Astaxanthin Biosynthesis Research Articles

Melatonin and calcium act synergistically to enhance the coproduction of astaxanthin and lipids in Haematococcus pluvialis under nitrogen deficiency and high light conditions

This study focused on the influence of integrating melatonin (MT) and calcium (Ca2+) on the simultaneous accumulation of astaxanthin and lipids in Haematococcus pluvialis under abiotic stress conditions. Compared with the control condition, MT induction enhanced astaxanthin and lipid contents by 65.89% and 27.38%, respectively. The highest contents of astaxanthin and lipids under combined exposure to MT and Ca2+ were 3.8% and 49.53%, respectively, which were 1.13- and 1.21-fold higher than those of cells treated with MT alone. The application of MT and Ca2+ also promoted the expression of carotenogenic and lipogenic genes and increased the levels of Ca2+ and γ-aminobutyric acid (GABA) but decreased reactive oxygen species (ROS) levels. Further evidence indicated that the increased cellular Ca2+ could promote astaxanthin biosynthesis under MT induction by regulating carotenogenic gene levels and GABA and ROS signalling. The integrated strategy efficiently improved the coproduction of astaxanthin and lipids in H. pluvialis.

Initial study of polymer-based nanoparticles effect on carotenogenesis of Haematococcus lacustris

The carotenogenesis in Haematococcus lacustris, accompanying by encystment starting from green motile cells to aplanospores, is suggested mediating by reactive oxygen species (ROS). Our previous study showed that isobutyl-cyanoacrylate nanoparticles (IBCA- NPs) induced the cell mortality, preceding by intracellular ROS accumulation, in most of Volvocales species but not H. lacustris. This study aimed to investigate the effect of IBCA- NPs exposure to H. lacustris on carotenogenesis. The cells were cultured on C medium then exposed to 100 mg · L−1 -1 of 180 nm of IBCA-NPs for the 14 days. The accumulation of astaxanthin was started after four days of IBCA-NPs exposure. The ratio of intermediate cells reached to 46% after 14 days of IBCA-NPs exposure, while the ratio of intermediate cells of untreated culture was only 11%. The results suggested that the addition of nanoparticles could enhance the production of astaxanthin. Further studies are required to investigate the correlation between nanoparticle exposure and ROS generation that leads to the biosynthesis of astaxanthin. The condition of cell growth and the addition of nanoparticles shall be optimized to increase the production of ketocarotenoid and to minimalize the negative effect of longer exposure time of IBCA-NP that could lead the cell mortality.

Astaxanthin accumulation difference between non-motile cells and akinetes of Haematococcus pluvialis was affected by pyruvate metabolism

BackgroundHaematococcus pluvialis is the best source of natural astaxanthin, known as the king of antioxidants. H. pluvialis have four cell forms: spore, motile cell, non-motile cell and akinete. Spores and motile cells are susceptible to photoinhibition and would die under photoinduction conditions. Photoinduction using non-motile cells as seeds could result in a higher astaxanthin production than that using akinetes. However, the mechanism of this phenomenon has not been clarified.ResultsTranscriptome was sequenced and annotated to illustrate the mechanism of this phenomenon. All differentially expressed genes involved in astaxanthin biosynthesis were up-regulated. Particularly, chyb gene was up-regulated by 16-fold, improving the conversion of β-carotene into astaxanthin. Pyruvate was the precursor of carotenoids biosynthesis. Pyruvate kinase gene expression level was increased by 2.0-fold at the early stage of akinetes formation. More changes of gene transcription occurred at the early stage of akinetes formation, 52.7% and 51.9% of total DEGs in control group and treatment group, respectively.ConclusionsGenes transcription network was constructed and the synthesis mechanism of astaxanthin was clarified. The results are expected to further guide the in-depth optimization of the astaxanthin production process in H. pluvialis by improving pyruvate metabolism.

