Effects of cement dust on volatile oil constituents and antioxidative metabolism of Aleppo pine (Pinus halepensis) needles

The effects of cement dust on the chemical composition of essential oil, lipid peroxidation and antioxidant enzyme activities of Aleppo pine (P. halepensis) needles were studied. Cement dust resulted in a significant decrease in the yield of essential oil with the effect being more pronounced in the close vicinity of the cement factory. A concomitant decrease in all components of the oil was observed and ??-2-carene, trans-carveol, trans-carvyl acetate, ??-terpinyl acetate, ??-copaene, (E,E)-??-farnesene, ??-calacorene, ??-cadinene, spathulenol, humulene oxide II, 8-epi-??-eudesmol, ?-muurolol, cubenol and ethyl hexadecanoate have been proposed as biological indicators of cement dust. Moreover, a redirection of the secondary metabolism toward the biosynthesis of monoterpenes has been evidenced. Malondialdehydes (MDA), a decomposition product of polyunsaturated fatty acids, often considered as a suitable biomarker for lipid peroxidation was induced in the needles exposed to cement dust. Similarly, a remarkable induction of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) activities was noticed. The positive relationships were observed among activities of antioxidant enzymes, and between MDA content and activities of antioxidant enzymes, indicating the cooperative action of these antioxidant enzymes to cope with the oxidative stress induced by cement dust. The results obtained indicate that P. halepensis needles are useful bio-monitors of cement dust pollution.     

Lipid and protein composition and thermotropic lipid phase transitions in fatty acid-homogeneous membranes of Acholeplasma laidlawii B

The membrane composition and lipid physical properties have been systematically investigated as a function of fatty acid composition for a series of Acholeplasma laidlawii B membrane preparations made homogeneous in various fatty acids by growing cells on single fatty acids and avidin, a potent fatty acid synthetic inhibitor. The membrane protein molecular weight distribution is essentially constant as a function of fatty acid composition, but the lipid/protein ratio varies over a 2-fold range when different fatty acid growth supplements are used. The membrane lipid head-group composition varies somewhat under these conditions, particularly in the ratio of the two major neutral glycolipids. Differential thermal analytical investigations of the thermotropic phase transitions of various combinations of membrane components suggest that these compositional changes are unlikely to result in qualitative changes in the nature of lipid-protein or lipid-lipid interactions, although lesser changes of a quantitative nature probably do occur. The total lipids of membranes made homogeneous in their lipid fatty acyl chain composition exhibit sharper than normal gel-to-liquid-crystalline phase transitions of which midpoint temperatures correlate very well with the phase transition temperatures of synthetic hydrated phosphatidylcholines with like acyl chains. Our results indicate that using avidin and suitable fatty acids to grow A. laidlawii B, it is possible to manipulate the position and the sharpness of the membrane lipid phase transition widely and independently without causing major modifications in other aspects of the membrane composition. This fact makes the fatty acid-homogeneous A. laidlawii B membrane a very useful biological membrane preparation in which to study lipid physical properties and their functional consequences.     

Fourier transform infrared spectroscopic identification of gel phase domains in reconstituted phosphilipid vesicles containing Ca2+-ATPase

