET (39.8±7.6 vs. 24.0±4.4s, P<0.001). kHIGH was lower in RT than ET (1.49±0.25 vs. 3.04±0.71min-1, P=0.001) and the difference in k (Δ k = kHIGH – kLOW) was less in RT than ET (0.29±0.16 vs 0.80±0.69 min-1, P=0.045). Conclusions: As hypothesized, non-invasive assessment of muscle functional indices of oxidative and diffusive O2 flow in vivo revealed significantly greater oxidative capacity (greater kHIGH) and a greater diffusion limitation (greater Δ k) in ET individuals compared with RT. The new NIRS method allows independent assessment of limitations in muscle oxidative and diffusive O2 flow in resistance and endurance trained individuals. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Differences in recent and future trends in the Arabian Sea oxygen minimum zone: processes and uncertainties

The Arabian Sea is an exceptionally complex system that hosts a highly productive marine ecosystem. This intense productivity leads to high oxygen consumption at depth that maintains, together with the sluggish circulation, the world’s thickest oxygen minimum zone (OMZ). While observations have been scarce in the region, evidence for a recent (1960-2020) decline in oxygen is emerging in the northern Arabian Sea. However, in the longer term (2050 to 2100) the future evolution of the OMZ is more uncertain, as the model projections that have been carried out are not consistent with each other. On the one hand, this reflects the limitations of current generation models that do not adequately represent key physical and biogeochemical processes, resulting in large O2 biases in the region under present-day conditions. On the other hand, the inherent difficulty of predicting future O2 conditions in the Arabian Sea is a consequence of the sensitivity of O2 supply and consumption to local and remote changes that evolve on different timescales. Here we aim to synthesize current knowledge of the Arabian Sea OMZ in relation to important factors controlling its intensity and review its recent change and potential future evolution. In particular, we explore potential causes of the differences in recent and future O2 trends in the region and identify key challenges to our ability to project future OMZ changes and discuss ideas for the way forward.

Photoactivation of Boronic Acid Prodrugs via a Phenyl Radical Mechanism: Iridium(III) Anticancer Complex as an Example.

Boronic acid (or ester) is a well-known temporary masking group for developing anticancer prodrugs responsive to tumoral reactive oxygen species (ROS), but their clinic application is largely hampered by the low activation efficiency. Herein, we report a robust photoactivation approach that can spatiotemporally convert boronic acid-caged iridium(III) complex IrBA into bioactive IrNH2 under hypoxic tumor microenvironments. Mechanistic studies show that the phenyl boronic acid moiety in IrBA is in equilibrium with phenyl boronate anion that can be photo-oxidized to generate phenyl radical, a highly reactive species that is capable of rapidly capturing O2 at extremely low concentrations (down to 0.02%). As a result, while IrBA could hardly be activated by intrinsic ROS in cancer cells, upon light irradiation, the prodrug is efficiently converted into IrNH2 even in limited O2 supply, along with direct damage to mitochondrial DNA and potent antitumor activities in hypoxic 2D monolayer cells, 3D tumor spheroids, and mice bearing tumor xenografts. Of note, the photoactivation approach could be extended to intermolecular photocatalytic activation by external photosensitizers with red absorption and to activate prodrugs of clinic compounds, thus offering a general approach for activation of anticancer organoboron prodrugs.

Aging and the carotid body: A scoping review

The carotid body (CB) is a neuroepithelial tissue consisting of O2-sensitive glomus cells that constantly scan the arterial blood for O2 and generate a discharge as an inverse function of O2 content. Aging is a cumulative result of decreased O2 supply paralleled by a decreased O2 tissue demand and oxidative damage to cells derived from aerobic metabolism. Here we studied how CB affects the aging process. This is a study of CB ultrastructural morphometry and immunohistochemical expression of proteins underlying CB responsiveness. The study was based on human CBs obtained from cadavers of people who died due to traumatic events in young and old age. The study was supplemented by investigations of CBs obtained from young and old rats subjected to chronic normoxic and hypoxic conditions. We found changes in the old normoxic CBs akin to the effects of chronic hypoxia such as enhanced extracellular matrix, reduced synaptic contacts between glomus cells, fewer glomus cells, secretory vesicles, and mitochondria. These changes were accompanied by enhanced expressions of hypoxia-inducible factor one-alpha (HIF-1α), vascular endothelial growth factor (VEGF), and nitric oxide synthase (NOS2). We conclude that hypoxia and aging share a common background consisting of deficient O2 tissue supply, mitochondrial dysfunction, and a limited ability to deal with increased cellular oxidative stress. Aging leads to adaptative reductions in CB responsiveness to hypoxia shifting the chemosensory setpoint upward. We submit that the attenuated CB sensitivity at old age may be tantamount to “physiological denervation” leading to a gradual loss of the chemosensing role in the prevention of tissue hypoxia by increasing lung ventilation.

