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1.
One of the objectives of microalgal culture is to provide reliable production technology for important live aquaculture feed organisms. Presented here are the results of experiments designed to provide a better understanding of the relationship between inorganic carbon availability and algal production.Our results suggest that through additions of CO 2 gas we were able to maintain sufficient dissolved carbon to stabilize outdoor algal cultures. Increases in the rate of addition of CO 2 increased levels of dissolved CO 2, total dissolved inorganic carbon (CO 2), and decreased pH in the growth medium. This translated into improved buffering capacity of the culture medium and higher growth rate. A minimum of 2.4 mM CO 2 was found necessary to maintain a maximal growth rate of 0.7 doublings/day. We also found that the increased productivity more than offsets the cost of adding the CO 2. 相似文献
2.
Flue gas from power plants can promote algal cultivation and reduce greenhouse gas emissions 1. Microalgae not only capture solar energy more efficiently than plants 3, but also synthesize advanced biofuels 2-4. Generally, atmospheric CO 2 is not a sufficient source for supporting maximal algal growth 5. On the other hand, the high concentrations of CO 2 in industrial exhaust gases have adverse effects on algal physiology. Consequently, both cultivation conditions (such as nutrients and light) and the control of the flue gas flow into the photo-bioreactors are important to develop an efficient “flue gas to algae” system. Researchers have proposed different photobioreactor configurations 4,6 and cultivation strategies 7,8 with flue gas. Here, we present a protocol that demonstrates how to use models to predict the microalgal growth in response to flue gas settings. We perform both experimental illustration and model simulations to determine the favorable conditions for algal growth with flue gas. We develop a Monod-based model coupled with mass transfer and light intensity equations to simulate the microalgal growth in a homogenous photo-bioreactor. The model simulation compares algal growth and flue gas consumptions under different flue-gas settings. The model illustrates: 1) how algal growth is influenced by different volumetric mass transfer coefficients of CO 2; 2) how we can find optimal CO 2 concentration for algal growth via the dynamic optimization approach (DOA); 3) how we can design a rectangular on-off flue gas pulse to promote algal biomass growth and to reduce the usage of flue gas. On the experimental side, we present a protocol for growing Chlorella under the flue gas (generated by natural gas combustion). The experimental results qualitatively validate the model predictions that the high frequency flue gas pulses can significantly improve algal cultivation. 相似文献
3.
Changes in pH, total alkalinity and O 2 concentration were followed in an aquatic medium with excised wheat roots ( Tritkum aestivum L.). Concentrations of total inorganic carbon and free CO 2 were calculated from total alkalinity and pH according to carbonate equilibria. The total inorganic carbon was estimated
by flow-injection infra-red gas analysis. Total alkalinity increased in the root medium during incubation. Respiratory CO 2 production was estimated best from the increase in total inorganic carbon measured with an infra-red gas analyser. 相似文献
4.
The accumulation of atmospheric CO 2, primarily due to combustion of fossil fuels, has been implicated in potential global climate change. The high rate of CO 2 bioremediation by microalgae has emerged as a favourable method for reducing coal-fired power plant emissions. However, coal-fired power station flue gas contains other chemicals such as SO x which can inhibit microalgal growth. In the current study, the effect of untreated flue gas as a source of inorganic carbon on the growth of Tetraselmis in a 1000 L industrial-scale split-cylinder internal-loop airlift photobioreactor was examined. The culture medium was recycled after each harvest. Tetraselmis suecica grew very well in this airlift photobioreactor during the 7-month experiment using recycled medium from an electroflocculation harvesting unit. Increased medium SO 4 2? concentration as high as 870 mg SO 4 2??L ?1 due to flue gas addition and media recycling had no negative effect on the overall growth and productivity of this alga. The potential organic biomass productivity and carbon sequestration using an industrial-scale airlift PBR at International Power Hazelwood, Gippsland, Victoria, Australia, are 178.9?±?30 mg L ?1 day ?1 and 89.15?±?20 mg?‘C’?L ?1 day ?1, respectively. This study clearly indicates the potential of growing Tetraselmis on untreated flue gas and using recycled medium for the purpose of biofuel and CO 2 bioremediation. 相似文献
5.
