Effect of oxygen on batch and continuous cultures of a nitrogen-fixing Arthrobacter sp.

Growth, acetylene reduction, and respiration rate were studied in batch and continuous cultures of Arthrobacter fluorescents at different oxygen partial pressures. The optimum pO2 values for growth and acetylene reduction were 0.05 and 0.025 atm, respectively, but microorganisms can tolerate higher pO2 values. The growth of cultures provided with combined nitrogen was dependent on oxygen availability, and strict anaerobic conditions did not support growth. Acetylene reduction of a population grown in continuous culture and adapted to low pO2 (0.02 atm) was much more sensitive to oxygenation than that of a population adapted to high pO2 (0.4 atm). Their maximum nitrogenase activity, at their optimal pO2 values, were quite different. The respiratory activity of nitrogen-fixing cultures increased with increasing oxygen tensions until a pO2 of 0.2 atm. At higher pO2 values, the respiration rate began to decrease.     

Electron paramagnetic resonance oximetry as a quantitative method to measure cellular respiration: a consideration of oxygen diffusion interference

Electron paramagnetic resonance (EPR) oximetry is being widely used to measure the oxygen consumption of cells, mitochondria, and submitochondrial particles. However, further improvement of this technique, in terms of data analysis, is required to use it as a quantitative tool. Here, we present a new approach for quantitative analysis of cellular respiration using EPR oximetry. The course of oxygen consumption by cells in suspension has been observed to have three distinct zones: pO(2)-independent respiration at higher pO(2) ranges, pO(2)-dependent respiration at low pO(2) ranges, and a static equilibrium with no change in pO(2) at very low pO(2) values. The approach here enables one to comprehensively analyze all of the three zones together-where the progression of O(2) diffusion zones around each cell, their overlap within time, and their potential impact on the measured pO(2) data are considered. The obtained results agree with previously established methods such as high-resolution respirometry measurements. Additionally, it is also demonstrated how the diffusion limitations can depend on cell density and consumption rate. In conclusion, the new approach establishes a more accurate and meaningful model to evaluate the EPR oximetry data on cellular respiration to quantify related parameters using EPR oximetry.     

O2 as the regulatory signal for FNR-dependent gene regulation in Escherichia coli.

With an oxystat, changes in the pattern of expression of FNR-dependent genes from Escherichia coli were studied as a function of the O2 tension (pO2) in the medium. Expression of all four tested genes was decreased by increasing O2. However, the pO2 values that gave rise to half-maximal repression (pO(0.5)) were dependent on the particular promoter and varied between 1 and 5 millibars (1 bar = 10(5) Pa). The pO(0.5) value for the ArcA-regulated succinate dehydrogenase genes was in the same range (pO(0.5) = 4.6 millibars). At these pO2 values, the cytoplasm can be calculated to be well supplied with O2 by diffusion. Therefore, intracellular O2 could provide the signal to FNR, suggesting that there is no need for a signal transfer chain. Genetic inactivation of the enzymes and coenzymes of aerobic respiration had no or limited effects on the pO(0.5) of FNR-regulated genes. Thus, neither the components of aerobic respiration nor their redox state are the primary sites for O2 sensing, supporting the significance of intracellular O2. Non-redox-active, structural O2 analogs like CO, CN-, and N3-, could not mimic the effect of O2 on FNR-regulated genes under anaerobic conditions and did not decrease the inhibitory effect of O2 under aerobic conditions.     

Response of the endophytic diazotroph Gluconacetobacter diazotrophicus on solid media to changes in atmospheric partial O(2) pressure