Ca²⁺-ATPase from rabbit sarcoplasmic reticulum has been isolated, purified, and reconstituted into lipid environments containing as primary components 1,2-dielaidoylphosphatidylcholine (DEPC) and acyl-chain perdeuterated 1,2-dimyristoylphosphatidylcholine (DMPC-d₅₄). Differential scanning calorimetry (DSC) has been used to elucidate the phase behavior of this lipid pair while Fourier transform infrared spectroscopy (FT-IR) has been used to monitor the state of each lipid component in the presence of protein. The lipid mixture shows gel state miscibility over at least most of the composition range, a result in good accord with Van Dijck et al. (Biochim. Biophys. Acta 470, 58–69 (1977)), for the binary mixture with proteated DMPC. Acyl chain perdeuteration thus does not greatly alter the miscibility properties of the lipid pair. Reconstitution of Ca²⁺-ATPase with this lipid pair proceeds with moderate efficiency. Up to 80% of the endogenous lipid can be replaced depending on the lipid composition. Unusual composition-dependent protein-induced effects on lipid melting properties are noticed. At low levels of DMPC-d₅₄, both the DEPC and DMPC-d₅₄ components have their melting processes broadened and shifted to lower temperatures, compared with binary lipid mixtures of the same composition. This suggests that protein perturbs both lipids in similar fashion. At high levels of DMPC-d₅₄, the DEPC component exhibits a highly cooperative melting process at temperatures close to that for pure DEPC. This strongly indicates that domains of DEPC are present (at least at low temperatures) in the bilayer, and that Ca²⁺-ATPase is excluded from these domains. The protein thus exhibits preferential interaction with the DMPC-d₅₄ component. This work demonstrates the utility of FT-IR for identification of the molecular origin of particular domains in reasonably complex lipid mixtures. The relevance of this work to native membrane systems where lipid domains have been observed by several groups is discussed.     

Effects of reduced salinity on the biochemical composition (lipid, protein) of zoea 1 decapod crustacean larvae

Effects of reduced salinities on dry weight (DW) and biochemical composition (total lipid and protein contents) of zoea 1 larvae were evaluated in four decapod crustacean species differing in salinity tolerance (Cancer pagurus, Homarus gammarus, Carcinus maenas, Chasmagnathus granulata). The larvae were exposed to two different reduced salinities (15‰ and 25‰ in C. granulata, 20‰ and 25‰ in the other species) for a long (ca. 50% of the zoea 1 moulting cycle) or a short period (16 h, starting at ca. 40% of the moulting cycle), while a control group was continually maintained in seawater (32‰).In general, the increments in dry weight, lipid and protein content were lower at the reduced salinities than in the control groups. In the zoea 1 of H. gammarus (stenohaline) and C. pagurus (most probably also stenohaline), the lipid and protein contents varied greatly among treatments: larvae exposed to low salinities exhibited very low lipid and protein contents at the end of the experiments compared to the controls. In some cases, there were negative growth increments, i.e. the larvae had, after the experimental exposure, lower lipid and protein contents than at the beginning of the experiment. C. maenas (moderately euryhaline) showed a lower variation in protein and lipid content than the above species. The zoea 1 of C. granulata (fairly euryhaline) showed the lowest variability in dry weight, protein and lipid content. Since salinity tolerance (eury- v. stenohalinity) is associated with the osmoregulatory capacity, our results suggest a relationship between the capability for osmoregulation and the degree of change in the biochemical composition of larvae exposed to variable salinities.Besides larval growth of these species should be affected by natural reductions of salinity occurring in coastal areas at different time scales. These effects may be potentially important for population dynamics since they should influence the number and quality of larvae reaching metamorphosis.     

A Novel Controlled-Release System for Antibacterial Enzyme Lysostaphin Delivery Using Hydroxyapatite/Chitosan Composite Bone Cement

In this work, a lysostaphin-loaded, control-released, self-setting and injectable porous bone cement with efficient protein delivery was prepared by a novel setting method using hydroxyapatite/chitosan (HA/CS) composite scaffold. The cement samples were made through cementitious reactions by mixing solid powder, a mixture of HA/CS composite particles, lysostaphin, Ca(OH)₂, CaCO₃ and NaHCO₃, with setting liquid containing citric acid, acetic acid, NaH₂PO₄, CaCl₂ and poloxamer. The setting parameters of the cement samples were determined. The results showed that the final setting time was 96.6±5.2 min and the pH value increased from approximately 6.2 to nearly 10 during the setting process and the porosity was 34% at the end. And the microstructure and composition were detected by scanning electron microscopy (SEM), x-ray diffraction and Fourier transform-infrared spectroscopy. For the release behavior of lysostaphin loaded in the cement sample, the in vitro cement extract experiment indicated that about 94.2±10.9% of the loaded protein was released before day 8 and the in vivo Qdot 625 fluorescence tracking experiment showed that the loaded protein released slower than the free one. Then the biocompatibility of the cement samples was evaluated using the methylthiazol tetrazolium assay, SEM and hematoxylin-eosin staining, which suggested good biocompatibility of cement samples with MC 3T3-E1 cells and subcutaneous tissues of mice. Finally the antibacterial activity assay indicated that the loaded lysostaphin had good release ability and strong antibacterial enzymatic activity against methicillin-resistant Staphylococcus aureus. Collectively, all the results suggested that the lysostaphin-loaded self-setting injectable porous bone cement released the protein in a controlled and effective way and the protein activity was well retained during the setting and releasing process. Thus this bone cement can be potentially applied as a combination of artificial bone substitute and controlled-release system for delivery of lysostaphin to treat bone defects and infections.     

