Regulation of lipid metabolism in the snow alga Chlamydomonas nivalis in response to NaCl stress: An integrated analysis by cytomic and lipidomic approaches

Salinity Stress Acclimation Strategies in Chlamydomonas sp. Revealed by Physiological, Morphological and Transcriptomic Approaches

Climate changes may include variations in salinity concentrations at sea by changing ocean dynamics. These variations may be especially challenging for marine photosynthetic organisms, affecting their growth and distribution. Chlamydomonas spp. are ubiquitous and are often found in extreme salinity conditions. For this reason, they are considered good model species to study salinity adaptation strategies. In the current study, we used an integrated approach to study the Chlamydomonas sp. CCMP225 response to salinities of 20‱ and 70‱, by combining physiological, morphological, and transcriptomic analyses, and comparing differentially expressed genes in the exponential and stationary growth phases under the two salinity conditions. The results showed that the strain is able to grow under all tested salinity conditions and maintains a surprisingly high photosynthetic efficiency even under high salinities. However, at the highest salinity condition, the cells lose their flagella. The transcriptomic analysis highlighted the up- or down-regulation of specific gene categories, helping to identify key genes responding to salinity stress. Overall, the findings may be of interest to the marine biology, ecology, and biotechnology communities, to better understand species adaptation mechanisms under possible global change scenarios and the potential activation of enzymes involved in the synthesis of bioactive molecules.

Effect of seawater on the biomass composition of Spirulina produced at a pilot-scale

The microalga Arthrospira platensis BEA 005B was produced in 11.4 m3 raceway photobioreactors and a culture medium based on commercial fertilisers and either freshwater or seawater. The biomass productivity of the reactors operated at a fixed dilution rate of 0.3 day-1 decreased from 22.9 g·m-2·day-1 when operated using freshwater to 16.3 g·m-2·day-1 when the biomass was produced using seawater. The protein content of the biomass produced in seawater was lower; however, the content of essential amino acids including valine, leucine and isoleucine was higher. Seawater also triggered the production of carotenoids and altered the synthesis and accumulation of fatty acids. For example, the biomass produced using seawater showed a 319% and 210% higher content of oleic and eicosenoic acid, respectively. The results demonstrate that it is possible to produce the selected microalga using seawater after an adaptation period and that the composition of the produced biomass is suitable for food applications.

Insights into the genetic and metabolic engineering approaches to enhance the competence of microalgae as biofuel resource: A review

Conventional fuel resources are overburden with speedy global energy demand which ensued the urgent need of alternate energy resources. Biofuel generation efficiency of microalgae is notable due to their comparatively rapid biomass production rate and high oil content. But, the employment of microalgae as biofuel resource is in infancy due to low productivity and high production cost. The issues can be addressed by employing engineered microalgal strains that would be able to efficiently generate enhanced levels of biomass with augmented lipid and/or carbohydrate content for proficient biofuel production. Genetic alterations and metabolic engineering of microalgal species might be helpful in developing high stress-tolerant strains with improved properties for biofuel generation. Various omics approaches appeared significant to upgrade the microalgal lipid production. Intervention of genetic and metabolic engineering approaches would facilitate the development of microalgae as a competent biofuel resource and inflate the economic commercialization of biofuels.

Regulatory mechanisms of lipid biosynthesis in microalgae

Microalgal lipids are highly promising feedstocks for biofuel production. Microalgal lipids, especially triacylglycerol, and practical applications of these compounds have received increasing attention in recent years. For the commercial use of microalgal lipids to be feasible, many fundamental biological questions must be addressed based on detailed studies of algal biology, including how lipid biosynthesis occurs and is regulated. Here, we review the current understanding of microalgal lipid biosynthesis, with a focus on the underlying regulatory mechanisms. We also present possible solutions for overcoming various obstacles to understanding the basic biology of microalgal lipid biosynthesis and the practical application of microalgae-based lipids. This review will provide a theoretical reference for both algal researchers and decision makers regarding the future directions of microalgal research, particularly pertaining to microalgal-based lipid biosynthesis.

