Exogenous sodium fumarate enhances astaxanthin accumulation in Haematococcus pluvialis by enhancing the respiratory metabolic pathway

A Study on the Effect of Various Media and the Supplementation of Organic Compounds on the Enhanced Production of Astaxanthin from Haematococcus lacustris (Girod-Chantrans) Rostafinski (Chlorophyta)

Natural astaxanthin is in high demand due to its multiple health benefits. The microalga Haematococcus lacustris has been used for the commercial production of astaxanthin. In this study, we investigated the effects of six different media with and without a nitrogen source and supplementation with nine organic compounds on the growth and astaxanthin accumulation of H. lacustris. The highest astaxanthin contents were observed in cultures of H. lacustris in Jaworski's medium (JM), with a level of 9.099 mg/L in JM with a nitrogen source supplemented with leucine (0.65 g/L) and of 20.484 mg/L in JM without a nitrogen source supplemented with sodium glutamate (0.325 g/L). Six of the nine organic compounds examined (leucine, lysine, alanine, sodium glutamate, glutamine, and cellulose) enhanced the production of astaxanthin in H. lacustris, while malic acid, benzoic acid, and maltose showed no beneficial effects.

The combination of uridine and nitrogen-deprivation promotes the efficient formation of astaxanthin-rich motile cells in Haematococcus pluvialis

Astaxanthin accumulation in Haematococcus pluvialis typically occurs alongside the formation of secondary cell wall (SCW), hindering astaxanthin extraction and bio-accessibility. A potential solution lies in cultivating astaxanthin-rich motile cells lacking SCW. This study explored the influence and underlying mechanism of nitrogen-deprivation (ND) on SCW formation and established a connection between pyrimidine metabolism and SCW development. Then, various pyrimidine and ND combinations were examined to cultivate astaxanthin-rich motile cells. The results indicated that, compared to the nitrogen-replete group, the combination of uridine and ND increased the proportion of motile cells by 25-33 times, achieving 95 %, and enhanced astaxanthin yield by 26.52 %. Moreover, the efficiency of astaxanthin extraction from intact, wet motile cells was 91 % - 95 %, which was 5.6-9.0 times that from non-motile cells. This study not only presents a promising method for producing astaxanthin-rich motile cells in H. pluvialis but also provides insights into the relationship between pyrimidine metabolism and SCW development.

Biotechnological strategies overcoming limitations to H. pluvialis-derived astaxanthin production and Morocco's potential

Haematococcus pluvialis is the richest source of natural astaxanthin, but the production of H. pluvialis-derived astaxanthin is usually limited by its slow cell proliferation and astaxanthin accumulation. Efforts to enhance biomass productivity, astaxanthin accumulation, and extraction are ongoing. This review highlights different approaches that have previously been studied in microalgal species for enhanced biomass productivity, as well as optimized methods for astaxanthin accumulation and extraction, and how these methods could be combined to bypass the challenges limiting natural astaxanthin production, particularly in H. pluvialis, at all stages (biomass production, and astaxanthin accumulation and extraction). Biotechnological approaches, such as overexpressing low CO2 inducible genes, utilizing complementary carbon sources, CRISPR-Cas9 bioengineering, and the use of active compounds, for biomass productivity are outlined. Direct astaxanthin extraction from H. pluvialis zoospores and Morocco's potential for microalgal-based astaxanthin production are equally discussed. This review emphasizes the need to engineer an optimized H. pluvialis-derived astaxanthin production system combining two or more of these strategies for increased growth, and astaxanthin productivity, to compete in the larger, lower-priced market in aquaculture and nutraceutical sectors.

A novel drying film culture method applying a natural phenomenon: Increased carotenoid production by Haematococcus sp

Low productivity and high cost remain major bottlenecks for the large-scale production of Haematococcus sp. This study explored biomass production and carotenoid accumulation in Haematococcus sp. (KCTC 12348BP) using drying film culture. The broth-cultured strain (3.2 × 106 cells/mL, 0.83 ± 0.02 mg/mL for a 21 d culture) was cultured under various conditions (different inoculum volumes and mist feeding intervals) in waterless agar plates at 28 ± 0.5 °C, under fluorescent light (12 h light-dark cycle) for 1 month. The maximum biomass obtained was 17.60 ± 0.72 g/m2, while the maximum astaxanthin concentration was 8.23 ± 1.13 mg/g in the culture using 1 mL inoculum and 3 d feeding interval. Drought stress in drying film culture effectively induced the accumulation of carotenoids from β-carotene, facilitating the production of canthaxanthin via the astaxanthin biosynthesis pathway. This cost-effective culture system can increase the biomass and carotenoid pigment production in Haematococcus sp.