Studies in the biochemistry of cirripede eggs. V. Changes in the general biochemical composition during development of Chthamalus stellatus (Poli)

The biochemical composition of the eggs of Chthamulus stellatus (Poli) during their development has been investigated. The eggs are incubated within the mantle cavity of the adult but no substrates are contributed by the latter. Carbohydrates, protein, and lipid are all utilized. In contrast to two cold-water species, Balanus balanoides and B. balanus perviously investigated lipid rather than protein is consumed during the early stages. Possible explanations for this are considered.     

Assessment of biochemical composition and energy reserves in larvae of the scallop Patinopecten yessoensis

Larvae of Patinopecten yessoensis increased in dry weight from ≈ 150 to 1000 ng per larva during the larval development period of 28 days. Microanalytical procedures were developed to determine the lipid, protein, carbohydrate, and ash contents from which energy levels and condition indices were derived. Replicate analyses of two sizes of P. yessoensis larvae gave coefficients of variation at or <5% for the biochemical analyses. Lipid and protein were identified as major components, and carbohydrate as a minor component providing 56.6,37.6, and 5.8 %, respectively, of the calculated energy content. The energy content of the eggs of P. yessoensis was 2.4 and 3.1 times higher than the larvae of P. yessoensis and Crassostrea gigas, respectively, derived from 20.6% lipid, 54.6% protein, and 7.2% carbohydrate. The carbohydrate in the eggs was stored principally as a glucan, considered to be glycogen, which was absent in the developing larvae. Changes in biochemical composition of P. yessoensis larvae during development showed that lipid and protein reserves were lost for ≈ 20 days and then lipid accumulated as the larvae reached premetamorphic condition.     

Lipid Clustering Correlates with Membrane Curvature as Revealed by Molecular Simulations of Complex Lipid Bilayers

Cell membranes are complex multicomponent systems, which are highly heterogeneous in the lipid distribution and composition. To date, most molecular simulations have focussed on relatively simple lipid compositions, helping to inform our understanding of in vitro experimental studies. Here we describe on simulations of complex asymmetric plasma membrane model, which contains seven different lipids species including the glycolipid GM3 in the outer leaflet and the anionic lipid, phosphatidylinositol 4,5-bisphophate (PIP₂), in the inner leaflet. Plasma membrane models consisting of 1500 lipids and resembling the in vivo composition were constructed and simulations were run for 5 µs. In these simulations the most striking feature was the formation of nano-clusters of GM3 within the outer leaflet. In simulations of protein interactions within a plasma membrane model, GM3, PIP₂, and cholesterol all formed favorable interactions with the model α-helical protein. A larger scale simulation of a model plasma membrane containing 6000 lipid molecules revealed correlations between curvature of the bilayer surface and clustering of lipid molecules. In particular, the concave (when viewed from the extracellular side) regions of the bilayer surface were locally enriched in GM3. In summary, these simulations explore the nanoscale dynamics of model bilayers which mimic the in vivo lipid composition of mammalian plasma membranes, revealing emergent nanoscale membrane organization which may be coupled both to fluctuations in local membrane geometry and to interactions with proteins.     

