A selenium-induced peroxidation of glutathione in algae

Two unicellular marine algae cultured in media containing sodium selenite were examined for glutathione peroxidase activity. The 400 g supernatant from disrupted cells of both the green alga Dunaliella primolecta and the red alga Porphyridium cruentum were able to enhance both the H₂O₂ and the tert-butyl hydroperoxide dependent oxidation of glutathione. The glutathione peroxidation activity of D. primolecta was reduced only slightly by heating the 400 g supernatant, a 30% decrease in the rate with H₂O₂ and 10% decrease in the rate with t-BuOOH being observed. Heating caused the H₂O₂ dependent activity in P. cruentum to be reduced by only 30%, but the activity with t-BuOOH was reduced by 90%. Freezing decreased the t-BuOOH dependent activity of P. cruentum by 90%, but did not lower the t-BuOOH dependent activity of D. primolecta or the H₂O₂ dependent activity of either alga. It was concluded that the heat and cold stable, glutathione peroxidation was non-enzymatic in nature. A variety of small molecules (ascorbate, Cu(NO₃)₂, selenocystine, dimethyldiselenide and selenomethionine) were shown to be able to enhance the hydroperoxide dependent oxidation of glutathione in the assay system employed in this study. Such compounds could be responsible for the activity observed in algae. The heat and cold labile t-BuOOH reductase activity of P. cruentumwas possibly enzymatic, but was not attributable to the presence of glutathione-S-transferase. Both algae, when cultured in the presence of added selenite, displayed an approximate doubling of the non-enzymatic H₂O₂ and t-BuOOH dependent glutathione oxidase activities. The heat and cold labile t-BuOOH reductase activity of P. cruentum was unaltered when the alga was grown in the presence of added selenite. These observations are consistent with the hypothesis that selenium compounds present in the algae are responsible for the selenium induced glutathione peroxidation.     

The binding of selenium to the lipids of two unicellular marine algae

Axenic cultures of the green algae $\text{Dunaliella}\text{primolecta}$ and red algae $\text{Porphyridium}\text{cruentum}$ were grown in the presence of sublethal quantities of selenite. All purified lipids from both algae were found to contain bound selenium, except for saturated hydrocarbons. Of the lipids which contain selenium, carotenoid pigments contain the greatest concentrations. Lipid-associated selenium is not metabolically incorporated. The selenium is probably non-covalently bound to the lipids.     

Selenium containing amino acids and proteins in marine algae

The unicellular marine algae, Dunaliella primolecta Butcher, Chlorella sp. and Porphyridium cruentum (S.F. Grey) were grown in artificial sea water containing a sublethal concentration of selenite, 10^?2 g Se/1. Both free-and protein-bound seleno-amino acids were identified. The initial steps of selenium incorporation seem to involve the use of the sulfur enzymatic machinery resulting in the replacement of some of the sulfur by selenium in both free amino acids and proteins. At relatively low selenium concentrations, selenium-specific enzymes seem to be in operation.     

The Quantum Yield of Photosynthesis in Porphyridium cruentum, and the Role of Chlorophyll a in the Photosynthesis of Red Algae

Quantum yield measurements were made with the red alga Porphyridium cruentum, cultured so as to give different proportions of chlorophyll and phycobilins. Totally absorbing suspensions were used so that there was no uncertainty in the amount of energy absorbed. These measurements have shown that chlorophyll, in this alga, has a photosynthetic efficiency as high as in other algal groups, and higher than the phycobilins—at least at wave lengths shorter than about 650 mµ. Wave lengths longer than this are beyond the range of maximum efficiency of chlorophyll. Under specified conditions of temperature and supplementary light full efficiency may be extended to longer wave lengths. The results of these measurements have made it unnecessary to suppose that in red algae chlorophyll plays a minor role while the phycobilins are the photosynthetic sensitizers of primary importance.     

