Respiration Kinetics Research Articles

Microbial community respiration kinetics and their dynamics in coastal seawater

Oxygen (O2) concentrations in coastal seawater have been declining for decades and models predict continued deoxygenation into the future. As O2 declines, metabolic energy use is progressively channelled from higher trophic levels into microbial community respiration, which in turn influences coastal ecology and biogeochemistry. Despite its critical role in deoxygenation and ecosystem functioning, the kinetics of microbial respiration at low O2 concentrations in coastal seawater remain uncertain and are mostly modeled based on parameters derived from laboratory cultures and a limited number of environmental observations. To explore microbial responses to declining O2, we measured respiration kinetics in coastal microbial communities in Hong Kong over the course of an entire year. We found the mean maximum respiration rate (Vmax) ranged between 560 ± 280 and 5930 ± 800 nmol O2 L−1 h−1, with apparent half-saturation constants (Km) for O2 uptake of between 50 ± 40 and 310 ± 260 nmol O2 L−1. These kinetic parameters vary seasonally in association with shifts in microbial community composition that were linked to nutrient availability, temperature, and biological productivity. In general, coastal communities in Hong Kong exhibited low affinities for O2, yet communities in the dry season had higher affinities, which may play a key role in shaping the relationship between community size, biomass, and O2 consumption rates through respiration. Overall, parameters derived from these experiments can be employed in models to predict the expansion of deoxygenated waters and associated effects on coastal ecology and biogeochemistry.

Environmental Impact of Choline Dihydrogenphosphate ([Chol][DHP]) on Seed Germination and Soil Microbial Activity

The applicability of ionic liquids has grown exponentially over the last few decades. This growth is due to the easy modification of these compounds formed by ions, through the proper choice of both moieties, and the possibility of introducing functional groups into their cations and anions. However, studies of their toxicity and effects on the environment remain scarce. This study analyses firstly the response to adding different concentrations of choline dihydrogen phosphate to the germination of seeds of eight plant species. It also examines the microbial population and the respiration of two soils with contrasting organic matter contents. Seeds were incubated in a Petri dish in a Phytotron with a photoperiod of 16 h under light at 24 °C and 8 h in darkness at 16 °C. The activity of microbial populations of untreated and treated soils was analysed by isothermal microcalorimetry at 25 °C. Basal soil respiration kinetics were measured at optimal moisture (80% of field water retention capacity) and temperature (25 °C) over 10 days. The results indicate that this compound has diverse effects on the different endpoints. Nevertheless, this compound can be classified as non-toxic considering its effects on seeds and on soil, at least in the medium- to long-term.

Efficient estimation of gas exchange and respiration kinetics in apple using pathlength-resolved GASMAS

Optimization of controlled atmosphere (CA) storage of pome fruit crucially depends on understanding of respiratory gas exchange. Different fruit properties are involved in describing gas transfer and respiration kinetics, which can vary between cultivars, fruit batches and individual fruit. Determination of these properties currently requires a combination of different time-consuming techniques and data analysis procedures. This study introduces a more efficient single method for O2 gas exchange characterization of fruit based on the non-destructive pathlength-resolved GASMAS (gas in scattering media absorption spectroscopy) technique. GASMAS was used to measure the absolute intercellular O2 concentration in fruit of different apple cultivars (Malus x domestica Borkh.) with distinct porosity including 'Jonagold', 'Braeburn', and 'Nicoter'. To resolve the ambiguity between variation in pathlength and O2 concentration inherent to GASMAS, the pathlength travelled through pores cavities was quantified through a second GASMAS measurement at the absorption line of H2O vapour. Dynamic experiments were then performed in which the fruit was subjected to varying external O2 concentrations while measuring the internal O2 response. The observed dynamic profiles of external and internal O2 concentration were fitted with a lumped -respiration model to estimate the effective mass transfer coefficient, maximum respiration rate and Michaelis Menten constant of intact fruit. The model showed a good fit (R2>0.95) with the measured data and reliable estimates for the model parameters. The proposed method provides a novel and more efficient way to estimate the gas exchange properties of fruit that are essential for optimizing CA storage conditions. Future challenges for the proposed method are with applications to other gasses such as CO2 and ethylene.