Algal biomass refineries for sustainable transportation fuels, in particular biodiesel, will benefit from algal strain enhancements to improve biomass and lipid productivity. Specifically, the supply of inorganic carbon to microalgal cultures represents an area of great interest due to the potential for improved growth of microalgae and the possibility for incorporation with CO 2 mitigation processes. Combinations of bicarbonate (HCO 3?) salt addition and application of CO 2 to control pH have shown compelling increases in growth rate and lipid productivity of fresh water algae. Here, focus was placed on the marine organism, Nannochloropsis gaditana, to investigate growth and lipid accumulation under various strategies of enhanced inorganic carbon supply. Three gas application strategies were investigated: continuous sparging of atmospheric air, continuous sparging of 5% CO 2 during light hours until nitrogen depletion, and continuous sparging of atmospheric air supplemented with 5% CO 2 for pH control between 8.0 and 8.3. These gas sparging schemes were combined with addition of low concentrations (5 mM) of sodium bicarbonate at inoculation and high concentration (50 mM) of sodium bicarbonate amendments just prior to nitrogen depletion. The optimum scenario observed for growth of N. gaditana under these inorganic carbon conditions was controlling pH with 5% CO 2 on demand, which increased both growth rate and lipid accumulation. Fatty acid methyl esters were primarily comprised of C16:0 (palmitic) and C16:1 (palmitoleic) aliphatic chains. Additionally, the use of high concentration (50 mM) of bicarbonate amendments further improved lipid content (up to 48.6%) under nitrogen deplete conditions when paired with pH-controlled strategies. 相似文献
6.
The marine cyanobacterium, Synechococcus sp. Nägeli (strain RRIMP N1) changes its affinity for external inorganic carbon used in photosynthesis, depending on the concentration of CO 2 provided during growth. The high affinity for CO 2 + HCO 3− of air-grown cells (K ½ < 80 nanomoles [pH 8.2]) would seem to be the result of the presence of an inducible mechanism which concentrates inorganic carbon (and thus CO 2) within the cells. Silicone-oil centrifugation experiments indicate that the inorganic carbon concentration inside suitably induced cells may be in excess of 1,000-fold greater than that in the surrounding medium, and that this accumulation is dependent upon light energy. The quantum requirements for O 2 evolution appear to be some 2-fold greater for low CO 2-grown cells, compared with high CO 2-grown cells. This presumably is due to the diversion of greater amounts of light energy into inorganic carbon transport in these cells. A number of experimental approaches to the question of whether CO2 or HCO3− is primarily utilized by the inorganic carbon transport system in these cells show that in fact both species are capable of acting as substrate. CO2, however, is more readily taken up when provided at an equivalent concentration to HCO3−. This discovery suggests that the mechanistic basis for the inorganic carbon concentrating system may not be a simple HCO3− pump as has been suggested. It is clear, however, that during steady-state photosynthesis in seawater equilibrated with air, HCO3− uptake into the cell is the primary source of internal inorganic carbon. 相似文献
7.