BIOGENESIS OF CHLOROPLAST MEMBRANES : IV. Lipid and Pigment Changes during Synthesis of Chloroplast Membranes in a Mutant of Chlamydomonas reinhardi y-1

The glycolipid, phospholipid, pigment, and fatty acid content in whole y-1 cells during the greening process have been investigated. The time course of their changes indicates that phosphatidyl glycerol and glycolipids are the main lipids synthesized specifically during illumination of dark-grown cells, concomitant with an increase in the polyunsaturated C18:2 and C18:3 fatty acids. The pigment complex of light-grown cells consists mainly of chlorophylls a and b, lutein, β-carotene, violaxanthin, and neoxanthin. During the greening process, chlorophylls a and b are synthesized in constant proportions (ratio a/b equals 2.6), β-carotene and violaxanthin do not change significantly, and lutein and neoxanthin increase. The molar ratios of the different lipids and pigment to total chlorophyll during greening has been calculated. It was found that during the initial phase of greening when chlorophyll is synthesized at increasing rates, the molar ratios of various lipids and pigments to chlorophyll decrease and tend to become constant when chlorophyll and membrane synthesis proceed at constant rates. The implication of these findings with respect to the concept of membrane assembly through a spontaneous single step process is discussed     

Effects of nitrogen source and irradiance on <Emphasis Type="Italic">Porphyridium cruentum</Emphasis>

We determined the effects of two nitrogen sources (ammonium and nitrate) and two irradiance levels (50 and 200 μmol photons m^?2 s^?1) on the growth rate, cell size, proximate composition, pigment content, and photosynthesis of the unicellular red alga, Porphyridium cruentum. Irradiance significantly affects growth rate, as well as carbohydrate, protein, and phycoerythrin content. Nitrogen form significantly affects cell size, total dry weight, organic dry weight, ash content, carotene content, phycocyanin content, allophycocyanin content, maximum relative electron transport rate (rETRm), and photosynthetic efficiency (α). However, the irradiance and nitrogen source had significantly interaction with the content of lipids and chlorophyll a content, relative electron transport rate (rETR), and irradiance of saturation (I_k). These findings demonstrate that irradiance and nitrogen source influence the metabolism of P. cruentum and that the combination of these two variables induces the production of chemical products for biotechnological, aquaculture, and nutraceutical industry.     

Formation of biomass,total protein,chlorophylls, lipids and fatty acids in green and blue-green algae during one growth phase.

Batch cultures (8–32 l.) of Chlorella vulgaris and Scenedesmus obliquus and of Anacystis nidulans and Microcystis aeruginosa were grown in media containing 0.001 % KNO₃ and at several stages in growth sampled for biomass, total protein, chlorophylls, lipids and fatty acids. With increasing time and decreasing nitrogen concentrations, the biomass of all of the algae increased, whereas the total protein and chlorophyll content dropped. Green and blue-green algae, however, behaved differently in their lipid metabolism. In the green algae the total lipid and fatty acid content as well as the composition of these compounds changed considerably during one growth phase and was dependent on the nitrogen concentration in the media at any given day of growth. More specifically, during the initial stages of growth the green algae produced larger amounts of polar lipids and polyunsaturated C₁₆ and C₁₈ fatty acids. Towards the end of growth, however, these patterns changed in that the main lipids of the green algae were neutral with mainly saturated fatty acids (mostly 18:1 and 16:0). Such changes did not occur in the blue-green algae. These differences between prokaryotic and eukaryotic algae can possibly be explained by the ‘endosymbiont theory’.     

