Red light and carbon dioxide differentially affect growth,lipid production,and quality in the microalga, <Emphasis Type="Italic">Ettlia oleoabundans</Emphasis>

Ettlia oleoabundans, a freshwater unicellular green microalga, was grown under different light qualities ± carbon dioxide-enriched air to determine the combined effects on growth and lipid production of this oleaginous species. Keeping total light intensity constant, when a portion of the cool white was replaced by red, volumetric lipid yield increased 2.8-fold mainly due to the greater yield of oleic acid, a desirable biodiesel precursor. Only 30 min of red light treatment was sufficient to increase lipid yield and quality to the same level as cultures provided red light for >14 days, indicating the potential role of red light in stimulating lipid production of this species. Carbon dioxide enrichment via air sparging enhanced exponential growth, carbon conversion efficiency, and nutrient consumption. Together, these results showed that light quality plays an important role in microalgal lipid production. Adjustment in light quality and gas delivery efficiency with carbon dioxide enrichment improved lipid yield and quality in this and possibly other oleaginous algal species.     

Carbon dioxide inhibition of yeast growth in biomass production

Saccharomyces cerevisiae was grown under aerobic and substrate-limiting conditions for efficient biomass production. Under these conditions, where the sugar substrate was fed incrementally, the growth pattern of the yeast cells was found to be uniform, as indicated by a constant respiratory quotient during the entire growing period. The effect of carbon dioxide was investigated by replacing portions of the nitrogen in the air stream with carbon dioxide, while maintaining the oxygen content at the normal 20% level, so that identical oxygen transfer rate and atmospheric pressure were maintained for all experiments with different partial pressures of carbon dioxide. Inhibition of yeast growth was negligible below 20% CO₂ in the aeration mixture. Slight inhibition was noted at the 40% CO₂ level and significant inhibition was noted above the 50% CO₂, level, corresponding to 1.6 × 10^?2M of dissolved CO₂ in the fermentor broth. High carbon dioxide content in the gas phase also inhibited the fermentation activity of baker's yeast.     

Supercritical carbon dioxide explosion as a pretreatment for cellulose hydrolysis

Summary Cellulosic material Avicel was treated with supercritical carbon dioxide to increase the reactivity of cellulose, thereby to enhance the rate and the extent of cellulose hydrolysis. Upon an explosive release of the carbon dioxide pressure, the disruption of the cellulosic structure increases the accessible surface area of the cellulosic substrate to enzymatic hydrolysis. This explosion pretreatment enhances the rate of the Avicel hydrolysis as well as increases glucose yield by as much as 50%.     

The Kinetics of Extracellular Glycollate Production by Chlorella pyrenoidosa

Extracellular glycollate is liberated by Chlorella pyrenoidosaduring growth in medium bubbled with air or 3 per cent carbondioxide in air. With air the rate of release of glycollate percell decreases, with 3 per cent carbon dioxide it increases,with increase in cell number. Glycollate is released duringshort-term experiments when C. pyrenoidasa, grown under lowlight and high carbon dioxide, is transferred suddenly to highlight and low carbon dioxide. No other combination of thesefactors produces a comparable release of glycollate. The quantityof glycollate released in short-term experiments increases exponentiallywith the relative growth-rate of the culture from which thecells are derived. A crucial condition for maximum glycollaterelease is that growth of the culture prior to the experimentshould not be limited by carbon-dixoide concentration. The effectof pH is related to its effect on growth-rate; i.e. C. pyrenoidosahas a lower relative growth-rate at pH 8.3 and produces correspondinglyless glycollate than faster growing cultures at pH 6.4. Duringshort-term experiments under high light and low carbon dioxidethe rate of glycollate release drops after 50–100 minutessuggesting exhaustion of the glycollate precursor.     

Photosynthetic carbon dioxide assimilation by Rhodospirillum rubrum

Summary Although Rhodospirillum rubrum, grown photoheterotrophically on malate, assimilates carbon dioxide less rapidly than it does when grown autotrophically, the difference is less marked than previously suggested.The rate of photoassimilation of carbon dioxide varies during batch culture on malate, reaching a maximum at about mid-exponential phase. It also varies with density and growth rate in a turbidostat continuous-flow culture on malate and increases with decreasing growth rate in a chemostat continuous-flow culture growing with limiting malate concentrations.The changing rates of carbon dioxide photoassimilation during photoheterotrophic growth under the various conditions are paralleled by changing activities of ribulose diphosphate carboxylase.Under conditions of maximum carbon dioxide fixation the rate by photoheterotrophic cultures approaches that shown by the bacterium growing autotrophically and is assimilated eight to ten times more slowly than is malate in chemostat cultures.The rate of carbon dioxide fixation also increases to that shown by autotrophic cells when photoheterotrophic cultures are deprived of malate, but without subjecting them to the conditions required for autotrophic growth.     

