Rate Of O2 Uptake Research Articles

Self-regenerable oxygen system using microalgae-bacterial consortium for ammonium removal from wastewater

This study investigated self-regenerable oxygen system using microalagae-bacterial consortium for ammonium removal from wastewater and its kinetic modeling based on a combined mechanistic and empirical approach. By mechanistic modeling using a simple microalgal-bacterial Monod model, based on algal growth due to NH4+, NO3− and NO2−, the nitrogen and DO profiles were accurately predicted under different nitrogen conditions (low, medium, and high NH4+ concentrations). The mathematical modeling results showed that sufficient oxygen was available for nitrification at low initial NH4+ ammonium concentration levels, even when dual nitrogen substrate (NH4+–NO2−, NH4+–NO3− or NO2−–NO3−) or all three in combination (NH4+–NO2−–NO3−) were used, compared with high initial ammonium concentration levels. The DO profile was successfully used to monitor N transformation and N uptake in the PSBR based on net O2 uptake rate, O2 production rate, and O2 saturation profile. By empirical modeling of the data obtained, the actual O2 produced by microalgae with the different N species was calculated based on N mass balance and empirical equations. The empirical model further revealed that low NH4+ concentration levels (up to 82.5 mg N/L) favored successful nitrification due to the sufficient production of O2 in the system. However, NH4+ concentration in the range 82.5–132.5 mg N/L affected the nitrification efficiency due to insufficient O2 produced in the system, whereas high ammonium concentration results in nitritation/partial nitrification due to the high demand of O2 by AOB and inhibition in the growth of NOB.

Reference values for leg effort during incremental cycle ergometry in non-trained healthy men and women, aged 19-85.

Heightened sensation of leg effort contributes importantly to poor exercise tolerance in patient populations. We aim to provide a sex- and age-adjusted frame of reference to judge symptom's normalcy across progressively higher exercise intensities during incremental exercise. Two-hundred and seventy-five non-trained subjects (130 men) aged 19-85 prospectively underwent incremental cycle ergometry. After establishing centiles-based norms for Borg leg effort scores (0-10 category-ratio scale) versus work rate, exponential loss function identified the centile that best quantified the symptom's severity individually. Peak O2 uptake and work rate (% predicted) were used to threshold gradually higher symptom intensity categories. Leg effort-work rate increased as a function of age; women typically reported higher scores at a given age, particularly in the younger groups (p < 0.05). For instance, "heavy" (5) scores at the 95th centile were reported at ~200 W (<40 years) and ~90 W (≥70 years) in men versus ~130 W and ~70 W in women, respectively. The following categories of leg effort severity were associated with progressively lower exercise capacity: ≤50th ("mild"), >50th to <75th ("moderate"), ≥75th to <95th ("severe"), and ≥ 95th ("very severe") (p < 0.05). Although most subjects reporting peak scores <5 were in "mild" range, higher scores were not predictive of the other categories (p > 0.05). This novel frame of reference for 0-10 Borg leg effort, which considers its cumulative burden across increasingly higher exercise intensities, might prove valuable to judging symptom's normalcy, quantifying its severity, and assessing the effects of interventions in clinical populations.

Assessing the Efficacy, Acute Toxicity, and Binding Modes of the Agricultural Nitrification Inhibitors 3,4-Dimethyl-1H-pyrazole (DMP) and Dicyandiamide (DCD) with Nitrosomonas europaea