Hierarchical Structure of Gold and Carbon Electrode for Bilirubin Oxidase-Biocathode.

Biofuel cells (BFCs) with enzymatic electrocatalysts have attracted significant attention, especially as power sources for wearable and implantable devices; however, the applications of BFCs are limited owing to the limited O2 supply. This can be addressed by using air-diffusion-type bilirubin oxidase (BOD) cathodes, and thus the further development of the hierarchical structure of porous electrodes with highly effective specific surface areas is critical. In this study, a porous layer of gold is deposited over magnesium-oxide-templated carbon (MgOC) to form BOD-based biocathodes for the oxygen reduction reaction (ORR). Porous gold structures are constructed via electrochemical deposition of gold via dynamic hydrogen bubble templating (DHBT). Hydrogen bubbles used as a template and controlled by the Coulomb number yield a porous gold structure during the electrochemical deposition process. The current density of the ORR catalyzed by BOD without a redox mediator on the gold-modified MgOC electrode was 1.3 times higher than that of the ORR on the MgOC electrode. Furthermore, the gold-deposited electrodes were modified with aromatic thiols containing negatively charged functional groups to improve the orientation of BOD on the electrode surface to facilitate efficient electron transfer at the heterogeneous surface, thereby achieving an ORR current of 12 mA cm-2 at pH 5 and 25 °C. These results suggest that DHBT is an efficient method for the fabrication of nanostructured electrodes that promote direct electron transfer with oxidoreductase enzymes.

Genome-Wide Analysis of Hypoxia-Inducible Factor Binding Reveals Targets Implicated in Impaired Human Placental Syncytiotrophoblast Formation under Low Oxygen

Preeclampsia (PE) is a common and serious complication of pregnancy with no cure except premature delivery. The root cause of PE is improper development of the placenta-the temporary organ supporting fetal growth and development. Continuous formation of the multinucleated syncytiotrophoblast (STB) layer via differentiation and fusion of cytotrophoblasts (CTBs) is vital for healthy placentation and is impaired in preeclamptic pregnancies. In PE, there is reduced/intermittent placental perfusion, likely resulting in a persistently low O2 environment. Low O2 inhibits differentiation and fusion of CTBs into STB and may thus contribute to PE pathogenesis; however, the underlying mechanisms are unknown. Because low O2 activates a transcription factor complex in cells known as the hypoxia-inducible factor (HIF), the objective of this study was to investigate whether HIF signaling inhibits STB formation by regulating genes required for this process. Culture of primary CTBs, the CTB-like cell line BeWo, and human trophoblast stem cells under low O2 reduced cell fusion and differentiation into STB. Knockdown of aryl hydrocarbon receptor nuclear translocator (a key component of the HIF complex) in BeWo cells restored syncytialization and expression of STB-associated genes under different O2 levels. Chromatin immunoprecipitation sequencing facilitated the identification of global aryl hydrocarbon receptor nuclear translocator/HIF binding sites, including several near genes implicated in STB development, such as ERVH48-1 and BHLHE40, providing new insights into mechanisms underlying pregnancy diseases linked to poor placental O2 supply.

An Overview on the Worlds Dead Liest Poison (Palytoxin and its Analogs)

Abstract: Palytoxin is a marine toxin found originally in soft corals Palythoa species of the Pacific Ocean. It is a thermostable, non-protein, coronary vasoconstrictor that leads to death by diminishing the supply of O2 to the Myocardium. Several analogs of PTX or PTLX such as Ostreocin-D, Ovatoxin are found in several dinoflagellates and other marine species such as Crabs (Demania reynaudii) and Smoked Fishes (Decapterus macrosoma) found in same ecological regions. Toxicological studies of PTX showed low lethal dose values in different mammals revealing the acute toxicity due to different routes of exposure. On exposure to PTX, symptoms such as Rhabdomyolysis (high dose), Na+- K+ pump and heart failure & other symptoms including abdominal cramps, vomiting, bradycardia, etc. are seen in Pescatarians. There is no particular antidote for the PTX compounds, but these compounds can be neutralized by the household bleach solution. Activated Carbon absorbed 99.7% of palytoxin in aquarium waters. In this paper, we review the current knowledge on Palytoxin & its analogs. In recent years, many methodologies have been described for the development of new techniques for the detection of palytoxin based on LC-MS/MS and a bio-technique Immunoassay.