Hypoxia in tomato (Solanum lycopersicum) fruit during ripening: biophysical elucidation by a 3D reaction-diffusion model.

Respiration provides energy, substrates and precursors to support physiological changes of the fruit during climacteric ripening. A key substrate of respiration is oxygen that needs to be supplied to the fruit in a passive way by gas transfer from the environment. Oxygen gradients may develop within the fruit due to its bulky size and the dense fruit tissues, potentially creating hypoxia that may have a role in the spatial development of ripening. This study presents a three-dimensional reaction-diffusion model using tomato (Solanum lycopersicum) fruit as a test subject, combining the multiscale fruit geometry generated from magnetic resonance imaging and micro-computed tomography with varying respiration kinetics and contrasting boundary resistances obtained through independent experiments. The model predicted low oxygen levels in locular tissue under atmospheric conditions and the oxygen level was markedly lower upon scar occlusion, aligning with microsensor profiling results. The locular region was in a hypoxic state, leading to its low aerobic respiration with high CO2 accumulation by fermentative respiration, while the rest of the tissues remained well oxygenated. The model further revealed that the hypoxia is caused by a combination of diffusion resistances and respiration rates of the tissue. Collectively, this study reveals the existence of the respiratory gas gradients and its biophysical causes during tomato fruit ripening, providing richer information for future studies on localized endogenous ethylene biosynthesis and fruit ripening.

Respiration kinetics and allometric scaling in the demosponge Halichondria panicea

BackgroundThe aquiferous system in sponges represents one of the simplest circulatory systems used by animals for the internal uptake and distribution of oxygen and metabolic substrates. Its modular organization enables sponges to metabolically scale with size differently than animals with an internal circulatory system. In this case, metabolic rate is typically limited by surface to volume constraints to maintain an efficient supply of oxygen and food. Here, we consider the linkeage between oxygen concentration, the respiration rates of sponges and sponge size.ResultsWe explored respiration kinetics for individuals of the demosponge Halichondria panicea with varying numbers of aquiferous modules (nmodules = 1–102). From this work we establish relationships between the sponge size, module number, maximum respiration rate (Rmax) and the half-saturation constant, Km, which is the oxygen concentration producing half of the maximum respiration rate, Rmax. We found that the nmodules in H. panicea scales consistently with sponge volume (Vsp) and that Rmax increased with sponge size with a proportionality > 1. Conversly, we found a lack of correlation between Km and sponge body size suggesting that oxygen concentration does not control the size of sponges.ConclusionsThe present study reveals that the addition of aquiferous modules (with a mean volume of 1.59 ± 0.22 mL) enables H. panicea in particular, and likely demosponges in general, to grow far beyond constraints limiting the size of their component modules and independent of ambient oxygen levels.

Non-linear heat and mass transfer in packed spherical horticultural produce: Heterogeneity and irreversibility

Heterogeneous distribution of heat generation from respiration reaction inside produce as well as irreversibility from different sources are still not analyzed especially for non-linear phenomena with different external operating conditions and internal produce properties. In this study, a numerical model of coupled heat and mass transfer with reaction kinetics of respiration is developed for packed spherical postharvest produce. We then analyze the distribution and irreversibility of respiration heat inside them under different inlet velocity, gas diffusivities and reaction rate of aerobic and anaerobic respiration. The result shows that non-linear distribution of respiration heat is identified as the transition of dominated mechanisms from convective mass transfer and diffusion of O2 resulting in local peaks between produce surface and center to convective cooling and thermal conduction leading to peak convergence with decreasing values near produce center. Increasing inflow air velocity causes reduced heterogeneity of respiration heat and earlier transition with shorter duration. Furthermore, in response to different gas diffusivity and respiration rate, non-linear variations of distribution characteristics for respiration heat are obtained by coupling effects of heat and mass transfer with complex reaction kinetics. While airflow and heat transfer processes are the main irreversibility sources, non-linear variations of entropy generation for mass transfer and respiration reaction are also obtained under external and internal influence.