Gluconacetobacter diazotrophicus is an N(2)-fixing endophyte isolated from sugarcane. G. diazotrophicus was grown on solid medium at atmospheric partial O(2) pressures (pO(2)) of 10, 20, and 30 kPa for 5 to 6 days. Using a flowthrough gas exchange system, nitrogenase activity and respiration rate were then measured at a range of atmospheric pO(2) (5 to 60 kPa). Nitrogenase activity was measured by H(2) evolution in N(2)-O(2) and in Ar-O(2), and respiration rate was measured by CO(2) evolution in N(2)-O(2). To validate the use of H(2) production as an assay for nitrogenase activity, a non-N(2)-fixing (Nif(-)) mutant of G. diazotrophicus was tested and found to have a low rate of uptake hydrogenase (Hup(+)) activity (0.016 +/- 0.009 micromol of H(2) 10(10) cells(-1) h(-1)) when incubated in an atmosphere enriched in H(2). However, Hup(+) activity was not detectable under the normal assay conditions used in our experiments. G. diazotrophicus fixed nitrogen at all atmospheric pO(2) tested. However, when the assay atmospheric pO(2) was below the level at which the colonies had been grown, nitrogenase activity was decreased. Optimal atmospheric pO(2) for nitrogenase activity was 0 to 20 kPa above the pO(2) at which the bacteria had been grown. As atmospheric pO(2) was increased in 10-kPa steps to the highest levels (40 to 60 kPa), nitrogenase activity decreased in a stepwise manner. Despite the decrease in nitrogenase activity as atmospheric pO(2) was increased, respiration rate increased marginally. A large single-step increase in atmospheric pO(2) from 20 to 60 kPa caused a rapid 84% decrease in nitrogenase activity. However, upon returning to 20 kPa of O(2), 80% of nitrogenase activity was recovered within 10 min, indicating a "switch-off/switch-on" O(2) protection mechanism of nitrogenase activity. Our study demonstrates that colonies of G. diazotrophicus can fix N(2) at a wide range of atmospheric pO(2) and can adapt to maintain nitrogenase activity in response to both long-term and short-term changes in atmospheric pO(2).     

Mitochondrial respiration and oxygen transport during various stages of lung inflammation

It is shown in rats with experimental lung inflammation that the phosphorylative and uncoupling mitochondrial respiration intensity rises at acute and reverses to the normal level at subacute inflammation. At chronic inflammation the 2,4-DNP-stimulated mitochondrial respiration enhances and the ADPO coefficient lowers. At all stages of inflammation the pO2 rise in muscles after O2-inhalation is less than in healthy animals. The disturbance of O2 transport in organism may be the reason of the described low energy shift at lung inflammation.     

Relation of transcutaneous to arterial pO2 in hypoxaemia, normoxaemia and hyperoxaemia. Investigations in adults with normal circulation and in patients with circulatory insufficiency

The transcutaneous oxygen tension was monitored continuously by a heated cutaneous polarographic electrode in 7 adult intensive care patients, 12 patients without circulatory insufficiency, and 5 healthy volunteers, Arterial pO2 values were varied from hypoxaemia to normoxaemia and hyperoxaemia by variations of the inspired oxygen concentration. In normal volunteers and in patients without circulatory failure, transcutaneous pO2 indicated on an average about 81-92% of the arterial pO2 in normoxaemia and hyperoxaemia with a correlation coefficient of 0.97. In hypoxaemia there was an over-proportional decrease of the transcutaneous pO2 to a mean value of 44% fo the arterial pO2. In one case the transcutaneous pO2 reproducibly dropped to zero at paO2 values of 41 respectively 38 mm Hg (5.5 respectively 5.1 kPa). In intensive care patients the transcutaneous pO2 values were considerably lower than the paO2 values. There was no constant transcutaneous to arterial pO2 ration in most of the intensive care patients at different pO2 levels. In adults without disturbance of peripheral perfusion paO2 can be predicted with satisfactory accuracy from transcutaneous pO2 values in normoxaemia and in hyperoxaemia. In hypoxaemia and in circulatory insufficiency, the transcutaneous pO2 is only an indicator of the trend of the arterial pO2. Under these conditions it does not allow a quantitative estimate of paO2 changes.     

Augmented rates of respiration and efficient nitrogen fixation at nanomolar concentrations of dissolved O2 in hyperinduced Azoarcus sp. strain BH72.

