Respiratory metabolism of Azotobacter vinelandii cells at oxygen concentrations that initially range from suboptimal to supraoptimal for nitrogenase activity

1991 ◽  
Vol 37 (4) ◽  
pp. 321-325 ◽  
Author(s):  
Jay B. Peterson
Keyword(s):  
Oxygen Uptake ◽  
Oxygen Concentration ◽  
Azotobacter Vinelandii ◽  
Nitrogenase Activity ◽  
Low Oxygen ◽  
Total Oxygen ◽  
Apparent Affinity ◽  
Lower Oxygen ◽  
Effect Of Oxygen ◽  
Oxygen Concentrations

The effects of three low oxygen concentrations on nitrogenase activity, total oxygen uptake, and respiratory parameters (Vmax and Ks(O2) of N2-grown Azotobacter vinelandii were studied in acetylene reduction assays during a 2-h incubation. The cell suspensions were taken from cultures grown at low aeration. Total oxygen uptake was higher with each increment in oxygen concentration. The highest oxygen concentration was initially supraoptimal for nitrogenase activity. The Ks(O2) values, representing the apparent affinity of the respiration system for oxygen, increased during the incubation of cells at the highest oxygen concentration. The Ks(O2) values at the two lower oxygen concentrations decreased and were very similar. A small effect of oxygen on the Vmax was observed. These results show that the metabolism determining the apparent affinity of the system for oxygen responds to the oxygen concentrations. Furthermore, this metabolism did not substantially increase the Ks(O2) unless the oxygen concentration was high enough to inhibit nitrogenase activity, indicating that the two processes may be linked. Key words: Azotobacter, oxygen regulation, nitrogen fixation.

Influence of some factors on oxygen uptake of canine cardiac Purkinje fibers

1963 ◽  
Vol 204 (1) ◽  
pp. 5-8 ◽  
Author(s):  
Kalman Greenspan ◽  
Paul F. Cranefield
Keyword(s):  
Oxygen Uptake ◽  
Oxygen Concentration ◽  
Diffusion Limitation ◽  
Purkinje Fibers ◽  
Ambient Oxygen ◽  
Cardiac Purkinje Fibers ◽  
Lower Oxygen ◽  
Wet Weight ◽  
Oxygen Tensions ◽  
Oxygen Concentrations

The rate of oxygen uptake of quiescent Purkinje fibers of the dog's heart was determined using a flow respirometer and oxygen polarography. At ambient oxygen concentrations of 60% or higher the rate of uptake was 0.739 mm3/mg wet weight per hr at 35 C. The temperature coefficient over the range 25–35° was 2.3. The uptake was independent of the ambient oxygen concentration at oxygen concentrations equal to or greater than 60% of an atmosphere. In lower oxygen concentrations the rate of uptake was found to be depressed. The depression of uptake in the lower oxygen tensions is probably the result of diffusion limitation; it may, however, reflect dependence of resting uptake on oxygen concentration.

Respiratory differences associated with culture aeration in Azotobacter vinelandii

1989 ◽  
Vol 35 (10) ◽  
pp. 918-924 ◽  
Author(s):  
Jay B. Peterson
Keyword(s):  
Nitrogen Fixation ◽  
Oxygen Uptake ◽  
Oxygen Concentration ◽  
Azotobacter Vinelandii ◽  
Partial Explanation ◽  
Respiration Rates ◽  
Carbon Substrates ◽  
Moderate Agitation ◽  
Different Levels ◽  
Oxygen Concentrations