Algal cultivation is a potential candidate for CO 2 mitigation. CO 2 plays important roles in mass cultivation of algae, including supplying carbon source and adjusting medium pH. To assess the possibility of using edible cyanobacterium Nostoc flagelliforme as carbon storage device, the growth characteristics of N. flagelliforme batch cultured under elevated CO 2 concentrations (0, 2.5, 5, 20, and 40%) were investigated in this study. Results showed that the net photosynthetic rate, efficiency and carbon sequestration rate at 20% CO 2 were increased at a maximum of 121 μmol O 2 (mg chl a) ?1 h ?1 8.40% and 0.17 g CO 2 L ?1 day ?1, and increased by 0.42, 1.03 and 1.13 folds compared with that of the control, respectively. Higher CO 2 concentration resulted in the declines in photosynthetic rate, efficiency and carbon sequestration rate because of medium pH reduction. Accordingly, the dry cell weight, amount of exopolysaccharides and protein content of N. flagelliforme cells at 20% CO 2 were obtained at a maximum of 1.45 g L ?1, 54.98 mg L ?1 and 57.75%, increased by 0.93, 0.29 and 0.8 folds compared with that of the control, respectively. These results provided important information for CO 2 mitigation by N. flagelliforme and would shed more light on elucidating the mechanisms of CO 2 tolerance in cyanobacterium. 相似文献
8.
Our research objectives are to determine under what conditions microalgal-based CO 2 capture from flue gases is economically attractive. Specifically, our objective here was to select microalgae that are temperature,
pH and flue gas tolerant. Microalgae were grown under five different temperatures, three different pH and five different flue
gas mixtures besides 100% CO 2 (gas concentrations that the cells were exposed to ranged 5.7–100% CO 2, 0–3504 ppm SO 2, 0–328 ppm NO, and 0–126 ppm NO 2). Our results indicate that the microalgal strains tested exhibit a substantial ability to withstand a wide range of temperature
(54 strains tested), pH (20 strains tested) and flue gas composition (24 strains tested) likely to be encountered in cultures
used for carbon sequestration from smoke stack gases. Our results indicate that microalgal photosynthesis is a limited but
viable strategy for CO 2 capture from flue gases produced by stationary combustion sources. 相似文献
9.
Scenedesmus is a genus of microalgae employed for several industrial uses. Industrial cultivations are performed in open ponds or in closed photobioreactors (PBRs). In the last years, a novel type of PBR based on immobilized microalgae has been developed termed porous substrate photobioreactors (PSBR) to achieve significant higher biomass density during cultivation in comparison to classical PBRs. This work presents a study of the growth of Scenedesmus vacuolatus in a Twin Layer System PSBR at different light intensities (600 μmol photons m−2 s−1 or 1000 μmol photons m−2 s−1), different types and concentrations of the nitrogen sources (nitrate or urea), and at two CO2 levels in the gas phase (2% or 0.04% v/v). The microalgal growth was followed by monitoring the attached biomass density as dry weight, the specific growth rate and pigment accumulation. The highest productivity (29 g m−2 d−1) was observed at a light intensity of 600 μmol photons m−2 s−1 and 2% CO2. The types and concentrations of nitrogen sources did not influence the biomass productivity. Instead, the higher light intensity of 1000 μmol photons m−2 s−1 and an ambient CO2 concentration (0.04%) resulted in a significant decrease of productivity to 18 and 10–12 g m−2 d−1, respectively. When compared to the performance of similar cultivation systems (15–30 g m−2 d−1), these results indicate that the Twin Layer cultivation System is a competitive technique for intensified microalgal cultivation in terms of productivity and, at the same time, biomass density. 相似文献
10.
In this work, a photobioreactor with microalgae biofilm was proposed to enhance CO2 biofixation and protein production using nickel foam with the modified surface as the carrier for immobilizing microalgae cells. The results demonstrated that, compared with microalgae suspension, microalgae biofilm lowered mass transfer resistance and promoted mass transfer efficiency of CO2 from the bubbles into the immobilized microalgae cells, enhancing CO2 biofixation and protein production. Moreover, parametric studies on the performance of the photobioreactor with microalgae biofilm were also conducted. The results showed that the photobioreactor with microalgae biofilm yielded a good performance with the CO2 biofixation rate of 4465.6 µmol m−3 s−1, the protein concentration of effluent liquid of 0.892 g L−1, and the protein synthesis rate of 43.11 g m−3 h−1. This work will be conducive to the optimization design of microalgae culture system for improving the performance of the photobioreactor. 相似文献
11.