Azoarcus sp. strain BH72 is an aerobic diazotrophic bacterium that was originally found as an endophyte in Kallar grass. Anticipating that these bacteria are exposed to dissolved O2 concentrations (DOCs) in the nanomolar range during their life cycle, we studied the impact of increasing O2 deprivation on N2 fixation and respiration. Bacteria were grown in batch cultures, where they shifted into conditions of low pO2 upon depletion of O2 by respiration. During incubation, specific rates of respiration (qO2) and efficiencies of carbon source utilization for N2 reduction increased greatly, while the growth rate did not change significantly, a phenomenon that we called "hyperinduction." To evaluate this transition from high- to low-cost N2 fixation in terms of respiratory kinetics and nitrogenase activities at nanomolar DOC, bacteria which had shifted to different gas-phase pO2s in batch cultures were subjected to assays using leghemoglobin as the O2 carrier. As O2 deprivation in batch cultures proceeded, respiratory Km (O2) decreased and Vmax increased. Nitrogenase activity at nanomolar DOC increased to a specific rate of 180 nmol of C2H4 min-1 mg of protein-1 at 32 nM O2. Nitrogenase activity was proportional to respiration but not to DOC in the range of 12 to 86 nM O2. Respiration supported N2 fixation more efficiently at high than at low respiratory rates, the respiratory efficiency increasing from 0.14 to 0.47 mol of C2H4 mol of O2 consumed-1. We conclude that (i) during hyperinduction, strain BH72 used an increasing amount of energy generated by respiration for N2 fixation, and (ii) these bacteria have a high respiratory capacity, enabling them to develop ecological niches at very low pO2, in which they may respire actively and fix nitrogen efficiently at comparatively high rates.     

Effect of cyclic nucleotides and isopropylnoradrenaline on oxygen tension and absorption]

Isopropylnoradrenaline (ISO), 3',5'-AMP and dibutyryl-3',5'-AMP decreased the oxygen tension (pO2) in the liver and the spleen and increased the body oxygen consumption (VO2). Time dynamics of these two effects was closely correlated for ISO and 3',5'-AMP. An increase of heat output was not accompanied by any significant changes in the respiration coefficient. Pempidine and dihydroergotamine failed to prevent 3',5'-AMP effects; inderal somewhat decreased these effects. Apparently, the catecholamine influence upon pO2 was a result of the VO2 increase through 3'5'-AMP effects are largely direct, but they include the in vivo and beta-receptor component; 2',3'-AMP decreased pO2 and VO2.     

Gas sensing in microplates with optodes: influence of oxygen exchange between sample, air, and plate material

Microplates with integrated optical oxygen sensors are a new tool to study metabolic rates and enzyme activities. Precise measurements are possible only if oxygen exchange between the sample and the environment is known. In this study we quantify gas exchange in plastic microplates. Dissolved oxygen was detected using either an oxygen-sensitive film fixed at the bottom of each well or a needle-type sensor. The diffusion of oxygen into wells sealed with different foils, paraffin oil, and paraffin wax, respectively, was quantified. Although foil covers showed the lowest oxygen permeability, they include an inevitable gas phase between sample and sealing and are difficult to manage. The use of oil was found to be critical due to the extensive shaking caused by movement of the plates during measurements in microplate readers. Thus, paraffin wax was the choice material because it avoids convection of the sample and is easy to handle. Furthermore, without shaking, significant gradients in pO2 levels within a single well of a polystyrene microplate covered with paraffin oil were detected with the needle-type sensor. Higher pO2 levels were obtained near the surface of the sample as well as near the wall of the well. A significant diffusion of oxygen through the plastic plate material was found using plates based on polystyrene. Thus, the location of a sensor element within the well has an effect on the measured pO2 level. Using a sensor film fixed on the bottom of a well or using a dissolved pO2-sensitive indicator results in pO2 offset and in apparently lower respiration rates or enzyme activities. Oxygen diffusion through a polystyrene microplate was simulated for measurements without convection--that is, for samples without oxygen diffusion through the cover and for unshaken measurements using permeable sealings. This mathematical model allows for calculation of the correct kinetic parameters.     