Modeling of dual-permeability gas and solute reactive transport in macroporous agricultural soils with a focus on GHG cycling and emissions

Agricultural soil is the domain where biogeochemical C-N turnover is affected by atmospheric and hydrologic processes, playing a vital role in anthropogenic greenhouse gas (GHG) emissions and thus affecting global climate change. GHG cycling and emissions are further complicated by the characteristics of soil structure, in particular macropores (i.e., preferential flow pathway). In this study, the processes of non-equilibrium gas diffusion and gas exchange were implemented into an existing dual-permeability flow and reactive solute transport model. The model was then used in a sensitivity analysis to evaluate the suitability of the modeling approach to account for development of anaerobic hotspots, with an emphasis on assessing N2O production and emissions. The sensitivity analysis combined with characteristic time scale analysis suggests that the development of anaerobic hotspots is controlled by a combination of both physical and geochemical parameters. Time scale analysis of O2 supply and consumption indicates that the occurrence of anaerobic hotspots is determined by the balance between characteristic times of O2 diffusion through the soil profile or exchange between macropores and the soil matrix, and the characteristic time of O2 consumption. Motivated by these findings, the present model was applied to simulate GHG cycling at a field site in Ontario, Canada, featuring macroporous agricultural soil. The model generally reproduced observed spatiotemporal variations in pore gas O2 and GHG concentrations and fluxes. Simulation results suggest that at this site, gas exchange processes between regions of preferential flow and the soil matrix play an important role in controlling the spatial variation of O2 in the soil. The simulations illustrate how the release of GHGs from the soil matrix into the macropores can lead to GHG emissions to the atmosphere. The modeling approach presented here, including dual domain flow and solute transport, as well as dual domain gas transport, shows promise for future studies with the aim to develop a more complete understanding of how soil structure affects complex GHG cycling in agricultural soils.

Tenrecs deal with poor air quality like reptiles

Dealing with dangerously high CO2 levels is a regular part of life for burrowing creatures. ‘Most animals that are able to tolerate such environments reduce their metabolic rate to re-balance their energy demands’, says Matthew Pamenter from the University of Ottawa, Canada. So, when he heard Frank van Breukelen of the University of Nevada, USA, talk about his burrowing tenrec (Tenrec ecaudatus) colony at a conference in 2019, he realised that the animals might also experience dangerous CO2 concentrations – up to 13.5%, compared with 0.04% in the atmosphere – when hibernating with burrow-mates for 8–9 months. Yet tenrecs are not regular mammals. They can remain active even when their body temperature plummets to 12°C; so how do they cope with the toxic air in their hibernation burrows?Pamenter contacted van Breukelen to suggest a collaboration, and in March 2020, Maiah Devereaux (University of Ottawa) joined Claudia Silva Rubio and van Breukelen at the University of Nevada to find out how tenrecs deal with excessive CO2 and low O2. ‘Our tenrecs are handled very frequently and so they are very docile. To be honest, they are kind of lazy!’ chuckles van Breukelen, who recalls that the animals were content to hang out in a respirometry chamber while Devereaux and Silva Rubio measured the tenrecs’ breath rate and O2 consumption to calculate their metabolic rate. The duo then modified the air mixture the tenrecs were breathing – first reducing the O2 content from 21% to 9% and 4%, before boosting the CO2 levels from 0% to 5% and 10% – at 28°C and 16°C, to find out how the mammals responded. ‘Trying to maintain a stable [gas] flow rate required some troubleshooting’, says van Breukelen.Even when the tenrecs were breathing normal air in the cooler conditions, the active animals’ metabolisms responded unconventionally. Some barely breathed at all – only consuming 2 ml O2 min−1 kg−1 – while others inhaled a colossal amount (23 ml O2 min−1 kg−1) relative to the warmer tenrecs, which only inhaled 12 ml O2 min−1 kg−1 at the most. Raising the CO2 levels in the air didn't affect the range of the cold tenrec's metabolic rates; however, when the team reduced the animals’ O2 supply, the chilly animals no longer had the wide range of metabolic rates they had when breathing normal air.The air temperature also had a major impact on the way the tenrecs breathed when their air was contaminated with CO2. The warmer animals began hyperventilating when the CO2 levels increased, in contrast to the cooler tenrecs, which were more like other burrowing mammals and did not hyperventilate.In short, the tenrecs’ breathing and metabolism were more affected by the environmental temperature than the build-up of toxic CO2 and quantity of O2 available. In addition, the animals in the colder conditions allowed their body temperatures to drift, with some cooling to 20°C while others remained at 32°C regardless of the air quality; all of the tenrecs in 28°C air maintained a warm body temperature (∼32°C) despite the air conditions. The physiological responses of the tenrecs were more like those of cold-blooded reptiles than those of warm-blooded burrowing mammals, probably because they don't have to maintain a high body temperature to survive. van Breukelen exclaims, ‘Many of the things that tenrecs do result in me saying, “How the heck do they do this?”’, and he is excited to find out how the animals cope with poor air quality when breathing as little as once every 45 min while hibernating.