Nitrification inhibitors have been coformulated with nitrogen fertilizers since the 1970s to modulate the microbiological conversion of nitrogen in agricultural soils. 3,4-Dimethyl-1H-pyrazole (DMP) and dicyandiamide (DCD) are currently the most used commercial nitrification inhibitors, but their mode of action is not well understood. This work seeks to fill this void by assessing for the first time in detail their mechanism of inhibition, efficacy, and acute toxicity with pure cell cultures of Nitrosomonas europaea. Bacterial assays based on the quantification of the nitrite (NO2–) production showed that both inhibitors reversibly target ammonia monooxygenase (AMO), which catalyzes the first step of the nitrification process. Michaelis–Menten kinetics suggest that both DMP and DCD act as uncompetitive inhibitors. Real-time measurements of the oxygen (O2) consumption confirmed the nonmechanistic mode of inhibition and showed that DMP reduced the O2 uptake rate by AMO much more at considerably lower concentrations than DCD, in line with the lower inhibitory efficiency of the latter. Acute toxicity tests revealed that DCD has a 10% higher toxicity than DMP when comparing treatments at the same inhibition efficacy (i.e., DMP at 10 ppm, DCD at 100 ppm), indicating that the inhibition of the nitrification process cannot simply be achieved by increasing the inhibitor concentration. The methods presented in this study could assist the development of more reliable nitrification inhibitors in the future.

Morphology and Size of Bacterial Colonies Control Anoxic Microenvironment Formation in Porous Media.

Bacterial metabolisms using electron acceptors other than oxygen (e.g., methanogenesis and fermentation) largely contribute to element cycling and natural contaminant attenuation/mobilization, even in well-oxygenated porous environments, such as shallow aquifers. This paradox is commonly explained by the occurrence of small-scale anoxic microenvironments generated by the coupling of bacterial respiration and dissolved oxygen (O2) transport by pore water. Such microenvironments allow facultative anaerobic bacteria to proliferate in oxic environments. Microenvironment dynamics are still poorly understood due to the challenge of directly observing biomass and O2 distributions at the microscale within an opaque sediment matrix. To overcome these limitations, we integrated a microfluidic device with transparent O2 planar optical sensors to measure the temporal behavior of dissolved O2 concentrations and biomass distributions with time-lapse videomicroscopy. Our results reveal that bacterial colony morphology, which is highly variable in flowing porous systems, controls the formation of anoxic microenvironments. We rationalize our observations through a colony-scale Damköhler number comparing dissolved O2 diffusion and a bacterial O2 uptake rate. Our Damköhler number enables us to predict the pore space fraction occupied by anoxic microenvironments in our system for a given bacterial organization.

Air-water CO2 and water-sediment O2 exchanges over a tidal flat in Tokyo Bay

Despite the potential for carbon storage in tidal flats, little is known about the details of relevant processes because of the complexity of intertidal physical and chemical environments and the uniqueness of the biota. We measured air-water carbon dioxide (CO2) fluxes and water-sediment oxygen (O2) fluxes over a tidal flat in Tokyo Bay by the eddy covariance method, which has the potential to facilitate long-term, broad-scale, continuous monitoring of carbon flows in tidal flats. The results indicated that throughout the tidal flat in Tokyo Bay, CO2 was taken up from the atmosphere at a rate of 6.05 ± 7.14 (mean ± SD) mmol m−2 hour−1, and O2 was taken up from the water into the sediment at a rate of 0.62 ± 1.14 (mean ± SD) mmol m−2 hour−1. The fact that the CO2 uptake rate was about 18 times faster than the previously reported average uptake rate in the whole area of Tokyo Bay was attributable to physical turbulence in the water column caused by bottom friction. Statistical analysis suggested that light intensity and water temperature were the major factors responsible for variations of CO2 and O2 exchange, respectively. Other factors such as freshwater inputs, atmospheric stability, and wind speed also affected CO2 and O2 exchange. High rates of O2 uptake from the water into the sediment surface and high rates of atmospheric CO2 uptake into the water column occurred simultaneously (R2 = 0.44 and 0.47 during day and night, respectively). The explanation could be that photosynthetic consumption of CO2 and production of O2 in the water column increased the downward CO2 (air to water) and O2 (water to sediment) fluxes by increasing the concentration gradients of those gases. Resuspension of sediment in the low-O2 layer by physical disturbance would also increase the O2 concentration gradient and the O2 flux in the water.

