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

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.

Synchronous enhancement of astaxanthin and lipid accumulation in Haematococcus lacustris through co-mutation of ethanol and atmospheric and room temperature plasma: Exploration of characteristics and underlying mechanisms

Haematococcus lacustris is a precious algal species renowned for its ability to simultaneous production of astaxanthin and lipid. However, its slow growth rate necessitates the development of appropriate mutagenesis methodologies to effectively enhance its synchronous production of both astaxanthin and lipid. This study introduced the co-mutation of Atmospheric and Room Temperature Plasma (ARTP) and ethanol. The performance and preliminary mechanisms underlying the combined accumulation of astaxanthin and lipid in H. lacustris under both mutations by ARTP and ethanol were comparatively analyzed. Combined astaxanthin and lipid contents relative to total cell mass in the 110-2 strain reached 54.4%, surpassing that of strain 0-3 and the control by 17.0% and 47.6% respectively. Transcriptome level analysis revealed how both ethanol and ARTP induction promote the expressions of carotenoid and lipid synthesis genes and related enzymatic activities. Upregulation of genes associated with cell activity contributed to lipid and astaxanthin metabolism in multi pathways.

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.

Astaxanthin production from the microalga Haematococcus lacustris with a dual substrate mixotrophy strategy

This study investigates the development of dual-substrate mixotrophy strategy to cultivate the microalga Haematococcus lacustris for astaxanthin production. The influence of different concentrations of acetate and pyruvate on biomass productivity was first assessed individually, and then both substrates were used together to improve biomass growth in the green phase and astaxanthin accumulation in red the phase. The results showed that dual-substrates mixotrophy significantly increased the biomass productivity during green growth phase up to 2-fold compared to phototrophic controls. Furthermore, supplementation of dual-substrate to the red phase increased astaxanthin accumulation by 10% in the dual-substrate group compared to single-substrate acetate and no substrate. This dual-substrate mixotrophy approach shows promise for cultivating Haematococcus for commercial production of biological astaxanthin in indoor closed systems.

Metabolite analysis of soybean oil on promoting astaxanthin production of Phaffia rhodozyma

BACKGROUND

Astaxanthin is a carotenoid with strong antioxidant property. In addition, it has anti-cancer, anti-tumor, anti-inflammatory and many other functions. The micro-organisms that mainly produce astaxanthin are Haematococcus pluvialis and Phaffia rhodozyma. Compared with H. pluvialis, P. rhodozyma has shorter fermentation cycle and easier to control culture conditions, but the yield of astaxanthin in P. rhodozyma is low. This article studied how to improve the astaxanthin production of P. rhodozyma.

RESULTS

The results showed that when 10 mL L^-1 soybean oil was added to the culture medium, astaxanthin production increased significantly, reaching 7.35 mg L^-1 , which was 1.4 times that of the control group, and lycopene and β-carotene contents also increased significantly. Through targeted metabolite analysis, the fatty acids in P. rhodozyma significantly increased under the soybean oil stimulation, especially the fatty acids closely related to the formation of astaxanthin esters, included palmitic acid (C16:0), stearic acid (C18:0), oleic acid (C18:1n9), linoleic acid (C18:2n6), α-linolenic acid (C18:3n3) and γ-linolenic acid (C18:3n6), thereby increasing the astaxanthin esters content.

CONCLUSION

It showed that the addition of soybean oil can promote the accumulation of astaxanthin by promoting the increase of astaxanthin ester content. © 2022 Society of Chemical Industry.

Development of a 5-aminolevulinic acid feeding strategy capable of enhancing Haematococcus pluvialis biomass, astaxanthin, and fatty acid yields

Effective inducers play essential roles in the regulation of cell growth and astaxanthin production in Haematococcus pluvialis. Here, a novel 5-aminolevulinic acid (5-ALA) feeding strategy was developed and found to enhance H. pluvialis biomass, fatty acid, and astaxanthin yields. Specifically, 5-ALA feeding (4 μM) on day 1 caused respective 23.8 %, 24.8 %, and 20.3 % increases in biomass, fatty acid, and astaxanthin yields. The observed enhancement of biomass accumulation associated with the provision of 5-ALA during the early stages of growth was attributable to enhanced photosynthetic carbon assimilation. This increased biomass accumulation, in turn, contributed to the measured increases in both fatty acid and astaxanthin yields. Overall, these results provide new insight into the importance of photosynthetic carbon assimilation as a determinant of biomass accumulation and a regulator of both fatty acid and astaxanthin production, while offering an effective strategy capable of accelerating astaxanthin production by H. pluvialis in commercial agricultural contexts.