Comparison of Helzel and OxyLite systems in the measurements of tumor partial oxygen pressure (pO2)

Wen, B., Urano, M., Humm, J. L., Seshan, V. E., Li, G. C. and Ling, C. C. Comparison of Helzel and OxyLite Systems in the Measurements of Tumor Partial Oxygen Pressure (pO(2)). Radiat. Res. 168, 67-75 (2008). It has been demonstrated in both experimental and human malignancies that hypoxic tumor cells are linked with aggressive disease phenotype. One of the methods to identify these cells is by direct physical measurement of tumor pO(2). This study compared pO(2) values measured with two systems, the Helzel Hypoximeter (successor of the polarographic Eppendorf electrode) and the Oxford-Optronix OxyLite (fiber-optic probe), in R3327-AT and R3327-AT/tkeGFP tumors. Partial oxygen pressure was measured in individual tumors with either system or in the same tumor with both systems. The similarities and discrepancies in pO(2) measurements between the two systems were also investigated when tumor-bearing animals were breathing pure oxygen. Our data showed a considerable heterogeneity in pO(2) values in each tumor using both the Helzel and OxyLite systems. Similar results were obtained with both systems for the mean and median pO(2) values, and the distributions of pO(2) values within the interval 0 < pO(2) < 40 mmHg (the range important for defining tumor hypoxia) were found to be statistically equivalent. However, the frequencies of high pO(2) values (>40 mmHg) and zero values measured by the two systems were statistically significantly different.     

Experimental analysis on the variations of acid-base balance in the chick embryo

1. The pH remains steady, 7.57. 2. The pCO2 increases gradually. We believe this is fundamental for hatching. 3. Bicarbonate and base excess increase from acidosis to alkalosis due to absorption of the egg shell. 4. The pO2 increases in stage 41 and 42 due to pulmonary respiration. 5. The pO2 drop prior to hatching due to involution of the chorioalantoid membrane and increasing requirements.     

Oxygen dynamics in submerged rice (Oryza sativa)

Complete submergence of plants prevents direct O(2) and CO(2) exchange with air. Underwater photosynthesis can result in marked diurnal changes in O(2) supply to submerged plants. Dynamics in pO(2) had not been measured directly for submerged rice (Oryza sativa), but in an earlier study, radial O(2) loss from roots showed an initial peak following shoot illumination. O(2) dynamics in shoots and roots of submerged rice were monitored during light and dark periods, using O(2) microelectrodes. Tissue sugar concentrations were also measured. On illumination of shoots of submerged rice, pO(2) increased rapidly and then declined slightly to a new quasi-steady state. An initial peak was evident first in the shoots and then in the roots, and was still observed when 20 mol m(-3) glucose was added to the medium to ensure substrate supply in roots. At the new quasi-steady state following illumination, sheath pO(2) was one order of magnitude higher than in darkness, enhancing also pO(2) in roots. The initial peak in pO(2) following illumination of submerged rice was likely to result from high initial rates of net photosynthesis, fuelled by CO(2) accumulated during the dark period. Nevertheless, since sugars decline with time in submerged rice, substrate limitation of respiration could also contribute to morning peaks in pO(2) after longer periods of submergence.     

Separating the effects of hypobaria and hypoxia on lettuce: growth and gas exchange

The objectives of this research were to determine the influence of hypobaria (reduced atmospheric pressure) and reduced partial pressure of oxygen (pO2) [hypoxia] on carbon dioxide (CO2) assimilation (C(A)), dark-period respiration (DPR) and growth of lettuce (Lactuca sativa L. cv. Buttercrunch). Lettuce plants were grown under variable total gas pressures [25 and 101 kPa (ambient)] at 6, 12 or 21 kPa pO2)(approximately the partial pressure in air at normal pressure). Growth of lettuce was comparable between ambient and low total pressure but lower at 6 kPa pO2 (hypoxic) than at 12 or 21 kPa pO2. The specific leaf area of 6 kPa pO2 plants was lower, indicating thicker leaves associated with hypoxia. Roots were most sensitive to hypoxia, with a 50-70% growth reduction. Leaf chlorophyll levels were greater at low than at ambient pressure. Hypobaria and hypoxia did not affect plant water relations. While hypobaria did not adversely affect plant growth or C(A), hypoxia did. There was comparable C(A) and a lower DPR in low than in ambient total pressure plants under non-limiting CO2 levels (100 Pa pCO2, nearly three-fold that in normal air). The C(A)/DPR ratio was higher at low than at ambient total pressure, particularly at 6 kPa pO2- indicating a greater efficiency of C(A)/DPR in low-pressure plants. There was generally no significant interaction between hypoxia and hypobaria. We conclude that lettuce can be grown under subambient pressure ( congruent with25% of normal earth ambient total pressure) without adverse effects on plant growth or gas exchange. Furthermore, hypobaric plants were more resistant to hypoxic conditions that reduced gas exchange and plant growth.     

