Effect of red cyst cell inoculation and iron(II) supplementation on autotrophic astaxanthin production by Haematococcus pluvialis under outdoor summer conditions

Microbial astaxanthin: from bioprocessing to the market recognition

The attractive biological properties and health benefits of natural astaxanthin (AXT), including its antioxidant and anti-carcinogenic properties, have garnered significant attention from academia and industry seeking natural alternatives to synthetic products. AXT, a red ketocarotenoid, is mainly produced by yeast, microalgae, wild or genetically engineered bacteria. Unfortunately, the large fraction of AXT available in the global market is still obtained using non-environmentally friendly petrochemical-based products. Due to the consumers concerns about synthetic AXT, the market of microbial-AXT is expected to grow exponentially in succeeding years. This review provides a detailed discussion of AXT's bioprocessing technologies and applications as a natural alternative to synthetic counterparts. Additionally, we present, for the first time, a very comprehensive segmentation of the global AXT market and suggest research directions to improve microbial production using sustainable and environmentally friendly practices. KEY POINTS: • Unlock the power of microorganisms for high value AXT production. • Discover the secrets to cost-effective microbial AXT processing. • Uncover the future opportunities in the AXT market.

Promoting the Growth of Haematococcus lacustris under High Light Intensity through the Combination of Light/Dark Cycle and Light Color

The unicellular microalgae Haematococcus lacustris is an astaxanthin-rich organism that is widely used for commercial cultivation, but its main limitation is its relatively low biomass yield. It is widely accepted that the use of appropriate high light intensity could promote algal growth; however, H. lacustris is very sensitive to high-intensity light, and its growth can be readily arrested by inappropriate illumination. To exploit the growth-promoting benefit of higher light intensities while avoiding growth arrestment, we examined the growth of H. lacustris under high light intensities using various light profiles, including different light colors and light/dark cycles. The results show that light color treatments could not alleviate cellular stress under high light intensities; however, it was interesting to find that red light was favored the most by cells out of all the colors. In terms of the light/dark cycle, the 2/2 h light/dark cycle treatment was shown to lead to the highest specific growth rate, which was 46% higher than that achieved in the control treatment (18 μmol/m2·s light intensity, white light). Therefore, in further experiments, the 2/2 h light/dark cycle with red-light treatment was examined. The results show that this combination enabled a significantly higher specific growth rate, which was 66.5% higher than that achieved in the control treatment (18 μmol/m2·s light intensity, white light). These findings offer new strategies for the optimization of illumination for the growth of H. lacustris and lay the foundations for more reasonable lighting utilization for the cultivation of commercially valuable algal species.

Nutraceutical productions from microalgal derived compounds via circular bioeconomy perspective

Circular bioeconomy has become a sustainable business model for commercial production that promises to reuse, recycle & recover while considering less environmental footprints in nutraceutical industries. Microalgae biotechnology has the synergy to bioremediate waste stream while generating high-value-added compounds such as astaxanthin, protein and polyunsaturated fatty acids that are potential compounds used in various industries, thus, the integration of this approach provides economic advantages. However, since the industrial production of these compounds is costly and affected byunstable climate in the Nordic regions such as low temperature, light intensity, and polar circle, the focus of biosynthesis has shifted from less tolerant commercial strains towards indigenous strains. Nutraceutical productions such as polyunsaturated fatty acids and protein can now be synthesized at low temperatures which significantly improve the industry's economy. In this review, the above-mentioned compounds with potential strains were discussed based on a Nordic region's perspective.