Mature landfill leachate treatment in a biological filter using scoria as media

Treatment of leachate and municipal wastewater has extended worldwide using already existing wastewater treatment plants. A biological aerated filter was used to treat leachate from Mexico City's largest landfill together with synthetic wastewater. After achieving stable operation of the filter under organic surface area loading rates of 8.1, 5.3, and 3.1 gCOD/m2·d, landfill leachate was added to the wastewater in volume proportions of 1, 2, and 3%. With leachate, COD removal decreases with increasing leachate concentration. Without leachate, complete nitrification was achieved with the two lower organic surface area loading rates and 93% NH4-N removal was achieved with the highest load. NH4-N removal was 71 and 39% with 2 and 3% leachate, respectively. The oxygen uptake rates decrease with increasing leachate concentration. With 3% leachate, O2 uptake rates for endogenous respiration are higher than for substrate respiration.

Determination of exercise intensity domains during upright versus supine cycling: a methodological study.

BackgroundThere is a growing interest among the research community and clinical practitioners to investigate cardiopulmonary exercise test (CPET) procedures and protocols utilized in supine cycling.Materials and MethodsThe current study investigated the effects of posture on indicators of exercise intensity including gas exchange threshold (GET), respiratory compensation point (RCP), and the rate of peak oxygen uptake (V̇O2 peak), as well as the role of V̇O2 mean response time (MRT) in determining exercise intensity domains in nineteen healthy men (age: 22 ± 3 years). Two moderate-intensity step-transitions from 20 to 100 Watt (W) were completed, followed by a maximal CPET. After completing the ramp test, participants performed a constant-load at 90% of their attained peak power output (PPO).ResultsNo differences were observed in the V̇O2 MRT between the two positions, although the phase II-time constant (τV̇O2p) was 7 s slower in supine position compared to upright (p = 0.001). The rate of O2 uptake in the supine position at GET and RCP were lower compared to the upright position (208 ± 200 mL·min−1 (p = 0.007) and 265 ± 235 mL·min−1 (p = 0.012) respectively). Besides, V̇O2 peak was significantly decreased (by 6%, p = 0.002) during supine position. These findings were confirmed by the wide limits of agreement between the measures of V̇O2 in different postures (V̇O2 peak: −341 to 859; constant-load test: −528 to 783; GET: −375 to 789; RCP: −520 to 1021 all in mL·min−1).ConclusionSince an accurate identification of an appropriate power output (PO) from a single-visit CPET remains a matter of debate, especially for supine cycling, we propose that moderate-intensity step-transitions preceding a ramp CPET could be a viable addition to ensure appropriate exercise-intensity domain determination, in particular upon GET-based prescription.

Benthic O2 uptake by coral gardens at the Condor seamount (Azores)

Using the non-invasive aquatic eddy covariance technique, we provide the first oxygen (O2) uptake rates from within coral gardens at the Condor seamount (Azores). To explore some of the key drivers of the benthic O2 demand, we obtained benthic images, quantified local hydrodynamics, and estimated phototrophic biomass and deposition dynamics with a long-term moored sediment trap. The coral gardens were dominated by the octocorals Viminella flagellum and Dentomuricea aff. meteor. Daily rates of O2 uptake within 3 targeted coral garden sites (203 to 206 m depth) ranged from 10.0 ± 0.88 to 18.8 ± 2.0 mmol m-2 d-1 (mean ± SE) and were up to 10 times higher than 2 local sandy reference sites within the seamount summit area. The overall mean O2 uptake rate for the garden (13.4 mmol m-2 d-1) was twice the global mean for sedimentary habitats at comparable depths. Combined with parallel ex situ incubations, the results suggest that the octocorals might contribute just ~5% of the observed O2 uptake rates. Deposition of particulate organic matter (POM) assessed by the sediment trap accounted for less than 10% of the O2 demand of the coral garden, implying a substantial POM supply circumventing the deployed traps. Our results expand the database for carbon turnover rates in cold-water coral habitats by including the first estimates from these largely understudied coral gardens.

