The role of extracellular carbonic anhydrase activity in inorganic carbon utilization of Phaeocystis globosa (Pyrmnesiophyceae): A comparison with other marine algae using isotopic disequilibrium technique (original) (raw)
Related papers
Physiologia Plantarum, 1994
Carbonic anhydrase activity and inorganic carbon fluxes in low-and high-Cj eells of Chiamydomonas reinhardtii and Scenedesmus ohliquus.-Physiol, Plant. 90; 537-547, Carbonic anhydrase iQ.\) activity associated with higb-and low-dissolved inorganic carbon (C.) grown cells was examined in whole cells by measuring '"O exchange from doubly labeled CO; ("C'*O"'O). Both aigal species showed the presence of extracellular (peripJasmic) as well as intracellular CA actiiily, which were both greatly increased in low-C, cells. The periplasmic CA activity was at least 40-fold higher in lowcompared to high-C, cells in both C, reinhardtii and 5, obliquus. while low-C, cells of S. ohiiquus showed the highest activity of intemai CA, The CA inhibitor ethoxyzolamide .showed a ,strong inhibition of the C, uptake process in both C, reinhardtii and S. ohiiquus as in eyanobacteria, which may indicate that the nature of the primary uptake process is similar in bolh green aigae and cyanobacteria. By using a mass spectrometric disequilibrium technique it w as possible to separate the C, fluxes of net HCO^-uptake and net CO;-uptake during steady-state photosynthesis in high-and low-C, grow'n cells of Chiamydomonas reinhardtii (WT, 2137-H and Scenedesmus ohiiquus (WT, D3), It was found that both high-and low-C; cells of the two algae ean utilize both CO; and HCOT for photosynthesis, although low-C, celis have a higher affinity for the uptake of both Ci species. Induction at iow-C; causes an increase in tbe affinity of both species for HCO; and CO;; changes in net CO;-uptake were, however, significantly greater.
PLANT PHYSIOLOGY, 2013
Many microalgae induce an extracellular carbonic anhydrase (eCA), associated with the cell surface, at low carbon dioxide (CO 2 ) concentrations. This enzyme is thought to aid inorganic carbon uptake by generating CO 2 at the cell surface, but alternative roles have been proposed. We developed a new approach to quantify eCA activity in which a reaction-diffusion model is fit to data on 18 O removal from inorganic carbon. In contrast to previous methods, eCA activity is treated as a surface process, allowing the effects of eCA on cell boundary-layer chemistry to be assessed. Using this approach, we measured eCA activity in two marine diatoms (Thalassiosira pseudonana and Thalassiosira weissflogii), characterized the kinetics of this enzyme, and studied its regulation as a function of culture pH and CO 2 concentration. In support of a role for eCA in CO 2 supply, eCA activity specifically responded to low CO 2 rather than to changes in pH or HCO 3 2 , and the rates of eCA activity are nearly optimal for maintaining cell surface CO 2 concentrations near those in the bulk solution. Although the CO 2 gradients abolished by eCA are small (less than 0.5 mM concentration difference between bulk and cell surface), CO 2 uptake in these diatoms is a passive process driven by small concentration gradients. Analysis of the effects of short-term and long-term eCA inhibition on photosynthesis and growth indicates that eCA provides a small energetic benefit by reducing the surface-to-bulk CO 2 gradient. Alternative roles for eCA in CO 2 recovery as HCO 3 2 and surface pH regulation were investigated, but eCA was found to have minimal effects on these processes.
Physiol Plant, 1994
Carbonic anhydrase activity and inorganic carbon fluxes in low-and high-Cj eells of Chiamydomonas reinhardtii and Scenedesmus ohliquus.-Physiol, Plant. 90; 537-547, Carbonic anhydrase iQ.\) activity associated with higb-and low-dissolved inorganic carbon (C.) grown cells was examined in whole cells by measuring '"O exchange from doubly labeled CO; ("C'*O"'O). Both aigal species showed the presence of extracellular (peripJasmic) as well as intracellular CA actiiily, which were both greatly increased in low-C, cells. The periplasmic CA activity was at least 40-fold higher in lowcompared to high-C, cells in both C, reinhardtii and 5, obliquus. while low-C, cells of S. ohiiquus showed the highest activity of intemai CA, The CA inhibitor ethoxyzolamide .showed a ,strong inhibition of the C, uptake process in both C, reinhardtii and S. ohiiquus as in eyanobacteria, which may indicate that the nature of the primary uptake process is similar in bolh green aigae and cyanobacteria. By using a mass spectrometric disequilibrium technique it w as possible to separate the C, fluxes of net HCO^-uptake and net CO;-uptake during steady-state photosynthesis in high-and low-C, grow'n cells of Chiamydomonas reinhardtii (WT, 2137-H and Scenedesmus ohiiquus (WT, D3), It was found that both high-and low-C; cells of the two algae ean utilize both CO; and HCOT for photosynthesis, although low-C, celis have a higher affinity for the uptake of both Ci species. Induction at iow-C; causes an increase in tbe affinity of both species for HCO; and CO;; changes in net CO;-uptake were, however, significantly greater.
