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Despite the rising interest in understanding how climate change could affect the emissions of greenhouse gases (GHGs) from river systems, including floodplains, we still lack a mechanistic understanding of how changing environmental conditions, such as moisture and nutrient availability, limit the temperature responses of GHG production in floodplain sediments. To examine the environmental co-limitations on the temperature responses of three major GHGs (CO2, CH4, and N2O) produced in floodplain sediments, sediments from a constructed wetland on the floodplain of the lower Han River were incubated for 24 d at four temperatures spanning 4–28 ℃, under three conditions (closed, open/wetting, and open/drying). The net production of all three GHGs exhibited nonlinear temperature responses with gas-specific patterns and magnitudes of response varying over the incubation period. During the later incubation phase, positive temperature responses were weakened for the net production of CO2 and CH4 in the dried treatments, whereas a similar weakening occurred for N2O production in the wet treatments. This, combined with incubation-induced changes in dissolved organic carbon and its fluorescence components, indicated the lack or excess of moisture and associated changes in O2 and organic carbon availability as critical co-limiting factors for the temperature responses of GHG production. Warming decreased δ13C in the CH4 emitted from wet and hypoxic sediments, implying a stronger warming effect on CH4 production over oxidation. Unlike many studies assuming a consistent relationship between temperature and GHG production in sediments irrespective of other environmental conditions, our results suggest that warming effects on the GHG emissions from floodplain sediments would depend on the balance between gas production and consumption under the prevailing constraints of moisture, O2, and labile carbon availability. [ABSTRACT FROM AUTHOR]

Abstract At a given exercise intensity, blood flow restriction (BFR) reduces the volume of exercise required to impair post‐exercise neuromuscular function. Compared to traditional exercise, the time course of recovery is less clear. After strenuous exercise, force output assessed with electrical muscle stimulation is impaired to a greater extent at low versus high stimulation frequencies, a condition known as prolonged low‐frequency force depression (PLFFD). It is unclear if BFR increases PLFFD after exercise. This study tested if BFR during exercise increases PLFFD and slows recovery of neuromuscular function compared to regular exercise. Fifteen physically active participants performed six low‐load sets of knee‐extensions across four conditions: resistance exercise to task failure (RETF), resistance exercise to task failure with BFR applied continuously (BFRCONT) or intermittently (BFRINT), and resistance exercise matched to the lowest exercise volume condition (REVM). Maximal voluntary contraction (MVC) force output, voluntary activation and a force–frequency (1–100 Hz) curve were measured before and 0, 1, 2, 3, 4 and 24 h after exercise. Exercise to task failure caused similar reductions at 0 h for voluntary activation (RETF = 81.0 ± 14.2%, BFRINT = 80.9 ± 12.4% and BFRCONT = 78.6 ± 10.7%) and MVC force output (RETF = 482 ± 168 N, BFRINT = 432 ± 174 N, and BFRCONT = 443 ± 196 N), which recovered to baseline values between 4 and 24 h. PLFFD occurred only after RETF at 1 h supported by a higher frequency to evoke 50% of the force production at 100 Hz (1 h: 17.5 ± 4.4 vs. baseline: 15 ± 4.1 Hz, P = 0.0023), BFRINT (15.5 ± 4.0 Hz; P = 0.03), and REVM (14.9 ± 3.1 Hz; P = 0.002), with a trend versus BFRCONT (15.7 ± 3.5 Hz; P = 0.063). These findings indicate that, in physically active individuals, using BFR during exercise does not impair the recovery of neuromuscular function by 24 h post‐exercise.

At a given exercise intensity, blood flow restriction (BFR) reduces the volume of exercise required to impair post‐exercise neuromuscular function. Compared to traditional exercise, the time course of recovery is less clear. After strenuous exercise, force output assessed with electrical muscle stimulation is impaired to a greater extent at low versus high stimulation frequencies, a condition known as prolonged low‐frequency force depression (PLFFD). It is unclear if BFR increases PLFFD after exercise. This study tested if BFR during exercise increases PLFFD and slows recovery of neuromuscular function compared to regular exercise. Fifteen physically active participants performed six low‐load sets of knee‐extensions across four conditions: resistance exercise to task failure (RETF), resistance exercise to task failure with BFR applied continuously (BFRCONT) or intermittently (BFRINT), and resistance exercise matched to the lowest exercise volume condition (REVM). Maximal voluntary contraction (MVC) force output, voluntary activation and a force–frequency (1–100 Hz) curve were measured before and 0, 1, 2, 3, 4 and 24 h after exercise. Exercise to task failure caused similar reductions at 0 h for voluntary activation (RETF = 81.0 ± 14.2%, BFRINT = 80.9 ± 12.4% and BFRCONT = 78.6 ± 10.7%) and MVC force output (RETF = 482 ± 168 N, BFRINT = 432 ± 174 N, and BFRCONT = 443 ± 196 N), which recovered to baseline values between 4 and 24 h. PLFFD occurred only after RETF at 1 h supported by a higher frequency to evoke 50% of the force production at 100 Hz (1 h: 17.5 ± 4.4 vs. baseline: 15 ± 4.1 Hz, P = 0.0023), BFRINT (15.5 ± 4.0 Hz; P = 0.03), and REVM (14.9 ± 3.1 Hz; P = 0.002), with a trend versus BFRCONT (15.7 ± 3.5 Hz; P = 0.063). These findings indicate that, in physically active individuals, using BFR during exercise does not impair the recovery of neuromuscular function by 24 h post‐exercise. What is the central question of this study?Does the addition of blood flow restriction (BFR) during resistance exercise impaired recovery of neuromuscular function in physically active individuals?What is the main finding and its importance?While BFR during exercise increased fatiguability compared to exercise without BFR, it did not further impair the 24‐h recovery in neuromuscular function compared to exercise without BFR. These findings are relevant for applying BFR exercise in the training and/or rehabilitation of physically active populations such that it does not appear to further exacerbate muscle contractile function compared to regular strenuous exercise. [ABSTRACT FROM AUTHOR]

Simple Summary: This study establishes how trout's swimming energy changes under various oxygen levels and temperatures, leading to the development of a model that predicts oxygen conditions inside the cages. A case study using the model reveals that a 10 °C rise in temperature causes oxygen concentration to drop threefold, necessitating a 3.7-fold increase in water flow to maintain optimal oxygen levels. To ensure optimal feed intake, growth, and general fish health in aquaculture sea cages, interactions between drivers that affect oxygen conditions need to be understood. The main drivers are oxygen consumption and water exchange, caused by flow through the cage. Swimming energetics in rainbow trout (Oncorhynchus mykiss) in normoxia and hypoxia at 10, 15, and 20 °C were determined. Using the determinations, a conceptual model of oxygen conditions within sea cages was created. By applying the model to a case study, results show that with a temperature increase of 10 °C, oxygen concentration will decrease three times faster. To maintain optimal oxygen concentration within the cage, the flow velocity must be increased by a factor of 3.7. The model is highly relevant for current farms since the model predictions can explain why and when suboptimal conditions occur within the cages. Using the same method, the model can be used to estimate the suitability of potential new aquaculture sites. [ABSTRACT FROM AUTHOR]