A strategy for stimulating astaxanthin and lipid production in Haematococcus pluvialis by exogenous glycerol application under low light

In large-scale outdoor cultivation, Haematococcus pluvialis cultures are frequently exposed to low light caused by continuous rain conditions. Low light significantly restricts biomass and astaxanthin accumulation, thereby decreasing astaxanthin productivity. In this study, the effects of exogenous glycerol on the growth, photosynthesis, and astaxanthin and lipid accumulation in H. pluvialis under low light were investigated. A strategy was developed for promoting astaxanthin and lipid production in H. pluvialis under low light by the application of exogenous glycerol. Under low light, exogenous glycerol did not change the biomass and photosynthetic capacity of H. pluvialis. The addition of 1 mL L−1 glycerol increased total lipid content by 36.8% by increasing the formation of fatty acids during an 11-day growth period. Furthermore, exogenous glycerol could directly accelerate astaxanthin production under low light by increasing the formation of substrates (e.g. pyruvate). Meanwhile, the elevated fatty acid level due to the addition of glycerol facilitated the esterification of astaxanthin, thereby accelerating the biosynthesis of astaxanthin indirectly, which is indicated by the fact that exogenous glycerol enhanced astaxanthin esters content significantly under low light. All these results suggest that H. pluvialis has the ability to utilize glycerol for astaxanthin and lipid production under low light.

Primary metabolism is associated with the astaxanthin biosynthesis in the green algae Haematococcus pluvialis under light stress

Haematococcus pluvialis is a kind of native bioresource, which accumulate high abundance of astaxanthin, one of the most important bioactive compounds, under various biotic and abiotic stress conditions particularly under high light. However, the global metabolic responses to high light in general and the relationship between primary metabolism and astaxanthin accumulation in particular are still obscure. In this study, non-targeted metabolomics approach was first to be used to profile the dynamic metabolic changes of H. pluvialis along astaxanthin accumulation under different light intensities, in which >200 low molecular metabolites were identified. The integration of metabolomics data with previous transcriptomic data uncovered several metabolic pathways including raffinose family oligosaccharides biosynthesis pathway, GSH metabolism pathways, pyrimidine and purine metabolism pathways, TCA cycle, and phospholipids, that are important for astaxanthin biosynthesis under high light intensity, pinpointing a metabolic shift from primary metabolism to astaxanthin biosynthesis. Exogenous application of related metabolites such as nucleotides, carbohydrates and amino acids in algal medium confirmed the metabolic link between primary metabolism and astaxanthin biosynthesis. Our results provides with a solid metabolic base for the manipulation of astaxanthin production under high light stress, and reveals metabolic insights into the adaption strategy of H. pluvialis against light stress conditions.

Discovery of Geranylgeranyl Pyrophosphate Synthase (GGPPS) Paralogs from Haematococcus pluvialis Based on Iso-Seq Analysis and Their Function on Astaxanthin Biosynthesis.

Haematococcus pluvialis is widely distributed in the world and well known as the richest natural source of astaxanthin that is a strong antioxidant with excellent commercial value. The pathway of astaxanthin biosynthesis in H. pluvialis has been documented as an enzymatic reaction. Several enzymes have been reported, but their isoforms or homologs have not been investigated genome-wide. To better understand the astaxanthin biosynthesis pathway in H. pluvialis, eight candidates of the geranylgeranyl pyrophosphate synthase gene (HpGGPPS) predicted from Iso-seq data were isolated in this study. The length of coding region of these candidates varied from 960 bp to 1272 bp, composing of 7–9 exons. The putative amino acids of all candidates composed the signature domain of GGPPS gene. However, the motifs in the domain region are varied, indicating different bio-functions. Phylogenetic analysis revealed eight candidates can be clustered into three groups. Only two candidates in Group1 encode the synthase participating in the astaxanthin formation. The yield of astaxanthin from these two candidates, 7.1 mg/g (DW) and 6.5 mg/g (DW) respectively, is significant higher than that from CrtE (2.4 mg/g DW), a GGPPS gene from Pantoea ananatis. This study provides a potential productive pathway for astaxanthin synthesis.