Aquatic Botany, 2011
The effects on photosynthesis of acetazolamide (AZ, an inhibitor of the external carbonic anhydrase) and TRIS buffer at pH 8.7 were assessed in 24 species of red macroalgae. Only Palmaria palmata was unaffected by both substances. The rest of species were classified into three groups according to their sensitivity to TRIS and AZ. Photosynthesis of fourteen species was significantly inhibited by both TRIS and AZ. Inhibition by TRIS varied from almost 100% to 25% while AZ produced similar effects. Inhibition by TRIS was completely reverted by increasing the dissolved inorganic carbon concentration (DIC). This species group had half-saturation constants for photosynthesis (K m(DIC) ) ranging from 0.5 to 1.1 mM of DIC. TRIS produced a significant increase of K m(DIC) . Altogether, these results indicate that the algae sensitive to TRIS are capable of using HCO 3 − efficiently at pH 8.7. Furthermore, the buffering capacity of TRIS was responsible for its inhibitory effect on photosynthesis suggesting that HCO 3 − use was facilitated by excretion of protons outside the plasma membrane, which creates regions of low pH resulting in a higher-thanambient CO 2 concentration. In contrast, photosynthesis by two Porphyra species analysed was slightly stimulated by TRIS and completely inhibited by AZ, suggesting that the mechanism was different. In a third group of seaweeds, photosynthesis was insensitive to TRIS but it was significantly inhibited by AZ. These species had relatively high values of K m(DIC) indicating that they relied on purely diffusive entry of CO 2 generated by external carbonic anhydrase activity. Consequently, the results demonstrate that external carbonic anhydrase is widespread among red macroalgae since only P. palmata was insensitive to AZ. The functional significance of this enzyme was quite variable among the tested species.
Journal of Phycology, 2009
The role of carbonic anhydrase (CA) in inorganic carbon acquisition (dissolved inorganic carbon, DIC) was examined in Alboran Sea phytoplankton assemblages. The study area was characterized by a relatively high variability in nutrient concentration and in abundance and taxonomic composition of phytoplankton. Therefore, the relationship between environmental variability and capacity for using HCO 3 ) via external CA (eCA) was examined. Acetazolamide (AZ, an inhibitor of eCA) inhibited the primary productivity (PP) in 50% of the samples, with inhibition percentages ranging from 13% to 60%. The AZ effect was more prominent in the samples that exhibited PP >1 mg C AE m )3 AE h )1 , indicating that the contribution of eCA to the DIC photosynthetic flux was irrelevant at low PP. The inhibition of primary productivity by AZ was significantly correlated to the abundance of diatoms. However, there was no a relationship between AZ effect and CO 2 partial pressure (pCO 2 ) or nutrient concentration, indicating that the variability in the PP percentage supported by eCA was mainly due to differences in taxonomic composition of the phytoplankton assemblages. Ethoxyzolamide (EZ, an inhibitor of both external and internal CA) affected 13 of 14 analyzed samples, with PP inhibition percentages varying from 50% % to 95% %. The effects of AZ and EZ were partially reversed by doubling DIC concentration. These results imply that CA activity (external and ⁄ or internal) was involved in inorganic carbon acquisition in most the samples. However, EZ effect was not correlated with pCO 2 or taxonomic composition of the phytoplankton.
Carbonic anhydrase activity and photosynthesis in marine diatoms
European Journal of Phycology, 2007
The photosynthesis and carbonic anhydrase activity of four marine diatoms currently found in oyster-ponds near the French Atlantic coast, Haslea ostrearia, Navicula phyllepta, Entomoneis paludosa and Amphora coffeaeformis, were investigated. Photosynthetic parameters determined from photosynthesis versus irradiance curves showed that A. coffeaeformis (a benthic species) had lower maximum net photosynthesis but a higher light utilization coefficient than the other species studied. Carbonic anhydrase (CA) activity was measured using intact cells (external CA) and extracts (total CA) of these four species. In all four diatoms, the internal CA activity accounted for between 56 and 63% of the total CA activity. Two or three active forms of CA were separated by polyacrylamide gel electrophoresis. Two enzymatic bands of low molecular mass (4.5 and 6.5 kDa) were found in all four diatoms. A third enzymatic band was detected at 33 kDa in H. ostrearia and 11.7 kDa in E. paludosa. Acetazolamide, an inhibitor of external CA, reduced the net photosynthesis in H. ostrearia, E. paludosa and A. coffeaeformis by about 13%, but could not be tested on N. phyllepta as it is permeable to this substance. Direct uptake of HCO À 3 was estimated using the anion-exchange inhibitor 4,4 0 -diisothiocyanatostilbene-2,2 0 -disulphonate. Bicarbonate accounted for about 50% of fixed inorganic carbon in E. paludosa, and for about 60% in the other species. The higher affinity (K 1/2 ) for dissolved inorganic carbon in H. ostrearia (24.5 mM) than in E. paludosa (38.2 mM) seemed to be related to greater external CA activity, and the presence of a more efficient anion exchange protein in the plasmalemma.