Control of photosynthesis during nitrogen depletion and recovery in a non-nitrogen-fixing cyanobacterium

When cells of Synechocystis strain PCC 6308 are starved for nitrogen, the amount of stored carbohydrate increases, the phycocyanin to chlorophyll a ratio decreases, and the rates of oxygen evolution and of carbon dioxide fixation decrease. When nitrate-nitrogen is replenished, the amount of carbohydrate decreases, the rate of oxygen evolution increases immediately, preceeding the increase in phycocyanin or carbon dioxide fixation. The rate of respiration first increases and then decreases upon nitrogen addition. Nitrogen-starved cells show no variable fluorescence; variable fluorescence recovered in parallel with oxygen evolution. This suggests that photosystem II is inactive in nitrogen depleted cells and not blocked by a build up of metabolic endproducts. Since carbon dioxide fixation does not increase until two to four hours after nitrate is replenished to nitrogen starved cells, it is suggested that reducing power may first be needed within the cell for some other process than photosynthesis, such as nitrate reduction.     

Comprehensive analysis of metabolic sensitivity of 1,4-butanediol producing Escherichia coli toward substrate and oxygen availability

Nowadays, chemical production of 1,4-butanediol is supplemented by biotechnological processes using a genetically modified Escherichia coli strain, which is an industrial showcase of successful application of metabolic engineering. However, large scale bioprocess performance can be affected by presence of physical and chemical gradients in bioreactors which are a consequence of imperfect mixing and limited oxygen transfer. Hence, upscaling comes along with local and time dependent fluctuations of cultivation conditions. This study emphasizes on scale-up related effects of microbial 1,4-butanediol production by comprehensive bioprocess characterization in lab scale. Due to metabolic network constraints 1,4-butanediol formation takes place under oxygen limited microaerobic conditions, which can be hardly realized in large scale bioreactor. The purpose of this study was to assess the extent to which substrate and oxygen availability influence the productivity. It was found, that the substrate specific product yield and the production rate are higher under substrate excess than under substrate limitation. Furthermore, the level of oxygen supply within microaerobic conditions revealed strong effects on product and by-product formation. Under strong oxygen deprivation nearly 30% of the consumed carbon is converted into 1,4-butanediol, whereas an increase in oxygen supply results in 1,4-butanediol reduction of 77%. Strikingly, increasing oxygen availability leads to strong increase of main by-product acetate as well as doubled carbon dioxide formation. The study provides clear evidence that scale-up of microaerobic bioprocesses constitute a substantial challenge. Although oxygen is strictly required for product formation, the data give clear evidence that terms of anaerobic and especially aerobic conditions strongly interfere with 1,4-butanediol production.     

High productivity and photosynthetic flexibility in a CAM plant

Summary In the annual succulent Mesembryanthemum crystallinum growing in situ, the balance between C₃ and CAM carbon fixation shifted rapidly in response to changes in water availability. When water was plentiful, M. crystallinum fixed carbon dioxide by the C₃ pathway and grew at rates comparable to other C₃ species. Under drought conditions, M. crystallinum fixed carbon by the CAM pathway at an average rate which exceeded 1 nanomole of carbon dioxide per square centimeter of leaf surface per second, a very high rate for a CAM plant.     

Microbial gas balance measurements: Basic interrelations and error estimation

The given paper represents formulae for calculation of oxygen consumption and of carbon dioxide formation in a microbial culture obtained from corrected measuring data of gas balance measurements. Basic relations between these measuring data the respiration quotient RQ were derived. The influence of measuring error to the accuracy of determination of oxygen consumption and of carbon dioxide formation at the analysis of gas concentrations and of air flow is discussed. It is shown that the determination of carbon dioxide formation rate is possible in many cultivation regimes with better accuracy than the determination of oxygen uptake rate.     

Growth of Listeria monocytogenes in meat juice under a modified atmosphere at 4°C with or without members of a microbial association from chilled lamb under a modified atmosphere

Listeria monocytogenes together with Gram-positive and Gram-negative bacteria was grown in axenic cultures in meat juice under an atmosphere enriched with carbon dioxide at 4°C. The size of the final population of listeriae was determined by that of the initial inoculum. Growth of L. monocytogenes ceased with glucose depletion. Glucose-6-phosphate was not catabolized by listeriae. In aerobic axenic cultures generation times of L. monocytogenes were shorter and glucose depletion was faster than with a carbon dioxide-enriched atmosphere. Oxidation of L- and D-lactic to acetic acid was probably associated with the subsequent die-off of L. monocytogenes.     

