Astaxanthin Production Research Articles

Astaxanthin from Jerusalem artichoke: Production by fed-batch fermentation using Phaffia rhodozyma and application in cosmetics

Abstract Jerusalem artichoke extract or powder was used for astaxanthin production using Phaffia rhodozyma without acidic or enzymatic inulin hydrolysis. The culture medium containing Jerusalem artichoke as carbon source was optimized, and feeding strategies, including constant, exponential, pH-stat, and substrate feedback fed-batch fermentations, were also compared for enhancing the cell biomass and astaxanthin synthesis by P. rhodozyma. Substrate-feedback fed-batch fermentation resulted in the highest dry cell weight of 83.60 g/L, with a carotenoid concentration and yield of 982.50 mg/L and 13.30 mg/g, respectively, under optimized medium components using Jerusalem artichoke extract as carbon source in a 3-L stirred-tank bioreactor. Moreover, 482.50 mg/L of carotenoids and 253.10 mg/L of astaxanthin were obtained by continuous feeding of Jerusalem artichoke powder, which was used as carbon source. Astaxanthin essence with high DPPH-scavenging activity was obtained from the extracted astaxanthin, and the DPPH free radical scavenging rate of 40 ppm astaxanthin essence reached 76.29%. When stored at 4 °C, astaxanthin essence showed the highest stability, with a minimum k value of 0.0099 week−1 and maximum half-life (t1/2) value of 70 weeks.

Enhanced production of astaxanthin by Chromochloris zofingiensis in a microplate-based culture system under high light irradiation

The green microalga Chromochloris zofingiensis is a promising producer of natural astaxanthin. In the present study, C. zofingiensis was first cultivated in shake flasks under low light irradiation and then subjected to continuous high light irradiation, which effectively promoted astaxanthin production. In addition, a microplate-based culture system in concert with high light irradiation from blue light and white light above 150μmolm−2s−1 was constructed and applied to improve astaxanthin production. Blue light exerted more positive influences on astaxanthin accumulation, but when the light intensity was increased to 300μmolm−2s−1, astaxanthin biosynthesis was substantially inhibited. Conversely, in a nitrogen-deprived culture under white light, the highest astaxanthin content for C. zofingiensis, 7.1mg/g, was obtained. The highest astaxanthin yield achieved was 38.9mg/L in a culture with 0.1g/L nitrate under the same culture conditions. This study demonstrates that C. zofingiensis has great potential for natural astaxanthin production.

Optimization of an integrated algae-based biorefinery for the production of biodiesel, astaxanthin and PHB

In this work, we address the optimal design of an integrated microalgae-based biorefinery through the formulation of a mixed integer nonlinear programming model for the production of biodiesel and potential high-added value products. Main bioproducts are poly (hydroxybutyrate) (PHB) and astaxanthin. A combined heat and power cycle to transform biogas generated by the anaerobic digestion of waste streams is also included in the superstructure. Mass and energy balances are formulated for the biorefinery. Different alternatives for PHB extraction are taken into account. The anaerobic digestion model accounts for detailed composition of the different feed streams. Detailed capital cost models for process equipment are formulated and implemented in GAMS to maximize net present value (NPV). Results show that the production of astaxanthin and PHB provides a way to make biodiesel production economically feasible. Open pond and surfactant-chelate are selected for microalgae cultivation and PHB extraction method, respectively. Biodiesel price can be reduced to $0.48 due to incomes from astaxanthin and PHB sales. Also, an economic sensitivity analysis is performed. Further comparison between domestic and international cost conditions is carried out, showing higher NPV in the domestic case.

Evaluation of hydrodynamic parameters and rheological behaviours for Haematococcus pluvialis production in stirred tank photobioreactor

Microalgae are increasingly used as commercial sources of high-value compounds. However, the nature and genetic basis of variation in commercially relevant traits remain understudied. This study focuses on the green alga Haematococcus pluvialis, well-known for accumulating the carotenoid astaxanthin. We examined intra- and interspecific variation and correlations between six traits related to astaxanthin productivity among 30 natural isolates and cultivated strains of two Haematococcus species. Significant intraspecific genotypic variation was found for all traits assessed in both species (broad sense heritability estimates H2 = 0.48–0.89), resulting in a fifteen-fold variation in astaxanthin productivity between the poorest and the best-performing strain. The two species differed in five of the six traits. Cultivated strains had a lower astaxanthin productivity compared to natural isolates of H. pluvialis, possibly reflecting loss of photoprotective capacity during long-term cultivation. In general, trait correlations were weak yet stronger in H. rubicundus than in H. pluvialis. Most of the variation in overall astaxanthin productivity could be explained by the differences in post-stress traits. Our results reveal extensive trait variation among isolates of a commercially interesting microalga. We recommend natural strain panels as a valuable tool for cost-efficient trait mapping and to select targets for genetic engineering, marker-assisted strain selection or breeding aiming at the optimization of astaxanthin productivity.