There has been considerable interest in cultivation of green microalgae (Chlorophyta) as a source of lipid that can alternatively be converted to biodiesel. However, almost all mass cultures of algae are carbon-limited. Therefore, to reach a high biomass and oil productivities, the ideal selected microalgae will most likely need a source of inorganic carbon. Here, growth and lipid productivities of Tetraselmis suecica CS-187 and Chlorella sp were tested under various ranges of pH and different sources of inorganic carbon (untreated flue gas from coal-fired power plant, pure industrial CO 2, pH-adjusted using HCl and sodium bicarbonate). Biomass and lipid productivities were highest at pH 7.5 (320?±?29.9 mg biomass L ?1 day ?1and 92?±?13.1 mg lipid L ?1 day ?1) and pH 7 (407?±?5.5 mg biomass L ?1 day ?1 and 99?±?17.2 mg lipid L ?1 day ?1) for T. suecica CS-187 and Chlorella sp, respectively. In general, biomass and lipid productivities were pH 7.5?>?pH 7?>?pH 8?>?pH 6.5 and pH 7?>?pH 7.5?=?pH 8?>?pH 6.5?>?pH 6?>?pH 5.5 for T. suecica CS-187 and Chlorella sp, respectively. The effect of various inorganic carbon on growth and productivities of T. suecica (regulated at pH?=?7.5) and Chlorella sp (regulated at pH?=?7) grown in bag photobioreactors was also examined outdoor at the International Power Hazelwood, Gippsland, Victoria, Australia. The highest biomass and lipid productivities of T. suecica (51.45?±?2.67 mg biomass L ?1 day ?1 and 14.8?±?2.46 mg lipid L ?1 day ?1) and Chlorella sp (60.00?±?2.4 mg biomass L ?1 day ?1 and 13.70?±?1.35 mg lipid L ?1 day ?1) were achieved when grown using CO 2 as inorganic carbon source. No significant differences were found between CO 2 and flue gas biomass and lipid productivities. While grown using CO 2 and flue gas, biomass productivities were 10, 13 and 18 %, and 7, 14 and 19 % higher than NaHCO 3, HCl and unregulated pH for T. suecica and Chlorella sp, respectively. Addition of inorganic carbon increased specific growth rate and lipid content but reduced biomass yield and cell weight of T. suecica. Addition of inorganic carbon increased yield but did not change specific growth rate, cell weight or content of the cell weight of Chlorella sp. Both strains showed significantly higher maximum quantum yield (F v/F m) when grown under optimum pH. 相似文献
12.
Microalgae have been exploited for biofuel generation in the current era due to its enormous energy content, fast cellular growth rate, inexpensive culture approaches, accumulation of inorganic compounds, and CO 2 sequestration. Currently, research is ongoing towards the advancement of the microalgae cultivation parameters to enhance the biomass yield. The main objective of this study was to delineate the progress of physicochemical parameters for microalgae cultivation such as gaseous transfer, mixing, light demand, temperature, pH, nutrients and the culture period. This review demonstrates the latest research trends on mass transfer coefficient of different microalgae culturing reactors, gas velocity optimization, light intensity, retention time, and radiance effects on microalgae cellular growth, temperature impact on chlorophyll production, and nutrient dosage ratios for cellulosic metabolism to avoid nutrient deprivation. Besides that, cultivation approaches for microalgae associated with mathematical modeling for different parameters, mechanisms of microalgal growth rate and doubling time have been elaborately described. Along with that, this review also documents potential lipid-carbohydrate-protein enriched microalgae candidates for biofuel, biomass productivity, and different cultivation conditions including open-pond cultivation, closed-loop cultivation, and photobioreactors. Various photobioreactor types, the microalgae strain, productivity, advantages, and limitations were tabulated. In line with microalgae cultivation, this study also outlines in detail numerous biofuels from microalgae. 相似文献
13.