Multiscale modeling of RQ-DCA storage of different pear cultivars using a hybrid physics-based stochastic approach

During respiratory quotient based dynamic controlled atmosphere (RQ-DCA) storage, the oxygen concentration in the room is reduced until the RQ measured in the air of the room (RQair) increases above a predefined threshold. This increase in RQ indicates an increased extent of fermentation within the fruit. Because of internal gas gradients, the oxygen concentration inside the fruit is lower than that of the storage atmosphere and, hence, the RQ value in the fruit (RQfruit,max) is larger than RQair. Moreover, due to biological variability and fluctuations in the storage conditions, both RQfruit,max and RQair vary. Currently, no information exists about how the RQ measured in the atmosphere correlates with the RQ value inside the fruit, and how representative this RQair is for all fruit inside the room. In this article, we investigated how variability affects the critical RQair threshold in RQ-DCA. Hereto we used a multiscale stochastic reaction-diffusion model to compute gas transport within pears of three different cultivars, ‘Cepuna’, ‘Conference’ and ‘Queen’s Forelle’. Biological variability in diffusion and respiration parameters and fluctuations in cool room conditions were taken into account by performing Monte-Carlo simulations. The results showed large variations in both RQfruit,max and RQair. The effect of cool room filling degree on both RQ values was negligible, while variations in fruit material properties (pear size, tissue gas diffusivity and respiration kinetics) showed to be of high importance. However, as RQair increased before fermentation started to dominate, the underestimation and variability of RQair did not inhibit a proper detection of hypoxia inside the fruit within the room. This finding indicates that RQair is a proper parameter to control DCA storage of various cultivars. Due to differences in fruit properties, the RQ-response varied between the cultivars. ‘Cepuna’ requires the highest O2 (0.61 kPa) to prevent fermentation, while ‘Conference’ and ‘Queen’s Forelle’ can be stored at lower O2 (0.33 and 0.22 kPa, respectively). The results obtained in this research can be used to optimize RQ-DCA storage of each cultivar.

Adaptive multi-paddock grazing management's influence on soil food web community structure for: increasing pasture forage production, soil organic carbon, and reducing soil respiration rates in southeastern USA ranches.

BackgroundMeasurement of two grazing management’s influence on pasture productivity, soil food web structure, soil organic carbon and soil microbial respiration efficiency was conducted on five southeastern US, across-the-fence ranch pairs to compare adaptive multi-paddock grazing (AMP) management, using short grazing events with planned, adaptive recovery periods, to conventional grazing (CG) management, with continuous grazing at low stock density.MethodologyA point-in-time experimental field analysis was conducted to compare five AMP or CG ranch pairs to better understand the influence of grazing management on (a) standing crop biomass productivity; (b) soil food web community population, structure and functionality; (c) soil organic carbon accrual; and d) soil-C (CO2) respiration kinetics.ResultsAMP grazing systems outperformed CG systems by generating: (a) 92.68 g m−2 more standing crop biomass (SCB), promoting 46% higher pasture photosynthetic capacity (Two sample Mann-Whitney; Z = 6.1836; no DF in MW; p = 6.26 × 10−10; Effect size = 0.35) (b) a strong positive linear relationship of SCB with fungal biomass (R = 0.9915; F(1,3) = 175.35; p = 0.015); fungal to bacterial (F:B) biomass ratio (R = 0.9616; F(1,3) = 36.75; p = 0.009) and a soil food web proxy (R = 0.9616; F(1,3) = 36.75; p = 0.009) and a concurrent very strong inverse relationship with bacteria biomass (R = −0.946; F(1,3) = 25.56; p = 0.015); (c) significant predator/prey interactions with an inverse relationship with bacterial population biomass (R = − 0.946; F(1,3) = 25.56; p = 0.015) and a positive relationship with total protozoa enumeration (R = 0.9826; F(1,3) = 83.68; p = 0.003) when compared to SCB; (d) a 19.52% reduction in soil C (CO2) respiration rates (Two sample t-test; T = −2.3581; DF = 52.3541; p = 0.0221; Effect size = 0.59); and (e) a 20.6% increase in soil organic carbon (SOC) in the top 10 cm of soil profile (Two sample Mann–Whitney; Z = 2.6507; no DF in MW; p = 0.008; Effect size = 0.24). Rancher conversion to AMP grazing strategies would appear to regenerate soil food web population, structure, diversity and biological functionality helping to improve: carbon flow into plant biomass, buildup of soil carbon, predator/prey nutrient cycling and soil microbial respiration efficiency while offering improved climate resilience and a strategy to increase the capture and storage of atmospheric CO2 in soils of the world’s rangeland.