Biomass production,total protein,chlorophylls, lipids and fatty acids of freshwater green and blue-green algae under different nitrogen regimes

Two green algae (Chlorella vulgaris and Scenedesmus obliquus) and four blue-green algae (Anacystis nidulans, Microcystis aeruginosa, Oscillatoria rubescens and Spirulina platensis) were grown in 81 batch cultures at different nitrogen levels. In all the algae increasing N levels led to an increase in the biomass (from 8 to 450 mg/l), in protein content (from 8 to 54 %) and in chlorophyll. At low N levels, the green algae contained a high percentage of total lipids (45 % of the biomass). More than 70 % of these were neutral lipids such as triacylglycerols (containing mainly 16:0 and 18:1 fatty acids) and trace amounts of hydrocarbons. At high N levels, the percentage of total lipids dropped to about 20 % of the dry weight. In the latter case the predominant lipids were polar lipids containing polyunsaturated C₁₆ and C₁₈ fatty acids. The blue-green algae, however, did not show any significant changes in their fatty acid and lipid compositions, when the nitrogen concentrations in the nutrient medium were varied. Thus the green but not the blue-green algae can be manipulated in mass cultures to yield a biomass with desired fatty acid and lipid compositions. The data may indicate a hitherto unrecognized distinction between prokaryotic and eukaryotic organisms.     

Behaviour of a glycosphingolipid with unsaturated fatty acid in phosphatidylcholine bilayers

N-(Oleoyl)galactosylceramide with perdeuterated acyl chain was prepared by partial synthesis, and studied by wide line ²H-NMR in phospholipid liposomes. Spectra were obtained for low glycolipid concentrations in bilayers of dimyristoyl-, distearoyl-, and 1-palmitoyl-2-oleoylphosphatidylcholines. In an attempt to isolate the effects of glycosphingolipid fatty acid cis unsaturation on glycolipid behaviour in membranes, spectral findings related to the above species were compared to literature NMR data for pure 1-palmitoyl-2-oleoylphosphatidylcholine bilayers in which the oleoyl chain of the phospholipid had been deuterated, and to analogously deuterated glycerol based lipids in Acholeplasma laidlawii membranes. The results for N-(oleoyl-d₃₃)galactosylceramide proved to be qualitatively and quantitatively very similar to published data dealing with glycerol based lipids at comparable temperatures. In addition, the results were strikingly similar for glycolipids dispersed in saturated and unsaturated phospholipid host matrices. It would appear that the primary effects of cis 9,10 fatty acid unsaturation in glycosphingolipids (at low concentration in fluid phospholipid membranes) are the same as those of fatty acid cis unsaturation in glycerolipids. It further appears that the overall dynamic behaviour of N-(oleoyl)galactosylceramide in fluid phospholipid membranes is very similar to that of glycerolipids with comparable acyl chains.     

Action Spectra for Photosystems I and II in Formaldehyde Fixed Algae

Action spectra were obtained for photosystems I and II in chemically fixed algal cells and for photosystem I in unfixed lysozyme treated cells. Untreated algal cells yielded neither of the 2 light reactions with the reaction mixtures used. The action spectra for photosystem I in the blue-green alga Anacystis nidulans and red alga Porphyridium cruentum follow the absorption spectrum of chlorophyll a with a small peak in the region of the accessory pigments. In the green alga Chlorella pyrenoidosa the photosystem I action spectrum follows the absorption spectrum of chlorophyll a. Photosystem II action spectra in A. nidulans and P. cruentum follow the absorption spectra of the accessory pigments while that in C. pyrenoidosa is shifted slightly toward the blue spectral region. These results provide additional evidence that formaldehyde fixed cells are valid models for studying the light reactions of photosynthesis.     

Selenium as Inducer of Glutathione Peroxidase in low-CO(2)-Grown Chlamydomonas reinhardtii

Culture of the green alga Chlamydomonas reinhardtii in the medium containing sodium selenite caused the activity of ascorbate peroxidase to disappear and the appearance of glutathione peroxidase. The induced maximum activity of glutathione peroxidase reached 350 micromole (milligram chlorophyll hour)⁻¹ under assay conditions used. The enzymic properties of the selenite-induced glutathione peroxidase closely resembled those of animal glutathione peroxidase that contains selenium.     