Multifaceted strategies for economic production of microalgae Haematococcus pluvialis-derived astaxanthin via direct conversion of CO2

Owing to its strong antioxidant properties, astaxanthin has a high market price in the nutraceutical and pharmaceutical fields, and its demand is increasing. Furthermore, with an increase in the demand for green technology, astaxanthin production through direct CO₂ conversion using the autotrophic green microalga Haematococcus pluvialis as a bio-platform has received much attention. Large-scale outdoor cultivation of H. pluvialis using waste CO₂ sources and sunlight can secure sustainability and improve economic efficiency. However, low strain performance, reduced light utilization because of increased cell density, and inefficient transfer of gaseous CO₂ into liquid culture broth hinder its large-scale commercialization of astaxanthin. Herein, we presented a multifaceted strategy, including the development of high-efficiency strains, a culture system for astaxanthin accumulation, and astaxanthin extraction from biomass, for economically producing astaxanthin from H. pluvialis through direct CO₂ conversion. Future perspectives were presented by comparing and analyzing various previous studies conducted using the latest technology.

Concurrent enhancement of CO2 fixation and productivities of omega-3 fatty acids and astaxanthin in Haematococcus pluvialis culture via calcium-mediated homeoviscous adaptation and biomineralization

Haematococcus pluvialis has attracted interest as a bio-platform for producing omega-3 fatty acids (ω-3 FA) and astaxanthin that have a great potential as anti-inflammatory drugs. This study aimed to concurrently enhance the CO₂ fixation and the productivities of ω-3 FA and astaxanthin, which have been difficult to achieve because of the dissimilar culture methods for each goal, via calcium-mediated homeoviscous adaptation and biomineralization. As a result of 3 mM of Ca²⁺ addition, ω-3 FA content was improved by 31% due to Ca²⁺-induced homeoviscous adaptation. Biomineralization was promoted by the extracellular carbonic anhydrase, which resulted in 46.3% improvement in CO₂ fixation. CaCO₃ from the biomineralization was beneficially re-used in the H. pluvialis culture and triggered 178- and 522-fold increased biomass productivity and astaxanthin content, respectively, thanks to its anisotropic nature. The Ca²⁺-based productivity enhancement strategy was applied to large-scale culture which resulted improvement in overall bioprocess performance.

"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.

Sequential Continuous Mixotrophic and Phototrophic Cultivation Might Be a Cost-Effective Strategy for Astaxanthin Production From the Microalga Haematococcus lacustris

Although Haematococcus lacustris has been developed for astaxanthin production for decades, the production cost is still high. In order to modify the production processes, we proposed a novel strategy of cultivation, featured by sequential indoor continuous mixotrophic cultivation for the production of green cells followed by outdoor phototrophic induction for astaxanthin accumulation. The continuous mixotrophic cultivation was first optimized indoor, and then the seed culture of mixotrophic cultivation was inoculated into outdoor open raceway ponds for photoinduction. The results showed that mixotrophically grown cultures could efficiently grow without losing their photosynthetic efficiency and yielded higher biomass concentration (0.655 g L⁻¹) and astaxanthin content (2.2% DW), compared to phototrophically grown seed culture controls. This novel strategy might be a promising alternative to the current approaches to advance the production technology of astaxanthin from microalgae.

Robust cyst germination induction in Haematococcus pluvialis to enhance astaxanthin productivity in a semi-continuous outdoor culture system using power plant flue gas

The microalgae Haematococcus pluvialis biologically converts CO₂ into natural astaxanthin that possesses a strong antioxidant activity; its low carbon footprint and economic viability have allowed it to garner great attention. However, low efficiency of the cultivation process is a major hurdle in its commercial production. Here, additional nitrogen was provided to fully grown cells to induce efficient cyst germination, thereby rapidly increasing the number of cells containing astaxanthin. After germination, these cells were rapidly converted from zooids to cysts by nitrogen depletion, while maintaining a steady astaxanthin content of 5.5%. Consequently, a 2.1-fold increase in astaxanthin productivity in comparison with that in a batch culture was achieved. Moreover, the germination-based semi-continuous process yielded 2.6 times higher astaxanthin productivity in a large-scale culture using power plant flue gas and a polymeric photobioreactor. This study provides a promising cultivation strategy for the commercial mass production of natural astaxanthin.