Leaf area is stimulated in Populus by free air CO2 enrichment (POPFACE), through increased cell expansion and production

The effects of free‐air CO₂ enrichment (FACE) on leaf growth in Populus, was studied. For the first time in field conditions, both the production and expansion of leaf cells were shown to be sensitive to atmospheric carbon dioxide. Leaf area expansion rate and final leaf size were stimulated under FACE for three species (Populus x euramericana (I‐214), P. nigra (Jean Pourtet) and P. alba (2AS‐11), with the largest effect observed for P. x euramericana (61%). In this species and in P. nigra, both epidermal cell size and cell number were increased, whereas for P. alba, only cell production was increased in FACE. Two findings suggest that changes in the cell wall may be important in explaining larger leaf cells in FACE: (i) Leaf cell wall extensibility of rapidly growing leaves increased in all species in FACE; and (ii) an increase in xyloglucan endotransglycosylase activity, a cell wall‐loosening enzyme, was increased in FACE and associated with leaf growth rate. The results suggest that the mechanisms by which FACE promotes leaf growth differ, depending on species. Despite this, increases in final leaf size provide an important component driving increased biomass accumulation in POPFACE, during this first year of rapid growth, prior to canopy closure. The question as to whether these effects are the result of a direct response to CO₂, or are driven indirectly through substrate availability remains unresolved, although evidence from the literature suggests that the latter mechanism is most likely.     

The dependence of respiration on photosynthetic substrate supply and temperature: integrating leaf, soil and ecosystem measurements

Interactions between photosynthetic substrate supply and temperature in determining the rate of three respiration components (leaf, belowground and ecosystem respiration) were investigated within three environmentally controlled, Populus deltoides forest bays at Biosphere 2, Arizona. Over 2 months, the atmospheric CO₂ concentration and air temperature were manipulated to test the following hypotheses: (1) the responses of the three respiration components to changes in the rate of photosynthesis would differ both in speed and magnitude; (2) the temperature sensitivity of leaf and belowground respiration would increase in response to a rise in substrate availability; and, (3) at the ecosystem level, the ratio of respiration to photosynthesis would be conserved despite week‐to‐week changes in temperature. All three respiration rates responded to the CO₂ concentration‐induced changes in photosynthesis. However, the proportional change in the rate of leaf respiration was more than twice that of belowground respiration and, when photosynthesis was reduced, was also more rapid. The results suggest that aboveground respiration plays a key role in the overall response of ecosystem respiration to short‐term changes in canopy photosynthesis. The short‐term temperature sensitivity of leaf respiration, measured within a single night, was found to be affected more by developmental conditions than photosynthetic substrate availability, as the Q₁₀ was lower in leaves that developed at high CO₂, irrespective of substrate availability. However, the temperature sensitivity of belowground respiration, calculated between periods of differing air temperature, appeared to be positively correlated with photosynthetic substrate availability. At the ecosystem level, respiration and photosynthesis were positively correlated but the relationship was affected by temperature; for a given rate of daytime photosynthesis, the rate of respiration the following night was greater at 25 than 20°C. This result suggests that net ecosystem exchange did not acclimate to temperature changes lasting up to 3 weeks. Overall, the results of this study demonstrate that the three respiration terms differ in their dependence on photosynthesis and that, short‐ and medium‐term changes in temperature may affect net carbon storage in terrestrial ecosystems.     