Regulation of marine plankton respiration: A test of models

Plankton respiration is a major process removing oxygen from pelagic environments and constitutes one of the largest oxygen transformations in the sea. Where the O2 supplies due to dissolution, advection and oxygenic photosynthesis are not sufficient, hypoxic, or anoxic waters may result. Coastal waters with limited water exchange are especially prone to have low oxygen levels due to eutrophication and climate change. To support marine environmental management in a period of rapid climate change, we investigated the current knowledge of regulating plankton respiration based on field and experimental studies reported in the literature. Models for regulation of plankton respiration was tested on a three-year field data set. Temperature is the most reported predictor positively influencing plankton respiration (mean r2 = 0.50, n=15). The organic carbon supply driven by primary production has a similar coefficient of determination but fewer reported relationships (mean r2 = 0.52, n=6). Riverine discharges of dissolved organic carbon can override the influence of primary production in estuaries precluding effects of nutrient reductions. The median predictions of respiration regulation produced by current models vary by a factor of 2 from the median of observed values and extreme values varied even more. Predictions by models are therefore still too uncertain for application at regional and local scales. Models with temperature as predictor showed best performance but deviated from measured values in some seasons. The combined dependence of plankton respiration on temperature, phytoplankton production and discharge of riverine organic carbon will probably lead to increased oxygen consumption and reduced oxygen levels with projected climate change. This will be especially pronounced where increased precipitation is expected to enhance riverine discharges of carbon compounds. The biologically mediated transfer of carbon for long-term storage in deeper layers will slow down. Implementation of plankton respiration measurements in long-term ecological monitoring programs at water body and basin scales is advocated, which would enable future multivariate analyses and improvements in model precision across aquatic environments.

A Critical Evaluation of Recent Studies on Packed-Bed Bioreactors for Solid-State Fermentation

Packed-bed bioreactors are often used for aerobic solid-state fermentation, since the forced aeration supplies O2 and removes metabolic heat from the bed. Motivated by the potential for applications in biorefineries, we review studies conducted on packed-bed bioreactors over the last decade, evaluating the insights these studies provide into how large-scale packed beds should be designed and operated. Many studies have used low superficial air velocities and suffer from preferential airflow, such that parts of the bed are not properly aerated. Moreover, some studies have proposed ineffective strategies, such as reversing the direction of the airflow or introducing air through perforated pipes within the bed. Additionally, many studies have used narrow water-jacketed packed-bed bioreactors, but these bioreactors do not reflect heat removal in wide large-scale packed beds, in which heat removal through the side walls makes a minor contribution. Finally, we conclude that, although some attention has been given to characterizing the porosities, water sorption isotherms and volumetric heat and mass transfer coefficients of substrate beds, this work needs to be extended to cover a wider range of solid substrates, and work needs to be done to characterize how these bed properties change due to microbial growth.

Mesocrystalline ZnS nanoparticles-augmented sonocatalytic full water splitting into H2/O2 for immunoactivating deep tumor

Therapeutic gas molecules have high tissue penetrability, but their sustainable supply and controlled release in deep tumor is a huge challenge. In this work, a concept of sonocatalytic full water splitting for hydrogen/oxygen immunotherapy of deep tumor is proposed, and a new kind of ZnS nanoparticles with a mesocrystalline structure (mZnS) is developed to achieve highly efficient sonocatalytic full water splitting for sustainable supply of H2 and O2 in tumor, achieving a high efficacy of deep tumor therapy. Mechanistically, locally generated hydrogen and oxygen molecules exhibit a tumoricidal effect as well as the co-immunoactivation of deep tumors through inducing the M2-to-M1 repolarization of intratumoral macrophages and the tumor hypoxia relief-mediated activation of CD8+ T cells, respectively. The proposed sonocatalytic immunoactivation strategy will open a new window to realize safe and efficient treatment of deep tumors.