Respiratory oxygen uptake of nitrogen-fixing Azotobacter vinelandii cells was altered by culturing at different levels of culture agitation (aeration). Cells were grown at low agitation or moderate agitation and with three different carbon substrates. The low-agitation cultures had much lower dissolved-oxygen concentrations than moderate-agitation cultures at the stage of growth at which they were studied. The respiration systems of cells from the moderate-agitation cultures had lower apparent affinities (higher Ks (O2) values) for oxygen than cells grown at low agitation. The higher Ks (O2)) values were dependent on the presence of Ca2+ and (or) Mg2+ in the medium. In low-agitation cultures, the oxygen concentrations were below the Ks (O2 values and the respiration rates in the cultures were therefore well below the maximal respiration (Vmax) rates. The oxygen concentrations in moderate-agitation cultures were above the Ks (O2) values and the culture respiration rates were much higher. The culture oxygen concentration relative to the Ks (O2) had a much greater effect on culture respiration rate than did the Vmax. It is proposed that changes in the respiration system resulting from culture agitation (aeration) reflect an "oxygen-sensing mechanism" that regulates respiration. This would provide at least a partial explanation for the increased respiration rates with increased culture oxygen concentration in A. vinelandii.Key words: Azotobacter, oxygen, respiration, nitrogen fixation.

Effect of Oxygen on Growth of Mycobacterium ulcerans in the BACTEC System

1998 ◽  
Vol 36 (11) ◽  
pp. 3420-3422 ◽  
Author(s):  
J. C. Palomino ◽  
A. M. Obiang ◽  
L. Realini ◽  
W. M. Meyers ◽  
F. Portaels
Keyword(s):  
Primary Culture ◽  
Oxygen Concentration ◽  
Oxygen Tension ◽  
Mycobacterium Ulcerans ◽  
Clinical Samples ◽  
Low Oxygen ◽  
Bactec System ◽  
Effect Of Oxygen ◽  
Low Oxygen Concentration

The effect of low oxygen concentration on the growth of 15 strains of Mycobacterium ulcerans was evaluated in the BACTEC system. Reduced oxygen tension enhanced the growth of M. ulcerans, suggesting that this organism has a preference for microaerobic environments. Application of this observation may improve rates of isolation of M. ulcerans in primary culture from clinical samples and promote isolation of the bacterium from environmental sources.

Large Eddy Simulation of Multiple-Stage Ignition Process of n-Heptane Spray Flame

2019 ◽  
Vol 141 (8) ◽  
Author(s):  
Wanhui Zhao ◽  
Lei Zhou ◽  
Wenjin Qin ◽  
Haiqiao Wei
Keyword(s):  
Oxygen Concentration ◽  
Mixture Fraction ◽  
Ignition Process ◽  
Low Oxygen ◽  
Nonpremixed Combustion ◽  
Eddy Simulation ◽  
Spray Flames ◽  
Large Eddy ◽  
Initial Oxygen ◽  
Oxygen Concentrations

Large eddy simulation of n-heptane spray flames is conducted to investigate the multiple-stage ignition process under extreme (low-temperature, low oxygen, and high-temperature, high-density) conditions. At low oxygen concentrations, the first-stage ignition initiates in the fuel-rich region and then moves to stoichiometric equivalence ratio regions by decreasing the initial temperature. It is also clear that at high temperatures, high oxygen concentrations, or high densities, the reactivity of the mixture is enhanced, where high values of progress variable are observed. Analysis of key intermediate species, including acetylene (C2H2), formaldehyde (CH2O), and hydroxyl (OH) in the mixture fraction and temperature space provides valuable insights into the complex combustion process of the n-heptane spray flames under different initial conditions. The results also suggest that C2H2 appears over a wider range in the mixture fraction space at higher temperature or oxygen concentration condition, implying that it mainly forms at the fuel-rich regions. The initial oxygen concentration of the ambient gas has great influence on the formation and oxidization of C2H2, and the maximum temperature depends on the initial oxygen concentration. OH is mainly formed at the stoichiometric equivalence ratio region, which moves to high-temperature regions very quickly especially at higher oxygen concentrations. Finally, analysis of the premixed and nonpremixed combustion regimes in n-heptane spray flames is also conducted, and both premixed and nonpremixed combustion coexist in spray flames.