Increasing production and bio-accessibility of natural astaxanthin in Haematococcus pluvialis by screening and culturing red motile cells under high light condition

The thick cell wall and low astaxanthin productivity were two important bottlenecks limiting industrial production of astaxanthin via Haematococcus pluvialis. This study reports a strategy for increasing production and bio-accessibility of astaxanthin in H. pluvialis by screening and culturing red motile cells under high light condition. Compared with the original strain NBU489, the biomass of the novel isolated strain RMS10 increased by 31.9% under low light condition, and the astaxanthin content (44.6 mg/g) increased by 53.3% after 9-day high light induction, which were readily extracted and digested without cell disruption. Subsequent transcriptomic analysis confirmed the accumulation of astaxanthin and lipids in RMS10 cells as expression of genes associated with biosynthesis of fatty acid and astaxanthin were up-regulated, while those involved in thick cell wall biosynthesis and reactive oxygen species scavenging were down-regulated in RMS10. Collectively, this study provides a simple and effective method for economical production of natural astaxanthin.

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.

Coelastrella terrestris for Adonixanthin Production: Physiological Characterization and Evaluation of Secondary Carotenoid Productivity

A novel strain of Coelastrella terrestris (Chlorophyta) was collected from red mucilage in a glacier foreland in Iceland. Its morphology showed characteristic single, ellipsoidal cells with apical wart-like wall thickenings. Physiological characterization revealed the presence of the rare keto-carotenoid adonixanthin, as well as high levels of unsaturated fatty acids of up to 85%. Initial screening experiments with different carbon sources for accelerated mixotrophic biomass growth were done. Consequently, a scale up to 1.25 L stirred photobioreactor cultivations yielded a maximum of 1.96 mg·L⁻¹ adonixanthin in free and esterified forms. It could be shown that supplementing acetate to the medium increased the volumetric productivity after entering the nitrogen limitation phase compared to autotrophic control cultures. This study describes a promising way of biotechnological adonixanthin production using Coelastrella terrestris.

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.

A strategy for promoting carbon flux into fatty acid and astaxanthin biosynthesis by inhibiting the alternative oxidase respiratory pathway in Haematococcus pluvialis

In the present study, the mechanisms for facilitating fatty acid and astaxanthin biosynthesis-related processes by inhibiting the alternative oxidase (AOX) respiratory pathway in Haematococcus pluvialis was investigated. The restriction of the AOX pathway induced the accumulation of reactive oxygen species, NAD(P)H and its substrates (acetyl-CoA, pyruvate and glyceraldehy-3-phosphate), which are required for fatty acid and astaxanthin production, thereby promoting the carbon flux into fatty acid and astaxanthin biosynthesis. During a 9-day incubation period, the fatty acid and astaxanthin contents increased by 20.6% and 20.7%, respectively, when the AOX pathway was inhibited approximately 37.7%. The AOX pathway may be inhibited by nutrient (nitrogen and phosphorus) removal, inhibitor addition and air/CO₂ aeration adjustments in the large-scale cultivation of H. pluvialis. Therefore, the current study provides a useful enhancement strategy for fatty acid and astaxanthin coproduction and elucidates the roles of the AOX pathway in regulating fatty acid and astaxanthin biosynthesis.