The study combined the use of biometric, behavioral, physiological and external tissue damage scoring systems to better understand how high stocking densities drive schooling behavior and other adaptive features during the finishing growing phase of farmed gilthead sea bream in the Western Mediterranean. Fish were grown at three different final stocking densities (LD, 8.5 kg/m3; MD, 17 kg/m3; HD, 25 kg/m3). Water oxygen concentration varied between 5 and 6 ppm in LD fish to 3-4 ppm in HD fish with the summer rise of water temperature from 19°C to 26°C (May-July). HD fish showed a reduction of feed intake and growth rates, but they also showed a reinforced social cohesion with a well-defined endogenous swimming activity rhythm with feeding time as a main synchronization factor. The monitored decrease of the breathing/swimming activity ratio by means of the AEFishBIT data-logger also indicated a decreased energy partitioning for growth in the HD environment with a limited oxygen availability. Plasma glucose and cortisol levels increased with the rise of stocking density, and the close association of glycaemia with the expression level of antioxidant enzymes (mn-sod, gpx4, prdx5) in liver and molecular chaperones (grp170, grp75) in skeletal muscle highlighted the involvement of glucose in redox processes via rerouting in the pentosephosphate-pathway. Other adaptive features included the depletion of oxidative metabolism that favored lipid storage rather than fatty acid oxidation to decrease the oxygen demand as last electron acceptor in the mitochondrial respiratory chain. This was coincident with the metabolic readjustment of the Gh/Igf endocrine-growth cascade that promoted the regulation of muscle growth at the local level rather than a systemic action via the liver Gh/Igf axis. Moreover, correlation analyses within HD fish displayed negative correlations of hepatic transcripts of igf1 and igf2 with the data-logger measurements of activity and respiration, whereas the opposite was found for muscle igf2, ghr1 and ghr2. This was indicative of a growth-regulatory transition that supported a proactive instead of a reactive behavior in HD fish, which was considered adaptive to preserve an active and synchronized feeding behavior with a minimized risk of oxidative stress and epidermal skin damage. [ABSTRACT FROM AUTHOR]

The study combined the use of biometric, behavioral, physiological and external tissue damage scoring systems to better understand how high stocking densities drive schooling behavior and other adaptive features during the finishing growing phase of farmed gilthead sea bream in the Western Mediterranean. Fish were grown at three different final stocking densities (LD, 8.5 kg/m3; MD, 17 kg/m3; HD, 25 kg/m3). Water oxygen concentration varied between 5 and 6 ppm in LD fish to 3–4 ppm in HD fish with the summer rise of water temperature from 19°C to 26°C (May–July). HD fish showed a reduction of feed intake and growth rates, but they also showed a reinforced social cohesion with a well-defined endogenous swimming activity rhythm with feeding time as a main synchronization factor. The monitored decrease of the breathing/swimming activity ratio by means of the AEFishBIT data-logger also indicated a decreased energy partitioning for growth in the HD environment with a limited oxygen availability. Plasma glucose and cortisol levels increased with the rise of stocking density, and the close association of glycaemia with the expression level of antioxidant enzymes (mn-sod, gpx4, prdx5) in liver and molecular chaperones (grp170, grp75) in skeletal muscle highlighted the involvement of glucose in redox processes via rerouting in the pentose-phosphate-pathway. Other adaptive features included the depletion of oxidative metabolism that favored lipid storage rather than fatty acid oxidation to decrease the oxygen demand as last electron acceptor in the mitochondrial respiratory chain. This was coincident with the metabolic readjustment of the Gh/Igf endocrine-growth cascade that promoted the regulation of muscle growth at the local level rather than a systemic action via the liver Gh/Igf axis. Moreover, correlation analyses within HD fish displayed negative correlations of hepatic transcripts of igf1 and igf2 with the data-logger measurements of activity and respiration, whereas the opposite was found for muscle igf2, ghr1 and ghr2. This was indicative of a growth-regulatory transition that supported a proactive instead of a reactive behavior in HD fish, which was considered adaptive to preserve an active and synchronized feeding behavior with a minimized risk of oxidative stress and epidermal skin damage.

To ensure optimal feed intake, growth, and general fish health in aquaculture sea cages, interactions between drivers that affect oxygen conditions need to be understood. The main drivers are oxygen consumption and water exchange, caused by flow through the cage. Swimming energetics in rainbow trout (Oncorhynchus mykiss) in normoxia and hypoxia at 10, 15, and 20 °C were determined. Using the determinations, a conceptual model of oxygen conditions within sea cages was created. By applying the model to a case study, results show that with a temperature increase of 10 °C, oxygen concentration will decrease three times faster. To maintain optimal oxygen concentration within the cage, the flow velocity must be increased by a factor of 3.7. The model is highly relevant for current farms since the model predictions can explain why and when suboptimal conditions occur within the cages. Using the same method, the model can be used to estimate the suitability of potential new aquaculture sites.

Dissolved organic matter (DOM) plays a vital role in biogeochemical processes and in determining the responses of soil organic matter (SOM) to global change. Although the quantity of soil DOM has been inventoried across diverse spatio‐temporal scales, the underlying mechanisms accounting for variability in DOM dynamics remain unclear especially in upland ecosystems. Here, a gradient of SOM storage across 12 croplands in northeast China was used to understand links between DOM dynamics, microbial metabolism, and abiotic conditions. We assessed the composition, biodegradability, and key biodegradable components of DOM. In addition, SOM and mineral‐associated organic matter (MAOM) composition, soil enzyme activities, oxygen availability, soil texture, and iron (Fe), Fe‐bound organic matter, and nutrient concentrations were quantified to clarify the drivers of DOM quality (composition and biodegradability). The proportion of biodegradable DOM increased exponentially with decreasing initial DOM concentration due to larger fractions of depolymerized DOM that was rich in small‐molecular phenols and proteinaceous components. Unexpectedly, the composition of DOM was decoupled from that of SOM or MAOM, but significantly related to enzymatic properties. These results indicate that microbial metabolism exhibited a dominant role in DOM generation. As DOM concentration declined, increased soil oxygen availability regulated DOM composition and enhanced its biodegradability mainly through mediating microbial metabolism and Fe oxidation. The oxygen‐induced oxidation of Fe(II) to Fe(III) removed complex DOM compounds with large molecular weight. Moreover, increased oxygen availability stimulated oxidase‐catalyzed depolymerization of aromatic substances, and promoted production of protein‐like DOM components due to lower enzymatic C/N acquisition ratio. As global changes in temperature and moisture will have large impacts on soil oxygen availability, the role of oxygen in regulating DOM dynamics highlights the importance of integrating soil oxygen supply with microbial metabolism and Fe redox status to improve model predictions of soil carbon under climate change. [ABSTRACT FROM AUTHOR]