scholarly journals Sensitivity to Oxygen of Nitrogenase Activity in Rhizobium Strain ANU289 of the Non-legume Parasponia (Ulmaceae)

1984 ◽  
Vol 37 (2) ◽  
pp. 31 ◽  
Author(s):  
S S Mohapatra ◽  
PM GresshoffA
Keyword(s):  
Carbon Source ◽  
Gas Phase ◽  
Cell Density ◽  
Oxygen Concentration ◽  
Oxygen Tension ◽  
Nitrogenase Activity ◽  
Rhizobium Strain ◽  
Low Oxygen ◽  
Liquid Cultures ◽  
Low Oxygen Tension

Nitrogenase activity can be detected in Rhizobium strain ANU289 of Parasponia in shaken liquid cultures. A combination of consistently low oxygen tension and appropriate cell density was found to be essential for rapid initiation and high specific rates (in the range of 50-60 nmoles of ethylene per milligram protein per hour). In the presence of succinate as carbon source and an oxygen concentration of 0�25% (v/v) in the gas phase, nitrogenase activity developed after incubation for 24 h. The requirement for an oxygen concentration in the range of O� 1 to 0�35% for derepression indicated a lack of any inherent tolerance to higher oxygen levels and thus suggests that plant-derived mechanisms are responsible for protection by oxygen in the nodule.

scholarly journals Oxygen-Sensing Reporter Strain of Pseudomonas fluorescens for Monitoring the Distribution of Low-Oxygen Habitats in Soil

1999 ◽  
Vol 65 (9) ◽  
pp. 4085-4093 ◽  
Author(s):  
Ole Højberg ◽  
Ursula Schnider ◽  
Harald V. Winteler ◽  
Jan Sørensen ◽  
Dieter Haas
Keyword(s):  
Nitrate Reductase ◽  
Water Content ◽  
Pseudomonas Fluorescens ◽  
Oxygen Concentration ◽  
Pore Space ◽  
Fold Increase ◽  
Arginine Deiminase ◽  
Reporter Strain ◽  
Low Oxygen ◽  
Oxygen Concentrations

ABSTRACT The root-colonizing bacterium Pseudomonas fluorescensCHA0 was used to construct an oxygen-responsive biosensor. An anaerobically inducible promoter of Pseudomonas aeruginosa, which depends on the FNR (fumarate and nitrate reductase regulation)-like transcriptional regulator ANR (anaerobic regulation of arginine deiminase and nitrate reductase pathways), was fused to the structural lacZ gene of Escherichia coli. By inserting the reporter fusion into the chromosomalattTn7 site of P. fluorescens CHA0 by using a mini-Tn7 transposon, the reporter strain, CHA900, was obtained. Grown in glutamate-yeast extract medium in an oxystat at defined oxygen levels, the biosensor CHA900 responded to a decrease in oxygen concentration from 210 × 102 Pa to 2 × 102 Pa of O2 by a nearly 100-fold increase in β-galactosidase activity. Half-maximal induction of the reporter occurred at about 5 × 102 Pa. This dose response closely resembles that found for E. colipromoters which are activated by the FNR protein. In a carbon-free buffer or in bulk soil, the biosensor CHA900 still responded to a decrease in oxygen concentration, although here induction was about 10 times lower and the low oxygen response was gradually lost within 3 days. Introduced into a barley-soil microcosm, the biosensor could report decreasing oxygen concentrations in the rhizosphere for a 6-day period. When the water content in the microcosm was raised from 60% to 85% of field capacity, expression of the reporter gene was elevated about twofold above a basal level after 2 days of incubation, suggesting that a water content of 85% caused mild anoxia. Increased compaction of the soil was shown to have a faster and more dramatic effect on the expression of the oxygen reporter than soil water content alone, indicating that factors other than the water-filled pore space influenced the oxygen status of the soil. These experiments illustrate the utility of the biosensor for detecting low oxygen concentrations in the rhizosphere and other soil habitats.