ACID-BASE RELATIONSHIPS WITHIN THE AVIAN EGG

1. In the newly laid egg of the domestic fowl the pH values of the albumen and yolk are about 7.6 and 6.0 respectively. 2. When the egg is stored in air there is a loss of carbon dioxide from the albumen and the pH of this fluid rises to a maximum value of about 9.5. A large proportion of the carbon dioxide which remains in the albumen is in the form of carbonate. 3. In the fertile incubated egg the pH of the albumen attains a maximum value within a period of about 2 days; the albumen then becomes less alkaline and it is nearly neutral by the end of the second week. The increasing acidity of the albumen can be attributed to (a) the secretion of hydrogen ions by the blastoderm and (b) the output of carbon dioxide by developing tissues. 4. During the first 2 weeks of incubation the pH of the yolk progressively increases to a maximum value of about 7.5: there is then a tendency for the pH of this fluid to fall and the yolk that is retained within the body of the hatched chick is slightly acidic. 5. The embryo may never come into direct contact with either the albumen or the yolk when the pH of these fluids are high and low respectively. At the beginning of embryonic development the blastoderm is separated from the albumen by the vitelline membrane and from the yolk by a layer of subgerminal fluid with a maximum pH of about 7.8. The vitelline membrane ruptures on day 4 but by this time the embryo is bathed in amniotic fluid with a pH of about 7.5. 6. The pH of amniotic fluid falls from a maximum value of about 7.5 during week I to a minimum value of about 6.5 during week 2. Amniotic fluid is a simple solution of salts until day 12; albumen then begins to flow into the amniotic cavity and the buffering capacity of amniotic fluid increases. 7. The principal end-product of nitrogenous metabolism in the chick embryo is uric acid and about 100 mg of this substance are deposited within the allantoic cavity. The pH of allantoic fluid may exceed 7.5 during week 1 but falls to 6.0 or below after day 13. 8. The tension of carbon dioxide within the egg is determined by the ratio of the rate of carbon dioxide production by the embryo to the permeability of the shell towards carbon dioxide. For the greater part of the period of incubation the permeability of the shell towards carbon dioxide is constant. Thus, as the carbon dioxide output of the embryo increases, the carbon dioxide tension within the egg rises. 9. The pH of the blood can be defined in terms of the ratio of the bicarbonate concentration to the carbon dioxide tension. There is a progressive increase in the carbon dioxide tension of the blood during the period of incubation but the pH is maintained at about 7.4 by an increase in bicarbonate concentration. 10. Part of the increase in bicarbonate is due to the removal of hydrogen ions from carbonic acid by haemoglobin. There is also a large influx of bicarbonate into the blood, but the source of this bicarbonate is not known; the evidence that renal mechanisms are involved is inconclusive and it is probable that the embryo utilizes the enormous potential store of bicarbonate in the egg shell.     

Does transpiration control stomatal responses to water vapour pressure deficit?

Three types of observations were used to test the hypothesis that the response of stomatal conductance to a change in vapour pressure deficit is controlled by whole-leaf transpiration rate or by feedback from leaf water potential. Varying the leaf water potential of a measured leaf by controlling the transpiration rate of other leaves on the plant did not affect the response of stomatal conductance to vapour pressure deficit in Glycine max. In three species, stomatal sensitivity to vapour pressure deficit was eliminated when measurements were made at near-zero carbon dioxide concentrations, despite the much higher transpiration rates of leaves at low carbon dioxide. In Abutilon theophrasti, increasing vapour pressure deficit sometimes resulted in both decreased stomatal conductance and a lower transpiration rate even though the response of assimilation rate to the calculated substomatal carbon dioxide concentration indicated that there was no ‘patchy’ stomatal closure at high vapour pressure deficit in this case. These results are not consistent with stomatal closure at high vapour pressure deficit caused by increased whole-leaf transpiration rate or by lower leaf water potential. The lack of response of conductance to vapour pressure deficit in carbon dioxide-free air suggests that abscisic acid may mediate the response.     

杜香挥发油的超临界CO2萃取实验条件优化

采用正交实验法对超临界CO₂萃取杜香挥发油的条件进行了优化。研究了萃取温度、萃取压力、CO₂流量等因素在不同水平下对杜香挥发油提取率的影响。得到了超临界CO₂萃取杜香挥发油的最佳实验条件：萃取压力为20 Mpa、萃取温度为35℃、CO₂的流量为60 kg·h^-1。     

Factors affecting bio-oxidation of sulfide minerals at high concentrations of solids: a review

Bio-oxidation has proved to be a viable process for the oxidative pretreatment of refractory gold-bearing sulfides. Generally, the oxidation rate is maximal at 20% solids for high sulfide content materials [ca. 30% sulfur]. Low grade ores [1% sulfur] have been successfully oxidized at 55% solids, indicating a link between the sulfide grade of the material and the optimal solids concentration for operation. Concentrations of high solids have been reported to lower oxidation rates, increase lag times, and decrease the ultimate extent of oxidation. This review discusses the various factors that have been proposed as causes of these phenomena. The factors include oxygen and carbon dioxide availability, low bacteria-solids ratio; mechanical damage or inhibition of the bacteria, inhibition of bacterial attachment, and the buildup of toxic leach products or other detrimental substances such as some flotation reagents. (c) 1993 John Wiley & Sons, Inc.     