Carbon acquisition mechanisms in Chara tomentosa
Aquatic Botany, 2003
Carbon uptake mechanisms of the stonewort Chara tomentosa from the brackish Baltic Sea were studied by recording changes in pH, alkalinity and inorganic carbon concentrations of the seawater medium during photosynthesis in a closed system. The use of inhibitors identified three mechanisms: (1) a vanadate-sensitive P-type H +-ATPase (proton pump) was involved in carbon uptake. This was previously shown for perfused cells of Chara corallina, but not for living cells. (2) Periplasmic carbonic anhydrase that catalyses the dehydration of HCO 3 − into CO 2 outside the cell membrane was highly active during carbon uptake, also at high pH (>9). (3) At high pH, there was direct uptake of HCO 3 − with the help of an anion exchange protein, which previously has not been shown in Chara. We also document here the occurrence of charasomes in the cell membrane of C. tomentosa, always with mitochondria located in their direct vicinity. The simultaneous high periplasmic carbonic anhydrase and proton pump activities and the occurrence of charasomes suggest proton-pump driven H + extrusion and membrane transport of CO 2 derived from HCO 3 − as the major form of DIC acquisition in this alga. Probably, this occurs in acidic bands in C. tomentosa in which we found a banding pattern of CaCO 3 incrustations (alkaline bands). The results were compared with a similar study on the green alga Cladophora glomerata from the same area, which had very low carbonic anhydrase activity (almost negligible), no structures isolating the periplasm from the bulk seawater medium analogous to charasomes and no CaCO 3 incrustation.
Physiologia plantarum, 2008
The effects of pH-induced changes in seawater carbonate chemistry on inorganic carbon (C(i)) acquisition and domoic acid (DA) production were studied in two potentially toxic diatom species, Pseudo-nitzschia multiseries and Nitzschia navis-varingica, and the non-toxic Stellarima stellaris. In vivo activities of carbonic anhydrase (CA), photosynthetic O(2) evolution and CO(2) and HCO(3)(-) uptake rates were measured by membrane inlet MS in cells acclimated to low (7.9) and high pH (8.4 or 8.9). Species-specific differences in the mode of carbon acquisition were found. While extracellular carbonic anhydrase (eCA) activities increased with pH in P. multiseries and S. stellaris, N. navis-varingica exhibited low eCA activities independent of pH. Half-saturation concentrations (K(1/2)) for photosynthetic O(2) evolution, which were highest in S. stellaris and lowest in P. multiseries, generally decreased with increasing pH. In terms of carbon source, all species took up both CO(2) and HCO(...
Bacterial metabolism of algal extracellular carbon
Hydrobiologia, 1989
Measurements of microbial utilization of extracellular organic carbon (EOC) released by phytoplankton commonly consider only EOC fractions subject to rapid uptake. Questions remain whether other EOC fractions are metabolized, what portion is labile, and with what assimilation efficiency this carbon substrate is utilized. ' 4 C-EOC was prepared by incubation of the natural mixed planktonic community from an oligotrophic lake with H' 4 CO3 in the light. 1 4 C-EOC which was not rapidly removed by heterotrophs remained in solution and was isolated by filtration. This residual EOC was inoculated with lake microheterotrophs in laboratory microcosms, and utilization kinetics were determined through long-term assays of cumulative 4 CO2 production. Time-courses for 1 4 CO2 production were consistent for all assays and were well described by a deterministic mixed-order degradation model. On twelve sampling occasions, from 29% to 76% of residual 1 4 C-EOC was labile to further metabolism by lake heterotrophs. First-order rate constants for EOC utilization showed a mode of 0.05 to 0.15 per day. From 33% to 78% of gross 4 C-EOC uptake was respired (mean 50%), indicating appreciable return of algal EOC to the pelagic food web as microbial biomass.
Related topics
Cited by
Carbonic anhydrase activity and photosynthesis in marine diatoms
European Journal of Phycology, 2007
The photosynthesis and carbonic anhydrase activity of four marine diatoms currently found in oyster-ponds near the French Atlantic coast, Haslea ostrearia, Navicula phyllepta, Entomoneis paludosa and Amphora coffeaeformis, were investigated. Photosynthetic parameters determined from photosynthesis versus irradiance curves showed that A. coffeaeformis (a benthic species) had lower maximum net photosynthesis but a higher light utilization coefficient than the other species studied. Carbonic anhydrase (CA) activity was measured using intact cells (external CA) and extracts (total CA) of these four species. In all four diatoms, the internal CA activity accounted for between 56 and 63% of the total CA activity. Two or three active forms of CA were separated by polyacrylamide gel electrophoresis. Two enzymatic bands of low molecular mass (4.5 and 6.5 kDa) were found in all four diatoms. A third enzymatic band was detected at 33 kDa in H. ostrearia and 11.7 kDa in E. paludosa. Acetazolamide, an inhibitor of external CA, reduced the net photosynthesis in H. ostrearia, E. paludosa and A. coffeaeformis by about 13%, but could not be tested on N. phyllepta as it is permeable to this substance. Direct uptake of HCO À 3 was estimated using the anion-exchange inhibitor 4,4 0 -diisothiocyanatostilbene-2,2 0 -disulphonate. Bicarbonate accounted for about 50% of fixed inorganic carbon in E. paludosa, and for about 60% in the other species. The higher affinity (K 1/2 ) for dissolved inorganic carbon in H. ostrearia (24.5 mM) than in E. paludosa (38.2 mM) seemed to be related to greater external CA activity, and the presence of a more efficient anion exchange protein in the plasmalemma.