An advanced model is developed to elucidate relationship between availability of oxygen and active corrosion, considering the equilibrium between gaseous and dissolved oxygen, as well as the equilibrium of oxygen diffusion and consumption. This research notably incorporates self-regulation mechanisms of cathodes and anodes in both macrocell and microcell corrosion. Accelerated corrosion experiments were performed under simulated marine environment, monitoring variations in corrosive medium concentration and electrochemical corrosion processes. Results indicate significant reduction in oxygen concentration following the activation of rebar. Potential inaccuracies in predicting corrosion rate arise from the adoption of a static cathodic to anodic area ratio was highlighted. • Availability of oxygen in cathodic areas throughout the steel corrosion process. • Self-regulation mechanisms of cathodes and anodes in both macrocell and microcell corrosion configurations. • Accelerated corrosion experiments under simulated marine environment. • Significant reduction in oxygen concentration following the activation of rebar. • Oxygen concentration ultimately achieving a steady state of equilibrium between influx and consumption. [ABSTRACT FROM AUTHOR]

Animals, including insects, need oxygen for aerobic respiration and eventually asphyxiate without it. Aerobic respiration, however, produces reactive oxygen species (ROS), which contribute to dysfunction and aging. Animals appear to balance risks of asphyxiation and ROS by regulating internal oxygen relatively low and stable, but sufficient levels. How much do levels vary among species, and how does variation depend on environment and life history? We predicted that lower internal oxygen levels occur in insects with either limited access to environmental oxygen (i.e., insects dependent on aquatic respiration, where low internal levels facilitate diffusive oxygen uptake, and reduce asphyxiation risks) or consistently low metabolic rates (i.e., inactive insects, requiring limited internal oxygen stores). Alternatively, we predicted insects with long life-stage durations would have internal oxygen levels > 1 kPa (preventing high ROS levels that are believed to occur under tissue hypoxia). We tested these predictions by measuring partial pressures of oxygen (PO 2 ) in tissues from juvenile and adult stages across 15 species comprising nine insect orders. Tissue PO 2 varied greatly (from 0 to 18.8 kPa) and variation across species and life stages was significantly related to differences in habitat, activity level, and life stage duration. Individuals with aquatic respiration sustained remarkably low PO 2 (mean = 0.88 kPa) across all species from Ephemeroptera (mayflies), Plecoptera (stoneflies), Trichoptera (caddisflies), and Diptera (true flies), possibly reflecting a widespread, but hitherto unknown, adaptation for extracting sufficient oxygen from water. For Odonata (dragonflies), aquatic juveniles had higher PO 2 levels (mean = 6.12 kPa), but these were still lower compared to terrestrial adults (mean = 13.3 kPa). Follow-up tests in juvenile stoneflies showed that tissue PO 2 remained low even when exposed to hyperoxia, suggesting that levels were down-regulated. This was further corroborated since levels could be modulated by ambient oxygen levels in dead individuals. In addition, tissue PO 2 was positively related to activity levels of insect life stages across all species and was highest in stages with short durations. Combined, our results support the idea that internal PO 2 is an evolutionarily labile trait that reflects the balance between oxygen supply and demand within the context of the environment and life-history of an insect., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2024 The Authors. Published by Elsevier B.V.)

Green turtle (Chelonia mydas) embryos are in an arrested state of development when the eggs are laid, but in the presence of oxygen, arrest is broken and development resumes within 12–16 h. However, the precise oxygen level at which embryos break arrest and continue development is not known. To better understand the impact of oxygen concentration on breaking of arrest and early embryonic development, we incubated freshly laid eggs of the green sea turtle for three days at each of six different oxygen concentrations (less than or equal to 1%, 3%, 5%, 7%, 9% and 21%) and monitored the appearance and growth of white spots on the shell, indicative of embryonic development. As reported previously, white spots did not develop on eggs incubated in anoxia (less than or equal to 1% oxygen). For all other treatments, mean time to white spot detection and white spot growth rate varied inversely with oxygen concentration. In nearly all cases the difference between eggs at different oxygen levels was statistically significant (p ≤ 0.05). This suggests that sea turtle embryonic development may respond to oxygen in a dose-dependent manner. Our results indicate that the development of green turtle embryos may be slowed if they are exposed to the most hypoxic conditions reported in mature natural nests.

In this study, Baltic Sea sediments, as a source of dissolved inorganic carbon (DIC), dissolved organic carbon (DOC), ammonium (NH4+), and phosphates (PO43−), were investigated based on samples obtained in 2017 and 2018, shortly after a sequence of inflows from the North Sea that occurred between 2014 and 2017. Two different data sets (I and II) were used to assess benthic diffusive fluxes and thus elucidate both the temporal conditions at the time of sampling (data set I) and the diffusion potential of the sediments (data set II). The estimated fluxes were characterized by a high spatial variability within the whole Baltic Sea and ranged between −0.01 and 3.33 mmol m−2 d−1 for DIC, −0.02 and 0.44 mmol m−2 d−1 for DOC, −40.5 and 1370.1 µmol m−2 d−1 for NH4+, and −5.9 and 60.9 µmol m−2 d−1 for PO43−. The estimated benthic diffusive fluxes indicated a high potential for DIC, DOC, NH4+, and PO43− release from Baltic Sea sediments. The high O2 concentrations in the water column of the Gulf of Bothnia together with major Baltic inflows (MBIs) bringing oxygenated seawater to the Baltic Proper and to some extent the Eastern Gotland Basin regulate the amounts of chemicals released from the sediment. Our study showed that a sequence of inflows has greater impact on the diminution of diffusive fluxes than does a single MBI and that the sediments of the Baltic Proper, even under the influence of inflows, are an important source of C, N, and P (159 kt yr−1 for DIC+DOC, 6.3 kt yr−1 for N-NH4+ and 3.7 kt yr−1 for P-PO43−) that should be considered in regional budget estimations.

Soil microorganisms support multiple agroecosystem functions, but responses of the microbiome to prolonged agricultural land-use and underlying mechanisms remain poorly understood. In this study, upland soils in the Mollisol region of Northeast China were selected along a 100-year cultivation chronosequence to examine the effects of intensive agriculture on the diversity, composition and co-occurrence network of bacterial and fungal communities. To elucidate the determinants driving the dynamics and interactions of microbial communities, the researchers quantified the functional groups and bioavailable fractions of soil organic carbon, and estimated the microenvironments including soil texture and oxygen availability. Our findings revealed that fungal diversity and community stability decreased over cultivation time, while that of bacteria showed a less significant decline. The increased oxygen availability and decreased soil carbon supply, particularly polyphenols, jointly drove the dynamics in the composition and stability of the microbial communities. Crucially, these microbial responses were significantly regulated by interspecific associations. Phylotypes showing stronger responses to changes in oxygen availability and carbon supply demonstrated a higher level of connectivity within co-occurrence networks, signifying their potential role as pivotal "hubs" in transmitting the environmental influences across the entire community via interspecific associations. Moreover, the decline in fungal diversity over longer cultivation periods could liberate more survival niches for bacterial species through fungi-bacteria associations, thereby bolstering the stability of the bacterial community. Overall, this study accentuates the pivotal role of trophic associations in facilitating the oxygen and carbon-induced succession of belowground microbiota in long-term cultivated Mollisols. In view of the agricultural intensification propelled by the increasing demand for crop production, these findings suggest strategies integrating improvements in soil structure and carbon with microbial processes to ensure the sustainability of agroecosystem functions. • Long-term cultivation reduced diversity and community stability of fungi. • Bacteria exhibited less diversity loss and resilient community stability. • Increased O 2 availability and reduced C supply destabilized microbial community. • Bacterial community stability was regulated by fungal diversity. • Species interactions governed the effect of carbon and oxygen supply on microbiota. [ABSTRACT FROM AUTHOR]