Enhanced β-carotene and Biomass Production by Induced Mixotrophy in Dunaliella salina across a Combined Strategy of Glycerol, Salinity, and Light

Current mixotrophic culture systems for Dunaliella salina have technical limitations to achieve high growth and productivity. The purpose of this study was to optimize the mixotrophic conditions imposed by glycerol, light, and salinity that lead to the highest biomass and β-carotene yields in D. salina. The combination of 12.5 mM glycerol, 3.0 M salinity, and 50 μmol photons m⁻² s⁻¹ light intensity enabled significant assimilation of glycerol by D. salina and consequently enhanced growth (2.1 × 10⁶ cell mL⁻¹) and β-carotene accumulation (4.43 pg cell⁻¹). The saline and light shock induced the assimilation of glycerol by this microalga. At last stage of growth, the increase in light intensity (300 μmol photons m⁻² s⁻¹) caused the β-carotene to reach values higher than 30 pg cell⁻¹ and tripled the β-carotene values obtained from photoautotrophic cultures using the same light intensity. Increasing the salt concentration from 1.5 to 3.0 M NaCl (non-isosmotic salinity) produced higher growth and microalgal β-carotene than the isosmotic salinity 3.0 M NaCl. The mixotrophic strategy developed in this work is evidenced in the metabolic capability of D. salina to use both photosynthesis and organic carbon, viz., glycerol that leads to higher biomass and β-carotene productivity than that of an either phototrophic or heterotrophic process alone. The findings provide insights into the key role of exogenous glycerol with a strategic combination of salinity and light, which evidenced unknown roles of this polyol other than that in osmoregulation, mainly on the growth, pigment accumulation, and carotenogenesis of D. salina.

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

Improvement of astaxanthin yield is a continuing objective in Haematococcus pluvialis cultivation. In this study, a new strategy combining exogenous sodium fumarate (SF) with nitrogen deficiency was demonstrated to promote astaxanthin accumulation in H. pluvialis. SF significantly accelerated astaxanthin synthesis over cell growth. Notably, under nitrogen deficiency, 10 mM SF increased the cellular astaxanthin content by 1.75-fold and 1.47-fold on day 7 and 12, respectively. Further studies indicated that SF increased the level of respiratory metabolites in the Embden-Meyerhof-Parnas pathway, tricarboxylic acid cycle and pentose phosphate pathway. An enhanced substrate pool due to the acceleration of respiratory metabolic pathways directly induced astaxanthin synthesis. Meanwhile, the accumulation of C18:1, C18:2 and C18:3 fatty acids enhanced astaxanthin synthesis indirectly by promoting the process of esterification. This study not only helps to elucidate the role of respiratory metabolic pathways in astaxanthin synthesis but also provides a new effective technique to improve astaxanthin production.

"Light modulates transcriptomic dynamics upregulating astaxanthin accumulation in Haematococcus: A review"

Haematococcus pluvialis is a green alga that can accumulate high astaxanthin content, a commercially demanding market keto food. Due to its high predicted market value of about 3.4 billion USD in 2027, it is essential to increase its production. Therefore, it is crucial to understand the genetic mechanism and gene expressions profile during astaxanthin synthesis. The effect of poly- and mono-chromatic light of different wavelengths and different intensities have shown to influence the gene expression towards astaxanthin production. This includes transcriptomic gene analysis in H. pluvialis underneath different levels of illumination stress. This review has placed the most recent data on the effects of light on bioastaxanthin production in the context of previous studies, which were more focused on the biochemical and physiological sides. Doing so, it contributes to delineate new ways along the biotechnological process with the aim to increase bioastaxanthin production while decreasing production costs.

Using green alga Haematococcus pluvialis for astaxanthin and lipid co-production: Advances and outlook

Astaxanthin is one of the secondary carotenoids involved in mediating abiotic stress of microalgae. As an important antioxidant and nutraceutical compound, astaxanthin is widely applied in dietary supplements and cosmetic ingredients. However, most astaxanthin in the market is chemically synthesized, which are structurally heterogeneous and inefficient for biological uptake. Astaxanthin refinery from Haematococcus pluvialis is now a growing industrial sector. H. pluvialis can accumulate astaxanthin to ∼5% of dry weight. As productivity is a key metric to evaluate the production feasibility, understanding the biological mechanisms of astaxanthin accumulation is beneficial for further production optimization. In this review, the biosynthesis mechanism of astaxanthin and production strategies are summarized. The current research on enhancing astaxanthin accumulation and the potential joint-production of astaxanthin with lipids was also discussed. It is conceivable that with further improvement on the productivity of astaxanthin and by-products, the algal-derived astaxanthin would be more accessible to low-profit applications.