scholarly journals Effects of low oxygen concentrations on aerobic methane oxidation in seasonally hypoxic coastal waters

2016 ◽  
Author(s):  
Lea Steinle ◽  
Johanna Maltby ◽  
Tina Treude ◽  
Annette Kock ◽  
Hermann W. Bange ◽  
...  
Keyword(s):  
Water Column ◽  
Methane Oxidation ◽  
Coastal Waters ◽  
Bacterial Biomass ◽  
Low Oxygen ◽  
Overlying Water ◽  
Hypoxic Conditions ◽  
Environmental Controls ◽  
Effect Of Oxygen ◽  
Oxygen Concentrations

Abstract. Coastal seas may account for more than 75 % of global oceanic methane emissions. There, methane is mainly produced microbially in anoxic sediments from where it can escape to the overlying water column. Aerobic methane oxidation (MOx) in the water column acts as a biological filter reducing the amount of methane that eventually evades to the atmosphere. The efficiency of the MOx filter is potentially controlled by the availability of dissolved methane and oxygen, as well as temperature, salinity, and hydrographic dynamics, and all of these factors undergo strong temporal fluctuations in coastal ecosystems. In order to elucidate the key environmental controls, specifically the effect of oxygen availability, on MOx in a seasonally stratified and hypoxic coastal marine setting, we conducted a 2-year time-series study with measurements of MOx and physico-chemical water column parameters in a coastal inlet in the southwestern Baltic Sea (Eckernförde Bay). We found that MOx rates always increased toward the seafloor, but were not directly linked to methane concentrations. MOx exhibited a strong seasonal variability, with maximum rates (up to 11.6 nmol l−1 d−1) during summer stratification when oxygen concentrations were lowest and bottom-water temperatures were highest. Under these conditions, 70–95 % of the sediment-released methane was oxidized, whereas only 40–60 % were consumed during the mixed and oxygenated periods. Laboratory experiments with manipulated oxygen concentrations in the range of 0.2–220 µmol l−1 revealed a sub-micromolar oxygen-optimum for MOx at the study site. In contrast, the fraction of methane-carbon incorporation into the bacterial biomass (compared to the total amount of oxidised methane) was up to 38-fold higher at saturated oxygen concentrations, suggesting a different partitioning of catabolic and anabolic processes under oxygen-replete and oxygen-starved conditions, respectively. Our results underscore the importance of MOx in mitigating methane emission from coastal waters and indicate an organism-level adaptation of the water column methanotrophs to hypoxic conditions.

Effect of Oxygen Concentration on Distributed Flame Regime

2017 ◽  
Author(s):  
Richard Scenna ◽  
Ashwani K. Gupta
Keyword(s):  
Carbon Monoxide ◽  
Oxygen Concentration ◽  
Chemical Reaction ◽  
Partial Oxidation ◽  
Product Distribution ◽  
Length Scales ◽  
Reaction Condition ◽  
Effect Of Oxygen ◽  
Reforming Reactions ◽  
Oxygen Concentrations

This work investigated the effect of oxygen concentrations in the reactor on the partial oxidation of JP8 under the distributed reaction condition. Reforming efficiency as high as 74% was achieved; syngas composition consisted of 20.7 to 22.3% hydrogen and 20.2 to 21.5% carbon monoxide. Reformate product distribution and quality was found to depend on the reactor oxygen concentrations and, to a lesser extent on flame regime. Previous works operating at similar conditions found that higher reformate quality was associated with the more distributed reactor conditions. An increase in reactor oxygen concentrations fostered a more rapid chemical reaction, which shortened chemical time and length scales. While this resulted in a less distributed reactor, the potential decrease in reformate quality was offset by the increased availability of oxygen. As the reactions were limited by the availability of oxygen, the addition of oxygen enhanced the extent of reforming reactions, to promote increased conversion and reforming efficiency.

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