Growth of Haematococcus pluvialis on a Small-Scale Angled Porous Substrate Photobioreactor for Green Stage Biomass

In the production of astaxanthin from Haematococcus pluvialis, the process of growing algal biomass in the vegetative green stage is an indispensable step in both suspended and immobilized cultivations. The green algal biomass is usually cultured in a suspension under a low light intensity. However, for astaxanthin accumulation, the microalgae need to be centrifuged and transferred to a new medium or culture system, a significant difficulty when upscaling astaxanthin production. In this research, a small-scale angled twin-layer porous substrate photobioreactor (TL-PSBR) was used to cultivate green stage biomass of H. pluvialis. Under low light intensities of 20–80 µmol photons m−2·s−1, algae in the biofilm consisted exclusively of non-motile vegetative cells (green palmella cells) after ten days of culturing. The optimal initial biomass density was 6.5 g·m−2, and the dry biomass productivity at a light intensity of 80 µmol photons m−2·s−1 was 6.5 g·m−2·d−1. The green stage biomass of H. pluvialis created in this small-scale angled TL-PSBR can be easily harvested and directly used as the source of material for the inoculation of a pilot-scale TL-PSBR for the production of astaxanthin.

Improvement of Photoautotrophic Algal Biomass Production after Interrupted CO2 Supply by Urea and KH2PO4 Injection

Microalgae-derived biomass is currently considered a sustainable feedstock for making biofuels, including biodiesel and direct combustion fuel. The photoautotrophic cultivation of microalgae using flue gas from power plants has been continuously investigated to improve the economic feasibility of microalgae processes. The utilization of waste CO2 from power plants is advantageous in reducing carbon footprints and the cost of carbon sources. Nonetheless, the sudden interruption of CO2 supply during microalgal cultivation leads to a severe reduction in biomass productivity. Herein, chemical fertilizers including urea and KH2PO4 were added to the culture medium when CO2 supply was halted. Urea (5 mM) and KH2PO4 (5 mM) were present in the culture medium in the form of CO2/NH4+ and K+/H2PO4−, respectively, preventing cell growth inhibition. The culture with urea and KH2PO4 supplementation exhibited 10.02-fold higher and 7.28-fold higher biomass and lipid productivity, respectively, compared to the culture with ambient CO2 supply due to the maintenance of a stable pH and dissolved inorganic carbon in the medium. In the mass cultivation of microalgae using flue gas from coal-fired power plants, urea and KH2PO4 were supplied while the flue gas supply was shut off. Consequently, the microalgae were grown successfully without cell death.

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.

Biotechnological production of astaxanthin from the microalga Haematococcus pluvialis

Although biotechnologies for astaxanthin production from Haematococcus pluvialis have been developed for decades and many production facilities have been established throughout the world, the production cost is still high. This paper is to evaluate the current production processes and production facilities, to analyze the R&D strategies for process improvement, and to review the recent research advances shedding light on production cost reduction. With these efforts being made, we intent to conclude that the production cost of astaxanthin from Haematococcus might be substantially reduced to the levels comparable to that of chemical astaxanthin through further R&D and the future research might need to focus on strain selection and improvement, cultivation process optimization, innovation of cultivation methodologies, and revolution of extraction technologies.

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.

Smart Method for Carotenoids Characterization in Haematococcus pluvialis red phase and Evaluation of Astaxanthin Thermal Stability

Haematococcus pluvialis microalgae is a promising source of astaxanthin, an excellent antioxidant carotenoid. H. pluvialis, as well as other species, could find more extensive applications as healthy food for a variegated carotenoids composition in addition to astaxanthin. Official method has not currently been used for this purpose. The objective of this work was to propose a method to characterize carotenoids in H. pluvialis after the comparison between spectrophotometric and liquid chromatography analysis. In addition, in order to improve the use of astaxanthin in the food industry, thermal stability was investigated. In this context, the effect of temperature at 40-80 °C, over a 16 h storage period was tested on astaxanthin produced by H. pluvialis. A further test was carried out at room temperature (20 °C) for seven days. A decrease in the astaxanthin concentration was observed at all tested temperatures with a decrease >50% of all-trans isomer at 80 °C after 16 h and an increase of 9-cis and 13-cis isomers. In conclusion, the obtained results showed the importance of evaluating the degradation effect of temperature on astaxanthin used as a food additive for a future greater enhancement of this bioproduct in the food field.