Applied Microbiology and Biotechnology, 2013
A detailed physiological and molecular analysis of lipid accumulation under a suite of conditions including nitrogen limitation, alkaline pH stress, bicarbonate supplementation, and organic acid supplementation was performed on the marine diatom Phaeodactylum tricornutum. For all tested conditions, nitrogen limitation was a prerequisite for lipid accumulation and the other culturing strategies only enhanced accumulation highlighting the importance of compounded stresses on lipid metabolism. Volumetric lipid levels varied depending on condition; the observed rankings from highest to lowest were for inorganic carbon addition (15 mM bicarbonate), organic acid addition (15 carbon mM acetate), and alkaline pH stress (pH9.0). For all lipidaccumulating cultures except acetate supplementation, a common series of physiological steps were observed. Upon extracellular nitrogen exhaustion, culture growth continued for approximately 1.5 cell doublings with decreases in specific protein and photosynthetic pigment content. As nitrogen limitation arrested cell growth, carbohydrate content decreased with a corresponding increase in lipid content. Addition of the organic carbon source acetate appeared to activate alternative metabolic pathways for lipid accumulation. Molecular level data on more than 50 central metabolism transcripts were measured using real-time PCR. Analysis of transcripts suggested the central metabolism pathways associated with bicarbonate transport, carbonic anhydrases, and C4 carbon fixations were important for lipid accumulation. Transcriptomic data also suggested that repurposing of phospholipids may play a role in lipid accumulation. This study provides a detailed physiological and molecular-level foundation for improved understanding of diatom nutrient cycling and contributes to a metabolic blueprint for controlling lipid accumulation in diatoms.
The ISME Journal, 2011
Climate change scenarios predict a doubling of the atmospheric CO 2 concentration by the end of this century. Yet, how rising CO 2 will affect the species composition of aquatic microbial communities is still largely an open question. In this study, we develop a resource competition model to investigate competition for dissolved inorganic carbon in dense algal blooms. The model predicts how dynamic changes in carbon chemistry, pH and light conditions during bloom development feed back on competing phytoplankton species. We test the model predictions in chemostat experiments with monocultures and mixtures of a toxic and non-toxic strain of the freshwater cyanobacterium Microcystis aeruginosa. The toxic strain was able to reduce dissolved CO 2 to lower concentrations than the non-toxic strain, and became dominant in competition at low CO 2 levels. Conversely, the non-toxic strain could grow at lower light levels, and became dominant in competition at high CO 2 levels but low light availability. The model captured the observed reversal in competitive dominance, and was quantitatively in good agreement with the results of the competition experiments. To assess whether microcystins might have a role in this reversal of competitive dominance, we performed further competition experiments with the wild-type strain M. aeruginosa PCC 7806 and its mcyB mutant impaired in microcystin production. The microcystinproducing wild type had a strong selective advantage at low CO 2 levels but not at high CO 2 levels. Our results thus demonstrate both in theory and experiment that rising CO 2 levels can alter the community composition and toxicity of harmful algal blooms.
Diatoms for Carbon Sequestration and Bio-Based Manufacturing
Biology
Carbon dioxide (CO2) is a major greenhouse gas responsible for climate change. Diatoms, a natural sink of atmospheric CO2, can be cultivated industrially in autotrophic and mixotrophic modes for the purpose of CO2 sequestration. In addition, the metabolic diversity exhibited by this group of photosynthetic organisms provides avenues to redirect the captured carbon into products of value. These include lipids, omega-3 fatty acids, pigments, antioxidants, exopolysaccharides, sulphated polysaccharides, and other valuable metabolites that can be produced in environmentally sustainable bio-manufacturing processes. To realize the potential of diatoms, expansion of our knowledge of carbon supply, CO2 uptake and fixation by these organisms, in conjunction with ways to enhance metabolic routing of the fixed carbon to products of value is required. In this review, current knowledge is explored, with an evaluation of the potential of diatoms for carbon capture and bio-based manufacturing.
Journal of the Marine Biological Association of the United Kingdom
pCO2/pH perturbation experiments were carried out under two different pCO2 levels to evaluate effects of CO2-driven ocean acidification on semi-continuous cultures of the marine diatom Skeletonema pseudocostatum CSA48. Under higher pCO2/lowered pH conditions, our results showed that CO2-driven acidification had no significant impact on growth rate, chlorophyll-a, cellular abundance, gross photosynthesis, dark respiration, particulate organic carbon and particulate organic nitrogen between CO2-treatments, suggesting that S. pseudocostatum is adapted to tolerate changes of ~0.5 units of pH under high pCO2 conditions. However, dissolved organic carbon (DOC) concentration and DOC/POC ratio were significantly higher at high pCO2, indicating that a greater partitioning of organic carbon into the DOC pool was stimulated by high CO2/low pH conditions. Total fatty acids (FAs) were significantly higher under low pCO2 conditions. The composition of FAs changed from low to high pCO2, with an in...