Assigning Membrane Binding Geometry of Cytochrome c by Polarized Light Spectroscopy

In this work we demonstrate how polarized light absorption spectroscopy (linear dichroism (LD)) analysis of the peptide ultraviolet-visible spectrum of a membrane-associated protein (cytochrome (cyt) c) allows orientation and structure to be assessed with quite high accuracy in a native membrane environment that can be systematically varied with respect to lipid composition. Cyt c binds strongly to negatively charged lipid bilayers with a distinct orientation in which its α-helical segments are on average parallel to the membrane surface. Further information is provided by the LD of the π-π^∗ transitions of the heme porphyrin and transitions of aromatic residues, mainly a single tryptophan. A good correlation with NMR data was found, and combining NMR structural data with LD angular data allowed the whole protein to be docked to the lipid membrane. When the redox state of cyt c was changed, distinct variations in the LD spectrum of the heme Soret band were seen corresponding to changes in electronic transition energies; however, no significant change in the overall protein orientation or structure was observed. Cyt c is known to interact in a specific manner with the doubly negatively charged lipid cardiolipin, and incorporation of this lipid into the membrane at physiologically relevant levels was indeed found to affect the protein orientation and its α-helical content. The detail in which cyt c binding is described in this study shows the potential of LD spectroscopy using shear-deformed lipid vesicles as a new methodology for exploring membrane protein structure and orientation.     

The role of lipid components of the diet in the regulation of the fatty acid composition of the rat liver endoplasmic reticulum and lipid peroxidation

The fatty acid compositions of the lipids and the lipid peroxide concentrations and rates of lipid peroxidation were determined in suspensions of liver endoplasmic reticulum isolated from rats fed on synthetic diets in which the fatty acid composition had been varied but the remaining constituents (protein, carbohydrate, vitamins and minerals) kept constant. Stock diet and synthetic diets containing no fat, 10% corn oil, herring oil, coconut oil or lard were used. The fatty acid composition of the liver endoplasmic reticulum lipid was markedly dependent on the fatty acid composition of the dietary lipid. Feeding a herring-oil diet caused incorporation of 8.7% eicosapentaenoic acid (C_20:5) and 17% docosahexaenoic acid (C_22:6), but only 5.1% linoleic acid (C_18:2) and 6.4% arachidonic acid (C_20:4), feeding a corn-oil diet caused incorporation of 25.1% C_18:2, 17.8% C_20:4 and 2.5% C_22:6 fatty acids, and feeding a lard diet caused incorporation of 10.3% C_18:2, 13.5% C_20:4 and 4.3% C_22:6 fatty acids into the liver endoplasmic-reticulum lipids. Phenobarbitone injection (100mg/kg) decreased the incorporation of C_20:4 and C_22:6 fatty acids into the liver endoplasmic reticulum of rats fed on a lard, corn-oil or herring-oil diet. Microsomal lipid peroxide concentrations and rates of peroxidation in the presence of ascorbate depended on the nature and quantity of the polyunsaturated fatty acids in the diet. The lipid peroxide content was 1.82±0.30nmol of malonaldehyde/mg of protein and the rate of peroxidation was 0.60±0.08nmol of malonaldehyde/min per mg of protein after feeding a fat-free diet, and the values were increased to 20.80nmol of malonaldehyde/mg of protein and 3.73nmol of malonaldehyde/min per mg of protein after feeding a 10% herring-oil diet in which polyunsaturated fatty acids formed 24% of the total fatty acids. Addition of α-tocopherol to the diets (120mg/kg of diet) caused a very large decrease in the lipid peroxide concentration and rate of lipid peroxidation in the endoplasmic reticulum, but addition of the synthetic anti-oxidant 2,6-di-t-butyl-4-methylphenol to the diet (100mg/kg of diet) was ineffective. Treatment of the animals with phenobarbitone (1mg/ml of drinking water) caused a sharp fall in the rate of lipid peroxidation. It is concluded that the polyunsaturated fatty acid composition of the diet regulates the fatty acid composition of the liver endoplasmic reticulum, and this in turn is an important factor controlling the rate and extent of lipid peroxidation in vitro and possibly in vivo.     