Lipids and lipid metabolism in the brown alga, Fucus serratus

The lipids of the brown alga Fucus serratus were isolated, identified and quantified. The major acyl lipids were the three glycosylglycerides, diacylgalactosylglycerol, diacyldigalactosylglycerol and diacylsulphoquinovosylglycerol. These represent over 70% of the total acyl lipids. The fatty acid compositions of the major lipids were examined and most showed rather distinctive fatty acid contents. For example, diacylgalactosylglycerol was enriched in n-3 polyunsaturated fatty acids while phosphatidylcholine and phosphatidylethanolamine had very high levels of arachidonate. Phosphatidylglycerol contained the unusual trans-Δ3-hexadecenoic acid. The labelling of lipids and fatty acids from [¹⁴C]acetate was examined and the distribution of label between individual components as a function of the incubation period and in algae collected at different times of the year is reported. Algae collected in the winter incorporated much more radioactivity into non-esterified fatty acids when compared to algae collected in the summer. All algae could label myristate, palmitate, stearate and oleate at high rates. Longer incubation times allowed the labelling of polyunsaturated fatty acids such as linoleic acid.     

Stoichiometry of Photosystem I, Photosystem II, and Phycobilisomes in the Red Alga Porphyridium cruentum as a Function of Growth Irradiance

Cells of the red alga Porphyridium cruentum (ATCC 50161) exposed to increasing growth irradiance exhibited up to a three-fold reduction in photosystems I and II (PSI and PSII) and phycobilisomes but little change in the relative numbers of these components. Batch cultures of P. cruentum were grown under four photon flux densities of continuous white light; 6 (low light, LL), 35 (medium light, ML), 180 (high light, HL), and 280 (very high light, VHL) microeinsteins per square meter per second and sampled in the exponential phase of growth. Ratios of PSII to PSI ranged between 0.43 and 0.54. About three PSII centers per phycobilisome were found, regardless of growth irradiance. The phycoerythrin content of phycobilisomes decreased by about 25% for HL and VHL compared to LL and ML cultures. The unit sizes of PSI (chlorophyll/P₇₀₀) and PSII (chlorophyll/Q_A) decreased by about 20% with increase in photon flux density from 6 to 280 microeinsteins per square meter per second. A threefold reduction in cell content of chlorophyll at the higher photon flux densities was accompanied by a twofold reduction in β-carotene, and a drastic reduction in thylakoid membrane area. Cell content of zeaxanthin, the major carotenoid in P. cruentum, did not vary with growth irradiance, suggesting a role other than light-harvesting. HL cultures had a growth rate twice that of ML, eight times that of LL, and slightly greater than that of VHL cultures. Cell volume increased threefold from LL to VHL, but volume of the single chloroplast did not change. From this study it is evident that a relatively fixed stoichiometry of PSI, PSII, and phycobilisomes is maintained in the photosynthetic apparatus of this red alga over a wide range of growth irradiance.     

Seasonal variation in lipid and fatty acid composition of ice algae from the Barents Sea

The fatty acid compositions of neutral lipid, glycolipid and phospholipid fractions from ice algae sampled from the Barents Sea in spring and autumn were examined for seasonal differences. The ice-algal assemblages were dominated by diatoms. In spring, Nitzschia frigida was the most common species whereas resting stages of Thalassiosira bioculata and Actinocyclus cf curvatulus predominated in autumn. With the exception of one spring sample, neutral lipids predominated over glycolipids and phospholipids in all algal samples. The lipid fractions displayed characteristic fatty acid compositions. In the spring samples the major fatty acids of the neutral lipid fraction were 16:0, 16:1(n-7) and 20:5(n-3) whilst the glycolipid fraction was characterised by higher levels of 20:5(n-3) and C16 polyunsaturated fatty acids, particularly 16:4(n-1). Phospholipids contained higher levels of 22:6(n-3) than the other two lipid fractions although 20:5(n-3) was still the major polyunsaturated fatty acid. In the autumn samples, the neutral lipid fraction contained higher proportions of saturated fatty acids and 16:1(n-7) than the two polar lipid fractions and 22:6(n-3) was most abundant in phospholipids. As with the spring samples, 20:5(n-3) was the major polyunsaturated fatty acid in all lipid fractions of the autumn algae. Overall, the fatty acid compositions of the lipid fractions from spring and autumn algal samples were similar and are consistent with diatoms being the predominant group in the ice algae studied. The high level of neutral lipids observed in both spring and autumn samples suggests that the production of neutral lipids is characteristic of ice algae regardless of season. Nevertheless, some species-specific differences in lipid production may exist since the neutral lipid content of autumn samples containing mainly A. curvatulus was substantially higher than those in which T. bioculata predominated. Received: 26 September 1997 / Accepted: 12 January 1998     