Scenedesmus cells grown on high CO 2, when adapted to air levels of CO 2 for 4 to 6 hours in the light, formed two concentrating processes for dissolved inorganic carbon: one for utilizing CO 2 from medium of pH 5 to 8 and one for bicarbonate accumulation from medium of pH 7 to 11. Similar results were obtained with assays by photosynthetic O 2 evolution or by accumulation of dissolved inorganic carbon inside the cells. The CO 2 pump with K 0.5 for O 2 evolution of less than 5 micromolar CO 2 was similar to that previously studied with other green algae such as Chlamydomonas and was accompanied by plasmalemma carbonic anhydrase formation. The HCO 3− concentrating process between pH 8 to 10 lowered the K 0.5 (DIC) from 7300 micromolar HCO 3− in high CO 2 grown Scenedesmus to 10 micromolar in air-adapted cells. The HCO 3− pump was inhibited by vanadate (K i of 150 micromolar), as if it involved an ATPase linked HCO 3− transporter. The CO 2 pump was formed on low CO 2 by high-CO 2 grown cells in growth medium within 4 to 6 hours in the light. The alkaline HCO 3− pump was partially activated on low CO 2 within 2 hours in the light or after 8 hours in the dark. Full activation of the HCO 3− pump at pH 9 had requirements similar to the activation of the CO 2 pump. Air-grown or air-adapted cells at pH 7.2 or 9 accumulated in one minute 1 to 2 millimolar inorganic carbon in the light or 0.44 millimolar in the dark from 150 micromolar in the media, whereas CO 2-grown cells did not accumulate inorganic carbon. A general scheme for concentrating dissolved inorganic carbon by unicellular green algae utilizes a vanadate-sensitive transporter at the chloroplast envelope for the CO 2 pump and in some algae an additional vanadate-sensitive plasmalemma HCO 3− transporter for a HCO 3− pump. 相似文献
14.
The rates of CO 2-dependent O 2 evolution by Chlamydomonas reinhardtii, grown with either air levels of CO 2 or air with 5% CO 2, were measured at varying external pH. Over a pH range of 4.5 to 8.5, the external concentration of CO 2 required for half-maximal rates of photosynthesis was constant, averaging 25 micromolar for cells grown with 5% CO 2. This is consistent with the hypothesis that these cells take up CO 2 but not HCO 3− from the medium and that their CO 2 requirement for photosynthesis reflects the Km(CO 2) of ribulose bisphosphate carboxylase. Over a pH range of 4.5 to 9.5, cells grown with air required an external CO 2 concentration of only 0.4 to 3 micromolar for half-maximal rates of photosynthesis, consistent with a mechanism to accumulate external inorganic carbon in these cells. Air-grown cells can utilize external inorganic carbon efficiently even at pH 4.5 where the HCO 3− concentration is very low (40 nanomolar). However, at high external pH, where HCO 3− predominates, these cells cannot accumulate inorganic carbon as efficiently and require higher concentrations of NaHCO 3 to maintain their photosynthetic activity. These results imply that, at the plasma membrane, CO 2 is the permeant inorganic carbon species in air-grown cells as well as in cells grown on 5% CO 2. If active HCO 3− accumulation is a step in CO 2 concentration by air-grown Chlamydomonas, it probably takes place in internal compartments of the cell and not at the plasmalemma. 相似文献
15.