Quantitative proteomic comparison of salt stress in Chlamydomonas reinhardtii and the snow alga Chlamydomonas nivalis reveals mechanisms for salt-triggered fatty acid accumulation via reallocation of carbon resources

BACKGROUND

Chlamydomonas reinhardtii is a model green alga strain for molecular studies; its fully sequenced genome has enabled omic-based analyses that have been applied to better understand its metabolic responses to stress. Here, we characterised physiological and proteomic changes between a low-starch C. reinhardtii strain and the snow alga Chlamydomonas nivalis, to reveal insights into their contrasting responses to salinity stress.

RESULTS

Each strain was grown in conditions tailored to their growth requirements to encourage maximal fatty acid (as a proxy measure of lipid) production, with internal controls to allow comparison points. In 0.2 M NaCl, C. nivalis accumulates carbohydrates up to 10.4% DCW at 80 h, and fatty acids up to 52.0% dry cell weight (DCW) over 12 days, however, C. reinhardtii does not show fatty acid accumulation over time, and shows limited carbohydrate accumulation up to 5.5% DCW. Analysis of the C. nivalis fatty acid profiles showed that salt stress improved the biofuel qualities over time. Photosynthesis and respiration rates are reduced in C. reinhardtii relative to C. nivalis in response to 0.2 M NaCl. De novo sequencing and homology matching was used in conjunction with iTRAQ-based quantitative analysis to identify and relatively quantify proteomic alterations in cells exposed to salt stress. There were abundance differences in proteins associated with stress, photosynthesis, carbohydrate and lipid metabolism proteins. In terms of lipid synthesis, salt stress induced an increase in dihydrolipoyl dehydrogenase in C. nivalis (1.1-fold change), whilst levels in C. reinhardtii remained unaffected; this enzyme is involved in acetyl CoA production and has been linked to TAG accumulation in microalgae. In salt-stressed C. nivalis there were decreases in the abundance of UDP-sulfoquinovose (- 1.77-fold change), which is involved in sulfoquinovosyl diacylglycerol metabolism, and in citrate synthase (- 2.7-fold change), also involved in the TCA cycle. Decreases in these enzymes have been shown to lead to increased TAG production as fatty acid biosynthesis is favoured. Data are available via ProteomeXchange with identifier PXD018148.

CONCLUSIONS

These differences in protein abundance have given greater understanding of the mechanism by which salt stress promotes fatty acid accumulation in the un-sequenced microalga C. nivalis as it switches to a non-growth state, whereas C. reinhardtii does not have this response.

Cold Adaptation Mechanisms of a Snow Alga Chlamydomonas nivalis During Temperature Fluctuations

Cold environments, such as glaciers and alpine regions, constitute unique habitats for organisms living on Earth. In these harsh ecosystems, snow algae survive, florish, and even become primary producers for microbial communities. How the snow algae maintain physiological activity during violent ambient temperature changes remains unsolved. To explore the cold adaptation mechanisms of the unicellular snow alga Chlamydomonas nivalis, we compared its physiological responses to a model organism from the same genus, Chlamydomonas reinhardtii. When both cell types were exposed to a shift from 22°C to 4°C, C. nivalis exhibited an apparent advantage in cold tolerance over C. reinhardtii, as C. nivalis had both a higher growth rate and photosynthetic efficiency. To determine the cold tolerance mechanisms of C. nivalis, RNA sequencing was used to compare transcriptomes of both species after 1 h of cold treatment, mimicking temperature fluctuations in the polar region. Differential expression analysis showed that C. nivalis had fewer transcriptomic changes and was more stable during rapid temperature decrease relative to C. reinhardtii, especially for the expression of photosynthesis related genes. Additionally, we found that transcription in C. nivalis was precisely regulated by the cold response network, consisting of at least 12 transcription factors and 3 RNA-binding proteins. Moreover, genes participating in nitrogen metabolism, the pentose phosphate pathway, and polysaccharide biosynthesis were upregulated, indicating that increasing resource assimilation and remodeling of metabolisms were critical for cold adaptation in C. nivalis. Furthermore, we identified horizontally transferred genes differentially expressed in C. nivalis, which are critical for cold adaptation in other psychrophiles. Our results reveal that C. nivalis adapts rapid temperature decrease by efficiently regulating transcription of specific genes to optimize resource assimilation and metabolic pathways, providing critical insights into how snow algae survive and propagate in cold environments.