Role of Oxygen in the Limitation and Inhibition of Nitrogenase Activity and Respiration Rate in Individual Soybean Nodules

Although infected cell O2 concentration (Oi) is known to limit respiration and nitrogenase activity in legume nodules, techniques have not been available to measure both processes simultaneously in an individual legume nodule. Consequently, details of the relationship between nitrogenase activity and Oi are not fully appreciated. For the present study, a probe was designed that allowed open circuit measurements of H2 evolution (nitrogenase activity) and CO2 evolution (respiration rate) in a single attached soybean nodule while simultaneously monitoring fractional oxygenation of leghemoglobin (and thereby Oi) with a nodule oximeter. Compared to measurements of whole nodulated roots, use of the probe led to inhibition of nitrogenase activity in the single nodules. During oximetry measurements, total nitrogenase activity (TNA; peak H2 evolution in Ar/O2) in the single nodules was 16% of that in whole nodulated roots and 48% of nodulated root activity when Oi was not being measured simultaneously. This inhibition did not affect the nodules' ability to regulate Oi, because exposure to Ar/O2 (80:20, v/v) caused nitrogenase activity and respiration rate to decline, and this decline was linearly correlated with a concurrent decrease in Oi. When the nodules were subsequently exposed to a linear increase in external pO2 from 20 to 100% O2 at 2.7% O2/min, fractional leghemoglobin oxygenation first increased gradually and then more rapidly, reaching saturation at a pO2 between 76 and 100% O2. Plots of nitrogenase activity and respiration rate against Oi showed that rates increased with Oi up to a value of 57 nM, with half-maximal rates being attained at Oi values between 10 and 14 nM O2. The maximum nitrogenase activity achieved during the increase in pO2 (potential nitrogenase activity) was 30 to 57% of that measured in intact nodulated roots, showing that O2 limitation of nitrogenase activity could account for a significant proportion of the inhibition of TNA associated with the use of the probe. However, some factor(s) in addition to O2 must have limited the activity of single nodules at both subsaturating and saturating Oi. At Oi values greater than about 57 nM, nitrogenase activity and nodule respiration were inhibited, but, because this inhibition has been shown previously to be readily reversible when the Oi was lowered, it was not attributed to direct O2 inactivation of the nitrogenase protein. These results indicate that maximum nitrogenase activity in legume nodules is supported by a narrow range of Oi values. Possible biochemical mechanisms are discussed for both O2 limitation of nitrogenase activity at low Oi and inhibition of nitrogenase activity at high Oi.     

Oxygen dynamics during submergence in the halophytic stem succulent Halosarcia pergranulata

