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1.
The objectives of this study are to find the robust strains for the centrate cultivation system and to evaluate the effect of environmental factors including light intensity, light–dark cycle, and exogenous CO2 concentration on biomass accumulation, wastewater nutrient removal and biodiesel production. The results showed that all 14 algae strains from the genus of Chlorella, Haematococcus, Scenedesmus, Chlamydomonas, and Chloroccum were able to grow on centrate. The highest net biomass accumulation (2.01 g/L) was observed with Chlorella kessleri followed by Chlorella protothecoides (1.31 g/L), and both of them were proved to be capable of mixotrophic growth when cultivated on centrate. Environmental factors had significant effect on algal biomass accumulation, wastewater nutrients removal and biodiesel production. Higher light intensity and exogenous CO2 concentration with longer lighting period promote biomass accumulation, biodiesel production, as well as the removal of chemical oxygen demand and nitrogen, while, lower exogenous CO2 concentration promotes phosphorus removal. 相似文献
2.
C. A. Santos M. E. Ferreira T. Lopes da Silva L. Gouveia J. M. Novais A. Reis 《Journal of industrial microbiology & biotechnology》2011,38(8):909-917
This paper describes the association of two bioreactors: one photoautotrophic and the other heterotrophic, connected by the
gas phase and allowing an exchange of O2 and CO2 gases between them, benefiting from a symbiotic effect. The association of two bioreactors was proposed with the aim of improving
the microalgae oil productivity for biodiesel production. The outlet gas flow from the autotrophic (O2 enriched) bioreactor was used as the inlet gas flow for the heterotrophic bioreactor. In parallel, the outlet gas flow from
another heterotrophic (CO2 enriched) bioreactor was used as the inlet gas flow for the autotrophic bioreactor. Aside from using the air supplied from
the auto- and hetero-trophic bioreactors as controls, one mixotrophic bioreactor was also studied and used as a model, for
its claimed advantage of CO2 and organic carbon being simultaneously assimilated. The microalga Chlorella protothecoides was chosen as a model due to its ability to grow under different nutritional modes (auto, hetero, and mixotrophic), and its
ability to attain a high biomass productivity and lipid content, suitable for biodiesel production. The comparison between
heterotrophic, autotrophic, and mixotrophic Chlorella protothecoides growth for lipid production revealed that heterotrophic growth achieved the highest biomass productivity and lipid content
(>22%), and furthermore showed that these lipids had the most suitable fatty acid profile in order to produce high quality
biodiesel. Both associations showed a higher biomass productivity (10–20%), when comparing the two separately operated bioreactors
(controls) which occurred on the fourth day. A more remarkable result would have been seen if in actuality the two bioreactors
had been inter-connected in a closed loop. The biomass productivity gain would have been 30% and the lipid productivity gain
would have been 100%, as seen by comparing the productivities of the symbiotic assemblage with the sum of the two bioreactors
operating separately (controls). These results show an advantage of the symbiotic bioreactors association towards a cost-effective
microalgal biodiesel production. 相似文献
3.
4.
Bryan Holmes Matthew B. Paddock Jean S. VanderGheynst Brendan T. Higgins 《Biotechnology and bioengineering》2020,117(1):62-72
Wastewater treatment is an energy-intensive process and a net emitter of greenhouse gas emissions. A large fraction of these emissions is due to intensive aeration of aerobic bacteria to facilitate break-down of organic compounds. Algae can generate dissolved oxygen at levels in excess of saturation, and therefore hold the potential to partially displace or complement mechanical aeration in wastewater treatment processes. The objective of this study was to develop an internally consistent experimental and modeling approach to test the hypothesis that algal photosynthetic aeration can speed the removal of organic constituents by bacteria. This framework was developed using a simplified wastewater treatment process consisting of a model bacteria (Escherichia coli), a model algae (Auxenochlorella protothecoides), and a single carbon source that was consumable by bacteria only. This system was then tested both with and without the presence of algae. A MATLAB model that considered mass transfer and biological kinetics was used to estimate the production and consumption of O2 and CO2 by algae and bacteria. The results indicated that the presence of algae led to 18–66% faster removal of COD by bacteria, and that roughly one-third of biochemical oxygen demand was offset by algal photosynthetic aeration. 相似文献
5.