Transcriptome analysis of Haematococcus pluvialis of multiple defensive systems against nitrogen starvation

Haematococcus pluvialis could accumulate large amounts of triacylglycerol (TAG) and astaxanthin under various environmental stresses. To gain insights into the multiple defensive systems for carbon metabolism against nitrogen starvation, transcriptome analysis was performed. It was found that the genes related to carbon fixation, glycolysis, fatty acid and carotenoid biosynthesis pathways were up-regulated remarkably. Glyceraldehyde 3-phosphate (G3P) biosynthesis was accelerated with the enhanced C3 and C4 pathway. Meanwhile, the pyruvate kinase (PK) and pyruvate dehydrogenase E2 component (aceF) genes were significantly increased 12.9-fold and 13.9-fold, respectively, resulting more pyruvate and acetyl-CoA generation, which were beneficial to carotenoids and fatty acid biosynthesis. Methylerythritol 4-phosphate (MEP) pathway mediated carotenoid precursor isopentenyl diphosphate (IPP) synthesis, as the all eight related genes were up-regulated. The carbon flux toward astaxanthin biosynthesis with the increased astaxanthin pathway genes. The redistribution of carbon was also promoted for TAG accumulation. In addition, the up-regulation of diacylglycerol acyltransferase (DGAT) and phospholipid: diacylglycerol acyltransferase (PDAT) genes indicated that both acyl-CoA dependent and independent pathway regulated TAG accumulation. Therefore, this work reveals the multiple defensive mechanism for carbon metabolism in response to nitrogen starvation, which extended our understanding on the carotenoids, TAG and other important metabolites synthesis.

Time-resolved carotenoid profiling and transcriptomic analysis reveal mechanism of carotenogenesis for astaxanthin synthesis in the oleaginous green alga Chromochloris zofingiensis

BackgroundChromochloris zofingiensis is emerging as an industrially relevant alga given its robust growth for the production of lipids and astaxanthin, a value-added carotenoid with broad applications. Nevertheless, poor understanding of astaxanthin synthesis has limited engineering of this alga for rational improvements.ResultsTo reveal the molecular mechanism underlying astaxanthin accumulation in C. zofingiensis, here we conducted an integrated analysis by combining the time-resolved transcriptomes and carotenoid profiling in response to nitrogen deprivation (ND). A global response was triggered for C. zofingiensis to cope with the ND stress. Albeit the little variation in total carotenoid content, individual carotenoids responded differentially to ND: the primary carotenoids particularly lutein and β-carotene decreased, while the secondary carotenoids increased considerably, with astaxanthin and canthaxanthin being the most increased ones. The carotenogenesis pathways were reconstructed: ND had little effect on the carbon flux to carotenoid precursors, but stimulated astaxanthin biosynthesis while repressing lutein biosynthesis, thereby diverting the carotenoid flux from primary carotenoids to secondary carotenoids particularly astaxanthin. Comparison between C. zofingiensis and Haematococcus pluvialis revealed the distinctive mechanism of astaxanthin synthesis in C. zofingiensis. Furthermore, potential bottlenecks in astaxanthin synthesis were identified and possible engineering strategies were proposed for the alga.ConclusionsCollectively, these findings shed light on distinctive mechanism of carotenogenesis for astaxanthin biosynthesis in C. zofingiensis, identify key functional enzymes and regulators with engineering potential and will benefit rational manipulation of this alga for improving nutritional traits.