Lipid profiles of autophagic structures isolated from wild type and Atg2 mutant Drosophila

Autophagy is mediated by membrane-bound organelles and it is an intrinsic catabolic and recycling process of the cell, which is very important for the health of organisms. The biogenesis of autophagic membranes is still incompletely understood. In vitro studies suggest that Atg2 protein transports lipids presumably from the ER to the expanding autophagic structures. Autophagy research has focused heavily on proteins and very little is known about the lipid composition of autophagic membranes. Here we describe a method for immunopurification of autophagic structures from Drosophila melanogaster (an excellent model to study autophagy in a complete organism) for subsequent lipidomic analysis. Western blots of several organelle markers indicate the high purity of the isolated autophagic vesicles, visualized by various microscopy techniques. Mass spectrometry results show that phosphatidylethanolamine (PE) is the dominant lipid class in wild type (control) membranes. We demonstrate that in Atg2 mutants (Atg2^?), phosphatidylinositol (PI), negatively charged phosphatidylserine (PS), and phosphatidic acid (PA) with longer fatty acyl chains accumulate on stalled, negatively charged phagophores. Tandem mass spectrometry analysis of lipid species composing the lipid classes reveal the enrichment of unsaturated PE and phosphatidylcholine (PC) in controls versus PI, PS and PA species in Atg2^?. Significant differences in the lipid profiles of control and Atg2^? flies suggest that the lipid composition of autophagic membranes dynamically changes during their maturation. These lipidomic results also point to the in vivo lipid transport function of the Atg2 protein, pointing to its specific role in the transport of short fatty acyl chain PE species.     

Variations of chemical composition and energy content in natural and genetically defined cultivars of Macrocystis from Chile

Seasonal and intra-thallus variations of energy content and chemical composition were assessed in an intertidal population of Macrocystis in southern Chile. Phylloid protein and lipid from cultured material were compared with seasonal variation in native Macrocystis. Furthermore, populations in northern and southern Chile and Falkland Islands were compared with various intra-/inter-cultivar genotypes of Chilean Macrocystis. Energetic values did not show seasonal or intra-thallus variations, with the exception of pneumatocysts, which had high levels of ash (49.9% DW) and low values of total energy (8.3% DW). Seasonal patterns were detected in protein and carbohydrate composition, with opposite trends. Likewise, holdfasts contained high amounts of protein (21.0% DW), and phylloids were high in soluble carbohydrates (4.5% DW). Lipids instead showed two peaks per year in an intertidal population and reached up to 0.4% DW. Alginic acid was the major organic compound in intertidal Macrocystis (46.8% DW), with differences on seasonal and intra-thallus levels. Mannitol content, in contrast, was erratic and lower than in other Laminariales (<5% DW). In general, protein and lipid content in our cultivars were 20% higher than in natural populations. Our experimental results indicate the possibility to manipulate the chemical composition of Macrocystis thalli through inter-/intra-specific crosses. This will be a basis, upon which selected genotypes can open new perspectives to Macrocystis mariculture industries in Chile.     

Lipid composition of a plasma membrane enriched fraction of maize roots

The lipid composition of a plasma membrane enriched fraction isolated from corn (Zea mays) roots was examined. On a wt basis, the lipid: protein ratio was 1.11. Phospholipids comprised 60% of total lipids with the major phospholipids being phosphatidylcholine (62%) and phosphatidylethanolamine (21%). Free sterol was the major neutral lipid. The sterol:phospholipid molar ratio was 0.31. The fatty acid composition of the membrane was predominantly linoleic (60%) and palmitic (30%).     