Safe and Complete Extraction of Astaxanthin from Haematococcus pluvialis by Efficient Mechanical Disruption of Cyst Cell Wall

Haematococcus pluvialis(H. pluvialis) can naturally accumulate high amounts of astaxanthin – a powerful antioxidant. However, complete recovery of astaxanthin from the cysts ofH. pluvialisis challenging because of the presence of a robust acetolysis resistant cell wall. Herein, a simple and effective planetary ball-milling pretreatment was developed to rupture the cells to attain an almost complete recovery of astaxanthin fromH. pluvialis, using a supercritical CO2and conventional organic solvent-based extraction. An optimized pretreatment using planetary ball mill under very mild conditions (150 rpm, 60 min) allowed the recovery of 31.4 mg/g dry weight of astaxanthin fromH. pluvialis, while slightly harsh milling (500 rpm) was found to be detrimental toward astaxanthin. The extracts in acetone exhibited higher antioxidant activity in 1-diphenyl-2-picrylhydrazyl assay than those in dichloromethane. These mild conditions were safe and highly effective for the complete extraction of astaxanthin along with the others extractables. This study opens a new avenue for the efficient recovery of valuable thermolabile ketocarotenoid species from microalgae, which can be applied to the development of economically viable biorefineries.

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.

Cellular accumulation and cytotoxic effects of zinc oxide nanoparticles in microalga Haematococcus pluvialis

Background

Zinc oxide nanoparticles (ZnO NPs) are widely used in household and cosmetic products which imply an increased releasing of these particles into the environment, especially aquatic ecosystems, resulting in the need of assessing the potential toxic effects of ZnO NPS on the aquatic organisms, particularly on microalgae which form the base for food chain of aquatic biota. The present study has investigated the dose- and time-dependent cellular accumulation and the corresponding cytotoxic effects of increasing concentrations of ZnO NPs from 10–200 μg/mL on microalga Haematococcus pluvialis at an interval of 24 h for 96 h.

Methods

The scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX) was used to qualitatively detect the cellular accumulation of ZnO NPs in algal cells, while inductively coupled plasma optical emission spectrometry (ICP OES) was performed to quantify the cell associated-zinc in algal cells. The percentage of cell death, reduction in algal biomass, and loss in photosynthetic pigments were measured to investigate the cytotoxic effects of ZnO NPs on H. pluvialis. Extracellular and intracellular changes in algal cells resulted from the treatment of ZnO NPs were demonstrated through optical, scanning, and transmission electron microscopic studies.

Results

SEM-EDX spectrum evidenced the accumulation of ZnO NPs in algal biomass and ICP OES results reported a significant (p < 0.05) dose- and time-dependent accumulation of zinc in algal cells from 24 h for all the tested concentrations of ZnO NPs (10–200 μg/mL). Further, the study showed a significant (p < 0.05) dose- and time-dependent growth inhibition of H. pluvialis from 72 h at 10–200 μg/mL of ZnO NPs. The morphological examinations revealed substantial surface and intracellular damages in algal cells due to the treatment of ZnO NPs.

Discussion

The present study reported the significant cellular accumulation of ZnO NPs in algal cells and the corresponding cytotoxic effects of ZnO NPs on H. pluvialis through the considerable reduction in algal cell viability, biomass, and photosynthetic pigments together with surface and intracellular damages.