Nature Communications, 2018
Photosynthesis by marine diatoms plays a major role in the global carbon cycle, although the precise mechanisms of dissolved inorganic carbon (DIC) uptake remain unclear. A lack of direct measurements of carbonate chemistry at the cell surface has led to uncertainty over the underlying membrane transport processes and the role of external carbonic anhydrase (eCA). Here we identify rapid and substantial photosynthesis-driven increases in pH and [CO 3 2-] primarily due to the activity of eCA at the cell surface of the large diatom Odontella sinensis using direct simultaneous microelectrode measurements of pH and CO 3 2-along with modelling of cell surface inorganic carbonate chemistry. Our results show that eCA acts to maintain cell surface CO 2 concentrations, making a major contribution to DIC supply in O. sinensis. Carbonate chemistry at the cell surface is therefore highly dynamic and strongly dependent on cell size, morphology and the carbonate chemistry of the bulk seawater.
Effects of biosynthesis and physiology on relative abundances and isotopic compositions of alkenones
Geochemistry, Geophysics, Geosystems, 2001
The number of double bonds in long-chain, unsaturated ketones (alkenones) produced by some members of the Haptophyceae is correlated with the ambient temperature at the time of synthesis. For these same organisms the depletion of carbon-13 in biosynthetic products relative to dissolved inorganic carbon is related directly to the specific growth rate and inversely to the concentration of dissolved carbon dioxide. This report summarizes issues relating to the physiology, metabolism, and biochemistry of alkenone producers and how they affect the abundances and isotopic compositions of alkenones. These considerations show that an understanding of cellular responses to parameters governing uptake of inorganic carbon (C i ), isotopic fractionation, growth under diverse nutrient conditions, and genetic variability, both in the field and in culture, is necessary for developing a conceptual understanding of the biological significance of the e P and U K H 37 indices. Emiliana huxleyi is the best known alkenone producer and can serve as a model organism for these studies. This report identifies knowledge gaps and appropriate objectives for both field-and laboratory-based research.
The carbonic anhydrase activity of sinking and suspended particles in the North Pacific Ocean
Limnology and Oceanography, 2019
The enzyme carbonic anhydrase (CA) is crucial to many physiological processes involving CO 2 , from photosynthesis and respiration, to calcification and CaCO 3 dissolution. We present new measurements of CA activity along a North Pacific transect, on samples from in situ pumps, sediment traps, discreet plankton samples from the ship's underway seawater line, plankton tows, and surface sediment samples from multicores. CA activity is highest in the surface ocean and decreases with depth, both in suspended and sinking particles. Subpolar gyre surface particles exhibit 10× higher CA activity per liter of seawater compared to subtropical gyre surface particles. Activity persists to 4700 m in the subpolar gyre, but only to 1000 m in the subtropics. All sinking CA activity normalized to particulate organic carbon (POC) follows a single relationship (CA/POC = 1.9 AE 0.2 × 10 −7 mol mol −1). This relationship is consistent with CA/POC values in subpolar plankton tow material, suspended particles, and core top sediments. We hypothesize that most subpolar CA activity is associated with rapidly sinking diatom blooms, consistent with a large mat of diatomaceous material identified on the seafloor. Compared to the basin-wide sinking CA/POC relationship, a lower subtropical CA/POC suggests that the inventory of subtropical biomass is different in composition from exported material. Pteropods also demonstrate substantial CA activity. Scaled to the volume within pteropod shells, first-order CO 2 hydration rate constants are elevated ≥ 1000× above background. This kinetic enhancement is large enough to catalyze carbonate dissolution within microenvironments, providing observational evidence for CA-catalyzed, respiration-driven CaCO 3 dissolution in the shallow North Pacific. The enzyme carbonic anhydrase (CA) is ubiquitous (Moroney et al. 2001). It catalyzes the interconversion of CO 2 and HCO − 3 through the hydration of CO 2 : CO 2 + H 2 O⇋ H 2 CO 3 ⇋HCO − 3 + H + : ð1Þ At pH 7 and room temperature, the equilibration time of CO 2 with bicarbonate is on the order of 54 s (Pinsent et al. 1956). Compared to the essentially instantaneous acid-base
Minerals, 2021
Alkaline (pH > 8.5) lakes have been common features of Earth’s surface environments throughout its history and are currently among the most biologically productive environments on the planet. The chemistry of alkaline lakes favors the deposition of aluminum-poor magnesian clays (e.g., sepiolite, stevensite, and kerolite) whose chemistry and mineralogy may provide a useful record of the biogeochemistry of the lake waters from which they were precipitated. In this forward-looking review, we present six data-driven, testable hypotheses devoted to furthering our understanding of the biogeochemical conditions in paleolake waters based on the geochemical behavior of Mg and SiO2. In the development of these hypotheses, we bring together a compilation of modern lake water chemistry, recently published and new experimental data, and empirical, thermodynamic, and kinetic relationships developed from these data. We subdivide the hypotheses and supporting evidence into three categories: (1) ...
Limnology and Oceanography, 2018
Harmful algal blooms (HABs) are a global problem, exacerbated by rising temperatures, cultural eutrophication, urbanization, and agricultural development. During these HABs, phytoplankton consumption of CO2 may result in conditions of C limitation, where algal taxa best adapted for these conditions will be at a competitive advantage. Many cyanobacteria are capable of alleviating CO2 limitation by a variety of strategies, including the active assimilation of . In this study, we utilized a high‐resolution, month‐long time series of stable C isotopes and high‐performance liquid chromatograph‐based algal taxonomy in the hypereutrophic Lake Taihu, China, to investigate whether cyanobacteria are indeed advantaged by CO2 limiting conditions. We employed a model of phytoplankton C acquisition to support the inferences derived from direct measurements. Diurnal cycles of production and respiration caused δ13CDIC to vary between −4‰ and −9‰, while δ13CPOC varied between −29.6‰ and −19.6‰. Meas...