Computer Solutions for Photosynthesis Rates from a Two Pigment Model

A kinetic model for a two pigment mechanism of photosynthesis based on observations made on the red alga Porphyridium cruentum is developed. The model supposes that different products are formed by chlorophyll and phycobilin pigments and that these products react to produce oxygen. The product of the chlorophyll reaction is also rapidly utilized for O₂ consumption both in light and in the dark. Rate equations based on the model reactions were derived and put into an analog computer. The effect of varying parameters on the time course curves for oxygen exchange resulting from the model was studied. Appropriate selection of parameters yielded computer curves which resembled fairly closely the oxygen exchange curves obtained using Porphyridium. The model showed the Emerson enhancement effect, chromatic transients, “respiratory stimulation,” and other effects observed with live algae.     

Changes of lipid composition in non-cultured and cultured porcine embryos

The objective of the present study was to evaluate the lipid composition of cultured and non-cultured pig embryos during cleavage using histochemical methods. The authors studied pig zygotes as well as 2-to 4-cell embryos, morulae, and blastocysts that were either non-cultured or cultured in NCSU-23 medium. To detect different types of lipids, the authors used the Churukian method with Oil red O, the Sudan black B method, the Cain method with Nile blue sulfate, and the modified osmium tetroxide-ethanol treatment. In the zygotic lipid droplets, diverse classes of unsaturated and saturated lipids were found, with particularly high levels of unsaturated hydrophobic lipids, mainly triglycerides and other esters, free fatty acids, and phospholipids. In the zygotic cytoplasm, the authors observed high levels of fatty acids and phospholipids. The total lipid content remained constant up to the morula stage, decreasing later at the blastocyst stage, but the overall amount of unsaturated lipids declined earlier, at the 2-to 4-cell stage. The amount of free fatty acids and phospholipids decreased during cleavage in both non-cultured and cultured porcine embryos. The main differences between the non-cultured and cultured embryos were the more pronounced reduction in the amount of unsaturated hydrophobic lipids in droplets and the cytoplasmic free fatty acids observed in the cultured morula and the lower content of phospholipids in the cytoplasm of the cultured 2-to 4-cell embryos relative to the non-cultured embryos. The decrease in the unsaturated lipid, free fatty acid, and phospholipid content during in vivo development and the differences in the amount of these types of lipids between developmentally matched cultured and non-cultured pig embryos correlate well with modifications of lipid and carbohydrate metabolism.     

The effect of rapamycin on biodiesel-producing protist Euglena gracilis

Rapamycin induces autophagy with lipid remodeling in yeast and mammalian cells. To investigate the lipid biosynthesis of Euglena gracilis, rapamycin was supplemented in comparison with two model algae, Chlamydomonas reinhardtii and Cyanidioschyzon merolae. In Euglena, rapamycin induced the reduction of chlorophylls and the accumulation of neutral lipids without deterring its cell proliferation. Its lipidomic profile revealed that the fatty acid composition did not alter by supplementing rapamycin. In Chlamydomonas, however, rapamycin induced serious growth inhibition as reported elsewhere. With a lower concentration of rapamycin, the alga accumulated neutral lipids without reducing chlorophylls. In Cyanidioschyzon, rapamycin did not increase neutral lipids but reduced its chlorophyll content. We also tested fatty acid elongase inhibitors such as pyroxasulfone or flufenacet in Euglena with no significant change in its neutral lipid contents. In summary, controlled supplementation of rapamycin can increase the yield of neutral lipids while the scheme is not always applicable for other algal species.     