Purpose: To examine the effect of normobaric hypoxia on pulmonary oxygen uptake (V˙O2) and muscle oxygenation kinetics during incremental and moderate-intensity exercise in children., Methods: Eight prepubertal boys (9-11 y) performed incremental cycle tests to exhaustion in both normoxia and hypoxia (fraction of inspired O2 of 15%) followed by repeat 6-minute transitions of moderate-intensity exercise in each condition over subsequent visits., Results: Maximal oxygen uptake (V˙O2max) was reduced in hypoxia compared with normoxia (1.69 [0.20] vs 1.87 [0.26] L·min-1, P = .028), although the gas exchange threshold was not altered in absolute terms (P = .33) or relative to V˙O2max (P = .78). During moderate-intensity exercise, the phase II V˙O2 time constant (τ) was increased in hypoxia (18 [9] vs 24 [8] s, P = .025), with deoxyhemoglobin τ unchanged (17 [8] vs 16 [6], P ≥ .28)., Conclusions: In prepubertal boys, hypoxia reduced V˙O2max and slowed V˙O2 phase II kinetics during moderate-intensity exercise, despite unchanged deoxyhemoglobin kinetics. These data suggest an oxygen delivery dependence of V˙O2max and moderate-intensity V˙O2 kinetics under conditions of reduced oxygen availability in prepubertal boys.

Abstract Background Production of 2,3-butanediol from renewable resources is a promising measure to decrease the consumption of fossil resources in the chemical industry. One of the most influential parameters on biotechnological 2,3-butanediol production is the oxygen availability during the cultivation. As 2,3-butanediol is produced under microaerobic process conditions, a well-controlled oxygen supply is the key parameter to control biomass formation and 2,3-butanediol production. As biomass is on the one hand not the final product, but on the other hand the essential biocatalyst, the optimal compromise between biomass formation and 2,3-butanediol production has to be defined. Results A shake flask methodology is presented to evaluate the effects of oxygen availability on 2,3-butanediol production with Bacillus licheniformis DSM 8785 by variation of the filling volume. A defined two-stage cultivation strategy was developed to investigate the metabolic response to different defined maximum oxygen transfer capacities at equal initial growth conditions. The respiratory quotient was measured online to determine the point of glucose depletion, as 2,3-butanediol is consumed afterwards. Based on this strategy, comparable results to stirred tank reactors were achieved. The highest space–time yield (1.3 g/L/h) and a 2,3-butanediol concentration of 68 g/L combined with low acetoin concentrations and avoided glycerol formation were achieved at a maximum oxygen transfer capacity of 13 mmol/L/h. The highest overall 2,3-butanediol concentration of 78 g/L was observed at a maximum oxygen transfer capacity of 4 mmol/L/h. Conclusions The presented shake flask approach reduces the experimental effort and costs providing a fast and reliable methodology to investigate the effects of oxygen availability. This can be applied especially on product and by-product formation under microaerobic conditions. Utilization of the maximum oxygen transfer capacity as measure for the oxygen availability allows for an easy adaption to other bioreactor setups and scales.

Next generation biofuels including longer-chain alcohols such as butanol are attractive as renewable, high-energy fuels. A barrier to microbial production of butanols is the increased toxicity compared to ethanol; however, the cellular targets and microbial defense mechanisms remain poorly understood, especially under anaerobic conditions used frequently in industry. Here we took a comparative approach to understand the response of Saccharomyces cerevisiae to 1-butanol, isobutanol, or ethanol, across three genetic backgrounds of varying tolerance in aerobic and anaerobic conditions. We find that strains have different growth properties and alcohol tolerances with and without oxygen availability, as well as unique and common responses to each of the three alcohols. Our results provide evidence for strain-by-alcohol-by-oxygen interactions that moderate how cells respond to alcohol stress.

Abstract Background Rapamycin is a potent inhibitor of the highly conserved TOR kinase, the nutrient-sensitive controller of growth and aging. It has been utilised as a chemotherapeutic agent due to its anti-proliferative properties and as an immunosuppressive drug, and is also known to extend lifespan in a range of eukaryotes from yeast to mammals. However, the mechanisms through which eukaryotic cells adapt to sustained exposure to rapamycin have not yet been thoroughly investigated. Methods Here, S. cerevisiae response to long-term rapamycin exposure was investigated by identifying the physiological, transcriptomic and metabolic differences observed for yeast populations inoculated into low-dose rapamycin-containing environment. The effect of oxygen availability and acidity of extracellular environment on this response was further deliberated by controlling or monitoring the dissolved oxygen level and pH of the culture. Results Yeast populations grown in the presence of rapamycin reached higher cell densities complemented by an increase in their chronological lifespan, and these physiological adaptations were associated with a rewiring of the amino acid metabolism, particularly that of arginine. The ability to synthesise amino acids emerges as the key factor leading to the major mechanistic differences between mammalian and microbial TOR signalling pathways in relation to nutrient recognition. Conclusion Oxygen levels and extracellular acidity of the culture were observed to conjointly affect yeast populations, virtually acting as coupled physiological effectors; cells were best adapted when maximal oxygenation of the culture was maintained in slightly acidic pH, any deviation necessitated more extensive readjustment to additional stress factors.

Exercise intensity variations throughout a cycling time trial (TT) might be influenced by subject's functional state. Purpose: The current study characterized the performance fatigability etiology, immediately after exercise cessation, and its relation to the dynamic changes in muscle O2 saturation (SmO2) at different TT phases. Methods: Twelve males performed three separated TT of different distances, in a crossover counterbalanced design, until the end of the fast-start (FS, 827 ± 135 m), even-pace (EP, 3590 ± 66 m), or end-spurt (ES, 4000 m) TT phases. Performance fatigability was characterized by using isometric maximal voluntary contractions (IMVC), whereas the maximal voluntary activation (VA) and contractile function of knee extensors (e.g., peak torque of potentiated twitches [TwPt]) were evaluated using electrically evoked contractions performed before and immediately after each exercise bouts. SmO2, power output (PO), and EMG were also recorded. Results: Immediately after the FS phase, there were lower values for IMVC (−23%), VA (−8%), and TwPt (−43%) (all P < 0.001), but no further changes were measured after EP (IMVC, −28%; VA, −8%; TwPt, −38%). After the ES phase, IMVC (−34%) and TwPt (−59%) further decreased compared with the previous phases (P < 0.05). There were lower SmO2 and higher EMG/PO values during FS and ES compared with EP phase. Conclusion: FS and EP phases had similar performance fatigability etiology, but ES showed further impairments in contractile function. This later finding might be due to the abrupt changes in SmO2 and EMG/PO because of the high exercise intensity during the ES, which elicited maximal decline in contractile function at the finish line. [ABSTRACT FROM AUTHOR]