Cardiorespiratory kinetics in exercise physiology: estimates and predictions using randomized changes in work rate

PurposeKinetics of cardiorespiratory parameters (CRP) in response to work rate (WR) changes are evaluated by pseudo-random binary sequences (PRBS testing). In this study, two algorithms were applied to convert responses from PRBS testing into appropriate impulse responses to predict steady states values and responses to incremental increases in exercise intensity.Methods13 individuals (age: 41 ± 9 years, BMI: 23.8 ± 3.7 kg m−2), completing an exercise test protocol, comprising a section of randomized changes of 30 W and 80 W (PRBS), two phases of constant WR at 30 W and 80 W and incremental WR until subjective fatigue, were included in the analysis. Ventilation (dot{V}_{{text{E}}}), O2 uptake (dot{V}{text{O}}_{2}), CO2 output (dot{V}{text{CO}}_{2}) and heart rate (HR) were monitored. Impulse responses were calculated in the time domain and in the frequency domain from the cross-correlations of WR and the respective CRP.ResultsThe algorithm in the time domain allows better prediction for dot{V}{text{O}}_{2} and dot{V}{text{CO}}_{2}, whereas for dot{V}_{{text{E}}} and HR the results were similar for both algorithms. Best predictions were found for dot{V}{text{O}}_{2} and HR with higher (3–4%) 30 W steady states and lower (1–4%) values for 80 W. Tendencies were found in the residuals between predicted and measured data.ConclusionThe CRP kinetics, resulting from PRBS testing, are qualified to assess steady states within the applied WR range. Below the ventilatory threshold, dot{V}{text{O}}_{2} and HR responses to incrementally increasing exercise intensities can be sufficiently predicted.

Uncoupling effect of lipid peroxidation in spinach thylakoids exposed to peroxyl radicals generated by 2,2′-azobis (2-amidinopropane) dihydrochloride

In this study, we characterized how lipid peroxidation alters the functionality of spinach thylakoids exposed to peroxyl radicals generated by the azo compound 2,2-azobis(2-amidinopropane) dihydrochloride (AAPH). Incubation of thylakoids in the presence of different concentrations (0 to 200 mmol·L–1) of AAPH inhibited the formation of ΔpH (IC50 ≈ 1.5 mmol·L–1) estimated by the quenching of 9-aminoacridine fluorescence (Q9-AA). The Q9-AA inhibition was correlated (R2 = 0.98) to the extent of lipid peroxidation determined by the accumulation of thiobarbituric acid reactive substances. Much higher AAPH concentrations were required to inhibit the maximum (Fv/Fm) and effective (ΔF/Fm′) photochemical efficiencies of photosystem II (IC50 ≈ 120 mmol·L–1 and 50 mmol·L–1, respectively), indicating that moderate lipid peroxidation caused the uncoupling of spinach thylakoids. This was confirmed by the 62% stimulation of the O2 uptake rates measured without the artificial uncoupler NH4Cl when the AAPH concentrations increased from 0 to 20 mmol·L–1, reaching similar values to the rates measured in the presence of NH4Cl. Above 20 mmol·L–1 AAPH, the O2 uptake rates measured with and without NH4Cl declined similarly to the decrease of ΔF/Fm′. These results suggest that the increased H+-leakiness of thylakoid membranes could be one of the primary effects of oxidative stress.

Resolving community metabolism of eelgrass Zostera marina meadows by benthic flume-chambers and eddy covariance in dynamic coastal environments