An insight into the role of silicon on retaliation to osmotic stress in finger millet (Eleusine coracana (L.) Gaertn)

Finger millet, a vital nutritional cereal crop provides food security. It is a well-established fact that silicon (Si) supplementation to plants alleviates both biotic and abiotic stresses. However, precise molecular targets of Si remain elusive. The present study attempts to understand the alterations in the metabolic pathways after Si amendment under osmotic stress. The analysis of transcriptome and metabolome of finger millet seedlings treated with distilled water (DW) as control, Si (10 ppm), PEG (15%), and PEG (15%) + Si (10 ppm) suggest the molecular alterations mediated by Si for ameliorating the osmotic stress. Under osmotic stress, uptake of Si has increased mediating the diversion of an enhanced pool of acetyl CoA to lipid biosynthesis and down-regulation of TCA catabolism. The membrane lipid damage reduced significantly by Si under osmotic stress. A significant decrease in linolenic acid and an increase of jasmonic acid (JA) in PEG + Si treatment suggest the JA mediated regulation of osmotic stress. The relative expression of transcripts corroborated with the corresponding metabolites abundance levels indicating the activity of genes in assuaging the osmotic stress. This work substantiates the role of Si in osmotic stress tolerance by reprogramming of fatty acids biosynthesis in finger millet.

Sanguina nivaloides and Sanguina aurantia gen. et spp. nov. (Chlorophyta): the taxonomy, phylogeny, biogeography and ecology of two newly recognised algae causing red and orange snow

Melting snowfields in polar and alpine regions often exhibit a red and orange colouration caused by microalgae. The diversity of these organisms is still poorly understood. We applied a polyphasic approach using three molecular markers and light and electron microscopy to investigate spherical cysts sampled from alpine mountains in Europe, North America and South America as well as from both polar regions. Molecular analyses revealed the presence of a single independent lineage within the Chlamydomonadales. The genus Sanguina is described, with Sanguina nivaloides as its type. It is distinguishable from other red cysts forming alga by the number of cell wall layers, cell size, cell surface morphology and habitat preference. Sanguina nivaloides is a diverse species containing a total of 18 haplotypes according to nuclear ribosomal DNA internal transcribed spacer 2, with low nucleotide divergence (≤3.5%). Based on molecular data we demonstrate that it has a cosmopolitan distribution with an absence of geographical structuring, indicating an effective dispersal strategy with the cysts being transported all around the globe, including trans-equatorially. Additionally, Sanguina aurantia is described, with small spherical orange cysts often clustered by means of mucilaginous sheaths, and causing orange blooms in snow in subarctic and Arctic regions.

Membrane Lipid Remodeling in Response to Salinity

Salinity is one of the most decisive environmental factors threatening the productivity of crop plants. Understanding the mechanisms of plant salt tolerance is critical to be able to maintain or improve crop yield under these adverse environmental conditions. Plant membranes act as biological barriers, protecting the contents of cells and organelles from biotic and abiotic stress, including salt stress. Alterations in membrane lipids in response to salinity have been observed in a number of plant species including both halophytes and glycophytes. Changes in membrane lipids can directly affect the properties of membrane proteins and activity of signaling molecules, adjusting the fluidity and permeability of membranes, and activating signal transduction pathways. In this review, we compile evidence on the salt stress responses of the major membrane lipids from different plant tissues, varieties, and species. The role of membrane lipids as signaling molecules in response to salinity is also discussed. Advances in mass spectrometry (MS)-based techniques have largely expanded our knowledge of salt-induced changes in lipids, however only a handful studies have investigated the underlying mechanisms of membrane lipidome regulation. This review provides a comprehensive overview of the recent works that have been carried out on lipid remodeling of plant membranes under salt treatment. Challenges and future perspectives in understanding the mechanisms of salt-induced changes to lipid metabolisms are proposed.

Delineating the molecular responses of a halotolerant microalga using integrated omics approach to identify genetic engineering targets for enhanced TAG production

BACKGROUND

Harnessing the halotolerant characteristics of microalgae provides a viable alternative for sustainable biomass and triacylglyceride (TAG) production. Scenedesmus sp. IITRIND2 is a fast growing fresh water microalga that has the capability to thrive in high saline environments. To understand the microalga's adaptability, we studied its physiological and metabolic flexibility by studying differential protein, metabolite and lipid expression profiles using metabolomics, proteomics, real-time polymerase chain reaction, and lipidomics under high salinity conditions.