HETEROTROPHY OF FOUR MARINE PHYTOPLANKTERS AT LOW SUBSTRATE CONCENTRATIONS1

Three pelagic marine phytoplankters, Coccolithus huxleyi, Skeletonema costatum, and Thalassiosira ro-tula, and a facultative heterotroph, Cyclotella cryp-tica, have been exposed to three organic substrates, viz, glucose, acetate, and glutamate, at low concentrations (organic carbon 0.25 mg/liter). Experiments were performed in the dark and light and the net assimilation of substrate was measured by using radiocarbon. The dark uptake of carbon dioxide was also determined, together with photosynthesis at near optimum light intensity. The expected heterotrophy was detected with Cyclotella cryptica. Thalassiosira rotula was found to assimilate glutamate at an appreciable rate. In all cases, however, the short-term uptake of carbon dioxide in the dark was the greatest assimilation rate measured. Values are discussed in relation to their ecological significance and it is concluded that heterotrophic survival of these and probably most other algae in the open ocean xuould be impossible unless they were in contact with a high concentration of substrate in the form of particulate matter.     

Some Effects of Temperature and Substrate Content upon Respiration and the Carbon Balance of Field Beans (Vicia faba L.)

The effects of substrate content and temperature upon the productionof carbon dioxide in the dark were investigated in Vicia fabaand Sorghum vulgare, using the time courses for carbon dioxiderelease. No endogenous rhythms were found. With V. faba at highsubstrate contents, a steady rate of respiration was measuredat low temperatures, suggesting that the rate of respirationis limited by a third factor such as enzyme activity. This steadyrate eventually decreased rapidly. There was a first order rateof decrease with time at higher temperatures. Low substratecontents gave a complex decay. The rate of decrease of the rateof respiration was affected by the initial state of the plantsover the same range of rates. Reasons for this are discussed.The temperature sensitivity of respiration was investigated.The respiration of plants with high substrate contents had alower temperature sensitivity than those with low substratecontents. This was further investigated by measuring the stoichiometryof carbon dioxide production in the dark from total solublecarbohydrate (as hexose equivalent). It is likely that incompletehexose respiration, which occurs at high substrate contents,is less temperature sensitive than complete hexose respirationor the respiration of some other substrate. Vicia faba, Sorghum oulgare, carbon dioxide, respiration, temperature, substrate content     

HETEROTROPHY OF FOUR MARINE PHYTOPLANKTERS AT LOW SUBSTRATE CONCENTRATIONS1

Three pelagic marine phytoplankters, Coccolithus huxleyi, Skeletonema costatum, and Thalassiosira rotula, and a facultative heterotroph, Cyclotella cryptica, have been exposed to three organic substrates, viz, glucose, acetate, and glutamate, at low concentrations (organic carbon 0.25 mg/liter). Experiments were performed in the dark and light and the net assimilation of substrate was measured by using radiocarbon. The dark uptake of carbon dioxide was also determined, together with photosynthesis at near optimum light intensity. The expected heterotrophy was detected with Cyclotella cryptica. Thalassiosira rotula was found to assimilate glutamate at an appreciable rate. In all cases, however, the short-term uptake of carbon dioxide in the dark was the greatest assimilation rate measured. Values are discussed in relation to their ecological significance and it is concluded that heterotrophic survival of these and probably most other algae in the open ocean would be impossible unless they were in contact with a high concentration of substrate in the form of particulate matter.     

Oxygen toxicity in Astasia

1. Exposure of Astasia longa to oxygen+carbon dioxide (95:5) at atmospheric pressure leads to an inhibition of growth rate and of respiration. Growth resumes at the normal rate as soon as the oxygenation is discontinued, but respiration recovers more slowly. 2. Mitochondria prepared from cells exposed to oxygen+carbon dioxide (95:5) during growth have considerably decreased activities of succinate-cytochrome c oxidoreductase, NADH-cytochrome c oxidoreductase, succinate dehydrogenase and succinate oxidase activities as compared with mitochondria obtained from cells exposed to air+carbon dioxide (95:5). Cytochrome oxidase activity is not appreciably inhibited by exposure of the cells to 95% oxygen. 3. The mitochondrial fraction of Astasia contains rhodoquinone. The rhodoquinone concentration increases in cells exposed to 95% oxygen. The content of ergosterol-containing compounds also increases in the mitochondria of cells exposed to 95% oxygen. There is little change in the ubiquinone content of the mitochondrial fraction. The ubiquinone of Astasia appears to be ubiquinone-45.