Simultaneous production of H(2) and O(2) in closed vessels by marine Cyanobacterium anabaena sp. TU37-1 under high-cell-density conditions

A marine cyanobacterium, Anabaena sp. TU37-1, exhibited stable production of hydrogen and oxygen in closed vessels. About 8.4 and 4.3 mL (at atmospheric pressure) of hydrogen and oxygen accumulated, respectively, in flasks with 20 mL gas phase during 48 h incubation. Thus, concentration of H(2) and O(2) became 26 and 13% of the gas phase, respectively. Duration of hydrogen production was prolonged by the periodic gas replacement in the reaction vessel. The conversion efficiencies of photosynthetically active radiation (fluorescent light, 22 W/m(2)) to hydrogen were 2.4 and 2.2% during the initial 12- and 24-h incubation periods, respectively. (c) 1995 John Wiley & Sons, Inc.     

Change in the H2 photoproduction capability in a synchronously grown aerobic nitrogen-fixing cyanobacterium,Synechococcus sp. Miami BG 043511

Synchronously growing cells of nitrogen-fixing Synechococcus sp. Miami BG 043511 were harvested periodically and the capability for hydrogen photoproduction in closed vessels was measured under hydrogen production conditions. The capability for hydrogen photoproduction in cells was correlated with that of cellular carbohydrate content. Cells with a high carbohydrate content exhibited a high capacity for hydrogen production and those with low carbohydrate content exhibited low capacity for hydrogen production. Nitrogenase activity at the onset of incubation did not coincide with a capability for the cells to produce hydrogen during the subsequent incubation period. Interestingly, when cells with a high capacity for hydrogen photoaccumulation were incubated, alternate periods of hydrogen and oxygen accumulation were observed at 12 hour intervals. About 0.5 ml of hydrogen per ml of cell suspension was accumulated in flasks during the initial 12-h incubation period. These observations indicate that the use of synchronous culture can be one of the ways of provide materials suitable not only for basic studies but also for applied aspects of hydrogen photoproduction.     

Photoproduction of Hydrogen by the Marine Heterocystous Cyanobacterium Anabaena Species TU37-1 Under a Nitrogen Atmosphere

Hydrogen production rates by Anabaena sp. strain TU37-1 obtained after an initial 1-day incubation period were approximately 70 to 80 and 3 to 9 µmol (mg chl)^–1 h^–1 under argon and nitrogen atmospheres, respectively. Hydrogen production under argon was not enhanced by addition of carbon dioxide, but was enhanced to some extent under nitrogen by increasing the initial carbon dioxide concentration. Rates of hydrogen and oxygen production during the initial 7-hour period were 15 and 220 µmol (mg chl)^–1 h^–1, respectively, in vessels with 18.5% initial carbon dioxide. Hydrogen production under nitrogen was enhanced by addition of carbon monoxide (1%). The rate obtained from the initial 1-day incubation period was about 40 µmol (mg chl)^–1 h^–1, which corresponded to about 60% of that under argon. On the basis of these observations, a possible strategy for hydrogen production by nitrogen-fixing cyanobacteria under nitrogen in the presence of carbon monoxide is indicated.     

Effect of hydrogen and carbon dioxide partial pressures on growth and sulfide production of the extremely thermophilic archaebacterium Pyrodictium brockii

The effect of hydrogen and carbon dioxide partial pressure on the growth of the extremely thermophilic archaebacterium Pyrodictium brockii at 98 degrees C was investigated. Previous work with this bacterium has been done using an 80:20 hydrogen-carbon dioxide gas phase with a total pressure of 4 atm; no attempt has been made to determine if this mixture is optimal. It was found in this study that reduced hydrogen partial pressures affected cell yield, growth rate, and sulfide production. The effect of hydrogen partial pressure on cell yield and growth rate was less dramatic when compared to the effect on sulfide production, which was not found to be growth-associated. Carbon dioxide was also found to affect growth but only at very low partial pressures. The relationship between growth rate and substrate concentration could be correlated with a Monod-type expression for either carbon dioxide or hydrogen as the limiting substrate. The results from this study indicate that a balance must be struck between cell yields and sulfide production in choosing an optimal hydrogen partial pressure for the growth of P. brockii.     