Algae of various taxonomic groups are capable of assimilating dissolved organic carbon (DOC) from their environments (mixotrophy). Recently, we reported that, with increasing biomass of mixotrophs, heterotrophic bacteria did not increase. We hypothesized that algal uptake of external DOC may outweigh their release of DOC by exudation (H1). Here, we addressed an alternative hypothesis that algae did not assimilate external DOC but constrained the release of DOC (H2). In chemostat experiments, we cultured the mixotrophic Chlamydomonas acidophila Negoro together with heterotrophic bacteria. As external substrates, we used glucose, which was potentially available for both bacteria and algae, or fructose, which was available only for bacteria. We increased the biomass of algae by the stepwise addition of phosphorus. Bacterial biomass did not increase in experiments using glucose or when fructose was offered, suggesting that mechanisms other than algal mixotrophy (H1) kept concentrations of bacteria low. Measured exudation rates (percent extracellular release, PER) of mixotrophic algae (Cd. acidophila, Chlorella protothecoides W. Krüger) were very low and ranged between 1.0% and 3.5% at low and moderately high phosphorus concentrations. In contrast, an obligately phototrophic alga (Chlamydomonas segnis H. Ettl) showed higher exudation rates, particularly under phosphorus limitation (70%). The results support H2. If mixotrophy is considered as a mechanism to recycle organic exudates from near the cell surface, this would explain why algae retained mixotrophic capabilities although they cannot compete with bacteria for external organic carbon. 相似文献
6.
Weiss E 《Journal of bacteriology》1970,101(1):133-137
Two strains of Saccharomycopsis guttulata, JB-1 and JB-3, isolated from stomach contents of domestic rabbits, were grown under different gas phases, and their growth rates were compared. Strain JB-1 grew exponentially at a maximal growth rate under a continuous gas phase of 15% CO2, 2% O2 in nitrogen. High cell yields with low cell granulation were obtained. The growth rates were almost the same between oxygen concentrations of 0.25 and 20% at 15% CO2. Poor growth and early cell granulation occurred in the absence of oxygen at 15% CO2. Growth increased at 2% O2 in direct proportion to the carbon dioxide concentration up to 10 to 15% CO2. A very high carbon dioxide content (e.g. 98%) was somewhat inhibitory. Cell granulation always occurred during the maximal stationary phase in media at pH 4, but was relatively slight at pH 5.6 or higher. Strain JB-3 responded to various gas phases in a similar manner except that it grew slowly in the absence of oxygen at 15% CO2 (pH 4). The effect of an optimal gas phase on the growth of strain JB-1 was examined in relation to other environmental conditions. In the presence of 15% CO2, 2% O2, this strain grew exponentially in yeast autolysate-Proteose Peptone-glucose medium at 37 C at pH 2, 4, and 5.6 at approximately the same rate; the growth rate was somewhat lower at pH 6.2. Under similar conditions, strain JB-1 grew at 30 C and pH 4 at one-sixth its maximal growth rate. Cell granulation was greatly reduced at this temperature. With adequate CO2 strain JB-1 also grew at a reduced rate in a yeast autolysate medium previously reported not to support growth. Results indicate that continuous gassing with an optimal gas phase increases the growth rate to the extent that the growth rate surpasses the death rate by a significant margin; as a result, granulated cells can be avoided almost entirely in the log phase. 相似文献
7.
Y. Azov 《Applied microbiology》1982,43(6):1300-1306
Biomass production by the green algae Scenedesmus obliquus and Chlorella vulgaris in intensive laboratory continuous cultures was considerably affected by the pH at which the cultures were maintained. Carbon photoassimilation experiments revealed that pH values in the range of 8 to 9 were important for determining the free CO2 concentrations in the medium. With higher pH values, additional pH effects were observed involving a decrease in the relative high affinity of low CO2-adapted algae to free CO2. The carbon uptake rate by high CO2-adapted algae after transfer to low free CO2 medium was characterized by a lag period of about 30 min, after which the affinity of the algae to CO2 increased considerably. Both continuous growth and carbon uptake experiments indicated that artificially maintained high free CO2 concentrations are recommended for maximal production in intensive outdoor algal cultures. 相似文献
8.