Bacterial populations rely on quorum sensing (QS) to coordinate their behaviors and are often challenged by the fluctuation in oxygen concentrations in their habitats. Oxygen is a crucial factor that affects bacterial metabolism in multiple ways. However, little is known about whether and how oxygen availability affects QS activities. To fill this gap, we used the facultative anaerobe Novosphingobium pentaromativorans US6-1 as a model system, and observed that the QS signal acyl homoserine-lactones (AHLs) were produced only in anoxic environments, such as biofilm, or liquid medium that initially contained less than 2 mg/L dissolved oxygen, but not in highly oxic environments. Comparative transcriptome analysis revealed that oxygen availability significantly affected the physiological activities in US6-1, including fatty acid metabolism, oxidative phosphorylation, citrate cycle, QS activities, and flagellar assembly. The absence of AHLs in the oxic culture was not due to degradation, but to the very low expression of the AHL synthase gene novI. High concentration of NADH during the middle log phase under static cultivation may be a trigger for AHL synthesis. This is the first report that production of AHLs is coupled with anoxic metabolism in a facultative anaerobe, which extends our knowledge on factors affecting bacterial QS occurrence. Key points: • AHL production is anoxic cultivation related. • Oxygen availability affects AHL synthesis by influencing novI expression. • Oxygen availability changes many metabolism activities including NADH production. [ABSTRACT FROM AUTHOR]

Oxygen deprivation within tumors is one of the most prevalent causes of resilient cancer cell survival and increased immune evasion in breast cancer (BCa). Current in vitro models do not adequately mimic physiological oxygen levels relevant to breast tissue and its tumor-immune interactions. In this study, we propose an approach to engineer a three-dimensional (3D) model (named 3D engineered oxygen, 3D-O) that supports the growth of BCa cells and generates physio- and pathophysiological oxygen levels to understand the role of oxygen availability in tumor-immune interactions. BCa cells (MDA-MB-231 and MCF-7) were embedded into plasma-derived 3D-O scaffolds that reflected physio- and pathophysiological oxygen levels relevant to the healthy and cancerous breast tissue. BCa cells grown within 3D-O scaffolds were analyzed by flow cytometry, confocal imaging, immunohistochemistry/immunofluorescence for cell proliferation, extracellular matrix protein expression, and alterations in immune evasive outcomes. Exosome secretion from 3D-O scaffolds were evaluated using the NanoSight particle analyzer. Peripheral blood mononuclear cells were incorporated on the top of 3D-O scaffolds and the difference in tumor-infiltrating capabilities as a result of different oxygen content were assessed by flow cytometry and confocal imaging. Lastly, hypoxia and Programmed death-ligand 1 (PD-L1) inhibition were validated as targets to sensitize BCa cells in order to overcome immune evasion. Low oxygen-induced adaptations within 3D-O scaffolds validated known tumor hypoxia characteristics such as reduced BCa cell proliferation, increased extracellular matrix protein expression, increased extracellular vesicle secretion and enhanced immune surface marker expression on BCa cells. We further demonstrated that low oxygen in 3D-O scaffolds significantly influence immune infiltration. CD8+ T cell infiltration was impaired under pathophysiological oxygen levels and we were also able to establish that hypoxia and PD-L1 inhibition re-sensitized BCa cells to cytotoxic CD8+ T cells. Bioengineering the oxygen-deprived BCa tumor microenvironment in our engineered 3D-O physiological and tumorous scaffolds supported known intra-tumoral hypoxia characteristics allowing the study of the role of oxygen availability in tumor-immune interactions. The 3D-O model could serve as a promising platform for the evaluation of immunological events and as a drug-screening platform tool to overcome hypoxia-driven immune evasion.

Abstract Background Azotobacter vinelandii is a bacterium that produces alginate and polyhydroxybutyrate (P3HB); however, the role of NAD(P)H/NAD(P)+ ratios on the metabolic fluxes through biosynthesis pathways of these biopolymers remains unknown. The aim of this study was to evaluate the NAD(P)H/NAD(P) + ratios and the metabolic fluxes involved in alginate and P3HB biosynthesis, under oxygen-limiting and non-limiting oxygen conditions. Results The results reveal that changes in the oxygen availability have an important effect on the metabolic fluxes and intracellular NADPH/NADP+ ratio, showing that at the lowest OTR (2.4 mmol L−1 h−1), the flux through the tricarboxylic acid (TCA) cycle decreased 27.6-fold, but the flux through the P3HB biosynthesis increased 6.6-fold in contrast to the cultures without oxygen limitation (OTR = 14.6 mmol L−1 h−1). This was consistent with the increase in the level of transcription of phbB and the P3HB biosynthesis. In addition, under conditions without oxygen limitation, there was an increase in the carbon uptake rate (twofold), as well as in the flux through the pentose phosphate (PP) pathway (4.8-fold), compared to the condition of 2.4 mmol L−1 h−1. At the highest OTR condition, a decrease in the NADPH/NADP+ ratio of threefold was observed, probably as a response to the high respiration rate induced by the respiratory protection of the nitrogenase under diazotrophic conditions, correlating with a high expression of the uncoupled respiratory chain genes (ndhII and cydA) and induction of the expression of the genes encoding the nitrogenase complex (nifH). Conclusions We have demonstrated that changes in oxygen availability affect the internal redox state of the cell and carbon metabolic fluxes. This also has a strong impact on the TCA cycle and PP pathway as well as on alginate and P3HB biosynthetic fluxes.

The largest muscles in fowl are the pectorals, which provide the power required for birds to fly. Tibetan chickens show specific adaptations to high-altitude conditions, but changes in the muscle transcriptome associated with these adaptations have not been characterized yet. Therefore, in this study, we used next-generation sequencing technologies to generate eight libraries of mRNA sequences for four Tibetan chickens and four Beijing fatty chickens. A comprehensive transcriptome analysis was performed. In the eight samples, 12 333 annotated protein-coding genes were expressed. Among these, 48 differentially expressed genes were found; all of which were upregulated in Tibetan chickens. These differentially expressed genes were mainly involved in kidney morphogenesis, which indicates that hypoxia has an important effect on renal tubule development. Only nine genes were involved in Kyoto Encyclopedia of Genes and Genomes pathways, such as the endocytosis pathway, the MAPK signaling pathway, the calcium signaling pathway and the TGF-beta signaling pathway. The differentially expressed genes identified in this study will be used to facilitate future research into the Tibetan chicken. [ABSTRACT FROM AUTHOR]

Abstract Background Understanding the effects of oxygen levels on yeast xylose metabolism would benefit ethanol production. In this work, xylose fermentative capacity of Scheffersomyces stipitis, Spathaspora passalidarum, Spathaspora arborariae and Candida tenuis was systematically compared under aerobic, oxygen-limited and anaerobic conditions. Results Fermentative performances of the four yeasts were greatly influenced by oxygen availability. S. stipitis and S. passalidarum showed the highest ethanol yields (above 0.44 g g−1) under oxygen limitation. However, S. passalidarum produced 1.5 times more ethanol than S. stipitis under anaerobiosis. While C. tenuis showed the lowest xylose consumption rate and incapacity to produce ethanol, S. arborariae showed an intermediate fermentative performance among the yeasts. NAD(P)H xylose reductase (XR) activity in crude cell extracts correlated with xylose consumption rates and ethanol production. Conclusions Overall, the present work demonstrates that the availability of oxygen influences the production of ethanol by yeasts and indicates that the NADH-dependent XR activity is a limiting step on the xylose metabolism. S. stipitis and S. passalidarum have the greatest potential for ethanol production from xylose. Both yeasts showed similar ethanol yields near theoretical under oxygen-limited condition. Besides that, S. passalidarum showed the best xylose consumption and ethanol production under anaerobiosis.