Transcriptomic and metabolic analysis of an astaxanthin-hyperproducing Haematococcus pluvialis mutant obtained by low-temperature plasma (LTP) mutagenesis under high light irradiation

Haematococcus pluvialis can accumulate sufficient levels of astaxanthin under various stress conditions. High light irradiation is essential for astaxanthin accumulation in Haematococcus pluvialis. However, a lack of genomic information limits the understanding of its physiological metabolism for high astaxanthin production. In this work, we investigated the wild-type (WT) strain and mutant strain (named as M3 which was obtained in our previous work) under high light irradiation and compared the difference in astaxanthin biosynthesis. We collected and analyzed the data of de novo transcriptome information of Haematococcus pluvialis at 24 h under high light stress. Our transcriptomic results indicated that M3 strain had higher utilization efficiency of CO2 to provide the precursors of carotenoid and fatty acid biosynthesis by increasing the expression levels of phosphoenolpyruvate carboxylase (PEPC), malate dehydrogenase (MDH), malate dehydrogenase (ME), ribulose bisphosphate carboxylase/oxygenase (Rubisco) activase (RCA) and glyceraldehyde 3-phosphate dehydrogenase (GAPDH) while decreasing the expression levels of fructose-1, 6-bisphosphatase (FBP). The analysis of pigments, chlorophyll fluorescence and the quantitative real-time polymerase chain reaction (qRT-PCR) analysis revealed that M3 strain maintained higher photosynthetic activity by regulating chlororespiration pathway and elevating non-photosynthetic pigment (lutein, β-carotene, and astaxanthin) content to alleviate photooxidative damage. Moreover, the M3 strain showed higher fatty acid content than the WT strain. Overall, combinative analysis of de novo transcriptomic and physiological data provided information necessary for not only a better understanding of the difference in astaxanthin biosynthesis between WT and M3 strains but also the feasibility of genetic engineering of Haematococcus pluvialis in the future.

Physiological and Metabolomics Analyses Reveal the Roles of Fulvic Acid in Enhancing the Production of Astaxanthin and Lipids in Haematococcus pluvialis under Abiotic Stress Conditions.

In this study, it was found that fulvic acid (FA) enhanced the contents of astaxanthin and lipids in Haematococcus pluvialis under high light and nitrogen starvation conditions by 2- and 1.2-fold, respectively. Meanwhile, the carbohydrate and chlorophyll contents were decreased by FA induction, whereas the levels of reactive oxygen species (ROS) and glutathione (GSH) as well as the expression of astaxanthin and lipid biosynthetic genes were increased. To further explore the interrelation between FA and the biosynthesis of astaxanthin and lipids, a metabolomics analysis of H. pluvialis by combined FA and abiotic stress exposure was conducted by using LC-MS/MS. The contents of some cytoprotective metabolites and signal molecules, including d-maltose, succinate, malic acid, melatonin (MT), and some amino acids, were increased under FA induction and abiotic stress conditions. These metabolites are intermediates in the TCA cycle and Calvin cycle, providing more precursors for the synthesis of astaxanthin and lipids. Moreover, the signal molecules might contribute to enhancing the abiotic stress tolerance. This study provided new insights into the regulatory mechanism of FA on astaxanthin and lipid accumulation in H. pluvialis.

Enhancement of Astaxanthin Biosynthesis in Oleaginous Yeast Yarrowia lipolytica via Microalgal Pathway.

Astaxanthin is a high-value red pigment and antioxidant used by pharmaceutical, cosmetics, and food industries. The astaxanthin produced chemically is costly and is not approved for human consumption due to the presence of by-products. The astaxanthin production by natural microalgae requires large open areas and specialized equipment, the process takes a long time, and results in low titers. Recombinant microbial cell factories can be engineered to produce astaxanthin by fermentation in standard equipment. In this work, an oleaginous yeast Yarrowia lipolytica was engineered to produce astaxanthin at high titers in submerged fermentation. First, a platform strain was created with an optimised pathway towards β-carotene. The platform strain produced 331 ± 66 mg/L of β-carotene in small-scale cultivation, with the cellular content of 2.25% of dry cell weight. Next, the genes encoding β-ketolase and β-hydroxylase of bacterial (Paracoccus sp. and Pantoea ananatis) and algal (Haematococcus pluvialis) origins were introduced into the platform strain in different copy numbers. The resulting strains were screened for astaxanthin production, and the best strain, containing algal β-ketolase and β-hydroxylase, resulted in astaxanthin titer of 44 ± 1 mg/L. The same strain was cultivated in controlled bioreactors, and a titer of 285 ± 19 mg/L of astaxanthin was obtained after seven days of fermentation on complex medium with glucose. Our study shows the potential of Y. lipolytica as the cell factory for astaxanthin production.