Enhanced biomass and lipid production of Neochloris oleoabundans under high light conditions by anisotropic nature of light-splitting CaCO3 crystal

The aim of this work was to study the anisotropic effect of crystalline CaCO₃ nanoparticles (CN)-driven multiple refraction/scattering from the CN-coated agglomerated cells on the rate of photosynthesis and the product yield under high light conditions in the freshwater microalgae Neochloris oleoabundans. The CN-coating via biomineralization significantly improved the biomass and lipid production of N. oleoabundans during second stage of autotrophic induction by sustaining relatively high rate of photosynthesis at high irradiance using the multiple-splitting effect of the anisotropic polymorphism. The CN were successfully produced, adsorbed and grown on the external cells under conditions of mild alkalinity (pH 7.5-8.0), mild CaCl₂ concentration (0.05 M) and under nitrogen starvation with strong light (400 µE m^-2 s^-1). Consequently, lipid content and productivity of N. oleoabundans cells cultured with 0.05 M CaCl₂ increased by 18.4% and 31.5%, respectively, compared to the cells cultured with 0.05 M CaCl₂ and acetazolamide to inhibit calcification.

Recent advances in biorefinery of astaxanthin from Haematococcus pluvialis

Haematococcus pluvialis is one of the most abundant sources of natural astaxanthin as compared to others microorganism. Therefore, it is important to understand the biorefinery of astaxanthin from H. pluvialis, starting from the cultivation stage to the downstream processing of astaxanthin. The present review begins with an introduction of cellular morphologies and life cycle of H. pluvialis from green vegetative motile stage to red non-motile haematocyst stage. Subsequently, the conventional biorefinery methods (e.g., mechanical disruption, solvent extraction, direct extraction using vegetable oils, and enhanced solvent extraction) and recent advanced biorefinery techniques (e.g., supercritical CO₂ extraction, magnetic-assisted extraction, ionic liquids extraction, and supramolecular solvent extraction) were presented and evaluated. Moreover, future prospect and challenges were highlighted to provide a useful guide for future development of biorefinery of astaxanthin from H. pluvialis. The review aims to serve as a present knowledge for researchers dealing with the bioproduction of astaxanthin from H. pluvialis.

Microalgal-Based Carbon Sequestration by Converting LNG-Fired Waste CO2 into Red Gold Astaxanthin: The Potential Applicability

The combinatorial approach of anthropogenic activities and CO2 sequestration is becoming a global research trend to alleviate the average global temperature. Although microalgae have been widely used to capture CO2 from industrial flue gas, the application of bioproducts was limited to bioenergy due to the controversy over the quality and safety of the products in the food and feed industry. Herein, the waste CO2 emitted from large point sources was directly captured using astaxanthin-hyperproducing microalgae Haematococcus pluvialis. Astaxanthin production was successfully carried out using the hypochlorous acid water-based axenic culture process under highly contamination-prone outdoor conditions. Consequently, after 36 days of autotrophic induction, the productivity of biomass and astaxanthin of H. pluvialis (the mutant) reached 0.127 g L−1 day−1 and 5.47 mg L−1 day−1 under high summer temperatures, respectively, which was 38% and 48% higher than that of wild type cell. After grinding the wet astaxanthin-enriched biomass, the extract was successfully approved by compliance validation testing from Korea Food and Drug Administration. The assorted feed improved an immune system of the poultry without causing any side effects. The flue gas-based bioproducts could certainly be used for health functional food for animals in the future.

Acidic cultivation of Haematococcus pluvialis for improved astaxanthin production in the presence of a lethal fungus

An acidic cultivation strategy was developed to prevent contamination of a lethal fungus Paraphysoderma sedebokerensis in Haematococcus pluvialis culture for astaxanthin production. Instead of generally used neutral pH, an acidic condition (pH 4) was applied to the cultivation, resulting in a significant inhibition of the fungal contamination. This could be ascribed to the acidity-associated denaturation of a surface protein of P. sedebokerensis, which plays an important role in recognition of H. pluvialis. Stress relief strategies including stepwise light irradiation and naturally occurring nitrogen deficiency were employed in the induction stage to minimize the reduction of astaxanthin production caused by acidic pH. Accordingly, an astaxanthin titer of 84.8 mg L^-1 was obtained, which is 141-fold of that from the completely contaminated culture and double of that without the stress relief methods. This strategy provides a persistent contamination control method that can be used for practical astaxanthin production by H. pluvialis.