Sediment resuspension is a common process in dynamic coastal settings, but its implications for remineralization and carbon turnover in seagrass meadows are poorly understood. Here, we assessed eelgrass Zostera marina metabolism in the Baltic Sea (SW Finland) using benthic flume-chambers and aquatic eddy covariance to critically evaluate the drivers of benthic O2 exchange during dynamic flow conditions. During quiescent weather conditions, the 2 methods resolved similar metabolic rates and net ecosystem autotrophy (±11% of each other). However, elevated flow speeds and sediment resuspension halfway through the study induced a 5-fold increase in the O2 uptake rates measured by eddy covariance, whereas chamber fluxes remained relatively unchanged. Following particle resettlement, instruments were redeployed and the benthic O2 uptake resolved by both techniques was just ~30% of the values measured before resuspension. Laboratory investigations revealed sediment resuspension could potentially increase benthic O2 uptake up to 6fold, mainly due to the reoxidation of reduced compounds (e.g. FeSx). This process was fully captured by the eddy O2 fluxes, but not by the chamber incubation. Consequently, the chamber and eddy net ecosystem metabolism amounted to -17 and -824 mmol C m-2, respectively, throughout the study period. The rapid reoxidation and long-term effects of resuspension on benthic O2 dynamics highlight the importance of fully capturing dynamic conditions when assessing the overall carbon turnover in coastal habitats. Future studies on the biogeochemical functioning of coastal environments should aim to capture the natural frequency and duration of resuspension events.

A model-based strategy for scaling-up traditional packed-bed bioreactors for solid-state fermentation based on measurement of O2 uptake rates

• O 2 uptake profiles are used to obtain the kinetics of metabolic heat generation. • The kinetics are incorporated in a two-phase heat and mass transfer model. • The model is validated with temperature profiles in a pilot-scale bioreactor. • The model is then used to explore packed-bed design and operation at large scale. • The approach is superior to previously published scale-up strategies for packed-beds. Model-based strategies for scaling up traditional packed-bed bioreactors used in solid-state fermentation have been available for over two decades. However, these strategies are theoretical, not being based on experimental data. A recently proposed strategy did use experimental data; however, it was based on data from a slow-growing fungus and also considered heat transfer in both the axial and radial directions, ignoring the fact that radial heat transfer is negligible in large-scale packed-bed bioreactors. The current work demonstrates a scale-up strategy based on a model describing heat transfer only in the axial direction. The strategy is demonstrated for the cultivation of Aspergillus niger , a fast-growing filamentous fungus. In the model, the kinetics of production of metabolic heat are based on an experimental time-course profile for the O 2 uptake rate. The model is validated by comparing its predictions for temperature profiles in the bed with temperatures measured experimentally in a pilot-scale bioreactor. Finally, the validated model is used to explore strategies for optimizing the performance of large-scale traditional packed-bed bioreactors. We conclude that a key strategy is to decrease the temperature of the inlet air during periods of peak heat generation.

The effect of temperature on Antarctic lichen cytochrome and alternative respiratory pathway rates

Respiration is a crucial process that provides all living organisms with energy and metabolites for growth and cellular maintenance. The processes that control respiration in lichens remain poorly understood. We investigated the effects of short-term temperature changes on the respiration rate, as well as the relative contributions of the cytochrome and alternative pathways of thalli from four green-algal lichen species collected from their natural habitats in Antarctica. Lichen respiration was sensitive to short-term temperature increases over a range of 5–35 °C. The total O2 uptake rate was increased by fourfold, and the mean respiratory coefficient (Q10) decreased from 2.5 to 1.3 as the temperature increased. An increase in temperature from 5 to 15 °C had a positive effect on cytochrome respiration coupled with energy production. Temperatures above 15 °C stimulated the activation of the alternative (energy-dissipating) respiratory pathway. Hyperthermia led to increased O2 consumption that was not associated with mitochondrial oxidases. The effects of increased temperature on the respiration rates were more pronounced in the bipolar lichens Umbilicaria decussata and Usnea sphacelata than in the Usnea aurantiaco-atra species with a narrower geographical distribution.

Kinetic characterization of microalgal-bacterial systems: Contributions of microalgae and heterotrophic bacteria to the oxygen balance in wastewater treatment