RESULTS

On exposure to salinity, the microalga rewired its cellular reserves and ultrastructure, restricted the ions channels, and modulated its surface potential along with secretion of extrapolysaccharide to maintain homeostasis and resolve the cellular damage. The algal-omics studies suggested a well-organized salinity-driven metabolic adjustment by the microalga starting from increasing the negatively charged lipids, up regulation of proline and sugars accumulation, followed by direction of carbon and energy flux towards TAG synthesis. Furthermore, the omics studies indicated both de-novo and lipid cycling pathways at work for increasing the overall TAG accumulation inside the microalgal cells.

CONCLUSION

The salt response observed here is unique and is different from the well-known halotolerant microalga; Dunaliella salina, implying diversity in algal response with species. Based on the integrated algal-omics studies, four potential genetic targets belonging to two different metabolic pathways (salt tolerance and lipid production) were identified, which can be further tested in non-halotolerant algal strains.

Peridinin Is an Exceptionally Potent and Membrane-Embedded Inhibitor of Bilayer Lipid Peroxidation

Antilipoperoxidant protein dysfunction is associated with many human diseases, suggesting that bilayer lipid peroxidation may contribute broadly to pathogenesis. Small molecule inhibitors of this membrane-localized chemistry could in theory enable better understanding and/or treatment of such diseases, but currently available compounds have important limitations. Many biological questions thus remain unanswered, and clinical trials have largely been disappointing. Enabled by efficient, building block-based syntheses of three atypical carotenoid natural products produced by microorganisms that thrive in environments of extreme oxidative stress, we found that peridinin is a potent inhibitor of nonenzymatic bilayer lipid peroxidation in liposomes and in primary human endothelial cells. We also found that peridinin blocks monocyte-endothelial cell adhesion, a key step in atherogenesis. A series of frontier solid-state NMR experiments with a site-specifically 13C-labeled isotopolog synthesized using the same MIDA boronate building block-based total synthesis approach revealed that peridinin is completely embedded within and physically spans the hydrophobic core of POPC membranes, maximizing its effective molarity at the site of the targeted lipid peroxidation reactions. Alternatively, the widely used carotenoid astaxanthin is significantly less potent and was found to primarily localize extramembranously. Peridinin thus represents a promising and biophysically well-characterized starting point for the development of small molecule antilipoperoxidants that serve as more effective biological probes and/or therapeutics.

Enhanced single cell oil production by mixed culture of Chlorella pyrenoidosa and Rhodotorula glutinis using cassava bagasse hydrolysate as carbon source

The single cell oil (SCO) production by the mono and mixed culture of microalgae Chlorella pyrenoidosa and red yeast Rhodotorula glutinis was investigated using non-detoxified cassava bagasse hydrolysate (CBH) as carbon source. The results suggested that the two strains were able to tolerate and even degrade some byproducts presented in the CBH, and the mixed culture approach enhanced the degradation of certain byproducts. Biomass (20.37 ± 0.38 g/L) and lipid yield (10.42 ± 1.21 g/L) of the mixed culture achieved in the batch culture were significantly higher than that of the mono-cultures (p < 0.05). The fed-batch culture further raised the biomass and lipid yield to 31.45 ± 4.93 g/L and 18.47 ± 3.25 g/L, respectively. The lipids mainly composed of oleic acid and palmitic acid, suggesting the potential applications such as biofuel feedstock, cosmetics, food additives and lubricant. This study provided new insights for the integration of the economical SCO production with agro-industrial waste disposal.

Leveraging algal omics to reveal potential targets for augmenting TAG accumulation

Ongoing global efforts to commercialize microalgal biofuels have expedited the use of multi-omics techniques to gain insights into lipid biosynthetic pathways. Functional genomics analyses have recently been employed to complement existing sequence-level omics studies, shedding light on the dynamics of lipid synthesis and its interplay with other cellular metabolic pathways, thus revealing possible targets for metabolic engineering. Here, we review the current status of algal omics studies to reveal potential targets to augment TAG accumulation in various microalgae. This review specifically aims to examine and catalog systems level data related to stress-induced TAG accumulation in oleaginous microalgae and inform future metabolic engineering strategies to develop strains with enhanced bioproductivity, which could pave a path for sustainable green energy.