Effect of Photon Fluence Rate on Oxygen Evolution and Uptake by Chlamydomonas reinhardtii Suspensions Grown in Ambient and CO(2)-Enriched Air 总被引:4,自引:4,他引:0
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A closed system consisting of an assimilation chamber furnished with a membrane inlet from the liquid phase connected to a mass spectrometer was used to measure O2 evolution and uptake by Chlamydomonas reinhardtii cells grown in ambient (0.034% CO2) or CO2-enriched (5% CO2) air. At pH = 6.9, 28°C and concentrations of dissolved inorganic carbon (DIC) saturating for photosynthesis, O2 uptake in the light (Uo) equaled O2 production (Eo) at the light compensation point (15 micromoles photons per square meter per second). Eo and Uo increased with increasing photon fluence rate (PFR) but were not rate saturated at 600 micromoles photons per square meter per second, while net O2 exchange reached a saturation level near 500 micromoles photons per square meter per second which was nearly the same for both, CO2-grown and air-grown cells. Comparison of the Uo/Eo ratios between air-grown and CO2-grown C. reinhardtii showed higher values for air-grown cells at light intensities higher than light compensation. For both, air-grown and CO2-grown algae the rates of mitochondrial O2 uptake in the dark measured immediately before and 5 minutes after illumination were much lower than Uo at PFR saturating for net photosynthesis. We conclude that noncyclic electron flow from water to NADP+ and pseudocyclic electron flow via photosystem I to O2 both significantly contribute to O2 exchange in the light. In contrast, mitochondrial respiration and photosynthetic carbon oxidation cycle are regarded as minor O2 consuming reactions in the light in both, air-grown and CO2-grown cells. It is suggested that the “extra” O2 uptake by air-grown algae provides ATP required for the energy dependent CO2/HCO3− concentrating mechanism known to be present in these cells. 相似文献
9.
The anoxygenic green sulfur bacteria (GSBs) assimilate CO2 autotrophically through the reductive (reverse) tricarboxylic acid (RTCA) cycle. Some organic carbon sources, such as acetate and pyruvate, can be assimilated during the phototrophic growth of the GSBs, in the presence of CO2 or HCO3−. It has not been established why the inorganic carbonis required for incorporating organic carbon for growth and how the organic carbons are assimilated. In this report, we probed carbon flux during autotrophic and mixotrophic growth of the GSB Chlorobaculum tepidum. Our data indicate the following: (a) the RTCA cycle is active during autotrophic and mixotrophic growth; (b) the flux from pyruvate to acetyl-CoA is very low and acetyl-CoA is synthesized through the RTCA cycle and acetate assimilation; (c) pyruvate is largely assimilated through the RTCA cycle; and (d) acetate can be assimilated via both of the RTCA as well as the oxidative (forward) TCA (OTCA) cycle. The OTCA cycle revealed herein may explain better cell growth during mixotrophic growth with acetate, as energy is generated through the OTCA cycle. Furthermore, the genes specific for the OTCA cycle are either absent or down-regulated during phototrophic growth, implying that the OTCA cycle is not complete, and CO2 is required for the RTCA cycle to produce metabolites in the TCA cycle. Moreover, CO2 is essential for assimilating acetate and pyruvate through the CO2-anaplerotic pathway and pyruvate synthesis from acetyl-CoA. 相似文献
10.
The growth, physiology, and ultrastructure of the marine, unicellular, diazotrophic cyanobacterium, Cyanothece sp. strain ATCC 51142, was examined under mixotrophic and chemoheterotrophic conditions. Several organic substrates were tested for the capacity to support heterotrophic growth. Glycerol was the only substrate capable of enhancing mixotrophic growth in the light and supporting chemoheterotrophic growth in the dark. Dextrose enhanced mixotrophic growth but could not support chemoheterotrophic growth. Chemoheterotrophic cultures in continuous darkness grew faster and to higher densities than photoautotrophic cultures, thus demonstrating the great respiratory capacity of this cyanobacterial strain. Only small differences in the pigment content and ultrastructure of the heterotrophic strains were observed in comparison to photoautotrophic control strains. The chemoheterotrophic strain grown in continuous darkness and the mixotrophic strain grown in light/dark cycles exhibited daily metabolic oscillations in N2 fixation and glycogen accumulation similar to those manifested in photoautotrophic cultures grown in light/dark cycles or continuous light. This “temporal separation” helps protect O2-sensitive N2 fixation from photosynthetic O2 evolution. The rationale for cyclic glycogen accumulation in cultures with an ample source of organic carbon substrate is unclear, but the observation of similar daily rhythmicities in cultures grown in light/dark cycles, continuous light, and continuous dark suggests an underlying circadian mechanism. 相似文献
11.