Formation of cyanate and carbamyl phosphate by electric discharges of model primitive gas

A mixed gas of nitrogen, carbon dioxide, and hydrogen was discharged over 100 ml of 0.2 M NaHCO3 solution in a 5 liter discharge apparatus which simulates the primitive Earth. The formation of cyanate, which is one of the possible primitive condensing agents, was demonstrated by the detection of [Cu(Py)2] (NCO)2 that was formed by the addition of copper sulfate-pyridine reagent to the solution. In a series of experiments the partial pressures of nitrogen and carbon dioxide in the starting gas were fixed at 10 cm Hg and 20 cm Hg, respectively, whereas that of hydrogen was varied between 5, 10, 15, 20, 25, and 30 cm Hg. The discharges were continued for one week. The rate of appearance of cyanate was strongly dependent upon the partial pressure of hydrogen. The maximum rate of the production of cyanate at the initial stage of the discharge was in the case of 10 cm Hg of hydrogen, in which condition the starting gas is in a predominantly oxidized state. In this case the concentration of cyanate reached about 0.012 M after one day. Another discharge experiment was carried out with 0.2 M phosphate solution, and the production of carbamyl phosphate was demonstrated through the formation of ATP by the incubation of the discharged solution with ADP and carbamyl phosphokinase.     

Growth and gas production for hyperthermophilic archaebacterium, Pyrococcus furiosus

Pyrococcus furiosus represents one of the most important hyperthermophilic bacteria isolated thus far because of its relatively high cell yields and rapid growth rates. Pyrococcus furiosus exhibits several interesting growth characteristics, especially in terms of biotic gas production, which were examined in this study. In the presence of elemental sulfur, both carbon dioxide and hydrogen sulfide production appeared to be strongly growth associated, while no significant hydrogen production was observed. In the absence of sulfur, hydrogen and carbon dioxide were produced by the organism and hydrogen inhibition was observed. The addition of elemental sulfur to the medium apparently eliminated, hydrogen inhibition as growth proceeded normally even when hydrogen was added to the gas phase. Also, no apparent substrate limitation or toxic product could be attributed to the cessation of growth as cell growth in spent media was at least as good as in fresh media. An unstructured growth model was used to correlate growth and gas production for P. furiosus in complex seawater-based media at 98 degrees C both in the absence and presence of elemental sulfur. The model was shown to be useful for examining some of the observations made in this study.     

Effects of controlled gas environments in solid-substrate fermentations of rice

The gas environment is solid-substrate fermentations of rice significantly affected levels of biomass and enzyme formation by a fungal species screened for high amylase production. Constant oxygen and carbon dioxide partial pressures were maintained at various levels in fermentations by Aspergillus oryzae. Control of the gas phase was maintained by a “static” aeration system admitting oxygen on demand and stripping excess carbon dioxide during fermentation. Constant water vapor pressures were also maintained by means of saturated salt solutions. High Oxygen pressures stimulated amylase productivity significantly. On the other hand, amylase production was severely inhibited at high carbon dioxide pressures. While relatively insensitive to oxygen pressure, maximum biomass productivities were obtained at an intermediate carbon dioxide pressure. High oxygen transfer rates were obtained at elevated oxygen pressures, suggesting, in view of the stimulatory effect of oxygen on amylase production, a stringent oxygen requirement for enzyme synthesis. Solid-substrate fermentations were highly advantageous as compared with submerged cultures in similar gas environments. Not only were amylase productivities significantly higher, but the enzyme was highly concentration in the aqueous phase of the semisolid substrate particles and could be extracted in a small volume of liquid. Results of this work suggest that biomass and product formation in microbial processes may be amenable to control by the gas environment. This is believed to offer an interesting potential for optimizing selected industrial fermentation processes with respect to productivity and energy consumption.     