Lipid characterization of red alga Rhodymenia pseudopalmata (Rhodymeniales,Rhodophyta)

Rhodymenia pseudopalmata is a red alga that grows at the Caribbean coast of the Yucatan Peninsula and has been proven successful in cultivation. In this study we present the lipid composition of R. pseudopalmata collected from wild populations during three different seasons of 2013. Cultured material was also analyzed and compared in order to evaluate its value as feedstock for biotechnological uses. Thin layer chromatography, ¹ H and ¹³ C NMR spectroscopy and gas chromatography‐mass spectrometry were used to assess variations in their lipid composition. Our results showed that the dominant lipid classes were phospholipids both in wild and cultured materials. The phospholipids phosphatidylcholine and phosphatidylglycerol and the glycolipid monogalactosyldiacylglycerol were present in both wild and cultured R. pseudopalmata, whereas the phospholipid lysophosphatidylcholine was only found in wild material. Fatty acids (FAs) showed a high monounsaturated FAs (MUFAs) content with oleic acid (C18:1ω9) as the dominant compound (78 and 94% of the MUFAs for wild and culture materials, respectively). Saturated FAs (SFAs) represented approximately 90% of the total fatty acid content, with palmitic acid (C16:0) reaching approximately 83% of the SFA content. Rhodymenia pseudopalmata was low in polyunsaturated FAs when compared to other red algae. Other compounds such as 1‐heptadecene, 1‐hexadecene, 15‐heptadecenal, 3‐eicosene 6,10,14‐trimethyl‐2‐pentadecanone, phytol, and heptadecane were also found. Lipid composition differences between the wild and cultured algae suggest that light and nutrients can be manipulated to modify lipid composition. Based on its lipid composition and cultivation feasibility, R. pseudopalmata could be a potential source for nutraceuticals and biofuels production.     

Low molecular weight carbohydrates in Cyanidium caldarium and some related algae

Floridoside (2-O-glycerol-α-d-galactopyranoside) and a small amount of iso-floridoside (1-O-glycerol-α-d- galactopyranoside) were found in Cyanidium caldarium. Floridoside was also found in the red algae Porphyridium cruentum and Porphyra yezoensis, although in the latter iso-floridoside was the main component. Sucrose and glucose were found in the green algae Chlorella pyrenoidosa and Scenedesmus obliquus, and also in a blue-green alga, Anacystis nidulans. Another blue-green alga, Phormidium foveolarum, contains mostly trehalose. From these results and from morphological considerations, it is suggested that Cyanidium caldarium belongs to the primitive Rhodophyta.     

Photosynthesis of Lipids from CO(2) in Spinacia oleracea

Young expanding spinach leaves exposed to ¹⁴CO₂ under physiological conditions for up to 20 minutes assimilated CO₂ into lipids at a mean rate of 7.6 micromoles per milligram chlorophyll per hour following a lag period of 5 minutes. Label entered into all parts of the lipid molecule and only 28% of the ¹⁴C fixed into lipids was found in the fatty acid moieties, i.e. fatty acids were synthesized from CO₂in vivo at a mean rate of 2.1 micromoles per milligram chlorophyll per hour. Intact spinach chloroplasts isolated from these leaves incorporated H¹⁴CO₃ into fatty acids at a maximal rate of 0.6 micromole per milligram chlorophyll per hour, but were unable to synthesize either the polar moieties of their lipids or polyunsaturated fatty acids. Since isolated chloroplasts will only synthesize fatty acids at rates similar to the one obtained with intact leaves in vivo if acetate is used as a precursor, it is suggested that acetate derived from leaf mitochondria is the physiological fatty acid precursor.