Two Systems for Concentrating CO(2) and Bicarbonate during Photosynthesis by Scenedesmus 总被引:5,自引:3,他引:2
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Scenedesmus cells grown on high CO2, when adapted to air levels of CO2 for 4 to 6 hours in the light, formed two concentrating processes for dissolved inorganic carbon: one for utilizing CO2 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 O2 evolution or by accumulation of dissolved inorganic carbon inside the cells. The CO2 pump with K0.5 for O2 evolution of less than 5 micromolar CO2 was similar to that previously studied with other green algae such as Chlamydomonas and was accompanied by plasmalemma carbonic anhydrase formation. The HCO3− concentrating process between pH 8 to 10 lowered the K0.5 (DIC) from 7300 micromolar HCO3− in high CO2 grown Scenedesmus to 10 micromolar in air-adapted cells. The HCO3− pump was inhibited by vanadate (Ki of 150 micromolar), as if it involved an ATPase linked HCO3− transporter. The CO2 pump was formed on low CO2 by high-CO2 grown cells in growth medium within 4 to 6 hours in the light. The alkaline HCO3− pump was partially activated on low CO2 within 2 hours in the light or after 8 hours in the dark. Full activation of the HCO3− pump at pH 9 had requirements similar to the activation of the CO2 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 CO2-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 CO2 pump and in some algae an additional vanadate-sensitive plasmalemma HCO3− transporter for a HCO3− pump. 相似文献
12.
The effect of atmospheric carbon dioxide concentrations on the performance of the mangrove Avicennia germinans over a range of salinities
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Ruth Reef Klaus Winter Jorge Morales Maria Fernanda Adame Dana L. Reef Catherine E. Lovelock 《Physiologia plantarum》2015,154(3):358-368
By increasing water use efficiency and carbon assimilation, increasing atmospheric CO2 concentrations could potentially improve plant productivity and growth at high salinities. To assess the effect of elevated CO2 on the salinity response of a woody halophyte, we grew seedlings of the mangrove Avicennia germinans under a combination of five salinity treatments [from 5 to 65 parts per thousand (ppt)] and three CO2 concentrations (280, 400 and 800 ppm). We measured survivorship, growth rate, photosynthetic gas exchange, root architecture and foliar nutrient and ion concentrations. The salinity optima for growth shifted higher with increasing concentrations of CO2, from 0 ppt at 280 ppm to 35 ppt at 800 ppm. At optimal salinity conditions, carbon assimilation rates were significantly higher under elevated CO2 concentrations. However, at salinities above the salinity optima, salinity had an expected negative effect on mangrove growth and carbon assimilation, which was not alleviated by elevated CO2, despite a significant improvement in photosynthetic water use efficiency. This is likely due to non‐stomatal limitations to growth at high salinities, as indicated by our measurements of foliar ion concentrations that show a displacement of K+ by Na+ at elevated salinities that is not affected by CO2. The observed shift in the optimal salinity for growth with increasing CO2 concentrations changes the fundamental niche of this species and could have significant effects on future mangrove distribution patterns and interspecific interactions. 相似文献
13.
Comparison of unitrophic and mixotrophic substrate metabolism by acetate-adapted strain of Methanosarcina barkeri 总被引:22,自引:12,他引:10
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We examined the unitrophic metabolism of acetate and methanol individually and the mixotrophic utilization of these compounds by using detailed 14C-labeled tracer studies in a strain of Methanosarcina barkeri adapted to grow on acetate as the sole carbon and energy source. The substrate consumption rate and methane production rate were significantly lower on acetate alone than during the unitrophic or mixotrophic metabolism of methanol. Cell yields (in grams per mole of substrate) were identical during exponential growth on acetate and exponential growth on methanol. During unitrophic metabolism of acetate, the methyl moiety accounted for the majority of the CH4 produced, but 14% of the CO2 generated originated from the methyl moiety. This correlated with the concurrent reduction of equivalent amounts of the C-1 of acetate to CH4. 14CH4 was also produced from added 14CO2, although to a lesser extent than from reduction of the C-1 of acetate. During mixotrophic metabolism, methanol and acetate were catabolized simultaneously. The rates of 14CH4 and 14CO2 generation from [2-14C]acetate were logarithmic and higher in mixotrophic than in unitrophic cultures at substrate concentrations of 50 mM. A comparison of the oxidoreductase activities in cell extracts of the acetate-adapted strain grown on acetate and of strain MS grown on methanol or on H2 plus CO2 indicated that the pyruvate, α-ketoglutarate, and isocitrate dehydrogenase activities remained constant, whereas the CO dehydrogenase activity was significantly higher (5,000 nmol/min per mg of protein) in the acetate-adapted strain. These results suggested that a significant intramolecular redox pathway is possible for the generation of CH4 from acetate, that energy metabolism from acetate by M. barkeri is not catabolite repressed by methanol, and that the acetate-adapted strain is a metabolic mutant with derepressed CO dehydrogenase activity. 相似文献
14.