Gas Exchange of Algae: II. Effects of Oxygen, Helium, and Argon on the Photosynthesis of Chlorella pyrenoidosa

Changes in the oxygen partial pressure of air over the range of 8 to 258 mm of Hg did not adversely affect the photosynthetic capacity of Chlorella pyrenoidosa. Gas exchange and growth measurements remained constant for 3-week periods and were similar to air controls (oxygen pressure of 160 mm of Hg). Oxygen partial pressures of 532 and 745 mm of Hg had an adverse effect on algal metabolism. Carbon dioxide consumption was 24% lower in the gas mixture containing oxygen at a pressure 532 mm of Hg than in the air control, and the growth rate was slightly reduced. Oxygen at a partial pressure of 745 mm of Hg decreased the photosynthetic rate 39% and the growth rate 37% over the corresponding rates in air. The lowered metabolic rates remained constant during 14 days of measurements, and the effect was reversible after this time. Substitution of helium or argon for the nitrogen in air had no effect on oxygen production, carbon dioxide consumption, or growth rate for 3-week periods. All measurements were made at a total pressure of 760 mm of Hg, and all gas mixtures were enriched with 2% carbon dioxide. Thus, the physiological functioning and reliability of a photosynthetic gas exchanger should not be adversely affected by: (i) oxygen partial pressures ranging from 8 to 258 mm of Hg; (ii) the use of pure oxygen at reduced total pressure (155 to 258 mm of Hg) unless pressure per se affects photosynthesis, or (iii) the inclusion of helium or argon in the gas environment (up to a partial pressure of 595 mm of Hg).     

Influence of H(2) stripping on methane production in conventional digesters

Hydrogen is a central metabolite in the methanization process. In this study the partial pressure of hydrogen in the gas phase of laboratory manure digesters was monitored over extensive periods of time and found to vary between 50 and 100.10(-6) atm. By sparging the gas phase of the digester through an auxiliary reactor, hydrogenotrophic methanogens were allowed to develop at the expense of hydrogen and carbon dioxide present in the biogas, independently of the liquid or cell residence time in the main reactor. By scrubbing ca. 100 volumes of biogas per liter reactor per day through an auxiliary reactor, hydrogen concentration could be decreased maximally 25%. This resulted in an increase in the gas production rate of the main digester of ca. 10% and a concomitant improved removal of volatile fatty acids from the mixed liquor. The results obtained indicate that considerable stripping of hydrogen from the digester could be achieved at acceptable energy expenditure. However, the microbial removal of the hydrogen at these low concentrations is extremely slow and limits the applicability of this approach.     

Alternative and cyclic appearance of H2 and O2 photoproduction activities under non-growing conditions in an aerobic nitrogen-fixing unicellular cyanobacterium Synechococcus sp.

With synchronously grown cells of an aerobic unicellular marine cyanobacterium Synechococcus sp. Miami BG 043511, changes in the activities of anoxygenic, nitrogenase-dependent hydrogen photoproduction and oxygen photoevolution were measured under non-growing hydrogen production conditions. Interestingly, synchronously grown cells, incubated in light under an argon atmosphere, exhibited cyclic changes in the activity of nitrogenase-catalyzed hydrogen production for approximately 20- to 25-h intervals. Cyclic photosynthetic oxygen production activity also appeared in approximately the same intervals. However, changes in hydrogen production and oxygen production activities were inversely correlated and temporally separated. Stepwise accumulation of hydrogen in closed vessels was also observed in approximately 24-h cycles in these non-growing cells. These observations in non-growing cells suggest that this unicellular aerobic, nitrogen-fixing cyanobacterium may have an endogenous system to control the exhibition of cyclic rhythms, in addition to the previously studied cell cycle-oriented system. Expression and switching between these two systems may be related to the sufficiency or insufficiency of nitrogen growth nutrients. The possibility of the existence of a common control factor of the two systems involving glycogen is also discussed.     