Related papers
PLANT PHYSIOLOGY, 1988
The induction of a dissolved inorganic carbon (DIC) accumulating mechanism in the two algal species Scenedesmus obliquus (WT) and Chlamydomonas reinhardtii (137 c+) was physiologically characterized by monitoring DIC uptake kinetics at a low and constant DIC concentration (120-140 micromolar), after transfer from high-DIC culturing conditions. A potentiometric titration method was used to measure and calculate algal DIC uptake. Full acclimation to low-DIC conditions was obtained within a period of 90 min, after which time the DIC uptake had been increased 7 to 10 times. Experiments were also conducted in the presence of inhibitors against DIC accumulation. The inhibitor of extracellular carbonic anhydrase (CA), acetazolamide (50 micromolar), inhibited the adaptation partly, while the inhibitor of both extra- and intracellular CA, ethoxyzolamide (50 micromolar) totally inhibited the acclimation. Cycloheximide (10 micrograms per milliliter), which inhibits protein synthesis on cytoplasmic ribosomes, and vanadate (180 micromolar), which inhibits the plasmamembrane bound ATPase, also inhibited the acclimation totally. These results taken together suggest that the algae are dependent on intracellular CA, plasmamembrane bound ATPase, and de novo protein synthesis for DIC accumulation. Also, these components are more important than extracellular CA for the overall function of the DIC-accumulating mechanism.
Plant Physiol, 2008
The oceans globally constitute an important sink for carbon dioxide (CO 2) due to phytoplankton photosynthesis. However, the marine environment imposes serious restraints to carbon fixation. First, the equilibrium between CO 2 and bicarbonate (HCO 3 2) is pH dependent, and, in normal, slightly alkaline seawater, [CO 2 ] is typically low (approximately 10 mM). Second, the rate of CO 2 diffusion in seawater is slow, so, for any cells unable to take up bicarbonate efficiently, photosynthesis could become carbon limited due to depletion of CO 2 from their immediate vicinity. This may be especially problematic for those dinoflagellates using a form II Rubisco because this form is less oxygen tolerant than the usually found form I enzyme. We have identified a carbonic anhydrase (CA) from the free-living marine dinoflagellate Lingulodinium polyedrum that appears to play a role in carbon acquisition. This CA shares 60% sequence identity with d-class CAs, isoforms so far found only in marine algae. Immunoelectron microscopy indicates that this enzyme is associated exclusively with the plasma membrane. Furthermore, this enzyme appears to be exposed to the external medium as determined by whole-cell CA assays and vectorial labeling of cell surface proteins with 125 I. The fixation of 14 CO 2 is strongly pH dependent, suggesting preferential uptake of CO 2 rather than HCO 3 2 , and photosynthetic rates decrease in the presence of 1 mM acetazolamide, a non-membranepermeable CA inhibitor. This constitutes the first CA identified in the dinoflagellates, and, taken together, our results suggest that this enzyme may help to increase CO 2 availability at the cell surface.
PLANT PHYSIOLOGY, 2008
The oceans globally constitute an important sink for carbon dioxide (CO 2) due to phytoplankton photosynthesis. However, the marine environment imposes serious restraints to carbon fixation. First, the equilibrium between CO 2 and bicarbonate (HCO 3 2) is pH dependent, and, in normal, slightly alkaline seawater, [CO 2 ] is typically low (approximately 10 mM). Second, the rate of CO 2 diffusion in seawater is slow, so, for any cells unable to take up bicarbonate efficiently, photosynthesis could become carbon limited due to depletion of CO 2 from their immediate vicinity. This may be especially problematic for those dinoflagellates using a form II Rubisco because this form is less oxygen tolerant than the usually found form I enzyme. We have identified a carbonic anhydrase (CA) from the free-living marine dinoflagellate Lingulodinium polyedrum that appears to play a role in carbon acquisition. This CA shares 60% sequence identity with d-class CAs, isoforms so far found only in marine algae. Immunoelectron microscopy indicates that this enzyme is associated exclusively with the plasma membrane. Furthermore, this enzyme appears to be exposed to the external medium as determined by whole-cell CA assays and vectorial labeling of cell surface proteins with 125 I. The fixation of 14 CO 2 is strongly pH dependent, suggesting preferential uptake of CO 2 rather than HCO 3 2 , and photosynthetic rates decrease in the presence of 1 mM acetazolamide, a non-membranepermeable CA inhibitor. This constitutes the first CA identified in the dinoflagellates, and, taken together, our results suggest that this enzyme may help to increase CO 2 availability at the cell surface.