Abstract Background Riboflavin, an intermediate of primary metabolism, is one kind of important food additive with high economic value. The microbial cell factory Bacillus subtilis has already been proven to possess significant importance for the food industry and have become one of the most widely used riboflavin-producing strains. In the practical fermentation processes, a sharp decrease in riboflavin production is encountered along with a decrease in the dissolved oxygen (DO) tension. Influence of this oxygen availability on riboflavin biosynthesis through carbon central metabolic pathways in B. subtilis is unknown so far. Therefore the unveiled effective metabolic pathways were still an unaccomplished task till present research work. Results In this paper, the microscopic regulation mechanisms of B. subtilis grown under different dissolved oxygen tensions were studied by integrating 13C metabolic flux analysis, metabolomics and transcriptomics. It was revealed that the glucose metabolic flux through pentose phosphate (PP) pathway was lower as being confirmed by smaller pool sizes of metabolites in PP pathway and lower expression amount of ykgB at transcriptional level. The latter encodes 6-phosphogluconolactonase (6-PGL) under low DO tension. In response to low DO tension in broth, the glucose metabolic flux through Embden–Meyerhof–Parnas (EMP) pathway was higher and the gene, alsS, encoding for acetolactate synthase was significantly activated that may result due to lower ATP concentration and higher NADH/NAD+ ratio. Moreover, ResE, a membrane-anchored protein that is capable of oxygen regulated phosphorylase activity, and ResD, a regulatory protein that can be phosphorylated and dephosphorylated by ResE, were considered as DO tension sensor and transcriptional regulator respectively. Conclusions This study shows that integration of transcriptomics, 13C metabolic flux analysis and metabolomics analysis provides a comprehensive understanding of biosynthesized riboflavin’s regulatory mechanisms in B. subtilis grown under different dissolved oxygen tension conditions. The two-component system, ResD–ResE, was considered as the signal receiver of DO tension and gene regulator that led to differences between biomass and riboflavin production after triggering the shifts in gene expression, metabolic flux distributions and metabolite pool sizes.

Forced aeration is one of the major energy consumption factors of the bioleaching process of run-of-mine ore. The effect of aeration in the microbial community has scarcely been studied at industrial level. Leptospirillum ferriphilum is one of the most representative species of the Fe3+ producing population in this kind of systems. We analyzed the effect of oxygen availability on L. ferriphilum by growth activity and transcriptional dynamics of its two terminal oxidases (cbb3 and bd complexes) under different experimental test: culture reactor, bioleaching column, and industrial heap tests. Relatively low O2 availability triggered important changes in the microbial community composition, cell growth, microbial activity and cydAB genes transcription in all cases of study. We assessed the potential role of the terminal oxidases on the adaptation to variable aeration conditions in different lifestyles of L. ferriphilum and identified transcriptional markers associated to oxygen metabolism in an industrial system. An interesting hypothesis about the possible role of the cbb3 complex in the response to oxidative stress as well as their role as a high oxygen-affinity oxidase in L. ferriphilum is proposed and discussed. This study successfully proves the function of the cydAB genes as valid genetic markers for low-grade copper industrial bioleaching systems.

Forced aeration is one of the major energy consumption factors of the bioleaching process of run-of-mine ore. The effect of aeration in the microbial community has scarcely been studied at industrial level. Leptospirillum ferriphilum is one of the most representative species of the Fe3+ producing population in this kind of systems. We analyzed the effect of oxygen availability on L. ferriphilum by growth activity and transcriptional dynamics of its two terminal oxidases (cbb3 and bd complexes) under different experimental test: culture reactor, bioleaching column, and industrial heap tests. Relatively low O2 availability triggered important changes in the microbial community composition, cell growth, microbial activity and cydAB genes transcription in all cases of study. We assessed the potential role of the terminal oxidases on the adaptation to variable aeration conditions in different lifestyles of L. ferriphilum and identified transcriptional markers associated to oxygen metabolism in an industrial system. An interesting hypothesis about the possible role of the cbb3 complex in the response to oxidative stress as well as their role as a high oxygen-affinity oxidase in L. ferriphilum is proposed and discussed. This study successfully proves the function of the cydAB genes as valid genetic markers for low-grade copper industrial bioleaching systems. [ABSTRACT FROM AUTHOR]

BACKGROUND: The carbon flux distribution in Shimwellia blattae (p424IbPSO) cultures when glucose is employed as carbon source is studied in a stirred tank bioreactor changing the oxygen availability. The strain has been constructed to produce isobutanol combining the branched‐chain amino acids pathway and Ehrlich pathway. The information of many similar genetic modified strains for this bioprocess in the literature presents significant discrepancies on the oxygen influence. RESULTS: The study carried out in this work pointed out the presence of other metabolites formed under aerobic conditions, such as isobutyric acid, 2,3‐butanedione, acetoin, 2,3‐butanediol and 3‐oxo‐1‐buten‐2‐yl ether, not previously reported in the literature on the production of isobutanol with S. blattae (p424IbPSO) strain. CONCLUSION: In this work the routes or the chemical reactions involved in the bioprocess as a function of the availability of oxygen are elucidated. Anaerobic conditions are the best for isobutanol production from glucose employing this strain; around 12 g L−1 of isobutanol are obtained under these conditions. Aerobic conditions are not adequate to produce isobutanol, although the need for oxygen, at least for growth, is also demonstrated. © 2018 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Acetoin is one of the bio-based platform chemicals and its optically pure isomers are important potential intermediates and precursors in the synthesis of novel optically active materials. (3R)-acetoin could be synthesized via enzymatic catalysis, whole-cell catalysis and fermentation. In this study a marine strain of Bacillus subtilis was isolated to produce optically pure (3R)-acetoin with glucose as carbon source. The effects of nutrients on the formation of (3R)-acetoin and conversion of glucose to (3R)-acetoin were evaluated by Plackett–Burman design, and the fermentation medium was optimized by central composite design. The impact of oxygen supply on the production of (3R)-acetoin was studied at different aeration rates. Under the optimal conditions, 83.7 g/L (3R)-acetoin with an optical purity of 99.4% was achieved by fed-batch fermentation, and the conversion of glucose to (3R)-acetoin was 91.5% of the theoretical value. The results indicate the industrial potential of this strain for (3R)-acetoin production via fermentation. [ABSTRACT FROM AUTHOR]