Capacity of chromatiaceae for chemotrophic growth. Specific respiration rates of Thiocystis violacea and Chromatium vinosum 总被引:2,自引:0,他引:2
The capacity for chemoautotrophic, mixotrophic and organotrophic growth in the dark was tested with 45 strains of 17 species (11 genera) of the Chromatiaceae. The auxanographic deep agar shake culture method was used; the gas phase contained 5% O2 and 1% CO2 in N2. All strains tested of Chromatium vinosum, C. minus, C. violascens, C. gracile, Thiocystis violacea, Amoebobacter roseus, Thiocapsa roseopersicina gave positive growth responses under chemoautotrophic and mixotrophic conditions (extra carbon source acetate); one strain of Thiocapsa roseopersicina grew also organotrophically on acetate alone. No growth was obtained with the remaining 17 strains of ten species. None of the five type species (three genera) of the Chlorobiaceae grew under chemotrophic conditions. With Thiocystis violacea 2311 a growth yield of 11.3g dry weight per mol thiosulfate consumed was obtained under chemoautotrophic conditions; under mixotrophic conditions with acetate the yield increased to 69g dry weight per mol thiosulfate consumed. With Thiocystis violacea 2311 maximal specific respiration rates were obtained with thiosulfate as electron donor irrespective of the presence or absence of sulfur globules in the cells; organic substrates served as carbon sources only and did not support respiration. With Chromatium vinosum D utilization of thiosulfate was not constitutive; maximal respiration rates on thiosulfate were obtained only with thiosulfate grown cells containing sulfur globules. Respiration rates were further increased by malate, fumarate or propionate; these substrates also served as sole electron donors for respiration. Acetate and pyruvate were used as carbon sources only. The ecological significance of the chemotrophic metabolism is discussed. 相似文献
15.
A CO2 assay circuit adapted to in vitro culture was designed to investigate CO2 exchanges in test tube-grown Vitis rupestris plantlets. The CO2 concentration of the air in culture tubes was measured by injection of samples in the open circuit. It was observed under the culture conditions used that the CO2 content stabilized during the light phase at 3 times the CO2 compensation point.Measurements of dark respiration under closed circuit conditions at every two-hour interval during the night did not reveal any limiting by lack of the substrate under mixotrophic culture conditions. A mathematical model of the influence of ambient CO2 concentration on net CO2 uptake rates under closed circuit conditions was devised and used to compare net photosynthesis at different lighting levels. Measurement of CO2 evolution into CO2-free air under open circuit conditions revealed a post-illumination burst characteristic of photorespiration which increased with the temperature. 相似文献
16.
Temperature affects the response of heterotrophic bacteria and mixotrophic algae to enhanced concentrations of soil extract 总被引:2,自引:0,他引:2
Norbert Kamjunke 《Hydrobiologia》2010,649(1):379-383
To investigate the consequences of increased temperature and enhanced input of dissolved organic matter (DOM) into lakes for
heterotrophicic bacteria and for mixotrophic algae which use DOM in addition to photosynthesis, the hypotheses were tested
whether (1) both bacteria and mixotrophic algae benefit from increased input of DOM, or (2) increased DOM input enhances bacterial
biomass and thereby decreases algal biomass. Growth experiments in batch cultures, exudation measurements, and competition
experiments in chemostats were performed at two temperature levels. Increased temperature stimulated the autotrophic growth
rate of Chlorella protothecoides. Bacteria and Chlorella increased their heterotrophic growth rates at higher DOM concentration at lower temperature whereas enhanced DOM concentration
hardly stimulated their growth at higher temperature. In chemostats, enhanced input of soil extract increased both bacterial
and algal biomass at lower temperature whereas bacterial biomass increased only slightly and algal biomass decreased at higher
temperature. Thus, the temperature determines the response of microorganisms to enhanced DOM concentration. 相似文献
17.