American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, 2000
Symbiotic cnidarians absorb inorganic carbon from seawater to supply intracellular dinoflagellates with CO2for their photosynthesis. To determine the mechanism of inorganic carbon transport by animal cells, we used plasma membrane vesicles prepared from ectodermal cells isolated from tentacles of the sea anemone, Anemonia viridis. H14[Formula: see text] uptake in the presence of an outward NaCl gradient or inward H+gradient, showed no evidence for a Cl−- or H+- driven [Formula: see text] transport. H14[Formula: see text] and36Cl−uptakes were stimulated by a positive inside-membrane diffusion potential, suggesting the presence of [Formula: see text] and Cl−conductances. A carbonic anhydrase (CA) activity was measured on plasma membrane (4%) and in the cytoplasm of the ectodermal cells (96%) and was sensitive to acetazolamide (IC50= 20 nM) and ethoxyzolamide (IC50= 2.5 nM). A strong DIDS-sensitive H+-ATPase activity was observed (IC50= 14 μM). This activity was also highly sensitive t...
PLANT PHYSIOLOGY, 2001
A single intracellular carbonic anhydrase (CA) was detected in air-grown and, at reduced levels, in high CO 2 -grown cells of the marine diatom Phaeodactylum tricornutum (UTEX 642). No external CA activity was detected irrespective of growth CO 2 conditions. Ethoxyzolamide (0.4 mm), a CA-specific inhibitor, severely inhibited high-affinity photosynthesis at low concentrations of dissolved inorganic carbon, whereas 2 mm acetazolamide had little effect on the affinity for dissolved inorganic carbon, suggesting that internal CA is crucial for the operation of a carbon concentrating mechanism in P. tricornutum. Internal CA was purified 36.7-fold of that of cell homogenates by ammonium sulfate precipitation, and two-step column chromatography on diethylaminoethyl-sephacel and p-aminomethylbenzene sulfone amide agarose. The purified CA was shown, by SDS-PAGE, to comprise an electrophoretically single polypeptide of 28 kD under both reduced and nonreduced conditions. The entire sequence of the cDNA of this CA was obtained by the rapid amplification of cDNA ends method and indicated that the cDNA encodes 282 amino acids. Comparison of this putative precursor sequence with the N-terminal amino acid sequence of the purified CA indicated that it included a possible signal sequence of up to 46 amino acids at the N terminus. The mature CA was found to consist of 236 amino acids and the sequence was homologous to -type CAs. Even though the zinc-ligand amino acid residues were shown to be completely conserved, the amino acid residues that may constitute a CO 2 -binding site appeared to be unique among the -CAs so far reported.
Aquacultural Engineering, 2005
Dissolved inorganic carbon uptake (DIC) was determined in batch culture of the marine microalgae Rhodomonas sp. and Isochrysis aff. galbana (Clone T-ISO) for seven days using a simple potentiometric technique. The system used allowed the determination of small variations of the three independent parameters: pH, dissolved inorganic carbon and total alkalinity (A t ). The aerated cultures began with 13 mmol kg À1 of CO 2 (calculated using C t -pH), but after the third day, the concentration was almost zero. Cultures of Rhodomonas sp. continued growing in the absence of CO 2 with a total DIC depletion of 1330.5 mmol kg À1 and a final pH of $10. Since HCO 3 À is the predominant form of inorganic carbon at alkaline pH, Rhodomonas sp. shows potential for direct HCO 3 À uptake. On the other hand, the cultures of I. aff. galbana only removed DIC during the first three days while CO 2 was available, and also when the pH from culture was below 9. Nutrients (PO 4 3À , NO 3 À , NO 2 À and NH 4 + ) uptakes were also analyzed for the two cultures. The nutrient uptake in both microalgae did not show dependency on any specific DIC form. An extra addition of CO 2 during cultivation is recommended for enhanced growth mainly in I. galbana. #
Mechanisms of inorganic carbon acquisition in Gracilaria gaditana nom. prov.(Rhodophyta)
1999
The mechanisms for acquisition of dissolved inorganic carbon (DIC) in the red macroalga Gracilaria gaditana nom. prov. have been investigated. The capacity for HCO À 3 use by an extracellular carbonic anhydrase (CA; EC 4.2.1.1), and by an anion exchanger with similar properties to that of red blood cells (AE1), has been quanti®ed. It was illustrated by comparing O 2 evolution rates with those theoretically supported by CO 2 , as well as by photosynthesis-pH curves. Both external and internal CA, and a direct uptake were involved in HCO À 3 use, since photosynthesis and pH evolution were aected by acetazolamide, 6-ethoxyzolamide (inhibitors of external and total CA, respectively) and 4,4¢-diisothiocyanatostilbene-2,2¢-disulfonate, (DIDS; an inhibitor of HCO À 3 exchanger protein). The activity of the external CA was detected by a potentiometric method and by an alternative method based on the study of O 2 evolution after addition of CO 2 and acetazolamide. The latter method showed a residual photosynthetic rate due to direct HCO À 3 use. Inhibitors caused a reduction in the pH compensation points in pH-drift experiments. The CO 2 compensation points for photosynthesis increased when the inhibitors were applied, indicating a suppresion of the pathways involved in the carbon-concentrating mechanism. The net photosynthesis rates as a function of DIC concentration displayed a biphasic pattern that could be supported by the occurrence of the two mechanisms of HCO À 3 use. The potential contribution to HCO À 3 acquisition by the DIDS-sensitive mechanism was higher after culturing at a high pH. Our results suggest that the HCO À 3 use by Gracilaria gaditana is carried out by the two DIC uptake mechanisms. These operate simultaneously with dierent anities for DIC, the indirect HCO À 3 use by an external CA activity being the main pathway. The presence of a carbon-concentrating mechanism confers eco-physiological advantages in a¯uctuating ecosystem subjected daily to high pHs and low DIC concentrations.