This study elucidated O2 dynamics in shoots and roots of submerged Halosarcia pergranulata (Salicornioideae), a perennial halophytic stem succulent that grows on floodprone mudflats of salt lakes. Oxygen within shoots and roots was measured using microelectrodes, for plants when waterlogged or completely submerged, with shoots in light or in darkness, in a controlled environment. Net photosynthesis (PN) when underwater, at a range of dissolved CO2 concentrations, was measured by monitoring O2 production rates by excised stems. The bulky nature and apparently low volume of gas-filled spaces of the succulent stems resulted in relatively high radial resistance to gas diffusion. At ambient CO2, quasi-steady state rates of PN by excised succulent stems were estimated to be close to zero; nevertheless, in intact plants, underwater photosynthesis provided O2 to tissues and led to radial O2 loss (ROL) from the roots, at least during the first several hours (the time period measured) after submergence or when light periods followed darkness. The influence of light on tissue O2 dynamics was confirmed in an experiment on a submerged plant in a salt lake in south-western Australia. In the late afternoon, partial pressure of O2 (pO2) in the succulent stem was 23.2 kPa (i.e. approximately 10% above that in the air), while in the roots, it was 6.2-9.8 kPa. Upon sunset, the pO2 in the succulent stems declined within 1 h to below detection, but then showed some fluctuations with the pO2 increasing to at most 2.5 kPa during the night. At night, pO2 in the roots remained higher than in the succulent stems, especially for a root with the basal portion in the floodwater. At sunrise, the pO2 increased in the succulent stems within minutes. In the roots, changes in the pO2 lagged behind those in the succulent stems. In summary, photosynthesis in stems of submerged plants increased the pO2 in the shoots and roots so that tissues experience diurnal changes in the pO2, but O2 from the H2O column also entered submerged plants.     

External respiration and the functional state of the respiratory center in hypoxia developing against a background of inactivated carbonic anhydrase]

Experiments were conducted on cats; inactivation of carboanhydrase with diamox prevented developmento f hypocapnia and disturbances of the rhythmic activity of the respiratory neurons associated with it in acute hypoxia. However, comparision of electrophysiological data, external respiration indices, of the acid-base balance, pO2 and pCO2 of arterial blood demonstrated that, preventing development of pathological Cheyne-Stokes respiration under conditions of hypoxia, inactivation of carboanhydrase with diamox caused dissociation of the thoracic and abdominal respiration and dyspnea. The latter led to shifts in the metabolic processes and to disturbance of the electrolyte metabolism at the cell level.     

Superoxide, hydrogen peroxide, and oxygen toxicity in two free-living nematode species

Two species of free-living nematodes, Turbatrix aceti and Caenorhabditis elegans, exhibited a marked sensitivity to 3 atm of 100% O2. Environmental changes in pH and temperature, which altered nematode respiration, resulted in alterations in the survival of these organisms under high pO2. Levels of defensive enzymes such as superoxide dismutase, catalase, glutathione peroxidase, and dianisidine peroxidase were measured in the two species. No changes in the level of superoxide dismutase or catalase activity were induced by exposure of the nematodes to high pO2. Manipulation of these two enzymes was however achieved using the inhibitors 3-amino-1,2,4-triazole and diethyldithiocarbamate. 3-Amino-1,2,4-triazole (20 mM) eliminated greater than or equal to 80% of the catalase activity in vivo and diethyldithiocarbamate (5 mM) decreased the level of CuZn superoxide dismutase by greater than or equal to 70%. Both of these compounds increased the sensitivity of C. elegans to high pO2 toxicity. Compounds capable of intracellular redox-cycling with O2- -production, such as plumbagin, increased CN- -resistant respiration in the nematodes and imposed an O2-dependent toxicity. These experiments demonstrate the toxicity of intracellular O2- and H2O2 in nematodes and the importance of superoxide dismutase and catalase in providing a defense against these toxic molecules in vivo.     

Metabolic and energetic control of Pseudomonas mendocina growth during transitions from aerobic to oxygen-limited conditions in chemostat cultures.