Abstract Metabolic activities of microalgae and heterotrophic bacteria were characterized in terms of dissolved O2 uptake and production rates under dark and light conditions, assessing the contribution of both microbial groups to the O2 balance during wastewater treatment. Up to 13 kinetic and stoichiometric parameters were determined, allowing a quantitative description of the O2 production and uptake dynamics. Under dark conditions, the maximum specific O2 uptake rates for microalgae and bacteria were 14.73 ± 2.02 mgO2 gVSS−1 h−1 and 2.37 ± 1.52 mgO2 gVSS−1 h−1, respectively. Microalgae were therefore the largest O2 consumers under dark conditions, being responsible for up to 86 % of the total heterotrophic respiration. Under light conditions (photosynthetic metabolism for microalgae and heterotrophic metabolism for bacteria), microalgae supported a maximum specific O2 production rate of 13.76 ± 1.48 mgO2 gVSS-1 h-1, while bacteria supported a maximum specific O2 uptake of 2.37 ± 1.52 mgO2 gVSS-1 h-1. The oxygenation performance of the microalgal community was therefore superior to the O2 respiration of heterotrophic bacteria under light conditions. The kinetic characterization performed provides critical information about the photosynthetic oxygenation potential, microbial growth and heterotrophic O2 uptake, which is essential for design, optimization, and modeling of wastewater treatment processes.

Evaluation of Heart Rate, Work Rate and O2 Uptake Relationships During Constant Load Exercise Test Work Load at the Anaerobic Threshold in Healthy Male

Objectives: During an incremental exercise test, increased metabolic demands of exercising muscle should be compensated with increased O2 uptake and heart rate until to their maximal levels. Anaerobic threshold (AT) describes the point of metabolic transition from aerobic to anaerobic metabolism and reflect moderate exercise intensity. The aim of this study was to evaluate O2 uptake to heart beat ratio (O2 pulse) and heat rate to work rate ratio (HR/WR) in response to constant load exercise at work load corresponded to AT.&#x0D; Method: Twelve healthy young male subjects initially performed an incremental exercise test (15 W/min) until exhaustion. Then, each subject performed a 30 min of constant load exercise test that work load at their AT on separate days. Pulmonary gas exchange parameters were measured breath-by breath using a metabolic gas analyser. Cardiac parameters were followed continuously beat-by beat using a 12 lead ECG. AT estimated non-invasively using V-slope method.&#x0D; Results: The heart rate for each watt of work production (HR/WR) was ranged between 0.97 beat/min/W to 1.76 beat/min/W and averaged 1.25±0.2 beat/min/W. The O2 pulse was ranged between 10.56 mL/min/beat to 16.15 mL/min/beat and averaged 13.38±1.5 mL/min/beat at the end of the test. A negative statistically significant correlation (R = - 0.90316, p

Effects of 3-month high-intensity interval training vs. moderate endurance training and 4-month follow-up on fat metabolism, cardiorespiratory function and mitochondrial respiration in obese adults.

The purpose of this study was to investigate, in obese adults, changes in body composition, physical capacities, fat oxidation and ex vivo mitochondrial respiration induced by a 3-month either moderate-intensity continuous training (MICT) or high-intensity interval training (HIIT); afterwards, the patients were followed for four months. Thirty-two patients (mean age 39years; mean body mass index [BMI] 36kg∙m-2) participated in this study attending ~ 34 sessions of training. At baseline (PRE), at the end of the program (POST) and after follow-up, body composition, peak O2 uptake (V'O2peak) and fat oxidation rate were measured. Vastus lateralis biopsies for the evaluation of mitochondrial respiration were performed only at PRE and POST. At POST, body mass (BM) and fat mass (FM) decreased (- 6 and - 14%, respectively, P < 0.05) in MICT and HIIT; V'O2peak increased in both groups (+ 6 and + 16%, respectively, P < 0.05). Maximal fat oxidation rate increased only after HIIT (P < 0.001). Maximal ADP-stimulated mitochondrial respiration normalized by citrate synthase increased (P < 0.05) by 67% and 36% in MICT and HIIT, respectively, without significant difference. After follow-up, BM and FM were still lower (- 4 and - 20%, respectively, P < 0.050) compared with baseline in both groups. Only after HIIT, V'O2peak (+ 8%) and maximal fat oxidation rate were still higher (P < 0.05). HIIT was more effective in improving and maintaining V'O2peak and fat oxidation. These results may be relevant for an appropriate prescription of training programs designed to optimize aerobic fitness in obese subjects.