Comprehensive understanding of the regulatory mechanism by which selenium nanoparticles boost CO2 fixation and cadmium tolerance in lipid-producing green algae under recycled medium

Recycled medium plus cadmium is a promising technique for reducing the cultivation cost and enhancing the yield of microalgae lipids. However, oxidative stress and cadmium toxicity significantly hinder the resulting photosynthetic efficiency, cell growth and cell activity. Herein, selenium nanoparticles (SeNPs) were used to increase the total biomass, biolipid productivity, and tolerance to cadmium. Wide-ranging analyses of photosynthesis, energy yield, fatty acid profiles, cellular ultrastructure, and oxidative stress biomarkers were conducted to examine the function of SeNPs in CO2 fixation and cadmium resistance in Ankistrodesmus sp. EHY. The application of 15 μM cadmium and 2 mg L-1 SeNPs further enhanced the algal biomass productivity and lipid productivity to 500.64 mg L-1 d-1 and 301.14 mg L-1 d-1, respectively. Moreover, the rates of CO2 fixation, chlorophyll synthesis and total nitrogen removal were similarly increased by the application of SeNPs. Exogenous SeNPs strengthened cell growth and cadmium tolerance by upregulating photosynthesis, the TCA cycle and the antioxidant system, reducing the uptake and translocation of cadmium, and decreasing the levels of reactive oxidative stress (ROS), extracellular polymeric substances (EPSs) and cellular Cd2+ level in EHY under recycled medium and cadmium stress conditions. Additionally, a maximum energy yield of 127.40 KJ L-1 and a lipid content of 60.15% were achieved in the presence of both SeNPs and cadmium stress. This study may inspire the efficient disposal of recycled medium and biolipid production while also filling the knowledge gaps regarding the mechanisms of SeNP functions in carbon fixation and cadmium tolerance in microalgae.

Astaxanthin: Past, Present, and Future

Astaxanthin (AX), a lipid-soluble pigment belonging to the xanthophyll carotenoids family, has recently garnered significant attention due to its unique physical properties, biochemical attributes, and physiological effects. Originally recognized primarily for its role in imparting the characteristic red-pink color to various organisms, AX is currently experiencing a surge in interest and research. The growing body of literature in this field predominantly focuses on AXs distinctive bioactivities and properties. However, the potential of algae-derived AX as a solution to various global environmental and societal challenges that threaten life on our planet has not received extensive attention. Furthermore, the historical context and the role of AX in nature, as well as its significance in diverse cultures and traditional health practices, have not been comprehensively explored in previous works. This review article embarks on a comprehensive journey through the history leading up to the present, offering insights into the discovery of AX, its chemical and physical attributes, distribution in organisms, and biosynthesis. Additionally, it delves into the intricate realm of health benefits, biofunctional characteristics, and the current market status of AX. By encompassing these multifaceted aspects, this review aims to provide readers with a more profound understanding and a robust foundation for future scientific endeavors directed at addressing societal needs for sustainable nutritional and medicinal solutions. An updated summary of AXs health benefits, its present market status, and potential future applications are also included for a well-rounded perspective.

Deciphering the toxicity mechanism of haloquinolines on Chlorella pyrenoidosa using QSAR and metabolomics approaches

The hazardous potential of haloquinolines (HQLs) is becoming an issue of great concern due to its wide and long-term usage in many personal care products. We examined the growth inhibition, structure-activity relationship, and toxicity mechanism of 33 HQLs on Chlorella pyrenoidosa using the 72-h algal growth inhibition assay, three-dimensional quantitative structure-activity relationship (3D-QSAR), and metabolomics. We found that the IC₅₀ (half maximal inhibitory concentration) values for 33 compounds ranged from 4.52 to > 150 mg·L^-1, most tested compounds were toxic (1 mg·L^-1 < IC₅₀ < 10 mg·L^-1) or harmful (10 mg·L^-1 < IC₅₀ < 100 mg·L^-1) for the aquatic ecosystem. Hydrophobic properties of HQLs dominate their toxicity. Halogen atoms with large volume appear at the 2, 3, 4, 5, 6, and 7-positions of the quinoline ring to significantly increase the toxicity. In algal cells, HQLs can block diverse carbohydrates, lipids, and amino acid metabolism pathways, thereby resulting in energy usage, osmotic pressure regulation, membrane integrity, oxidative stress disorder, thus fatally damaging algal cells. Therefore, our results provide insight into the toxicity mechanism and ecological risk of HQLs.