Lipidomic Analysis: From Archaea to Mammals

Lipids are among the most important organic compounds found in all living cells, from primitive archaebacteria to flowering plants or mammalian cells. They form part of cell walls and constitute cell storage material. Their biosynthesis and metabolism play key roles in faraway topics such as biofuel production (third-generation biofuels produced by microorganisms, e.g. algae) and human diseases such as adrenoleukodystrophy, Zellweger syndrome, or Refsum disease. Current lipidomic analysis requires fast and accurate processing of samples and especially their characterization. Because the number of possible lipids and, more specifically, molecular species of lipids is of the order of hundreds to thousands, it is necessary to process huge amounts of data in a short time. There are two basic approaches to lipidomic analysis: shotgun and liquid chromatography-mass spectometry. Both methods have their pros and cons. This review deals with lipidomics not according to the type of ionization or the lipid classes analyzed but according to the types of samples (organisms) under study. Thus, it is divided into lipidomic analysis of archaebacteria, bacteria, yeast, fungi, algae, plants, and animals.

Carotenogenic response in photosynthetic organisms: a colorful story

Carotenoids are a diverse group of terpenoid pigments ubiquitous in and essential for functioning of phototrophs. Most of the researchers in the field are focused on the primary carotenoids serving light harvesting, photoprotection, and supporting the structural integrity of the photosynthetic apparatus (PSA) within the thylakoid membranes. A distinct group of the pigments functionally and structurally uncoupled from the PSA and accumulating outside of the thylakoids is called secondary carotenoids. Induction of the biosynthesis and massive accumulation of the latter termed as secondary carotenogenesis and carotenogenic response (CR), respectively, is a major though insufficiently studied stress response discovered in many phototrophic organisms ranging from single-celled algae to terrestrial higher plants. The CR protects cell by means of optical shielding of cell structures vulnerable photodamage, consumption of potentially harmful dioxygen, augmenting sink capacity of photoassimilates, and exerting an antioxidant effect. The secondary carotenoids exhibit a remarkable photostability in situ. Therefore, the CR-based photoprotective mechanism, unlike, e.g., antioxidant enzyme-based protection in the chloroplast, does not require continuous investment of energy and metabolites making it highly suitable for long-term stress acclimation in phototrophs. Capability of the CR determines the strategy of acclimation of photosynthetic organisms to different stresses such as excessive irradiance, drought, extreme temperatures, and salinities. Build-up of the CR might be accompanied by gradual disengagement of 'classical' active (energy-dependent) photoprotective mechanisms such as non-photochemical quenching. In addition to that, the CR has great ecological significance. Illustrious examples of this are extremely stress-tolerant 'snow' algae and conifer species developing red coloration during winter. The CR has also considerable practical implications since the secondary carotenoids exert a plethora of beneficial effects on human and animal health. The carotenogenic microalgae are the richest biotechnological sources of natural value-added carotenoids such as astaxanthin and β-carotene. In the present review, we summarize current functional, mechanistic, and ecological insights into the CR in a broad range of organisms suggesting that it is obviously more widespread and important stress response than it is currently thought to be.

Antioxidative ability and membrane integrity in salt-induced responses of Casuarina glauca Sieber ex Spreng. in symbiosis with N2-fixing Frankia Thr or supplemented with mineral nitrogen

The actinorhizal tree Casuarina glauca tolerates extreme environmental conditions, such as high salinity. This species is also able to establish a root-nodule symbiosis with N2-fixing bacteria of the genus Frankia. Recent studies have shown that C. glauca tolerance to high salt concentrations is innate and linked to photosynthetic adjustments. In this study we have examined the impact of increasing NaCl concentrations (200, 400 and 600mM) on membrane integrity as well as on the control of oxidative stress in branchlets of symbiotic (NOD+) and non-symbiotic (KNO3+) C. glauca. Membrane selectivity was maintained in both plant groups at 200mM NaCl, accompanied by an increase in the activity of antioxidative enzymes (superoxide dismutase, ascorbate peroxidase, glutathione reductase and catalase). Regarding cellular membrane lipid composition, linolenic acid (C18:3) showed a significant decline at 200mM NaCl in both NOD+ and KNO3+ plants. In addition, total fatty acids (TFA) and C18:2 also decreased in NOD+ plants at this salt concentration, resulting in malondialdehyde (MDA) production. Such initial impact at 200mM NaCl is probably due to the fact that NOD+ plants are subjected to a double stress, i.e., salinity and low nitrogen availability. At 400mM NaCl a strong reduction of TFA and C18:3 levels was observed in both plant groups. This was accompanied by a decrease in the unsaturation degree of membrane lipids in NOD+. However, in both NOD+ and KNO3+ lipid modifications were not reflected by membrane leakage at 200 or 400mM, suggesting acclimation mechanisms at the membrane level. The fact that membrane selectivity was impaired only at 600mM NaCl in both groups of plants points to a high tolerance of C. glauca to salt stress independently of the symbiotic relation with Frankia.