A mechanism of bicarbonate uptake with a high sensitivity to the putative anion-exchange inhibitor 4,4h-diisothiocyanostilbene-2,2hdisulphonic acid (DIDS) has been previously reported in green algae. In this study, DIDS inhibited net oxygen evolution by Dunaliella tertiolecta by up to 22 %, but internal pH regulation, intracellular CO # accumulation, carbon fixation and affinity for dissolved inorganic carbon (DIC) in Dunaliella tertiolecta showed low or insignificant sensitivity to DIDS. However, in cells grown and tested at pH 9n5, treatment with DIDS elevated the k ! n & (HCO $ − ), suggesting there may be a minor role for a DIDS-sensitive anion-exchange-type HCO $ − transporter in DIC acquisition by D. tertiolecta at high pH. In contrast, significant external carbonic anhydrase (CA ext ) activity and up to 70 % inhibition of DIC-dependent O # evolution by acetozolamide (AZ) suggest that CA ext has an important role in DIC acquisition in D. tertiolecta, in normal seawater conditions and at elevated pH. Furthermore, the rate of DIC-dependent photosynthesis at high pH, in the presence of AZ, was 12 times higher than the calculated uncatalysed rate of CO # supply from HCO $ − . This requires some system for direct HCO $ − uptake by D. tertiolecta, which may include a DIDS-insensitive mechanism. The effects of DIDS upon indirect measures of DIC acquisition should be interpreted cautiously as DIDS may have non-specific effects upon whole cell function, and affect ion transport processes not directly related to HCO $ − uptake.
European Journal of Phycology, 2001
A mechanism of bicarbonate uptake with a high sensitivity to the putative anion-exchange inhibitor 4,4h-diisothiocyanostilbene-2,2hdisulphonic acid (DIDS) has been previously reported in green algae. In this study, DIDS inhibited net oxygen evolution by Dunaliella tertiolecta by up to 22 %, but internal pH regulation, intracellular CO # accumulation, carbon fixation and affinity for dissolved inorganic carbon (DIC) in Dunaliella tertiolecta showed low or insignificant sensitivity to DIDS. However, in cells grown and tested at pH 9n5, treatment with DIDS elevated the k ! n & (HCO $ − ), suggesting there may be a minor role for a DIDS-sensitive anion-exchange-type HCO $ − transporter in DIC acquisition by D. tertiolecta at high pH. In contrast, significant external carbonic anhydrase (CA ext ) activity and up to 70 % inhibition of DIC-dependent O # evolution by acetozolamide (AZ) suggest that CA ext has an important role in DIC acquisition in D. tertiolecta, in normal seawater conditions and at elevated pH. Furthermore, the rate of DIC-dependent photosynthesis at high pH, in the presence of AZ, was 12 times higher than the calculated uncatalysed rate of CO # supply from HCO $ − . This requires some system for direct HCO $ − uptake by D. tertiolecta, which may include a DIDS-insensitive mechanism. The effects of DIDS upon indirect measures of DIC acquisition should be interpreted cautiously as DIDS may have non-specific effects upon whole cell function, and affect ion transport processes not directly related to HCO $ − uptake.
Sources of inorganic carbon for photosynthesis in a strain of Phaeodactylum tricornutum
Limnology and Oceanography, 2002
Diatoms are an important functional group of marine phytoplankton because of their role in the fixation of atmospheric carbon dioxide (CO 2 ) and transfer of organic carbon to deep waters. Carbon-concentrating-mechanisms, such as active CO 2 and bicarbonate (HCO ) uptake and carbonic Ϫ 3 anhydrase activity, are believed to be essential to marine photosynthesis, because the main carbon-fixing enzyme, ribulose-1,5-bisphosphate carboxylase-oxygenase, is less than half saturated at normal seawater CO 2 concentrations. On the basis of short-term inorganic 14 C uptake experiments, Tortell et al. (1997; Nature 390: 243-244) recently argued that marine diatoms are capable of HCO uptake. However, as discussed Ϫ 3 herein, the extent of HCO uptake cannot be assessed on the Ϫ 3 basis of these experiments. Using short-term 14 CO 2 -disequilibrium experiments, we show that a clone of the marine diatom Phaeodactylum tricornutum takes up little or no HCO even Ϫ 3 under conditions of severe CO 2 limitation. Predicting the response of the oceans to increased CO 2 concentrations will require, among other things, a careful assessment of the extent to which marine algae take up HCO or CO 2 . Because the Ϫ 3 plasmalemma of microalgae is gas permeable, all phytoplankton exchange CO 2 with the growth medium. Experimental results that are merely consistent with HCO uptake are insuf-Ϫ 3 ficient to prove that HCO uptake is occurring. Our results are Ϫ 3
Loading Preview
Sorry, preview is currently unavailable. You can download the paper by clicking the button above.