Next generation biofuels including longer-chain alcohols such as butanol are attractive as renewable, high-energy fuels. A barrier to microbial production of butanols is the increased toxicity compared to ethanol; however, the cellular targets and microbial defense mechanisms remain poorly understood, especially under anaerobic conditions used frequently in industry. Here we took a comparative approach to understand the response of Saccharomyces cerevisiae to 1-butanol, isobutanol, or ethanol, across three genetic backgrounds of varying tolerance in aerobic and anaerobic conditions. We find that strains have different growth properties and alcohol tolerances with and without oxygen availability, as well as unique and common responses to each of the three alcohols. Our results provide evidence for strain-byalcohol- by-oxygen interactions that moderate how cells respond to alcohol stress. [ABSTRACT FROM AUTHOR]

The Gh/Prl/Sl family has evolved differentially through evolution, resulting in varying relationships between the somatotropic axis and growth rates within and across fish species. This is due to a wide range of endogenous and exogenous factors that make this association variable throughout season and life cycle, and the present minireview aims to better define the nutritional and environmental regulation of the endocrine growth cascade over precisely defined groups of fishes, focusing on Mediterranean farmed fishes. As a result, circulating Gh and Igf-i are revitalized as reliable growth markers, with a close association with growth rates of gilthead sea bream juveniles with deficiency signs in both macro- or micro-nutrients. This, together with other regulated responses, promotes the use of Gh and Igf-i as key performance indicators of growth, aerobic scope, and nutritional condition in gilthead sea bream. Moreover, the sirtuin-energy sensors might modulate the growth-promoting action of somatotropic axis. In this scenario, transcripts of igf-i and gh receptors mirror changes in plasma Gh and Igf-i levels, with the ghr-i/ghr-ii expression ratio mostly unaltered over season. However, this ratio is nutritionally regulated, and enriched plant-based diets or diets with specific nutrient deficiencies downregulate hepatic ghr-i , decreasing the ghr-i / ghr-ii ratio. The same trend, due to a ghr-ii increase, is found in skeletal muscle, whereas impaired growth during overwintering is related to increase in the ghr-i / ghr-ii and igf-ii / igf-i ratios in liver and skeletal muscle, respectively. Overall, expression of insulin receptors and igf receptors is less regulated, though the expression quotient is especially high in the liver and muscle of sea bream. Nutritional and environmental regulation of the full Igf binding protein 1–6 repertoire remains to be understood. However, tissue-specific expression profiling highlights an enhanced and nutritionally regulated expression of the igfbp-1/-2/-4 clade in liver, whereas the igfbp-3/-5/-6 clade is overexpressed and regulated in skeletal muscle. The somatotropic axis is, therefore, highly informative of a wide-range of growth-disturbing and stressful stimuli, and multivariate analysis supports its use as a reliable toolset for the assessment of growth potentiality and nutrient deficiencies and requirements, especially in combination with selected panels of other nutritionally regulated metabolic biomarkers. [ABSTRACT FROM AUTHOR]

Abstract The kinetics of astaxanthin degradation and lipid oxidation in shrimp oil from hepatopancreas of Pacific white shrimp (Litopenaeus vannamei) as affected by storage temperature were studied. When shrimp oil was incubated at different temperatures (4, 30, 45 and 60 °C) for 16 h, the rate constants (k) of astaxanthin degradation and lipid oxidation in shrimp oil increased with increasing temperatures (p

This study assessed the feasibility of using bleached cellulose pulp from Eucalyptus wood as a feedstock for the production of itaconic acid by fermentation. Additionally, different process strategies were tested with the aim of selecting suitable conditions for an efficient production of itaconic acid by the fungus Aspergillus terreus. The feasibility of using cellulose pulp was demonstrated through assays that revealed the preference of the strain in using glucose as carbon source instead of xylose, mannose, sucrose or glycerol. Additionally, the cellulose pulp was easily digested by enzymes without requiring a previous step of pretreatment, producing a glucose-rich hydrolysate with a very low level of inhibitor compounds, suitable for use as a fermentation medium. Fermentation assays revealed that the technique used for sterilization of the hydrolysate (membrane filtration or autoclaving) had an important effect in its composition, especially on the nitrogen content, consequently affecting the fermentation performance. The carbon-to-nitrogen ratio (C:N ratio), initial glucose concentration and oxygen availability, were also important variables affecting the performance of the strain to produce itaconic acid from cellulose pulp hydrolysate. By selecting appropriate process conditions (sterilization by membrane filtration, medium supplementation with 3 g/L (NH4)2SO4, 60 g/L of initial glucose concentration, and oxygen availability of 7.33 (volume of air/volume of medium)), the production of itaconic acid was maximized resulting in a yield of 0.62 g/g glucose consumed, and productivity of 0.52 g/L·h.

The potential to produce high isobutanol concentrations from glucose with a new genetically modified microorganism, Shimwellia blattae (p424IbPSO), has been studied. The influences of several operating conditions (media composition, oxygen availability and pH) have been studied. Yeast extract concentration can be reduced 3.3 times from the more usual concentration, reducing the cost of the bioprocess, but obtaining no change in isobutanol yield: 0.173 g Ib  g Gc −1 . The influence of the oxygen availability on isobutanol production has also been considered. The use of higher air proportion into sealed bottles led to the best results in isobutanol concentration and productivity: 6 g L −1 and 0.19 g L −1  h −1 , respectively. The study of the pH strategy shows that the best one is to begin at an initial pH value of 6.8, to let the pH fall freely to a value of 6.0 and then to control the pH at this value, obtaining about 11 g L −1 of isobutanol titer and about 0.286 g Ib  g Gc −1 of yield. [ABSTRACT FROM AUTHOR]

The composting is a proven technology to manage various organic wastes and reduces organic matter, heavy metals and harmful pathogens. The current research work provides the insight on the physics involved in composting of lignocellulose aquatic waste amended with inoculum and the bulking agent that plays a crucial role in handling, management, and utilization of waste product to an application of an end product in agriculture production. The physical parameters (temperature, bulk density, porosity, free air space, and particle density) during composting of E Crassipes, inoculum and bulking agent (in the ratio 6:3:1) were evaluated. The study indicated an advanced thermophilic temperature (52.3 °C) with 24% reduction in moisture content. As a result of volume reduction, the bulk density was found to be increasing whereas free airspace observed as 59% at the end of the composting process. The various physical parameters also exhibited the strong relationship to each other, which was derived using statistical analysis. The free air space correlated positively with bulk density and volatile solids. [ABSTRACT FROM AUTHOR]