An evaluation of lipid metabolism in the insect trypanosomatid Herpetomonas muscarum uncovers a pathway for the uptake of extracellular insect lipoproteins

Lipid uptake and metabolism by trypanosomatid parasites from vertebrate host blood have been well established in the literature. However, there is a lack of knowledge regarding the same aspects concerning the parasites that cross the hemolymph of their invertebrate hosts. We have investigated the lipid composition and metabolism of the insect trypanosomatid Herpetomonas muscarum by ³H- palmitic acid and phosphate (³²Pi) and the parasite interaction with Lipophorin (Lp) the main lipid carrying protein of insect hemolymph. Gas chromatography-mass spectrometry (GC–MS) analyses were used to identify the fatty acids and sterols composition of H.muscarum. Furthermore, we investigated the Lp binding site in the plasma membrane of parasite by Immunolocalization. We showed that H. muscarum incorporated 3H-palmitic acid and inorganic phosphate (32Pi) which were readily used as precursor molecules of lipid biosynthetic pathways. Furthermore, H. muscarum was able to take up both protein and lipid moieties of Lp which could be used as nutrient sources. Moreover, we have also demonstrated for the first time the presence of a Lp binding site in the membrane of a parasite. Such results point out the role of describing the metabolic pathways of trypanosomatids in order to provide a better understanding of parasite-host interaction peculiarities. Such studies may enhance the potential form the identification of novel chemotherapeutic targets in harmful parasites.     

Storage and mobilisation of nutriment for uterine milk synthesis by Glossina morsitans

Nitrogen content of eggs and larvae of Glossina morsitans was a constant proportion of dry weight and equivalent to ca. 55% protein assuming tsetse proteins contain 16% nitrogen. The larval gut content (uterine milk) contained 40% protein. Fatty acid composition of lipids in the milk and in the larval body was similar, with Palmitic (35–38%), Palmitoleic (31–35%) and Oleic acid (23–25%) predominating. Results support the hypothesis that uterine milk contains both protein and lipid and that its composition is relatively constant throughout the period of its synthesis and secretion.Patterns of incorporation of radioactivity by fertilized adult females from injected [¹⁴C]-leucine changed throughout a pregnancy cycle. High levels of incorporation into lipid (22–30%) during early pregnancy fell to around 10% during late pregnancy. Over the same period low levels of incorporation into protein (5%) increased to 15%. Results support the hypothesis that uterine milk is synthesized from a lipid store laid down in early pregnancy coupled with protein derived largely from blood meals ingested later. Such a system would not require the insect to store proteins for larval growth and is economical in terms of energy expenditure.     

What CHO is made of: Variations in the biomass composition of Chinese hamster ovary cell lines

BackgroundCell line-specific, genome-scale metabolic models enable rigorous and systematic in silico investigation of cellular metabolism. Such models have recently become available for Chinese hamster ovary (CHO) cells. However, a key ingredient, namely an experimentally validated biomass function that summarizes the cellular composition, was so far missing. Here, we close this gap by providing extensive experimental data on the biomass composition of 13 parental and producer CHO cell lines under various conditions.ResultsWe report total protein, lipid, DNA, RNA and carbohydrate content, cell dry mass, and detailed protein and lipid composition. Furthermore, we present meticulous data on exchange rates between cells and environment and provide detailed experimental protocols on how to determine all of the above. The biomass composition is converted into cell line- and condition-specific biomass functions for use in cell line-specific, genome-scale metabolic models of CHO. Finally, flux balance analysis (FBA) is used to demonstrate consistency between in silico predictions and experimental analysis.ConclusionsOur study reveals a strong variability of the total protein content and cell dry mass across cell lines. However, the relative amino acid composition is independent of the cell line and condition and thus needs not be explicitly measured for each new cell line. In contrast, the lipid composition is strongly influenced by the growth media and thus will have to be determined in each case. These cell line-specific variations in biomass composition have a small impact on growth rate predictions with FBA, as inaccuracies in the predictions are rather dominated by inaccuracies in the exchange rate spectra. Cell-specific biomass variations only become important if the experimental errors in the exchange rate spectra drop below twenty percent.     

