scholarly journals The hydrogen threshold of obligately methyl-reducing methanogens

2020 ◽  
Vol 367 (17) ◽  
Author(s):  
Christopher Feldewert ◽  
Kristina Lang ◽  
Andreas Brune
Keyword(s):  
Carbon Dioxide ◽  
Anaerobic Degradation ◽  
Partial Pressures ◽  
The Family ◽  
Methoxy Groups ◽  
Methanosphaera Stadtmanae ◽  
High Detection ◽  
Order Of Magnitude ◽  
Common Substrate ◽  
Hydrogenotrophic Methanogens

ABSTRACT Methanogenesis is the final step in the anaerobic degradation of organic matter. The most important substrates of methanogens are hydrogen plus carbon dioxide and acetate, but also the use of methanol, methylated amines, and aromatic methoxy groups appears to be more widespread than originally thought. Except for most members of the family Methanosarcinaceae, all methylotrophic methanogens require external hydrogen as reductant and therefore compete with hydrogenotrophic methanogens for this common substrate. Since methanogenesis from carbon dioxide consumes four molecules of hydrogen per molecule of methane, whereas methanogenesis from methanol requires only one, methyl-reducing methanogens should have an energetic advantage over hydrogenotrophic methanogens at low hydrogen partial pressures. However, experimental data on their hydrogen threshold is scarce and suffers from relatively high detection limits. Here, we show that the methyl-reducing methanogens Methanosphaera stadtmanae (Methanobacteriales), Methanimicrococcus blatticola (Methanosarcinales), and Methanomassiliicoccus luminyensis (Methanomassiliicoccales) consume hydrogen to partial pressures < 0.1 Pa, which is almost one order of magnitude lower than the thresholds for M. stadtmanae and M. blatticola reported in the only previous study on this topic. We conclude that methylotrophic methanogens should outcompete hydrogenotrophic methanogens for hydrogen and that their activity is limited by the availability of methyl groups.

scholarly journals The mechanism of the carbon dioxide-carbon reaction

1948 ◽  
Vol 193 (1034) ◽  
pp. 357-376 ◽  
Keyword(s):  
Carbon Dioxide ◽  
Carbon Monoxide ◽  
Carbon Surface ◽  
General Nature ◽  
Exponential Factor ◽  
Carbon Dioxide Molecule ◽  
Partial Pressures ◽  
Rate Of Reaction ◽  
Order Of Magnitude ◽  
The Individual

The detailed mechanism of the reaction between carbon dioxide and coconut shell charcoal has been studied by both flow and static methods. The temperature has been varied in the range 700 to 830° C and the pressures of the gases from 10 to 760 mm. The static method has been used to investigate the adsorption of the gases on the carbon surface during the course of the reaction, and thus to illustrate in a very direct way the general nature of the mechanism. Accurate measurements of the rate of reaction have been made by the flow method. At a given temperature the rate of reaction can be represented in terms of the partial pressures of the gases by an expression of the form rate = k 1 pco 2 / 1+k 2 pco + k 3 pco 2 . The three separate constants have been evaluated and each has been found to vary exponentially with temperature. From these results the rates of the individual stages of the mechanism have been calculated. The first stage is the decomposition of the carbon dioxide molecule into an atom of oxygen which is adsorbed by the carbon and a molecule of carbon monoxide which passes into the gas phase. Only certain sites on the charcoal surface take part in the reaction; they represent about 0-5 % of the total area and probably consist of some of the less firmly bound carbon atoms situated at lattice discontinuities. The rate of the first stage can be accounted for by assuming that reaction occurs in those collisions in which the combined energy of the active carbon atom and the incident carbon dioxide molecule exceeds 68 kcal. The second stage is the evaporation of the adsorbed oxygen atom, together with an atom of carbon from the solid, to form gaseous carbon monoxide; the activation energy is thought to be 38 kcal., and the low value of 107 sec. -1 obtained for the non-exponential factor is discussed. The retarding effect of carbon monoxide is due to the adsorption of the gas on the reaction sites, the heat given out in the change being 46 kcal. On the basis of this value, which implies that the molecule is adsorbed chemically, it is possible to calculate theoretically the order of magnitude of the retardation constant, k 2 .

Inspiratory Speech as a Management Option for Spastic Dysphonia

1992 ◽  
Vol 101 (5) ◽  
pp. 375-382 ◽  
Author(s):  
Gordon A. Harrison ◽  
Richard H. Troughear ◽  
Pamela J. Davis ◽  
Alison L. Winkworth
Keyword(s):  
Carbon Dioxide ◽  
Gas Exchange ◽  
Voice Quality ◽  
Management Option ◽  
Communication Problems ◽  
Partial Pressures ◽  
The Subject ◽  
And Control ◽  
Laryngeal Resistance