High-intensity interval training accelerates oxygen uptake kinetics and improves exercise tolerance for individuals with cystic fibrosis

BackgroundExercise training provides benefits for individuals with cystic fibrosis; however, the optimal program is unclear. High-intensity interval training is safe and effective for improving ‘functional capacity’ in these individuals with peak rate of O2 uptake typically referenced. The ability to adjust submaximal rate of oxygen uptake (V̇O2 kinetics) might be more important for everyday function because maximal efforts are usually not undertaken. Moreover, the ability of high-intensity training to accelerate V̇O2 kinetics for individuals with cystic fibrosis could be enhanced with O2 supplementation during training.MethodsNine individuals with cystic fibrosis completed incremental cycling to limit of tolerance followed by 8 weeks of high-intensity interval cycling (2 sessions per week x ~ 45 min per session) either with (n = 5; O2+) or without (AMB) oxygen supplementation (100%). Each session involved work intervals at 70% of peak work rate followed by 60 s of recovery at 35%. For progression, duration of work intervals was increased according to participant tolerance.ResultsBoth groups experienced a significant increase in work-interval duration over the course of the intervention (O2+, 1736 ± 141 v. 700 ± 154 s; AMB, 1463 ± 598 v. 953 ± 253 s; P = 0.000); however, the increase experienced by O2+ was greater (P = 0.027). During low-intensity constant-work-rate cycling, the V̇O2 mean response time was shortened post compared to pre training (O2+, 34 ± 11 v. 44 ± 9 s; AMB, 39 ± 14 v. 45 ± 17 s; P = 0.000) while during high-intensity constant-work-rate cycling, time to exhaustion was increased (O2+, 1628 ± 163 v. 705 ± 133 s; AMB, 1073 ± 633 v. 690 ± 348 s; P = 0.002) and blood [lactate] response was decreased (O2+, 4.5 ± 0.9 v. 6.3 ± 1.4 mmol. L− 1; AMB, 4.5 ± 0.6 v. 5.2 ± 1.4 mmol. L− 1; P = 0.003). These positive adaptations were similar regardless of gas inspiration during training.ConclusionEight weeks of high-intensity interval training for patients with cystic fibrosis accelerated V̇O2 kinetics and increased time to exhaustion. This provides some evidence that these patients may benefit from this type of exercise.Trial registrationThis study was retrospectively registered in the ISRTCN registry on 22/06/2019 (#ISRCTN13864650).

Newly designed multi-stacked circular tray solid-state bioreactor: analysis of a distributed parameter gas balance during solid-state fermentation with influence of variable initial moisture content arrangements

BackgroundThe growth of Aspergillus awamori and Aspergillus oryzae in a self-designed, multi-stacked circular tray solid-state bioreactor (SSB), operating in solid-state fermentation (SSF) conditions at a laboratory scale, was studied. The bioreactor was divided into six layers by six circular perforated trays. Wheat bran was used as both a carrier of bound mycelia and nutrient medium for the growth of A. awamori and A. oryzae. The new tray SSB is equipped with instrumentation (an oxygen (O2)/carbon dioxide (CO2) gas analyser and a thermocouple) to continuously monitor O2 consumption and CO2 and heat evolved, which can directly be used to monitor the fungal biomass. The integrated Gompertz model was used to describe the accumulated evolution of CO2.ResultsThe results from the models strongly suggest that the evolved and accumulated CO2 can be used to excellently describe fungal growth. Another important parameter that can be determined by the gas balance method is the respiratory quotient (RQ). This is the ratio of the CO2 evolution rate (CER) to the O2 uptake rate (OUR). The use of CER and OUR confirmed that correlated measurements of microbial activity are available, and the determination of RQ may propose an explanation for differences from expected levels. The kinetic behaviour of the fungal culture, using raw CO2, which represents an accumulation term, was integrated with respect to time and fitted to a Gompertz model, a log-like equation. The model can be used to generate parameter values that may be used to verify the experimental data, and also to simulate and optimise the process.ConclusionOverall, A. awamori and A. oryzae have their own ability to degrade and utilise the complex compositions contained in the solid substrate, and fermentation conditions may lead to possible comparisons. In addition, multi-stacked circular tray SSB systems demonstrated an excellent system for further investigations of mass transfer and possibly for large-scale operation, though considerable optimisation work remains to be done; for example, the height/diameter ratio and total number of trays should be optimised.