Astaxanthin biosynthesis: A two-step optimization approach and model construction with Response Surface Methodology and Artificial Neural Network

The first part of this research is investigating and comparing yield of a synthetic medium submerged three sugars (glucose, fructose and sucrose) at four different concentrations and solid fermentation systems with wheat bran and lentil waste for biosynthesis of astaxanthin (ASX) pigment by Xanthophyllomyces dendrorhous ATCC 24202 and Sporidiobolus salmonicolor ATCC 24259 microorganisms. The second part is modeling and optimizing the most efficient biosynthesis depending on waste, yeast and production variables consisted of moisture content, pH and temperature using a design matrix. The yields produced by X. dendrorhous were 51.88 µg of ASX/g glucose for the submerged medium with the least glucose, and 210.49 µg of ASX/g glucose for the wheat bran fermentation system. It was understood that the yield values of the submerged systems were lower and there was no requirement for the addition of any supplement to the waste systems. It was found that R2=0.9869 was the highest value with the maximum predicted ASX amount of 109.23 µg of ASX/g wheat bran with X. dendrorhous using Artificial Neural Network modeling and the moisture content was the most significant production parameter.

Effects of Methanol on Carotenoids as Well as Biomass and Fatty Acid Biosynthesis in Schizochytrium limacinum B4D1.

Schizochytrium is a promising source for the production of docosahexaenoic acid and astaxanthin. The effects of different methanol concentrations on astaxanthin, biomass, and production of the lipids, squalene, and total sterol in Schizochytrium limacinum B4D1 were investigated. Astaxanthin began to accumulate when the methanol concentration reached 3.2% and peaked at 5.6% methanol, with a 2,000-fold increase over that in the control. However, under cultivation with 5.6% methanol, the biomass, lipids, squalene, and total sterol decreased to various degrees. Transcriptomic analysis was performed to explore the effects of different methanol concentrations (0%, 3.2%, and 5.6%) on the expression profile of B4D1. Three key signaling pathways were found to play important roles in regulating cell growth and metabolism under cultivation with methanol. Five central carbon metabolism-associated genes were significantly downregulated in response to 5.6% methanol and thus were expected to result in less ATP and NADPH being available for cell growth and synthesis. High methanol conditions significantly downregulated three genes involved in fatty acid and squalene/sterol precursor biosynthesis but significantly upregulated geranylgeranyl diphosphate synthase, lycopene β-cyclase, and β-carotene 3-hydroxylase, which are involved in astaxanthin synthesis, thus resulting in an increase in the levels of precursors and the final production of astaxanthin. Additionally, the transcriptional levels of three stress response genes were upregulated. This study investigates gene expression profiles in the astaxanthin producer Schizochytrium when grown under various methanol concentrations. These results broaden current knowledge regarding genetic expression and provide important information for promoting astaxanthin biosynthesis in SchizochytriumIMPORTANCESchizochytrium strains are usually studied as oil-producing strains, but they can also synthesize other secondary metabolites, such as astaxanthin. In this study, methanol was used as an inducer, and we explored its effects on the production of astaxanthin, a highly valuable substance in Schizochytrium Methanol induced Schizochytrium to synthesize large amounts of astaxanthin. Transcriptomic analysis was used to investigate the regulation of signaling and metabolic pathways (mainly relative gene expression) in Schizochytrium grown in the presence of various concentrations of methanol. These results contribute to the understanding of the underlying molecular mechanisms and may aid in the future optimization of Schizochytrium for astaxanthin biosynthesis.