In vitro Unfolding and Refolding of the Small Multidrug Transporter EmrE

The composition of the lipid bilayer is increasingly being recognised as important for the regulation of integral membrane protein folding and function, both in vivo and in vitro. The folding of only a few membrane proteins, however, has been characterised in different lipid environments. We have refolded the small multidrug transporter EmrE in vitro from a denatured state to a functional protein and monitored the influence of lipids on the folding process. EmrE is part of a multidrug resistance protein family that is highly conserved amongst bacteria and is responsible for bacterial resistance to toxic substances. We find that the secondary structure of EmrE is very stable and only small amounts are denatured even in the presence of unusually high denaturant concentrations involving a combination of 10 M urea and 5% SDS. Substrate binding by EmrE is recovered after refolding this denatured protein into dodecylmaltoside detergent micelles or into lipid vesicles. The yield of refolded EmrE decreases with lipid bilayer compositional changes that increase the lateral chain pressure within the bilayer, whilst conversely, the apparent rate of folding seems to increase. These results add further weight to the hypothesis that an increased lateral chain pressure hinders protein insertion across the bilayer. Once the protein is inserted, however, the greater pressure on the transmembrane helices accelerates correct packing and final folding. This work augments the relatively small number of biophysical folding studies in vitro on helical membrane proteins.     

Changes in lipophorin composition during the fourth to fifth instar molt of Manduca sexta

During the feeding stage of the fourth instar of the tobacco hornworm, Manduca sexta, lipophorin has a density of 1.144 g/ml and is comprised of 55% protein and 45% lipid, mainly diacylglycerol and phospholipid. These values are similar to those found during the corresponding period of the fifth instar. However, during the intermolt period the lipid composition of lipophorin changes to 45% protein and 55% lipid and the density decreases to 1.112 g/ml. The onset of these changes in lipid content correspond to the increase in ecdysteroid titer which signals the beginning of molting. At the end of molting both the lipid content and density return to those characteristic of the fifth instar. These data further confirm the complex nature of lipophorin metabolism in M. sexta larva and suggest that ecdysone may be the trigger for lipid mobilization during the intermolt period.     

The effect of nitrogen limitation on lipid productivity and cell composition in Chlorella vulgaris

Chlorella vulgaris accumulates lipid under nitrogen limitation, but at the expense of biomass productivity. Due to this tradeoff, improved lipid productivity may be compromised, despite higher lipid content. To determine the optimal degree of nitrogen limitation for lipid productivity, batch cultures of C. vulgaris were grown at different nitrate concentrations. The growth rate, lipid content, lipid productivity and biochemical and elemental composition of the cultures were monitored for 20 days. A starting nitrate concentration of 170 mg L^?1 provided the optimal tradeoff between biomass and lipid production under the experimental conditions. Volumetric lipid yield (in milligram lipid per liter algal culture) was more than double that under nitrogen-replete conditions. Interpolation of the data indicated that the highest volumetric lipid concentration and lipid productivity would occur at nitrate concentrations of 305 and 241 mg L^?1, respectively. There was a strong correlation between the nitrogen content of the cells and the pigment, protein and lipid content, as well as biomass and lipid productivity. Knowledge of the relationships between cell nitrogen content, growth, and cell composition assists in the prediction of the nitrogen regime required for optimal productivity in batch or continuous culture. In addition to enhancing lipid productivity, nitrogen limitation improves the lipid profile for biodiesel production and reduces the requirement for nitrogen fertilizers, resulting in cost and energy savings and a reduction in the environmental burden of the process.     

Effect of phosphorus on lipid accumulation in freshwater microalga Chlorella sp.

Microalgae have already been investigated as a potential resource for biofuel in many reports. In this study, the effect of phosphorus concentration on lipid content was analyzed using the freshwater microalga Chlorella sp as a model. In addition, the carbohydrate and protein content were also analyzed in order to investigate the variations of biochemical composition under different phosphorus levels. Results showed that both lipid content and lipid productivity were increased under low phosphorus conditions. Furthermore, it was also found that lipid accumulation in cells decreased by supplementing the growth media with K₂HPO₄ in the late growth phase. The analysis of the total protein and the carbohydrate content showed that the former remained unaffected by external phosphorus variation; while the latter was directly correlated to phosphorus concentration. In summary, lipid accumulation had significant relationship with phosphorus concentration.