Global Metabolic Regulation of the Snow Alga Chlamydomonas nivalis in Response to Nitrate or Phosphate Deprivation by a Metabolome Profile Analysis

In the present work, Chlamydomonas nivalis, a model species of snow algae, was used to illustrate the metabolic regulation mechanism of microalgae under nutrient deprivation stress. The seed culture was inoculated into the medium without nitrate or phosphate to reveal the cell responses by a metabolome profile analysis using gas chromatography time-of-flight mass spectrometry (GC/TOF-MS). One hundred and seventy-one of the identified metabolites clustered into five groups by the orthogonal partial least squares discriminant analysis (OPLS-DA) model. Among them, thirty of the metabolites in the nitrate-deprived group and thirty-nine of the metabolites in the phosphate-deprived group were selected and identified as “responding biomarkers” by this metabolomic approach. A significant change in the abundance of biomarkers indicated that the enhanced biosynthesis of carbohydrates and fatty acids coupled with the decreased biosynthesis of amino acids, N-compounds and organic acids in all the stress groups. The up- or down-regulation of these biomarkers in the metabolic network provides new insights into the global metabolic regulation and internal relationships within amino acid and fatty acid synthesis, glycolysis, the tricarboxylic acid cycle (TCA) and the Calvin cycle in the snow alga under nitrate or phosphate deprivation stress.

The enhanced lipid accumulation in oleaginous microalga by the potential continuous nitrogen-limitation (CNL) strategy

A potential continuous nitrogen-limitation (CNL) strategy was proposed to enhance lipid accumulation by oleaginous Chlorella vulgaris in this study. The highest biomass (4.61 g/L) with CNL was nearly close to the maximum biomass (4.88 g/L) achieved by the traditional batch nitrogen-starvation strategy (BNS) under laboratory condition. CNL was further found to diminish the photosynthetic activity and trigger the degradation of nitrogenous compounds (e.g. protein, chlorophyll, DNA) consequently resulted in enhanced lipid accumulation. The maximal lipid productivity of 305.71 mg/L/d was accomplished by CNL, which presented 1.35-fold more than that of BNS. Furthermore, the identified lipid accumulation-related metabolic checkpoints (MDH and GPDH) provide the possibilities to develop high-lipid engineering microalgae. The aforementioned results imply that CNL nitrogen-deficiency strategy for lipid production on large-scale deserves further exploration.

Efficacy of EDTA and Phosphorous on Biomass Yield and Total Lipid Accumulation in Two Green Microalgae with Special Emphasis on Neutral Lipid Detection by Flow Cytometry

Chlorella ellipsoidea and Chlorococcum infusionum, promising microalgae for biodiesel feedstock production, were treated with ethylenediaminetetraacetate (EDTA) and phosphorous to induce stress which was then followed by flow cytometry to study the enhanced intracellular neutral lipid content. Treatment resulted in up to a threefold increase in total lipid content of Chlorella (41.8±1.9% at 16 days of incubation period) and more than twofold increases in Chlorococcum (31.3±1.0% at 18 days of incubation period) under phosphorous starvation in the culture. It was observed that maximum biomass yields in Chlorella and Chlorococcum were 1.56±0.06 and 2.17±0.12 g/L at 1.5 g/L of phosphorous after 20 and 18 days of incubation periods, respectively. The qualitative analyses of neutral lipid bodies under stress conditions were performed by confocal microscopy and revealed bright golden-yellow lipid droplets in stress exposed cells. Significant increase of monounsaturated fatty acids under the nutrient limited conditions was suitable to produce biodiesel. The maximum biomass (g/L) and lipid content (% dry cell weight) at different stresses showed significant results (p<0.05) by single-factor Analysis of Variance (ANOVA) followed by Duncan’s Multiple Range Test (DMRT).