Carotenoids from fungi and microalgae: A review on their recent production, extraction, and developments

The demand for carotenoids from natural sources obtained by biological extraction methods is increasing with the development of biotechnology and the continued awareness of food safety. Natural plant-derived carotenoids have a relatively high production cost and are affected by the season, while microbial-derived carotenoids are favored due to their natural, high-efficiency, low production cost, and ease of industrialization. This article reviewed the following aspects of natural carotenoids derived from microorganisms: (1) the structures and properties of main carotenoids; (2) fungal and microalgal sources of the main carotenoids; (3) influencing factors and modes of improvement for carotenoids production; (4) efficient extraction methods for carotenoids; and (5) the commercial value of carotenoids. This review provided a reference and guidance for the development of natural carotenoids derived from microorganisms.

Simultaneous promotion of photosynthesis and astaxanthin accumulation during two stages of Haematococcus pluvialis with ammonium ferric citrate

To simultaneously promote biomass yield and astaxanthin content of Haematococcus pluvialis, ammonium ferric citrate (AFC) was employed to stimulate light harvest in photosynthesis during the green stage and oxidation induction in astaxanthin accumulation during the red stage. AFC not only improved chlorophyll synthesis by 22.5% to provide more electrochemical potential energy in the green stage, but also alleviated photosystem II damage to maintain a high level of effective quantum yield by enhancing carotenoid production. The citrate derived from AFC stimulated acetyl-CoA and NADPH production through citric acid cycle and transaminase cycle during the red stage, resulting in an increased lipid content by 1.77-fold. The astaxanthin content in H. pluvialis cells cultivated with 5 μM AFC was 12.5% higher than that without AFC, which was attributed to severe oxidative stress caused by AFC through Haber-Weiss reaction. These results provided a new approach to reduce emission of greenhouse gasses with producing high-value products.

Novel Insights into the Biotechnological Production of Haematococcus pluvialis-Derived Astaxanthin: Advances and Key Challenges to Allow Its Industrial Use as Novel Food Ingredient

Astaxanthin shows many biological activities. It has acquired a high economic potential and its current market is dominated by its synthetic form. However, due to the increase of the health and environmental concerns from consumers, natural forms are now preferred for human consumption. Haematococcus pluvialis is artificially cultured at an industrial scale to produce astaxanthin used as a dietary supplement. However, due to the high cost of its cultivation and its relatively low biomass and pigment productivities, the astaxanthin extracted from this microalga remains expensive and this has probably the consequence of slowing down its economic development in the lower added-value market such as food ingredient. In this review, we first aim to provide an overview of the chemical and biochemical properties of astaxanthin, as well as of its natural sources. We discuss its bioavailability, metabolism, and biological activities. We present a state-of-the-art of the biology and physiology of H. pluvialis, and highlight novel insights into the biotechnological processes which allow optimizing the biomass and astaxanthin productivities. We are trying to identify some lines of research that would improve the industrial sustainability and economic viability of this bio-production and to broaden the commercial potential of astaxanthin produced from H. pluvialis.

Recent Advances in Astaxanthin Micro/Nanoencapsulation to Improve Its Stability and Functionality as a Food Ingredient

Astaxanthin is a carotenoid produced by different organisms and microorganisms such as microalgae, bacteria, yeasts, protists, and plants, and it is also accumulated in aquatic animals such as fish and crustaceans. Astaxanthin and astaxanthin-containing lipid extracts obtained from these sources present an intense red color and a remarkable antioxidant activity, providing great potential to be employed as food ingredients with both technological and bioactive functions. However, their use is hindered by: their instability in the presence of high temperatures, acidic pH, oxygen or light; their low water solubility, bioaccessibility and bioavailability; their intense odor/flavor. The present paper reviews recent advances in the micro/nanoencapsulation of astaxanthin and astaxanthin-containing lipid extracts, developed to improve their stability, bioactivity and technological functionality for use as food ingredients. The use of diverse micro/nanoencapsulation techniques using wall materials of a different nature to improve water solubility and dispersibility in foods, masking undesirable odor and flavor, is firstly discussed, followed by a discussion of the importance of the encapsulation to retard astaxanthin release, protecting it from degradation in the gastrointestinal tract. The nanoencapsulation of astaxanthin to improve its bioaccessibility, bioavailability and bioactivity is further reviewed. Finally, the main limitations and future trends on the topic are discussed.