Deoxynivalenol, acetyl deoxynivalenol, and zearalenone formation by Canadian isolates of Fusarium graminearum on solid substrates.

Three isolates of Fusarium graminearum (DAOM 180377, 180378, and 180379) were screened for their ability to produce mycotoxins on the solid substrates corn and rice. They all produced deoxynivalenol and zearalenone on corn. On rice, only DAOM 180378 and 180379 produced significant amounts of these mycotoxins, with levels of deoxynivalenol being much higher than those of zearalenone. The effects of the initial moisture content before autoclaving, incubation temperature, and time were studied with isolate DAOM 180378. At 19.5 degrees C the main product was zearalenone, whereas at 25 degrees C both deoxynivalenol and zearalenone were formed. Higher incubation temperatures (28 degrees C) favored deoxynivalenol formation, the maximum amount being 515 ppm (515 micrograms/g) formed after 24 days at an initial moisture content of 40%. The maximum level of zearalenone produced at the same temperature was 399 ppm, but at an initial moisture content of 35%. Other factors, such as pH, oxygen and carbon dioxide concentrations, and size of the culture flask also appeared to affect the production of mycotoxins.     

Effects of Barometric Pressure and Abnormal Gas Mixtures on Gaseous Exchange by the Avian Embryo

Gas moves through the pores of the egg shell by diffusion inthe gas phase. The gas flux is therefore determined by the productof the effective conductance of the shell and the partial pressuregradient of the gas between the ambient air and the inner sideof the shell. The partial pressure gradient of oxygen is decreasedby a reduction of the oxygen partial pressure in the ambientair. This can be achieved by reducing barometric pressure atnormal ambient oxygen concentration or by reducing ambient oxygenconcentration at standard barometric pressure. Both methodsare reported to decrease oxygen consumption of the embryo butto a different degree. At the same ambient oxygen pressure thereduction is less in eggs exposed to a reduced barometric pressure.In an attempt to explain this difference, chicken embryos aged16–19 days were exposed to various oxygen concentrationsand carbon dioxide production was measured. At subnormal oxygenconcentrations carbon dioxide output diminished as the oxygenconcentration was lowered and the duration of exposure was prolonged.At oxygen concentrations above normal a small but significantincrease in carbon dioxide production was found. Finally theresults are compared with those in the literature on the diverseeffects of a continuous reduction of barometric pressure andambient oxygen concentration. This difference is ascribed tothe fact that a reduction of barometric pressure not only decreasesoxygen partial pressure in the ambient air but also increaseseffective conductance of the egg shell, the latter being inverselyproportional to the barometric pressure.     

Ethanol and acetate synthesis from waste gas using batch culture of Clostridium ljungdahlii

Single inorganic carbon source was used for production of chemicals and fuels via fermentation processes. Clostridium ljungdahlii, a strictly anaerobic autotrophic bacterium, was grown on synthesis gas to produce acetate and ethanol from gaseous substrates. C. ljungdahlii was grown on a various concentrations of carbon monoxide with synthesis gas total pressures of 0.8–1.8 atm with an interval of 0.2 atm. The cell and product yields were 0.015 g cell/g CO and 0.41 g acetate/g CO, respectively. Formation of acetate was steady and the production trend was about the same for all of the gases initial pressure and at constant cell density. The ethanol concentration was enhanced by the initial presence of hydrogen and carbon dioxide in the liquid phase. There was no substrate inhibition while C. ljungdahlii was grown in the batch fermentation, even at high system pressure of 1.6 and 1.8 atm. A desired product molar ratio of ethanol:acetate (5:1) was achieved with total gas pressure of 1.6 and 1.8 atm.     