Modelling Mixed Microbial Culture Polyhydroxyalkanoate Accumulation Bioprocess towards Novel Methods for Polymer Production Using Dilute Volatile Fatty Acid Rich Feedstocks.

Volatile fatty acid (VFA) rich streams from fermentation of organic residuals and wastewater are suitable feedstocks for mixed microbial culture (MMC) Polyhydroxyalkanoate (PHA) production. However, many such streams have low total VFA concentration (1–10 gCOD/L). PHA accumulation requires a flow-through bioprocess if the VFAs are not concentrated. A flow through bioprocess must balance goals of productivity (highest possible influent flow rates) with goals of substrate utilization efficiency (lowest possible effluent VFA concentration). Towards these goals, dynamics of upshift and downshift respiration kinetics for laboratory and pilot scale MMCs were evaluated. Monod kinetics described a hysteresis between the upshift and downshift responses. Substrate concentrations necessary to stimulate a given substrate uptake rate were significantly higher than the concentrations necessary to sustain the attained substrate uptake rate. A benefit of this hysteresis was explored in Monte Carlo based PHA accumulation bioprocess numerical simulations. Simulations illustrated for a potential to establish continuous flow-through PHA production bioprocesses even at a low (1 gCOD/L) influent total VFA concentration. Process biomass recirculation into an engineered higher substrate concentration mixing zone, due to the constant influent substrate flow, enabled to drive the process to maximal possible PHA production rates without sacrificing substrate utilization efficiency.

Microaerobic Lifestyle at Nanomolar O2 Concentrations Mediated by Low-Affinity Terminal Oxidases in Abundant Soil Bacteria.

ABSTRACTHigh-affinity terminal oxidases (TOs) are believed to permit microbial respiration at low oxygen (O2) levels. Genes encoding such oxidases are widespread, and their existence in microbial genomes is taken as an indicator for microaerobic respiration. We combined respiratory kinetics determined via highly sensitive optical trace O2 sensors, genomics, and transcriptomics to test the hypothesis that high-affinity TOs are a prerequisite to respire micro- and nanooxic concentrations of O2 in environmentally relevant model soil organisms: acidobacteria. Members of the Acidobacteria harbor branched respiratory chains terminating in low-affinity (caa3-type cytochrome c oxidases) as well as high-affinity (cbb3-type cytochrome c oxidases and/or bd-type quinol oxidases) TOs, potentially enabling them to cope with varying O2 concentrations. The measured apparent Km (Km(app)) values for O2 of selected strains ranged from 37 to 288 nmol O2 liter−1, comparable to values previously assigned to low-affinity TOs. Surprisingly, we could not detect the expression of the conventional high-affinity TO (cbb3 type) at micro- and nanomolar O2 concentrations but detected the expression of low-affinity TOs. To the best of our knowledge, this is the first observation of microaerobic respiration imparted by low-affinity TOs at O2 concentrations as low as 1 nM. This challenges the standing hypothesis that a microaerobic lifestyle is exclusively imparted by the presence of high-affinity TOs. As low-affinity TOs are more efficient at generating ATP than high-affinity TOs, their utilization could provide a great benefit, even at low-nanomolar O2 levels. Our findings highlight energy conservation strategies that could promote the success of Acidobacteria in soil but might also be important for as-yet-unrevealed microorganisms.IMPORTANCE Low-oxygen habitats are widely distributed on Earth, ranging from the human intestine to soils. Microorganisms are assumed to have the capacity to respire low O2 concentrations via high-affinity terminal oxidases. By utilizing strains of a ubiquitous and abundant group of soil bacteria, the Acidobacteria, and combining respiration kinetics, genomics, and transcriptomics, we provide evidence that these microorganisms use the energetically more efficient low-affinity terminal oxidases to respire low-nanomolar O2 concentrations. This questions the standing hypothesis that the ability to respire traces of O2 stems solely from the activity of high-affinity terminal oxidases. We propose that this energetically efficient strategy extends into other, so-far-unrevealed microbial clades. Our findings also demonstrate that physiological predictions regarding the utilization of different O2 concentrations based solely on the presence or absence of terminal oxidases in bacterial genomes can be misleading.