Metabolomic analysis reveals astaxanthin biosynthesis in heterotrophic microalga Chromochloris zofingiensis

The utilization of gibberellic acid-3, high carbon/nitrogen ratio and salinity concentration can effectively enhance astaxanthin biosynthesis in Chromochloris zofingiensis under the heterotrophic conditions, but the underlying mechanisms remained yet to be investigated. The metabolomics analysis revealed that enhancement of the glycolysis, pentose phosphate pathways (PPP), and tricarboxylic acid (TCA) cycle led to astaxanthin accumulation under the induction conditions. The increased fatty acids can significantly increase astaxanthin esterification. The addition of appropriate concentrations of glycine (Gly) and γ-aminobutyric acid (GABA) promoted astaxanthin biosynthesis in C. zofingiensis, as well as benefiting for biomass yield. With the addition of 0.5 mM GABA, the astaxanthin yield increased to 0.35 g·L^-1, which was 1.97-fold higher than that of the control. This study advanced understanding about astaxanthin biosynthesis in heterotrophic microalga, and provided novel strategies for enhanced astaxanthin production in C. zofingiensis.

Photoprotective carbon redistribution in mixotrophic Haematococcus pluvialis under high light stress

Mixotrophy of Haematococcus pluvialis is a potential strategy for producing astaxanthin. However, this strategy has not been extensively commercialized because the mixotrophic mechanisms by which H. pluvialis overcomes high light stress are unclear. This study analyzed the biochemical compositions and differential proteomics of mixotrophic H. pluvialis under different light conditions. High light exposure substantially increased astaxanthin, carbohydrate, and fatty acid contents. A total of 119 and 81 proteins were significantly up- and down-regulated after two days of high light exposure. These proteins mainly enriched pathways for photosynthetic metabolism, glyoxylate cycle, and biosynthesis of secondary metabolites. This study proposed a regulatory model through which mixotrophic H. pluvialis copes with high light stress. The model includes pathways for modulating photosynthetic apparatus, increasing astaxanthin accumulation by enhancing photorespiration, pentose phosphate and Embden-Meyerhof-Parna pathways, while thickening the cell wall by malate-oxaloacetate shuttle.

A strategy for interfering with the formation of thick cell walls in Haematococcus pluvialis by down-regulating the mannan synthesis pathway

The challenges associated with effective cell wall disruption remain an important bottleneck that has restricted efforts to extract astaxanthin from Haematococcus pluvialis. Here, available transcriptomic data and an Agrobacterium tumefaciens-mediated transformation system were used to establish an H. pluvialis strain in which the key cell wall formation-related enzyme α-1,6-mannosyltransferase (HpOCH1) was downregulated in an effort to thin cell walls and thereby simplify the astaxanthin extraction process. The cell wall remodeling activity observed in these HpOch1 knockdown H. pluvialis cells resulted in dramatic reductions in the mannan organization and protective ability of the established cell walls. The cell fragmentation rate increased by 58% in HpOch1^- group relative to the control group. Critically, astaxanthin synthesis was not altered in the HpOch1 knockdown cells. Overall, this study highlights a novel technical approach to artificial cell wall thinning, offering a foundation for further efforts to more effectively leverage the astaxanthin resources of H. pluvialis.