Aerobic Hydrogen Accumulation by a Nitrogen-Fixing Cyanobacterium, Anabaena sp

Hydrogen evolution by a nitrogen-fixing cyanobacterium, Anabaena sp. strain N-7363, was tested in order to develop a water biophotolysis system under aerobic conditions. A culture of the strain supplemented with carbon dioxide under an air atmosphere evolved hydrogen and oxygen gas, which reached final concentrations of 9.7 and 69.8%, respectively, after 12 days of incubation. Hydrogen uptake activity was not observed during incubation, and nitrogenase was thought to be the sole enzyme responsible for the hydrogen evolution.     

Effects of Ammonium Ions, Oxygen, Carbon Monoxide, and Acetylene on Anaerobic and Aerobic Hydrogen Formation by Anabaena cylindrica B629

An investigation was made of various factors, both experimental and physiological, which influenced the formation of hydrogen gas by the heterocystous cyanobacterium Anabaena cylindrica B629 when incubated in both argon and air. A. cylindrica B629 produces hydrogen in air in the presence of carbon monoxide, acetylene, or both, with a short lag period. The rate of production in air at optimal concentrations of these compounds was found to be comparable with that in an argon atmosphere. Whereas under argon, ammonium ions (0.5 to 6 mM) were found to inhibit hydrogen formation in a manner which was dependent on light intensity and not relieved by oxygen (1 to 20% of gas phase), in air-carbon monoxide-acetylene, these ions (up to at least 0.5 mM) slightly stimulated hydrogen production for at least 24 h. Conclusions are drawn about short-term aerobic and anaerobic hydrogen formation by A. cylindrica B629 and the effects of ammonium ions, oxygen, carbon monoxide, and acetylene on these processes.     

Formation of cyanate and carbamyl phosphate by electric discharges of model primitive gas

A mixed gas of nitrogen, carbon dioxide, and hydrogen was discharged over 100 ml of 0.2M NaHCO₃ solution in a 5 liter discharge apparatus which simulates the primitive Earth. The formation of cyanate, which is one of the possible primitive condensing agents, was demonstrated by the detection of [Cu(Py)₂] (NCO)₂ that was formed by the addition of copper sulfate-pyridine reagent to the solution. In a series of experiments the partial pressures of nitrogen and carbon dioxide in the starting gas were fixed at 10 cm Hg and 20 cm Hg, respectively, whereas that of hydrogen was varied between 5, 10, 15, 20, 25, and 30 cm Hg. The discharges were continued for one week. The rate of appearance of cyanate was strongly dependent upon the partial pressure of hydrogen. The maximum rate of the production of cyanate at the initial stage of the discharge was in the case of 10 cm Hg of hydrogen, in which condition the starting gas is in a predominantly oxidized state. In this case the concentration of cyanate reached about 0.012M after one day. Another discharge experiment was carried out with 0.2M phosphate solution, and the production of carbamyl phosphate was demonstrated through the formation of ATP by the incubation of the discharged solution with ADP and carbamyl phosphokinase.     