A combined mathematical model to represent transpiration, respiration, and water activity changes in fresh cape gooseberry (Physalis peruviana) fruits

In this work, a combined respiration and transpiration model is proposed for fresh cape gooseberry fruits, also considering changes in water activity (aw) and moisture content. Initially, a correlation of parameters was obtained from experimental data to determine the kinetics of O2 consumption and CO2 production for cape gooseberry fruits at different temperatures. From the data on the change in gas concentration, a parameter adjustment was made evaluating three kinetic models to represent respiration: 1) Power-Law Chemical kinetics (PL), 2) Simple Michaelis–Menten kinetics (MM), and 3) Michaelis–Menten with uncompetitive inhibition by CO2 (MMU). The temperature-dependence was considered in the three models by integrating an Arrhenius equation in the kinetic parameters. Afterward, a combined model was obtained to describe the fruit transpiration, coupling the moisture sorption isotherm (logistic model), and including the temperature-dependence and the most suitable respiration kinetics. It was determined that with the MMU kinetics it was possible to obtain a high goodness of fit with the experimental behaviour for the changes in the O2 and CO2 concentrations (R2adj. = 0.964 and 0.981). The MM kinetics had an acceptable fit (R2adj. = 0.940 and 0.941), while the PLK model could not explain the observed behaviour (R2adj. = 0.247 and 0.647). It was found that a logistic model appropriately described the relationship between the fruit moisture content and aw (R2adj. = 0.998). A close relationship was determined between the fruit's transpiration and its respiration rate, the change in the water activity, and the surrounding temperature and relative humidity (R2adj. = 0.998). As the temperature decreased, and as the relative humidity increased, the change in water activity and the transpiration rate decreased. Through the parameters established for each model, it is possible to predict the behaviour of processes such as respiration, transpiration, and changes in aw to configure a storage and packaging system by proposing the gas balance equations (O2, CO2, and water vapour) that allow obtaining favourable gas levels for the preservation of the fresh fruits.

Phosphorus Availability Promotes Bacterial DOC-Mineralization, but Not Cumulative CO2-Production.

The current trend of increasing input of terrestrially derived dissolved organic carbon (DOC) to boreal freshwater systems is causing increased levels of carbon dioxide (CO2) supersaturation and degassing. Phosphorus (P) is often the most limiting nutrient for bacterial growth and would thus be expected to increase overall mineralization rates and CO2 production. However, high carbon (C) to P ratios of terrestrially derived DOC could also cause elevated cell-specific respiration of the excess C in heterotrophic bacteria. Using data from a survey of 75 Scandinavian lakes along an ecosystem gradient of DOC, we estimated in situ CO2 production rates. These rates showed a unimodal response with DOC-specific CO2 production negatively related to DOC:total phosphorus (TP) ratio, and a turning point at 5 mg C L−1, indicating higher DOC turnover rates in productive than in unproductive lakes. To further assess the dependency of bacterial respiration (BR) on DOC and P, we monitored CO2 production in incubations of water with a gradient of DOC crossed with two levels of inorganic P. Finally, we crossed DOC and P with a temperature gradient to test the temperature dependency of respiration rates [as oxygen (O2) consumption]. While total CO2 production seemed to be unaffected by P additions, respiration rates, and growth yields, as estimated by ribosomal gene copy numbers, suggest increased bacterial growth and decreased cell-specific respiration under non-limited P conditions. Respiration rates showed a sigmoid response to increasing DOC availability reaching a plateau at about 20 mg C L−1 of initial DOC concentrations. In addition to these P and DOC level effects, respiration rates responded in a non-monotonic fashion to temperature with an increase in respiration rates by a factor of 2.6 (±0.2) from 15 to 25°C and a decrease above 30°C. The combined results from the survey and experiments highlight DOC as the major determinant of CO2 production in boreal lakes, with P and temperature as significant modulators of respiration kinetics.