Transcriptome Analysis of the Accumulation of Astaxanthin in Haematococcus pluvialis Treated with White and Blue Lights as well as Salicylic Acid

Haematococcus pluvialis is the most commercially valuable microalga for the production of natural astaxanthin, showing enhanced production of astaxanthin with the treatments of high-intensity light and hormones. The molecular mechanisms regulating the biosynthesis of astaxanthin in H. pluvialis treated with white light, blue light, and blue light with salicylic acid (SA) were investigated based on the transcriptome analysis. Results showed that the combined treatment with both blue light and SA generated the highest production of astaxanthin. A total of 109,443 unigenes were identified to show that the genes involved in the tricarboxylic acid (TCA) cycle, the pentose phosphate pathway (PPP), and the astaxanthin biosynthesis were significantly upregulated to increase the production of the substrates for the synthesis of astaxanthin, i.e., pyruvate and glyceraldehyde-3-phosphate generated in the TCA cycle and PPP, respectively. Results of transcriptome analysis were further verified by the quantitative real-time PCR (qRT-PCR) analysis, showing that the highest content of astaxanthin was obtained with the expression of the bkt gene significantly increased. Our study provided the novel insights into the molecular mechanisms regulating the synthesis of astaxanthin and an innovative strategy combining the exogenous hormone and physical stress to increase the commercial production of astaxanthin by H. pluvialis.

Sustainable production of astaxanthin in microorganisms: the past, present, and future

Astaxanthin (3,3'-dihydroxy-4,4'-diketo-β-carotene) is a type of C40 carotenoid with remarkable antioxidant characteristics, showing significant application prospects in many fields. Traditionally, the astaxanthin is mainly obtained from chemical synthesis and natural acquisition, with both approaches having many limitations and not capable of meeting the growing market demand. In order to cope with these challenges, novel techniques, e.g., the innovative cell engineering strategies, have been developed to increase the astaxanthin production. In this review, we first elaborated the biosynthetic pathway of astaxanthin, with the key enzymes and their functions discussed in the metabolic process. Then, we summarized the conventional, non-genetic strategies to promote the production of astaxanthin, including the methods of exogenous additives, mutagenesis, and adaptive evolution. Lastly, we reviewed comprehensively the latest studies on the synthesis of astaxanthin in various recombinant microorganisms based on the concept of microbial cell factory. Furthermore, we have proposed several novel technologies for improving the astaxanthin accumulation in several model species of microorganisms.

The Dynamic Behaviors of Photosynthesis during Non-Motile Cell Germination in Haematococcus pluvialis

Haematococcus pluvialis undergoes a three-phase process during the process of germination: first, repeated mitotic events; next, cytokinesis to form the zoospore; and finally, a fast release of motile cells. Physiological properties were measured using chlorophyll a fluorescence (OJIP) transient. The most obvious increase in K-value and L-value appeared at 17 h, suggesting that oxygen-evolving complex damage and lower energetic connectivity of the photosystem II units of the mother non-motile cell occurred. Compared to phase I, the values of the maximum quantum yield of PSII photochemistry (FV/FM) and PIABS increased significantly in phases II and III, suggesting that photosynthetic photochemical activity was greatly up-regulated during cytokinesis to form zoospores and the fast release of motile cells. Moreover, the significant increase in the K-band at 17 h and 22 h indicates that the PSII donor side was the limiting factor during the initial period of germination. All these results suggest that the cellular photosynthetic activity continues to strengthen during cytokinesis to form the zoospore and the fast release of motile cells, and it was postulated to meet the demands for sporangium swelling and new organelle formation.

Enhancement of astaxanthin accumulation in Haematococcus pluvialis by exogenous oxaloacetate combined with nitrogen deficiency

Effective inducers and stress conditions play an essential role in the regulation of astaxanthin biosynthesis. This study reports a strategy developed by combining exogenous addition of oxaloacetate (OA) with nitrogen deficiency to facilitate astaxanthin production in Haematococcus pluvialis. Significantly, addition of 10 mM-OA enhanced the cellular astaxanthin content about 7.18-fold under nitrogen deficiency on day 7, with the content of astaxanthin esters increased concomitantly. To further elucidate the role and mechanism of OA on astaxanthin synthesis, the physiological and metabolic analyses of H. pluvialis treated with exogenous OA were performed. The results showed that exogenous OA promoted respiration over photosynthesis. Concurrently, the metabolite levels in the Embden-Meyerhof-Parnas pathway, pentose phosphate pathway and tricarboxylic acid cycle obviously increased. The enhancement of respiratory metabolic pathways led to elevated levels of substrates, thus directly promoted astaxanthin synthesis. The present findings provide a new and effective approach for optimizing astaxanthin production.