The species of inorganic carbon (CO 2 or HCO 3−) taken up a source of substrate for photosynthetic fixation by isolated Asparagus sprengeri mesophyll cells is investigated. Discrimination between CO 2 or HCO 3− transport, during steady state photosynthesis, is achieved by monitoring the changes (by 14C fixation) which occur in the specific activity of the intracellular pool of inorganic carbon when the inorganic carbon present in the suspending medium is in a state of isotopic disequilibrium. Quantitative comparisons between theoretical (CO 2 or HCO 3− transport) and experimental time-courses of 14C incorporation, over the pH range of 5.2 to 7.5, indicate that the specific activity of extracellular CO 2, rather than HCO 3−, is the appropriate predictor of the intracellular specific activity. It is concluded, therefore, that CO 2 is the major source of exogenous inorganic carbon taken up by Asparagus cells. However, at high pH (8.5), a component of net DIC uptake may be attributable to HCO 3− transport, as the incorporation of 14C during isotopic disequilibrium exceeds the maximum possible incorporation predicted on the basis of CO 2 uptake alone. The contribution of HCO 3− to net inorganic carbon uptake (pH 8.5) is variable, ranging from 5 to 16%, but is independent of the extracellular HCO 3− concentration. The evidence for direct HCO 3− transport is subject to alternative explanations and must, therefore, be regarded as equivocal. Nonlinear regression analysis of the rate of 14C incorporation as a function of time indicates the presence of a small extracellular resistance to the diffusion of CO 2, which is partially alleviated by a high extracellular concentration of HCO 3−. 相似文献
16.
The external inorganic carbon pool (CO 2 + HCO 3−) was measured in both high and low CO 2-grown cells of Chlamydomonas reinhardtii, using a silicone oil layer centrifugal filtering technique. The average internal pH values were measured for each cell type using [ 14C]dimethyloxazolidinedione, and the internal inorganic carbon pools were recalculated on a free CO 2 basis. These measurements indicated that low CO 2-grown cells were able to concentrate CO 2 up to 40-fold in relation to the external medium. Low and high CO 2-grown cells differed in their photosynthetic affinity for external CO 2. These differences could be most readily explained as being due to the relative CO 2-concentrating capacity of each cell type. This physiological adaptation appeared to be based on changes in the abilities of the cells actively to accumulate inorganic carbon using an energy-dependent transport system. 相似文献
17.
The possibility of HCO 3− transport into isolated leaf mesophyll cells of Asparagus sprengeri Regel has been investigated. Measurement of the inorganic carbon pool in these cells over an external pH range 6.2 to 8.0, using the silicone-fluid filtration technique, indicated that the pool was larger than predicted by passive 14CO 2 distribution, suggesting that HCO 3− as well as CO 2 crosses the plasmalemma. Intracellular pH values, calculated from the distribution of 14CO 2 between the cells and the medium, were found to be higher (except at pH 8.0) than those previously determined by 5,5-dimethyl[2- 14C]oxazolidine-2,4-dione distribution. It is suggested that the inorganic carbon accumulated above predicted concentrations may be bound to proteins and membranes and thus may not represent inorganic carbon actively accumulated by the cells, inasmuch as in a closed system at constant CO 2 concentration, the photosynthetic rates at pH 7.0 and 8.0 were 5 to 8 times lower than the maximum rate which could be supported by CO 2 arising from the spontaneous dehydration of HCO 3−. Furthermore, CO 2 compensation points of the cells in liquid media at 21% O 2 at pH 7.0 and 8.0, and the K ½ CO 2 (CO 2 concentration supporting the half maximal rate of O 2 evolution) at 2% O 2 at pH 7.0 and 8.0 are not consistent with HCO 3− transport. These results indicate that the principal inorganic carbon species crossing the plasmalemma in these cells is CO 2. 相似文献
18.
Summary Six independently isolated mutants of Chlamydomonas reinhardtii that require elevated CO 2 for photoautotrophic growth were tested by complementation analysis. These mutants are likely to be defective in some aspect of the algal concentrating mechanism for inorganic carbon as they exhibit CO 2 fixation and inorganic carbon accumulation properties different from the wild-type. Four of the six mutants defined a single complementation group and appear to be defective in an intracellular carbonic anhydrase. The other two mutations represent two additional complementation groups.Abbreviations HS
high salt medium which has 13 mM phosphate at pH 6.8
- HSA
high salt plus 36 mM acetate medium
- YA
high salt medium with 4 g yeast extract per L and 36mM acetate
- Arg
arginine
- cia -
CO 2 accumulation mutants that cannot grow on low CO 2
- C i
inorganic carbon (CO 2+HCO
-
3
)
- CA
carbonic anhydrase
- mt
mating type
Supported in part by the McKnight Foundation and by NSF grant PCM 8005917 and published as journal article 11924 from the Michigan State Agriculatural Experiment Station 相似文献
19.