Senegalese sole Solea senegalensis is currently farmed in recirculation aquaculture systems that often involve water re-oxygenation, which in turn may cause acute or prolonged hyperoxia exposures. In order to understand the impact of acute hyperoxia on the fish immune system and peripheral tissues such as gills and gut, Senegalese sole juveniles (30.05 ± 1.72 g) were exposed to normoxia (100% O 2sat ) as control and two hyperoxic conditions (150 and 200% O 2sat ) and sampled at 4 and 24 h. Fish haematological profile, total and differential blood cell counts and plasma immune parameters were analysed. Histomorphology and immunofluorescence analyses of gills and intestine were performed, respectively, whereas head-kidney samples were used for assessing the expression of immune-related genes. Results indicate that acute hyperoxia exposure may reduce fish erythrocyte and haemoglobin levels. Moreover, decreases in total leucocytes numbers, circulating lymphocytes, monocytes, alternative complement pathway activity and expression of cyclooxygenase-2 were observed in fish exposed to hyperoxia. In contrast, hyperoxia did not induce major effects on gill histomorphology nor in the protein content of ion and glucose cotransporters as well as a macrophage marker (V-ATPase) in the intestine. Although the activation of humoral mechanisms and immune-related genes were not dramatically affected by acute hyperoxia, the compromised immune cell status and the reduction of some inflammatory indicators are issues to consider under acute hyperoxia conditions. [ABSTRACT FROM AUTHOR]

Background: Azotobacter vinelandii is a bacterium that produces alginate and polyhydroxybutyrate (P3HB); however, the role of NAD(P)H/NAD(P)+ ratios on the metabolic fluxes through biosynthesis pathways of these biopolymers remains unknown. The aim of this study was to evaluate the NAD(P)H/NAD(P)+ ratios and the metabolic fluxes involved in alginate and P3HB biosynthesis, under oxygen-limiting and non-limiting oxygen conditions. Results: The results reveal that changes in the oxygen availability have an important effect on the metabolic fluxes and intracellular NADPH/NADP+ ratio, showing that at the lowest OTR (2.4 mmol L-1 h-1), the flux through the tricarboxylic acid (TCA) cycle decreased 27.6-fold, but the flux through the P3HB biosynthesis increased 6.6-fold in contrast to the cultures without oxygen limitation (OTR = 14.6 mmol L-1 h-1). This was consistent with the increase in the level of transcription of phbB and the P3HB biosynthesis. In addition, under conditions without oxygen limitation, there was an increase in the carbon uptake rate (twofold), as well as in the flux through the pentose phosphate (PP) pathway (4.8-fold), compared to the condition of 2.4 mmol L-1 h-1. At the highest OTR condition, a decrease in the NADPH/NADP+ ratio of threefold was observed, probably as a response to the high respiration rate induced by the respiratory protection of the nitrogenase under diazotrophic conditions, correlating with a high expression of the uncoupled respiratory chain genes (ndhII and cydA) and induction of the expression of the genes encoding the nitrogenase complex (nifH). Conclusions: We have demonstrated that changes in oxygen availability affect the internal redox state of the cell and carbon metabolic fluxes. This also has a strong impact on the TCA cycle and PP pathway as well as on alginate and P3HB biosynthetic fluxes. [ABSTRACT FROM AUTHOR]

Oxygen availability is a critical factor in regulating cell viability that ultimately contributes to the normal morphogenesis and functionality of human tissues. Among various cell culture platforms, construction of 3D multicellular spheroids based on microwell arrays has been extensively applied to reconstitute in vitro human tissue models due to its precise control of tissue culture conditions as well as simple fabrication processes. However, an adequate supply of oxygen into the spheroidal cellular aggregation still remains one of the main challenges to producing healthy in vitro spheroidal tissue models. Here, we present a novel design for controlling the oxygen distribution in concave microwell arrays. We show that oxygen permeability into the microwell is tightly regulated by varying the poly-dimethylsiloxane (PDMS) bottom thickness of the concave microwells. Moreover, we validate the enhanced performance of the engineered microwell arrays by culturing non-proliferated primary rat pancreatic islet spheroids on varying bottom thickness from 10 μm to 1050 μm. Morphological and functional analyses performed on the pancreatic islet spheroids grown for 14 days prove the long-term stability, enhanced viability, and increased hormone secretion under the sufficient oxygen delivery conditions. We expect our results could provide knowledge on oxygen distribution in 3-dimensional spheroidal cell structures and critical design concept for tissue engineering applications. Statement of Significance In this study, we present a noble design to control the oxygen distribution in concave microwell arrays for the formation of highly functional pancreatic islet spheroids by engineering the bottom of the microwells. Our new platform significantly enhanced oxygen permeability that turned out to improve cell viability and spheroidal functionality compared to the conventional thick-bottomed 3-D culture system. Therefore, we believe that this could be a promising medical biotechnology platform to further develop high-throughput tissue screening system as well as in vivo -mimicking customised 3-D tissue culture systems. [ABSTRACT FROM AUTHOR]

A series of Ag/CeO 2 catalysts was synthesized by the incipient wetness method. Compared with Ag/Al 2 O 3 and CeO 2 catalysts, Ag/CeO 2 catalysts are more promising candidates for naphthalene oxidation, in which Ce x + act as the main active sites and are efficiently promoted by Ag species. By characterizing the solid properties and the redox ability, the mechanism of ceria catalysis by the Ag-modified catalysts was investigated. It was found that Ag species can work as an oxygen pump to enhance the oxygen availability in the ceria bulk. They also promote the oxygen regeneration capacity by the oxygen spillover effect. However, such an effect would also decrease the ability for active oxygen regeneration at higher Ag loading, which arises from the lower surface oxygen vacancy concentration. Because of the balance between these two factors, the Ag/CeO 2 catalyst with 1 wt.% Ag shows the best performance for isothermal catalytic oxidation of naphthalene. [ABSTRACT FROM AUTHOR]

Nearly half of US lakes are impaired, primarily resulting from excessive nutrients and resultant eutrophication. The stability and recycling of sediment P results in differing degrees of internal P loading, which can alter lake water quality. In this study, we asked: (1) What are the underlying mechanisms controlling internal loading (net release) and retention of P? and (2) How does trophic state, specifically a hypereutrophic condition, affect internal P loading in agricultural reservoirs? We show that shifts in internal P loading are related to trophic-level indicators, including total P (TP) and chl- a concentrations. All study reservoirs were classified as hypereutrophic, and we grouped them as 'less eutrophic' or 'more eutrophic' based on TP and chl- a concentrations. In less eutrophic lakes, chemical variables (for example, oxygen) and sediment iron-bound P primarily controlled internal P loading under anaerobic conditions. However, in the more eutrophic lakes, biological variables, including phytoplankton biomass (as indicated by chl- a concentrations) and extracellular enzyme activity, drove internal P loading or reduced P retention under aerobic conditions. Biologically controlled aerobic internal P cycling was related to higher sediment organic P pools being broken down by enzymatic hydrolysis. Therefore, we theorize that as lakes become hypereutrophic, biological mechanisms begin to amplify internal P release by acting under both anaerobic and aerobic conditions, thus creating a perpetual cycle of internal P loading. Thus, the role of biological processes and oxygen availability should be considered in water quality management strategies aimed at alleviating eutrophication in lakes. [ABSTRACT FROM AUTHOR]