Fed-batch cultivation of Saccharomyces cerevisiae in a hyperbaric bioreactor

Fed-batch is the dominating mode of operation in high-cell-density cultures of Saccharomyces cerevisae in processes such as the production of baker's yeast and recombinant proteins, where the high oxygen demand of these cultures makes its supply an important and difficult task. The aim of this work was to study the use of hyperbaric air for oxygen mass transfer improvement on S. cerevisiae fed-batch cultivation. The effects of increased air pressure up to 1.5 MPa on cell behavior were investigated. The effects of oxygen and carbon dioxide were dissociated from the effects of total pressure by the use of pure oxygen and gas mixtures enriched with CO(2). Fed-batch experiments were performed in a stirred tank reactor with a 600 mL stainless steel vessel. An exponential feeding profile at dilution rates up to 0.1 h(-)(1) was used in order to ensure a subcritical flux of substrate and, consequently, to prevent ethanol formation due to glucose excess. The ethanol production observed at atmospheric pressure was reduced by the bioreactor pressurization up to 1.0 MPa. The maximum biomass yield, 0.5 g g(-)(1) (cell mass produced per mass of glucose consumed) was attained whenever pressure was increased gradually through time. This demonstrates the adaptive behavior of the cells to the hyperbaric conditions. This work proved that hyperbaric air up to 1.0 MPa (0.2 MPa of oxygen partial pressure) could be applied to S. cerevisiae cultivation under low glucose flux. Above that critical oxygen partial pressure value, i.e., for oxygen pressures of 0.32 and 0.5 MPa, a drastic cell growth inhibition and viability loss were observed. The increase of carbon dioxide partial pressure in the gas mixture up to 48 kPa slightly decreased the overall cell mass yield but had negligible effects on cell viability.     

Gas phase composition effects on suspension cultures of Taxus cuspidata

The effect of different concentrations and combinations of oxygen, carbon dioxide, and ethylene on cell growth and taxol production in suspension cultures of Taxus cuspidata was investigated using several factorial design experiments. Low head space oxygen concentration (10% v/v) promoted early production oftaxol. High carbon dioxide concentration (10% v/v) inhibited taxol production. The most effective gas mixture composition in terms of taxol production was 10% (v/v) oxygen, 0.5% (v/v) carbon dioxide, and 5 ppm ethylene. Cultures grown underambient concentration of oxygen had a delayed uptake of glucose and fructose compared to cultures grown under 10% (v/v) oxygen. Average calcium uptake rates into the cultured cells decreased and average phosphate uptake rates increased as ethylene was increased from 0 to 10 ppm. These results may indicate that gas composition alters partitioning of nutrients, which in turn affects secondary metabolite production. (c) 1995 John Wiley & Sons, Inc.     

Effect of respiratory gases on compliance of intrapulmonary arteries and veins

A method was developed that permitted changes in the pressure-volume characteristics of large intrapulmonary vessels occurring with changes in the composition of alveolar gas to be studied in excised lungs. The capillary bed was emptied by keeping intravascular pressure well below alveolar pressure, and the relationship between changes in the volume of the pulmonary arteries or veins with changes in transpulmonary pressure was measured. The volume of the arteries and veins always decreased with a decrease in transpulmonary pressure, but when the alveoli contained carbon dioxide, the decrease in vascular volume was less, for the same decrease in transpulmonary pressure, than when the alveoli contained oxygen or nitrogen without carbon dioxide. This change with carbon dioxide was probably due to a decrease in the compliance of the larger intrapulmonary arteries and veins. Since there was no pathway for carbon dioxide to enter these vessels except by diffusion from the alveoli, it is concluded that carbon dioxide can act directly on the intrapulmonary arteries and veins to reduce their compliance, but it is not known whether this effect has physiological significance. No effect on the large pulmonary vessels was found with variations in alveolar concentrations of oxygen. blood vesselsblood volumecarbon dioxidediffusionlungspulmonary circulation     

In vitro cultivation of Dipetalonema viteae third-stage larvae: effect of the gas phase

The effect of the gas phase on the in vitro growth and development of Dipetalonema viteae (Nematoda: Filarioidea) third-stage larvae obtained from the tick vector and 3 day infections of jirds was examined. Measurements of the oxygen (pO2) and carbon dioxide (pCO2) tensions and the pH in the medium were made for each gas phase. In cultures gassed with 5% carbon dioxide in nitrogen the pO2 was between 32 and 50 mm Hg, the pCO2 ranged from 25 to 40 mm Hg and the pH was between 7.2 and 7.4. This gas phase resulted in the best growth and development of third-stage larvae to the fourth-stage. Survival and development of larvae were decreased in cultures with oxygen tensions less than 20 mm Hg and greater than 50 mm Hg.