A case study is reported of a subject who has used inspiratory speech (IS) for 6 years as a means of overcoming the communication problems of long-standing adductor spastic dysphonia (ASD). The subject was studied to confirm his use of IS, determine the mechanisms of its production, investigate its effects on ventilatory gas exchange, and confirm that it was perceptually preferable to ASD expiratory speech (ES). Results showed that the production and control of a high laryngeal resistance to airflow were necessary for usable IS. Voice quality was quantitatively and perceptually poor; however, the improved fluency and absence of phonatory spasm made IS the preferred speaking mode for both the listener and the speaker. Transcutaneous measurements of the partial pressures of oxygen and carbon dioxide in the subject's blood were made during extended speaking periods. These measurements indicated that ventilation was unchanged during IS, and that ventilation during ES was similar to the “hyperventilation” state of normal speakers. The reasons for the absence of phonatory spasm during IS are discussed, and the possibility of its use as a noninvasive management option for other ASD sufferers is addressed.

scholarly journals The Active Transport of Oxygen and Carbon Dioxide into the Swim-Bladder of Fish

1966 ◽  
Vol 49 (6) ◽  
pp. 1209-1220 ◽  
Author(s):  
H.J. KUHN ◽  
E. MARTI
Keyword(s):  
Carbon Dioxide ◽  
Lactic Acid ◽  
Active Transport ◽  
Bladder Pressure ◽  
Swim Bladder ◽  
Rete Mirabile ◽  
Partial Pressures ◽  
Gas Gland ◽  
Counter Current ◽  
Good Agreement

The active transport of oxygen and carbon dioxide into the swim-bladder of fish is discussed. The rete mirabile is a capillary network which is involved in the gas secretion into the bladder. The rete is regarded as a counter-current multiplier. Lactic acid which is produced in the gas gland generates in the rete single concentrating effects for oxygen and carbon dioxide; i.e., for equal partial pressures the concentrations of the gases in the afferent rete capillaries are higher than those in the efferent ones. The single concentrating effects were calculated from measurements of sea robin blood (Root, 1931). The multiplication of these effects within the rete for different rete lengths and different transport rates was numerically evaluated. The calculated O2 and CO2 pressures in the bladder are in good agreement with the experimental results of Scholander and van Dam (1953). The descent velocities at equilibrium between bladder pressure and hydrostatic pressure are discussed for fishes with different rete lengths.

Effect of hypothermia on ventilatory response to carbon dioxide inhalation and carbon dioxide infusion in dogs

1960 ◽  
Vol 15 (3) ◽  
pp. 397-401 ◽  
Author(s):  
John Salzano ◽  
F. G. Hall
Keyword(s):  
Carbon Dioxide ◽  
Body Temperature ◽  
Lower Order ◽  
Ventilatory Response ◽  
Water Immersion ◽  
Carbon Dioxide Tension ◽  
Order Of Magnitude ◽  
Gaseous Carbon Dioxide ◽  
Ice Water ◽  
Immersion Hypothermia

Some respiratory and circulatory responses to carbon dioxide stress during ice-water immersion hypothermia were studied in 13 dogs. Stresses were imposed by increasing the carbon dioxide tension of the inspired gas in eight animals and by intravenous infusion of gaseous carbon dioxide in five other animals. It was found that when compensation is made for the depressed ventilation exhibited at low body temperature, animals responded to the carbon dioxide stresses in essentially the same manner in the hypothermic as in the normothermia state. However, the responses are of a lower order of magnitude. Submitted on November 19, 1959

scholarly journals Methane and carbon dioxide emissions from thermokarst lakes on mineral soils

2018 ◽  
Vol 4 (4) ◽  
pp. 584-604 ◽  
Author(s):  
Alex Matveev ◽  
Isabelle Laurion ◽  
Warwick F. Vincent
Keyword(s):  
Carbon Dioxide ◽  
Surface Water ◽  
Surface Waters ◽  
Carbon Dioxide Emissions ◽  
Mineral Soil ◽  
Permafrost Degradation ◽  
Thermokarst Lakes ◽  
Order Of Magnitude ◽  
Mineral Soils ◽  
Diffusive Fluxes

Thermokarst lakes are known to emit methane (CH4) and carbon dioxide (CO2), but little attention has been given to those formed from the thawing and collapse of lithalsas, ice-rich mineral soil mounds that occur in permafrost landscapes. The present study was undertaken to assess greenhouse gas stocks and fluxes in eight lithalsa lakes across a 200 km gradient of permafrost degradation in subarctic Québec. The northernmost lakes varied in their surface-water CO2 content from below to above saturation, but the southern lakes in this gradient had much higher surface concentrations that were well above air-equilibrium. Surface-water CH4 concentrations were at least an order of magnitude above air-equilibrium values at all sites, and the diffusive fluxes of both gases increased from north to south. Methane oxidation in the surface waters from a northern lake was only 10% of the emission rate, but at the southern end it was around 60% of the efflux to the atmosphere, indicating that methanotrophy can play a substantive role in reducing net emissions. Overall, our observations show that lithalsa lakes can begin emitting CH4 and CO2 soon after they form, with effluxes of both gases that persist and increase as the permafrost continues to warm and erode.

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