Carbon dioxide concentrating mechanisms (CCMs) act to improve the supply of CO 2 at the active site of ribulose‐1,5‐bisphosphate carboxylase/oxygenase. There is substantial evidence that in some microalgal species CCMs involve an external carbonic anhydrase (CA ext) and that CA ext activity is induced by low CO 2 concentrations in the growth medium. However, much of this work has been conducted on cells adapted to air‐equilibrium concentrations of CO 2, rather than to changing CO 2 conditions caused by growing microalgal populations. We investigated the role of CA ext in inorganic carbon (C i) acquisition and photosynthesis at three sampling points during the growth cycle of the cosmopolitan marine diatom Chaetoceros muelleri. We observed that CA ext activity increased with decreasing C i, particularly CO 2, concentration, supporting the idea that CA ext is modulated by external CO 2 concentration. Additionally, we found that the contribution of CA ext activity to carbon acquisition for photosynthesis varies over time, increasing between the first and second sampling points before decreasing at the last sampling point, where external pH was high. Lastly, decreases in maximum quantum yield of photosystem II (F v/F m), chlorophyll, maximum relative electron transport rate, light harvesting efficiency (α) and maximum rates of C i‐ saturated photosynthesis (V max) were observed over time. Despite this decrease in photosynthetic capacity an up‐regulation of CCM activity, indicated by a decreasing half‐saturation constant for CO 2 (K 0.5CO 2), occurred over time. The flexibility of the CCM during the course of growth in C. muelleri may contribute to the reported dominance and persistence of this species in phytoplankton blooms. 相似文献
20.
Mechanisms of inorganic carbon assimilation were investigated in the deep-water alga Phyllariopsis purpurascens (C. Agardh) Henry et South (Laminariales, Phaeophyta). The gross photosynthetic rate as a function of external pH, at a constant
concentration of 2 mM dissolved inorganic carbon (DIC), decreased sharply from pH 7.0 to 9.0, and was not substantially different
from 0 above pH 9.0. These data indicate that P. purpurascens is inefficient in the use of external HCO 3
− as a carbon source in photosynthesis. Moreover, the photosynthetic rate as a function of external DIC and the highest pH
(9.01 ± 0.07) that this species can achieve in a closed system were consistent with a low capacity to use HCO 3
−, in comparison to many other species of seaweeds. The role of external carbonic anhydrase (CA; EC 4.2.1.1) on carbon uptake
was investigated by measuring both the HCO 3
−-dependent O 2 evolution and the CO 2 uptake, at pH 5.5 and 8.0, and the rate of pH change in the external medium, in the presence of selected inhibitors of extra-
and intracellular CA. Photosynthetic DIC-dependent O 2 evolution was higher at pH 5.5 (where CO 2 is the predominant form of DIC) than at pH 8.0 (where the predominant chemical species is HCO 3
−). Both intra- and extracellular CA activity was detected. Dextran-bound sulfonamide (DBS; a specific inhibitor of extracellular
CA) reduced the photosynthetic O 2 evolution and CO 2 uptake at pH 8.0, but there was no effect at pH 5.5. The pH-change rate of the medium, under saturating irradiance, was reduced
by DBS. Phyllariopsis purpurascens has a low efficiency in the use of HCO 3
− as carbon source in photosynthesis; nevertheless, the ion can be used after dehydration, in the external medium, catalyzed
by extracellular CA. This mechanism could explain why the photosynthetic rate in situ was higher than that supported solely
by the diffusion of CO 2 from seawater.
Received: 6 March 1998 / Accepted: 22 June 1998 相似文献
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