Fast-track production of astaxanthin by reduced cultivation time with the “red cell inoculation system” (RCIS) and various chemical cues in Haematococcus lacustris

Slow growth is the major obstacle in the production of astaxanthin in Haematococcus lacustris. Introduction of a “red cell inoculation system (RCIS)” reduced the culture time of H. lacustris by 43% by increasing its growth rate and inducing the earlier synthesis of astaxanthin. Red mature H. lacustris cells rather than green cyst cells were re-inoculated to decrease the growth period from 7 to 4 days by producing more zoospore cells. Starved red cells could take up nutrients quickly, thereby achieving faster growth. To further shorten the astaxanthin induction time, FeSO4, NaCl, and NaHCO3 were added to the cells, and their effects were compared. These chemicals accelerated astaxanthin biosynthesis, decreasing the production period from 7 to 4 days. This study focused on faster astaxanthin production to achieve economic feasibility by RCIS and chemical cues. Fast-track growth and a synthesis induction strategy enabled a more economic and efficient production of astaxanthin in H. lacustris.

Transcriptomic analysis unveils survival strategies of autotrophic Haematococcus pluvialis against high light stress

Haematococcus pluvialis, a commercial microalga, accumulates massive astaxanthin under biotic and abiotic stress conditions, particularly under high light conditions. Upon exposure to high light stress, the green motile cells rapidly differentiate into non-motile red cyst, which undergo dramatic morphology changes during subsequent encystment, including fall off the flagella, and formation of a thick secondary cell wall, finally accumulate abundant astaxanthin. Cell photosynthetic activities are inhibited first at day 1 under high light, while enhanced later when astaxanthin is highly accumulated after adapting to the stress condition. To further understand the adaptive responses of H. pluvialis to high light stress at transcriptional level, cells exposed to high light for 0, 1, 5 and 10 days were subjected to transcriptome analysis. High light caused significant transcriptomic alterations in cells. High light promoted astaxanthin biosynthesis by enhancing the expression of key genes involved in the MEP and astaxanthin biosynthesis pathway, and simultaneously inhibiting the expression of genes in the branch pathways. High light down-regulated the expression of genes associated with photosynthesis at day 1 while up-regulated those at day 5 and day 10. All those transcriptomic changes were consistent with above mentioned morphological and physiological changes. In addition, high light stressed cells maintained a ROS homeostasis via simultaneously up- and down-regulating different sets of paralogs genes of antioxidant enzyme. Furthermore, high light up-regulated constantly the expression of 29 transcriptional factors, potential key players in the defense response to high light stress and in the regulation of astaxanthin biosynthesis. This study reveals the survival strategies of H. pluvialis against high light stress and lays a theoretic foundation for metabolic engineering of astaxanthin in H. pluvialis.

A novel fed-batch strategy to boost cyst cells production based on the understanding of intracellular carbon and nitrogen metabolism in Haematococcus pluvialis

Haematococcus pluvialis is a prominent feedstock of astaxanthin. The ratio of carbon to nitrogen (C/N) strongly influences the metabolic pathways of mixotrophic-grown microalgae, however, its role involved in astaxanthin biosynthesis is still not fully understood. In this study, integrative metabolic and physiologic profiles were analyzed in elucidating how C/N affected carbon and nitrogen assimilation and thereby exerted influence on astaxanthin biosynthesis. It was demonstrated that high C/N up-regulated the activities of acetate kinase by increase of 5.76 folds in early logarithmic phase, leading a significant increase of acetyl-CoA. The increased carbon skeletons were then funneled into astaxanthin biosynthesis. Additionally, high C/N increased the proportion of carotenoid-intermediates in cytoplasm from chloroplast. Finally, a fed-batch cultivation strategy based on C/N gradient was developed. Biomass attained 9.18 g L−1 in 100% type of immotile cyst cells, which presented astaxanthin productivity at 15.45 mg L−1 d−1 afterward, exhibiting a promising paradigm in commercial production.

Validating biochemical features at the genome level in the Antarctic bacterium Hymenobacter sp. strain UV11.