An integrated salinity-driven workflow for rapid lipid enhancement in green microalgae for biodiesel application

A laboratory based integrated approach was undertaken for improvement of lipid accumulation in green microalgae under sodium chloride (NaCl) stress.

Salinity induced oxidative stress enhanced biofuel production potential of microalgae Scenedesmus sp. CCNM 1077

Microalgal biomass is considered as potential feedstock for biofuel production. Enhancement of biomass, lipid and carbohydrate contents in microalgae is important for the commercialization of microalgal biofuels. In the present study, salinity stress induced physiological and biochemical changes in microalgae Scenedesmus sp. CCNM 1077 were studied. During single stage cultivation, 33.13% lipid and 35.91% carbohydrate content was found in 400 mM NaCl grown culture. During two stage cultivation, salinity stress of 400 mM for 3 days resulted in 24.77% lipid (containing 74.87% neutral lipid) along with higher biomass compared to single stage, making it an efficient strategy to enhance biofuel production potential of Scenedesmus sp. CCNM 1077. Apart from biochemical content, stress biomarkers like hydrogen peroxide, lipid peroxidation, ascorbate peroxidase, proline and mineral contents were also studied to understand the role of reactive oxygen species (ROS) mediated lipid accumulation in microalgae Scenedesmus sp. CCNM 1077.

Rapid neutral lipid accumulation of the alkali-resistant oleaginous Monoraphidium dybowskii LB50 by NaCl induction

NaCl is an effective inducer of lipid accumulation in freshwater microalgae, but little is known on whether the enhanced lipid components are desired. To address this issue, Monoraphidium dybowskii LB50 from a freshwater habitat was selected, cultivated, and subjected to NaCl induction at different scales outdoors. Results showed that the optimal salt concentration reduced glycolipid (GL) content, as well as enhanced neutral lipid (NL) and phospholipid (PL) contents. Moreover, GL was preferentially converted to NL at 20gL(-1) NaCl. Total lipid and NL contents respectively increased to 41.7% and 17.48% in 1d. The highest NL productivity was also achieved at both the 5L (24.13mgL(-1)d(-1)) and 140L (13.05mgL(-1)d(-1), 3.43gm(-2)d(-1)) scales. These results suggest that NL accumulated effectively and rapidly at different scales, indicating that this strategy has broad application prospects for the scale-up cultivation of oily algae.

Lipidomic profiling of snow algae by ESI-MS and silver-LC/APCI-MS

The main analytical benefit of this study is the development of methods enabling a rapid determination of total lipids of algae by lipidomic analysis and detailed identification and quantification of a complex mixture of natural TAGs by silver-LC/APCI-MS and NARP-LC/APCI-MS. Both types of chromatography can readily identify, both qualitatively and semiquantitatively, triacylglycerols containing 16:3 and 16:4 acids in the molecule. We conclude that the genus Chloromonas is a major producer of C16 PUFAs mostly contained in TAGs. Since more detailed studies in this field have been stymied by the shortage of 16:3 and 16:4 FAs, we decided to study the alga Chloromonas as a potential biotechnological source of C16 PUFAs.

Photoautotrophic outdoor two-stage cultivation for oleaginous microalgae Scenedesmus obtusus XJ-15

In this study, Scenedesmus obtusus XJ-15 was firstly selected from seven strains microalgae (Chlorophyta, Scenedesmaceae) and then cultivated using a two-stage strategy, which composed of fast cell growth in stage I and followed by lipid induction in stage II in 5-L flasks outdoors. In stage I, the biomass productivity was increased from 139.4 to 212.1 mg L(-1) d(-1). In stage II, lipid content was increased from 26.1% to 47.7% by adding NaCl into the culture. This two-stage process was also realized in an 140-L photobioreactor outdoors, with a biomass productivity of 86.5 mg L(-1) d(-1) and CO2 fixation rate of 170.0 mg L(-1) d(-1) in the first stage, and high lipid content of 42.1% in the second stage. With such a culture strategy, the overall lipid productivity was improved and better biodiesel quality was obtained. These results suggested the photoautotrophic two-stage system was not only feasible but also effective.