Performance and potential appraisal of various microalgae as direct combustion fuel

Direct combustion of biomass is considered the most effective and simple means to contribute to CO₂ reduction. In this context, the life-cycle potential of microalgal solid fuel, which has been overlooked so far, was comprehensively scrutinized ranging from cultivation to direct combustion. According to the quantitative data, using the raw fuel was confirmed to offer great benefits over the conventional lipid-targeted microalgal fuel systems through exploiting all of the biomass' energy potential, thereby being able to significantly increase the energy yield from biomass. The solid fuel is shown to exhibit diverse positive aspects owing to its remarkable calorific value, productivity and CO₂ fixation ability. The combustion test reveals coal-microalgae co-combustion brings beneficial consequences on combustibility and environmental impacts with no notable thermal efficiency drop. This holistic appraisal shows microalgae patently possess high potential as a direct combustion fuel, even outperforming that of extensively used woody fuels.

Rapid selection of astaxanthin-hyperproducing Haematococcus mutant via azide-based colorimetric assay combined with oil-based astaxanthin extraction

The aim of this work was to develop a new approach for simple and high-throughput selection of astaxanthin-hyperproducing Haematococcus mutants through a sequential combination method of azide-based colorimetric assessment and oil-based astaxanthin quantification. Randomly mutagenized cells were spotted on solid culture medium containing 50 µM of sodium azide to accelerate the biosynthesis of astaxanthin. After 3 days, highly-induced mutants were preliminarily isolated by visual inspection and their astaxanthin accumulations were rapidly quantified by soybean oil-based extraction method. On the whole, the selected mutants showed reduced vegetative growth rates but eventually exhibited higher astaxanthin productions than the parental strain owing to their improved inductive growths. Among them, M13 showed 174.7 ± 5.69 mg L^-1 of the highest astaxanthin production, which is 1.59-times higher than that of wild-type. This wide-scope screening method expedites both upstream and downstream astaxanthin quantification, making it a useful tool for isolating microalgae with high astaxanthin production.

Butylated hydroxytoluene induces astaxanthin and lipid production in Haematococcus pluvialis under high-light and nitrogen-deficiency conditions

The aim of this study was to investigate the effects of butylated hydroxytoluene (BHT) on the production of astaxanthin and lipids in Haematococcus pluvialis LUGU under high-light and nitrogen-deficiency conditions. Astaxanthin and lipid contents were increased by 71.13% and 10.71%, respectively, in algal cells treated with 2 mg L^-1 BHT. The maximal contents of astaxanthin and lipids were 3.17% and 46%, respectively. The levels of reactive oxygen species (ROS) in the presence of BHT were lower than in the control, and this effect involved strong activation of several antioxidases. Additionally, BHT application upregulated endogenous nitric oxide (NO) production. These results showed that this approach is useful for stimulating production of astaxanthin and lipids in H. pluvialis and that exogenous BHT induces astaxanthin and lipid production, which is responsible for the signalling molecule responses against abiotic stress conditions in H. pluvialis.

Effect of nutrients on the growth and physiological features of newly isolated Haematococcus pluvialis TMU1

The vegetative growth of Haematococcus pluvialis TMU1 was studied under batchwise cultivation in three common media, namely BBM, BG11, and 3NBBM. The BBM provided the best condition for the algal growth. It was further studied at different levels of nitrate and phosphate as macronutrients as well as iron and boron as trace elements. The dose-response of the algal growth to these macro/micronutrients was modeled with Monod/hormetic-type kinetics. Applying the modified BBM with 3-fold higher phosphate led to the highest cell density and up to 86% increase in the growth rate. At an inoculum size of 2 × 10⁵ cells mL^-1, the algal growth rate in BBM containing either 0.185 mM boron or 0.046 mM iron was higher than the medium containing half or twice ion levels. These optimal concentrations depend on inoculum size, so that changes from the optima increased the level of peroxide signaling molecules and induced defense pathways.