Reverse translation: effects of acclimation temperature and acute temperature challenges on oxygen consumption, diffusive water flux, net sodium loss rates, Q10 values and mass scaling coefficients in the rainbow trout (Oncorhynchus mykiss).

Our understanding is limited on how fish adjust the effective permeability of their branchial epithelium to ions and water while altering O2 uptake rate (MO2) with acute and chronic changes in temperature. We investigated the effects of acclimation temperature (8°C, 13°C and 18°C) and acute temperature challenges [acute rise (acclimated at 8°C, measured at 13°C and 18°C), acute drop (acclimated at 18°C, measured at 8°C and 13°C) and intermediate (acclimated at 13°C, measured at 8°C and 18°C)] on routine MO2, diffusive water flux, and net sodium loss rates in 24-h fasted rainbow trout (Oncorhynchus mykiss). In the temperature challenge tests, measurements were made during the first hour. In acclimated trout at all temperatures, allometric mass scaling coefficients were much higher for diffusive water flux than for MO2. Furthermore, the diffusive water flux rate was more responsive (overall Q10 = 2.75) compared to MO2 (Q10 = 1.80) over the 8-18°C range, and for both, Q10 values were greater at 8-13°C than at 13-18°C. The net Na+ flux rates were highly sensitive to acclimation temperature with an overall Q10 of 3.01 for 8-18°C. In contrast, very different patterns occurred in trout subjected to acute temperature challenges. The net Na+ flux rate was temperature-insensitive with a Q10 around 1.0. Both MO2 and diffusive water flux rates exhibited lower Q10 values than for the acclimated rates in response to either acute increases or decreases in temperature. These results fit Pattern 5 of Precht (undercompensation, reverse effect) and more precisely Pattern IIB of Prosser (reverse translation). These inverse compensatory patterns suggest that trout do not alter their rates very much when undergoing acute thermal challenges (diurnal fluctuations, migration through the thermocline). The greater changes seen with acclimation may be adaptive to long-term seasonal changes in temperature. We discuss the roles of aquaporins, spontaneous activity, and recent feeding in these responses.

The utility and determination of Pcrit in fishes.

The critical O2 tension (Pcrit) is the lowest PO2 at which an animal can maintain some benchmark rate of O2 uptake (ṀO2 ). This PO2 has long served as a comparator of hypoxia tolerance in fishes and aquatic invertebrates, but its usefulness in this role, particularly when applied to fishes, has recently been questioned. We believe that Pcrit remains a useful comparator of hypoxia tolerance provided it is determined using the proper methods and hypoxia tolerance is clearly defined. Here, we review the available methods for each of the three steps of Pcrit determination: (1) measuring the most appropriate benchmark ṀO2 state for Pcrit determination (ṀO2,std, the ṀO2 required to support standard metabolic rate); (2) reducing water PO2 ; and (3) calculating Pcrit from the ṀO2 versus PO2 curve. We make suggestions on best practices for each step and for how to report Pcrit results to maximize their comparative value. We also discuss the concept of hypoxia tolerance and how Pcrit relates to a fish's overall hypoxia tolerance. When appropriate methods are used, Pcrit provides useful comparative physiological and ecological information about the aerobic contributions to a fish's hypoxic survival. When paired with other hypoxia-related physiological measurements (e.g. lactate accumulation, calorimetry-based measurements of metabolic depression, loss-of-equilibrium experiments), Pcrit contributes to a comprehensive understanding of how a fish combines aerobic metabolism, anaerobic metabolism and metabolic depression in an overall strategy for hypoxia tolerance.