Wastewaters from citrus processing industry as natural biostimulants for soil microbial community

Citrus fruit processing wastewaters (CWWs), being rich in organic matter, may be a valuable resource for agricultural irrigation and, possibly, for the improvement of soil organic carbon (TOC). This issue is becoming crucial for soils of arid and semiarid environments increasingly experiencing water scarcity and continuous decline of TOC towards levels insufficient to sustain crop production. However, before using CWWs in agriculture their effects on the soil living component have to be clarified. Therefore, in this study we assessed the impact of CWWs on soil chemical and biochemical properties. Under laboratory conditions, lemon, orange and tangerine wastewaters were separately added to a sandy clay soil reaching 1/3, 2/3 and 3/3 of its 50% water holding capacity. Then soils were incubated for 56 days at 22–24 °C in the dark and analyzed for total and extractable organic C, microbial biomass C and N, and the main microbial groups at days 7, 28 and 56, while microbial respiration kinetics was fitted to a first-order decay model by nine distinct daily rates measurements throughout incubation. During the first 3 days following the addition of CWWs, soil pH decreased by 2–3 units; however, afterwards the soil recovered its initial pH values. Total and extractable C pools, as well as microbial biomass C and N, were stimulated by CWWS with such a stimulation depending on CWWs type and added dose. Also microbial respiration kinetics was greatly affected by CWWs, although the effects were generally ephemeral at the lowest two doses, whereas at the highest dose still persisted up to day 56, especially in orange and lemon wastewaters. The concomitant general increase of both microbial and metabolic quotients after the addition of CWWs suggested that also under stress conditions, soil microorganisms were able to immobilize C. Both bacteria and fungi were stimulated by CWWs but the latter, at the beginning of incubation, were more favored probably due to a transient soil acidification by CWWs. In conclusion, CWWs when added to a sandy-clay soil increased total and labile C pools, stimulated soil microbial activity and biomass, i.e. improved the overall biological soil fertility, thus suggesting a possible role of CWWs in sustainable agriculture. However, soil electrical conductivity has to be monitored when CWWs are applied recurrently.

Modeling on respiration kinetics and modified atmospheric packaging of fig fruit

The article demonstrates the effect of the respiration rate of fig fruit at different storage temperatures (5–35 °C) and the designing of its modified atmospheric packaging. The average O2 consumption rates $$\left( {{\text{R}}_{{{\text{O}}_{2} }} } \right)$$ and CO2 evolution rate $$\left( {{\text{R}}_{{{\text{CO}}_{2} }} } \right)$$ of fig fruits within 5–35 °C were varied from 4.02 to 26.18 mL kg−1 h−1 and 4.89 to 29.19 mL kg−1 h−1, respectively. The respiration rate at 35 °C was increased up to 6.51 times in terms of O2 and 5.97 times in terms of CO2 than the respiration rate at 5 °C. The results showed that under steady state condition at 35 °C there were almost 43.3% and 42.8% decrease in $${\text{R}}_{{{\text{O}}_{2} }}$$ and $${\text{R}}_{{{\text{CO}}_{2} }}$$ values with respect to increase in time. The enzyme kinetics model in combination with the Arrhenius equation precisely predicted the respiration rate of fig fruit at different storage temperatures. The maximum respiration rate (Vm) for the enzyme kinetics model was increased from 10.910 to 45.620 mL kg−1 h−1 in terms of O2 and from 12.670 to 50.310 mL kg−1 h−1 in terms of CO2. The designing of modified atmospheric packaging was done to evaluate the influence of time and temperature on the respiration rate of fig fruit with various packaging materials. The modified atmosphere in polypropylene package with equilibrium concentration for O2 (0.0878) and CO2 (0.0971) was established within a period of 14 h was found to be the best suitable packaging material for extending the shelf life of fig fruit.