Quantifying carbon dioxide exchange and understanding the response of key environmental factors in various ecosystems are critical to understanding regional carbon budgets and ecosystem behaviors. For this study, CO2 fluxes were measured in a variety of ecosystems with an eddy covariance observation matrix between June 2012 and September 2012 in the Zhangye oasis area of Northwest China. The results show distinct diurnal variations in the CO2 fluxes in vegetable field, orchard, wetland, and maize cropland. Diurnal variations of CO2 fluxes were not obvious, and their values approached zero in the sandy desert, desert steppe, and Gobi ecosystems. Additionally, daily variations in the Gross Primary Production (GPP), Ecosystem Respiration (Reco) and Net Ecosystem Exchange (NEE) were not obvious in the sandy desert, desert steppe, and Gobi ecosystems. In contrast, the distributions of the GPP, Reco, and NEE show significant daily variations, that are closely related to the development of vegetation in the maize, wetland, orchard, and vegetable field ecosystems. All of the ecosystems are characterized by their carbon absorption during the observation period. The ability to absorb CO2 differed significantly among the tested ecosystems. We also used the Michaelis-Menten equation and exponential curve fitting methods to analyze the impact of Photosynthetically Active Radiation (PAR) on the daytime CO2 flux and impact of air temperature on Reco at night. The results show that PAR is the dominant factor in controlling photosynthesis with limited solar radiation, and daytime CO2 assimilation increases rapidly with PAR. Additionally, the carbon assimilation rate was found to increase slowly with high solar radiation. The light response parameters changed with each growth stage for all of the vegetation types, and higher light response values were observed during months or stages when the plants grew quickly. Light saturation points are different for different species. Nighttime Reco increases exponentially with air temperature. High Q10 values were observed when the vegetation coverage was relatively low, and low Q10 values occurred when the vegetables grew vigorously. 相似文献
18.
Pigment contents and proximate compositions are important traits to evaluate the nutritional value of microalgae. The environmental condition and nutrient availability in the culture medium are hypothesised to regulate algal colour, nutritional composition and production. This study aimed to compare the pigment and proximate compositions in Tisochrysis lutea under phototrophic and mixotrophic conditions in an attempt to improve algal product quality. Algae were grown in the phototrophic and mixotrophic conditions at 50 μmol photons m?2 s?1 for 12 h daily, but 50 mM glycerol was added as a carbon source in the mixotrophic culture. The pigment contents in algae significantly increased in the mixotrophic condition, and the contents of chlorophylls a and c and carotenoids increased nearly 60 % compared with those in the phototrophic condition. The contents of saturated and polyunsaturated fatty acids in algae were significantly higher while the content of monounsaturated fatty acids was significantly lower in the mixotrophic condition than those in the phototrophic condition. Although the contents of protein, lipid and carbohydrate in T. lutea were not different, their overall production was significantly enhanced in the mixotrophic condition compared to the phototrophic condition. This study indicates that mixotrophic culture promotes pigment and proximate production and the change of fatty acid profile in algae depends on the addition of organic carbon to the culture medium. 相似文献
19.
20.
Two Polypeptides in the Inner Chloroplast Envelope of Dunaliella tertiolecta Induced by Low CO(2) 总被引:2,自引:2,他引:0
Unicellular green algae have a mechanism for concentrating dissolved inorganic carbon (DIC) only when grown in low CO2. To find proposed transporter protein(s) for DIC, we isolated intact chloroplasts from Dunaliella tertiolecta cells, separated the chloroplast envelopes by isopyknic centrifugation, and separated their polypeptides by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Two peptides of apparent molecular masses of 45 and 47 kD were constituents of the inner chloroplast envelope only if the cells had been adapted to low CO2 in the light or grown in low CO2. These two low CO2-induced peptides appear to be part of the algal DIC pump. 相似文献