We present experimental data that complement and validate some biochemical features at the genome level in the UVC-resistant Antarctic bacterium Hymenobacter sp. UV11 strain. The genome was sequenced, assembled and annotated. It has 6 096 246 bp, a GC content of 60.6% and 5155 predicted genes. The secretome analysis, by combining in silico predictions with shotgun proteomics data, showed that UV11 strain produces extracellular proteases and carbohydrases with potential biotechnological uses. We observed the formation of outer membrane vesicles, mesosomes and carbon-storage compounds by using transmission electron microscopy. The in silico analysis of the genome revealed the presence of genes involved in the metabolism of glycogen-like molecules and starch. By HPLC-UV-Vis analysis and 1H-NMR spectra, we verified that strain UV11 produces xanthophyll-like carotenoids such as 2'-hydroxyflexixanthin, and the in silico analysis showed that this bacterium has genes involved in the biosynthesis of cathaxanthin, zeaxanthin and astaxanthin. We also found genes involved in the repair of UV-damaged DNA such as a photolyase, the nucleotide excision repair system and the production of ATP-dependent proteases that are important cellular components involved in the endurance to physiological stresses. This information will help us to better understand the ecological role played by Hymenobacter strains in the extreme Antarctic environment.

Ethanol induced jasmonate pathway promotes astaxanthin hyperaccumulation in Haematococcus pluvialis

Haematococcus pluvialis is a main biological resource for the antioxidant astaxanthin production, however, potential modulators and molecular mechanisms underpinning astaxanthin accumulation remain largely obscured. We discovered that provision of ethanol (0.4%) significantly triggered the cellular astaxanthin content up to 3.85% on the 4th day of treatment. Amongst, 95% of the accumulated astaxanthin was esterified, particularly enriched with monoesters. Ultrastructural analysis revealed that ethanol altered cell wall structure and physiological properties. Antioxidant analyses revealed that astaxanthin accumulation offset the ethanol induced oxidative stress. Ethanol treatment reduced carbohydrates while increased lipids and jasmonic acid production. Transcriptomic analysis uncovered that ethanol orchestrated the expression of crucial genes involved in carotenogenesis, e.g. PSY, BKT and CRTR-b were significantly upregulated. Moreover, methyl jasmonic acid synthesis was induced and played a major role in regulating the carotenogenic genes. The findings uncovered the novel viewpoint in the intricate transcriptional regulatory mechanisms of astaxanthin biosynthesis.

Advances in astaxanthin biosynthesis in Haematococcus pluvialis

Astaxanthin is widely applied as a nutraceutical, pharmaceutical, and aquaculture feed additive because of its high antioxidant activity. Haematococcus pluvialis is a microalgal species that can largely accumulate astaxanthin under adverse environmental conditions. Here we review the research progress of astaxanthin biosynthesis in H. pluvialis, including the induction and regulation of massive astaxanthin, the relationship between astaxanthin synthesis, photosynthesis and lipid metabolism.

Multilevel heuristic LED regime for stimulating lipid and bioproducts biosynthesis in Haematococcus pluvialis under mixotrophic conditions

Enhanced biosynthesis and overproduction of lipid and high-value bioproducts endows microalgae as a promising feedstock for the cost-effective development of advanced bioenergy currently. In this study, multilevel heuristic LED regimes, designed with the coordination of light, nitrogen and carbons in terms of cell physiology and morphology, have been implemented to significantly induce the growth and bioproducts accumulation of Haematococcus pluvialis under mixotrophic conditions. The white-red regime with C5 organic carbon showed a good potential for enhancing microalgal biomass and lipid synthesis, especially for saturated fatty acids. The astaxanthin biosynthesis has been significantly enhanced and the highest content of 3.3% was achieved with gluconate at the white-blue regime. Additionally, white-blue regime enhanced the protein content of H. pluvialis up to 45%, increased by 40% over the white-red culture. The multilevel LED protocol can be developed synergistically with the different adaptation and tolerance of algal cell physiology and morphology for target bioproducts.