Several metabolic fluxes were analyzed during gradual transitions from aerobic to oxygen-limited conditions in chemostat cultures of Pseudomonas mendocina growing in synthetic medium at a dilution rate of 0.25 h-1. P. mendocina growth was glucose limited at high oxygen partial pressures (70 and 20% pO2) and exhibited an oxidative type of metabolism characterized by respiratory quotient (RQ) values of 1.0. A similar RQ value was obtained at low pO2 (2%), and detectable levels of acetic, formic, and lactic acids were determined in the extracellular medium. RQs of 0.9 +/- 0.12 were found at 70% pO2 for growth rates ranging from 0.025 to 0.5 h-1. At high pO2, the control coefficients of oxygen on catabolic fluxes were 0.19 and 0.22 for O2 uptake and CO2 production, respectively. At low pO2 (2%), the catabolic and anabolic fluxes were highly controlled by oxygen. P. mendocina showed a mixed-type fermentative metabolism when nitrogen was flushed into chemostat cultures. Ethanol and acetic, lactic, and formic acids were excreted and represented 7.5% of the total carbon recovered. Approximately 50% of the carbon was found as uronic acids in the extracellular medium. Physiological studies were performed under microaerophilic conditions (nitrogen flushing) in continuous cultures for a wide range of growth rates (0.03 to 0.5 h-1). A cell population, able to exhibit a near-maximum theoretical yield of ATP (YmaxATP = 25 g/mol) with a number of ATP molecules formed during the transfer of an electron towards oxygen along the respiration chain (P/O ratio) of 3, appears to have adapted to microaerophilic conditions.(ABSTRACT TRUNCATED AT 250 WORDS)     

Metabolic and energetic control of Pseudomonas mendocina growth during transitions from aerobic to oxygen-limited conditions in chemostat cultures.

Several metabolic fluxes were analyzed during gradual transitions from aerobic to oxygen-limited conditions in chemostat cultures of Pseudomonas mendocina growing in synthetic medium at a dilution rate of 0.25 h-1. P. mendocina growth was glucose limited at high oxygen partial pressures (70 and 20% pO2) and exhibited an oxidative type of metabolism characterized by respiratory quotient (RQ) values of 1.0. A similar RQ value was obtained at low pO2 (2%), and detectable levels of acetic, formic, and lactic acids were determined in the extracellular medium. RQs of 0.9 +/- 0.12 were found at 70% pO2 for growth rates ranging from 0.025 to 0.5 h-1. At high pO2, the control coefficients of oxygen on catabolic fluxes were 0.19 and 0.22 for O2 uptake and CO2 production, respectively. At low pO2 (2%), the catabolic and anabolic fluxes were highly controlled by oxygen. P. mendocina showed a mixed-type fermentative metabolism when nitrogen was flushed into chemostat cultures. Ethanol and acetic, lactic, and formic acids were excreted and represented 7.5% of the total carbon recovered. Approximately 50% of the carbon was found as uronic acids in the extracellular medium. Physiological studies were performed under microaerophilic conditions (nitrogen flushing) in continuous cultures for a wide range of growth rates (0.03 to 0.5 h-1). A cell population, able to exhibit a near-maximum theoretical yield of ATP (YmaxATP = 25 g/mol) with a number of ATP molecules formed during the transfer of an electron towards oxygen along the respiration chain (P/O ratio) of 3, appears to have adapted to microaerophilic conditions.(ABSTRACT TRUNCATED AT 250 WORDS)     

Energy metabolism in relation to oxygen partial pressure in human skeletal muscle during exercise.

1. The intramuscular oxygen partial pressure (pO2) in human gastrocnemius muscle was monitored during exercise and compared with metabolite concentrations reflecting the energy and the redox state in the tissue. Ten normal subjects and ten patients with peripheral vascular occlusive disease were investigated. 2. In normal subjects the pO2 at the end of exercise was related to the intensity of the exercise, expressed as effect (J/s) per contraction. 3. In both patients and normal subject the pO2 was related to the [ATP]/[ADP] ratio, the [lactate/[pyruvate] ratio and the phosphocreatine concentration in the muscle tissue at rest and during exercise. 4. At each pO2 value, a lower [lactate/[pyruvate] ratio was found in the muscle tissue of the patients compared with that of normal subjects. This was interpreted as a beneficial effect of the higher oxidative-enzyme capacity in the muscle of the patients. 5. The results show the importance of pO2 for the regulation of the energy and the redox state of the tissue. During exercise the changes induced in pO2 and thus the energy state will stimulate the respiratory rate. This might be an important link in triggering the oxidative-enzyme capacity in response to physical training as well as in peripheral vascular occlusive disease.