Apparent respiratory quotient observed in headspace of static respirometers underestimates cellular respiratory quotient of pear fruit

Abstract A three-compartment non-equilibrium gas transport model of ‘Conference’ pear fruit under controlled atmosphere (CA) storage was developed. The model fruit tissue consists of cells, in which the concentrations of respiratory gasses can show gradients, and intercellular space, in which gasses are uniformly distributed. Non-equilibrium of gas concentrations in the cell compartment and intercellular space is assumed. A respiration model based on Michaelis-Menten respiration kinetics without inhibition of respiration by CO2 and incorporating down-regulation of the maximal O2 consumption rate in response to O2 was developed. Conversion of CO2 dissolved in the cell compartment to hydrogen carbonate at a constant pH of 5.0 was included. The model was validated based on experimental data of ‘Conference’ pear fruit during a complete depletion experiment starting from 3.58 mol m−3 O2 and 0.00 mol m−3 CO2. Model predictions match experimental observations well. Gas concentrations in the cell compartment were found to be in equilibrium with the gas concentrations in the intercellular space. The model was used to calculate apparent respiration rates and RQ as if measured in the storage headspace. Apparent values were compared to actual values in the fruit cells and it was found that apparent respiration rates and RQ, calculated based on headspace measurements, underestimated the actual respiration rate and respiratory quotient in the fruit cells. Relative differences of 4 %, 41 % and 41 % were found for the apparent O2 consumption rate, CO2 production rate and RQ, respectively. This affects the design of commercial RQ based DCA systems.

Modelling respiration rate of dragon fruit as a function of gas composition and temperature

The application of controlled atmosphere and modified atmosphere packaging to extend the shelf life of dragon fruit requires insight into the respiration behaviour of the fruit under different storage conditions. To this end, this study focused on characterising the respiration kinetics of dragon fruit using a dynamic closed depletion system. An integrated data analysis was performed using a Michaelis-Menten based respiration model extended with an Arrhenius equation to account for the effects of O2, CO2 and temperature. Iterative analysis of the data using different model versions eventually revealed that the classical Arrhenius equation did not suffice to explain the observed respiration behaviour over the whole temperature range (2 °C–35 °C). The experimental data consistently showed lower respiration at 35 °C as compared to what was predicted by the classical Arrhenius equation. To overcome this problem, a modified Arrhenius equation, incorporating the Boltzmann distribution function, was successfully introduced to account for this observed temperature effect, predicting a maximal respiration rate at 33.9 °C. The parameters of the final model were estimated with high precision, explaining 98 % the data variance. Additionally, it was shown that CO2 had an uncompetitive inhibition on oxidative respiration, while O2 concentration affected both oxidative respiration and fermentation. This is the first documented example of postharvest fruit respiration not following the classical Arrhenius’ law at what could still be considered near field temperatures.

The Influence of Omega-3 Fatty Acids on Skeletal Muscle Protein Turnover in Health, Disuse, and Disease.

Ingestion of omega-3 fatty acids is known to exert favorable health effects on a number of biological processes such as improved immune profile, enhanced cognition, and optimized neuromuscular function. Recently, data have emerged demonstrating a positive influence of omega-3 fatty acid intake on skeletal muscle. For instance, there are reports of clinically-relevant gains in muscle size and strength in healthy older persons with omega-3 fatty acid intake as well as evidence that omega-3 fatty acid ingestion alleviates the loss of muscle mass and prevents decrements in mitochondrial respiration during periods of muscle-disuse. Cancer cachexia that is characterized by a rapid involuntary loss of lean mass may also be attenuated by omega-3 fatty acid provision. The primary means by which omega-3 fatty acids positively impact skeletal muscle mass is via incorporation of eicosapentaenoic acid (EPA; 20:5n−3) and docosahexaenoic acid (DHA; 22:6n−3) into membrane phospholipids of the sarcolemma and intracellular organelles. Enrichment of EPA and DHA in these membrane phospholipids is linked to enhanced rates of muscle protein synthesis, decreased expression of factors that regulate muscle protein breakdown, and improved mitochondrial respiration kinetics. However, exactly how incorporation of EPA and DHA into phospholipid membranes alters these processes remains unknown. In this review, we discuss the interaction between omega-3 fatty acid ingestion and skeletal muscle protein turnover in response to nutrient provision in younger and older adults. Additionally, we examine the role of omega-3 fatty acid supplementation in protecting muscle loss during muscle-disuse and in cancer cachexia, and critically evaluate the molecular mechanisms that underpin the phenotypic changes observed in skeletal muscle with omega-3 fatty acid intake.