Improvement in modular scalability of polymeric thin-film photobioreactor for autotrophic culturing of Haematococcus pluvialis using industrial flue gas

The aim of this study is investigate the effect of column diameter (D), height/diameter (H/D) ratio, and gas flow rate on microalgae cultivation, Haematococcus pluvialis. Bubble column reactors with various D and H/D ratio were tested to assess the hydrodynamic properties and biomass production performance. Then, H. pluvialis was cultured under outdoor autotrophic conditions using industrial flue gas. By optimizing the reactor module, reactor volume increased to 354% with minimized biomass loss. Compared to the control, developed module showed biomass and astaxanthin productivity of 0.052 versus 0.053 g/L/day, and 1.48 versus 1.47 mg/L/day, respectively. Consequently, biomass productivity was maintained with increased reactor scale, and the result is applicable to the scale up of overall microalgae cultivation process.

Transcriptome Analysis in Haematococcus pluvialis: Astaxanthin Induction by High Light with Acetate and Fe2

Haematococcus pluvialis is a commercial microalga, that produces abundant levels of astaxanthin under stress conditions. Acetate and Fe²⁺ are reported to be important for astaxanthin accumulation in H. pluvialis. In order to study the synergistic effects of high light stress and these two factors, we obtained transcriptomes for four groups: high light irradiation (HL), addition of 25 mM acetate under high light (HA), addition of 20 μM Fe²⁺ under high light (HF) and normal green growing cells (HG). Among the total clean reads of the four groups, 156,992 unigenes were found, of which 48.88% were annotated in at least one database (Nr, Nt, Pfam, KOG/COG, SwissProt, KEGG, GO). The statistics for DEGs (differentially expressed genes) showed that there were more than 10 thousand DEGs caused by high light and 1800–1900 DEGs caused by acetate or Fe²⁺. The results of DEG analysis by GO and KEGG enrichments showed that, under the high light condition, the expression of genes related to many pathways had changed, such as the pathway for carotenoid biosynthesis, fatty acid elongation, photosynthesis-antenna proteins, carbon fixation in photosynthetic organisms and so on. Addition of acetate under high light significantly promoted the expression of key genes related to the pathways for carotenoid biosynthesis and fatty acid elongation. Furthermore, acetate could obviously inhibit the expression of genes related to the pathway for photosynthesis-antenna proteins. For addition of Fe²⁺, the genes related to photosynthesis-antenna proteins were promoted significantly and there was no obvious change in the gene expressions related to carotenoid and fatty acid synthesis.

A Mathematical Model of Neutral Lipid Content in terms of Initial Nitrogen Concentration and Validation in Coelastrum sp. HA-1 and Application in Chlorella sorokiniana

Microalgae are considered to be a potential major biomass feedstock for biofuel due to their high lipid content. However, no correlation equations as a function of initial nitrogen concentration for lipid accumulation have been developed for simplicity to predict lipid production and optimize the lipid production process. In this study, a lipid accumulation model was developed with simple parameters based on the assumption protein synthesis shift to lipid synthesis by a linear function of nitrogen quota. The model predictions fitted well for the growth, lipid content, and nitrogen consumption of Coelastrum sp. HA-1 under various initial nitrogen concentrations. Then the model was applied successfully in Chlorella sorokiniana to predict the lipid content with different light intensities. The quantitative relationship between initial nitrogen concentrations and the final lipid content with sensitivity analysis of the model were also discussed. Based on the model results, the conversion efficiency from protein synthesis to lipid synthesis is higher and higher in microalgae metabolism process as nitrogen decreases; however, the carbohydrate composition content remains basically unchanged neither in HA-1 nor in C. sorokiniana.