Spatial distribution of gas concentrations and RQ in a controlled atmosphere storage container with pear fruit in very low oxygen conditions

Fruit that is stored in sub-optimal controlled atmosphere (CA) condition is susceptible to internal disorders and off-flavours. Understanding spatial variation in fruit respiration and gas exchange in the storage environment may aid in developing more robust and dynamic storage protocols that prevent unfavourable conditions. A computational fluid dynamics (CFD) model of transport of respiratory gases (O2 and CO2) in a CA storage container with pear fruit was constructed and validated using measured air velocity and gas concentration profiles, and respiratory quotient (RQ) values. The model incorporated the actual pear fruit (cv. ‘Conference’) geometry using a statistical shape model, and filling of the fruit inside the ventilated box was done using discrete element simulations. The model calculates air circulation, fruit respiration kinetics and transport of the respiratory gases in and between the surrounding air and the fruit. The dynamic response of the gas concentrations inside the CA storage system was predicted as a consequence of fruit respiration and air circulation. Air circulation greatly improved the uniformity of the respiratory gas distribution inside the CA storage system. There was a good agreement between the measured and predicted air velocity with an average relative error of 18.61%. The overall average relative error of the predicted O2 and CO2 distribution in the surrounding free air region was 1.90% and 0.63%, respectively. The model revealed that the volumetric average gas concentration and values of RQ inside the pear internal air space and pear cells were different from those measured in the surrounding air of the container. O2 and CO2 concentrations in the fruit were affected by fruit size. Larger fruits showed relatively lower O2 and higher CO2 at the fruit mass centres. During very low oxygen storage (0.22 kPa) with an average RQ = 3.04 in the surrounding air but 5.08 in the cells, the cellular oxygen concentration of the fruits was below the critical concentration for ATP imbalance (0.043 kPa), thereby increasing susceptibility to hypoxia related disorders.

Optimizing Oxygen Input Profiles for Efficient Estimation of Michaelis-Menten Respiration Models

Models based on mass balances and Michaelis-Menten respiration kinetics are increasingly used to determine optimal storage conditions of fresh fruits and vegetables. The model parameters are usually estimated from respiration experiments at different, but fixed, gas conditions according to a response surface design. This is a tedious procedure that requires a gas mixing facility or a series of gas cylinders with appropriate composition. In this paper, we consider a simpler approach, in which the respiration kinetics of pear fruit are modeled using a single experiment with a time-varying O2 input profile. To optimize the information content produced by the O2 profile, we apply optimal dynamic experimental design principles and present a modified coordinate-exchange algorithm to achieve this goal. Finally, we demonstrate the added value of our approach by comparing the optimal O2 input profiles to several intuitive benchmark experiments.

The Absence of Active Creatine Kinase System Influences Cardiac Calcium Handling

Creatine kinase (CK) system is known as a phosphoryl buffering and transfer system between mitochondria and ATPases. Functional coupling between CK and adenine nucleotide translocase, ATPases, and ATP-sensing potassium channel, has been demonstrated suggesting a major role of the CK system in the heart. To study CK system role, we used two lines of creatine-deficient mice, which lack either guanidinoacetate methyltransferase (GAMT) or arginine-glycine amidinotransferase (AGAT) on creatine synthesis pathway. Intriguingly, there have been no significant adaptations to the absence of active CK system in GAMT and AGAT mice cardiomyocytes from bioenergetics perspective: mitochondrial arrangement, respiration kinetics, activities of alternative pathway enzymes, intracellular compartmentation are the same in wild-type (WT) and knock-out (KO) littermates. Using whole-cell patch clamp, we studied how the absence of CK system influences calcium handling in cardiomyocytes of AGAT KO and WT littermates. Voltage dependence of L-type calcium channel (LTCC) current was significantly different in KO and WT animals with the significant differences between sexes within groups. LTCC amplitude was influenced by the absence of active CK system only in female mice in control conditions but was found to be the same in KO and WT male mice and mice of both sexes after adrenergic stimulation. The absence of active CK system had a major impact on calcium uptake, with the KO mice requiring more time for reducing calcium concentration to the resting level at the lower uptake rates. The effects of the active CK system absence on LTCC and calcium uptake, presumingly mainly by SR calcium ATPase, were fully reversed by creatine feeding to the KO animals. Our results suggest that there is a major role of the CK system in providing energy to excitation-contraction machinery in the heart to maintain normal calcium homeostasis.