Biosynthesis of Astaxanthin as a Main Carotenoid in the Heterobasidiomycetous Yeast Xanthophyllomyces dendrorhous.

Carotenoids are organic lipophilic yellow to orange and reddish pigments of terpenoid nature that are usually composed of eight isoprene units. This group of secondary metabolites includes carotenes and xanthophylls, which can be naturally obtained from photosynthetic organisms, some fungi, and bacteria. One of the microorganisms able to synthesise carotenoids is the heterobasidiomycetous yeast Xanthophyllomyces dendrorhous, which represents the teleomorphic state of Phaffia rhodozyma, and is mainly used for the production of the xanthophyll astaxanthin. Upgraded knowledge on the biosynthetic pathway of the main carotenoids synthesised by X. dendrorhous, the biotechnology-based improvement of astaxanthin production, as well as the current omics approaches available in this yeast are reviewed in depth.

Rapid Estimation of Astaxanthin and the Carotenoid-to-Chlorophyll Ratio in the Green Microalga Chromochloris zofingiensis Using Flow Cytometry.

The green microalga Chromochloris zofingiensis can accumulate significant amounts of valuable carotenoids, mainly natural astaxanthin, a product with applications in functional food, cosmetics, nutraceuticals, and with potential therapeutic value in cardiovascular and neurological diseases. To optimize the production of astaxanthin, it is essential to monitor the content of astaxanthin in algal cells during cultivation. The widely used HPLC (high-performance liquid chromatography) method for quantitative astaxanthin determination is time-consuming and laborious. In the present work, we present a method using flow cytometry (FCM) for in vivo determination of the astaxanthin content and the carotenoid-to-chlorophyll ratio (Car/Chl) in mixotrophic C. zofingiensis. The method is based on the assessment of fluorescent characteristics of cellular pigments. The mean fluorescence intensity (MFI) of living cells was determined by FCM to monitor pigment formation based on the correlation between MFI detected in particular channels (FL1: 533 ± 15 nm; FL2: 585 ± 20 nm; FL3: >670 nm) and pigment content in algal cells. Through correlation and regression analysis, a linear relationship was observed between MFI in FL2 (band-pass filter, emission at 585 nm in FCM) and astaxanthin content (in HPLC) and applied for predicting astaxanthin content. With similar procedures, the relationships between MFI in different channels and Car/Chl ratio in mixotrophic C. zofingiensis were also determined. Car/Chl ratios could be estimated by the ratios of MFI (FL1/FL3, FL2/FL3). FCM is thus a highly efficient and feasible method for rapid estimation of astaxanthin content in the green microalga C. zofingiensis. The rapid FCM method is complementary to the current HPLC method, especially for rapid evaluation and prediction of astaxanthin formation as it is required during the high-throughput culture in the laboratory and mass cultivation in industry.

Integrated Haematococcus pluvialis biomass production and nutrient removal using bioethanol plant waste effluent

Abstract The integrated system of astaxanthin and microalgal biomass production, and wastewater treatment is a promising process. Haematococcus pluvialis is a suitable microalgae for this coupled system to achieve this dual purpose in a single approach. In this study, biomass production and nutrient removal from bioethanol plant wastewater by H. pluvialis were investigated. An air-lift photobioreactor was used to utilize the wastewater as well as a CO2-enriched gas supply. The maximum biomass density and maximum specific growth rate achieved were 4.37 ± 0.007 g/L and 0.317 day−1, respectively, by culturing H. pluvialis in an air-lift photobioreactor, supplemented with 5% CO2 in air. Removal of 91.7% total nitrogen and 100% total phosphorous from the wastewater was achieved. The residual microalgal biomass, obtained after astaxanthin extraction (1.109 ± 0.009 mg/g DW), was characterized as a potential bioenergy feedstock due to its elevated higher heating value 15.6 ± 0.01 MJ/kg. Hence, integrating H. pluvialis cultivation with bioethanol effluent serves the combined purpose of wastewater treatment, CO2 utilization, and simultaneous production of astaxanthin, which has a potential market value of over USD 2000 per kg, and carbohydrate rich microalgal biomass, which can be applied to bioenergy production.

Screening for enhanced astaxanthin accumulation among Spirulina platensis mutants generated by atmospheric and room temperature plasmas

In this study, a high-throughput screening procedure was employed to generate mutants of Spirulina platensis for enhanced astaxanthin production using an atmospheric and room temperature plasma (ARTP) based on random mutagenesis process. The optimal culture conditions for cultivation of S. platensis in the laboratory were established to be 29°C, 6.3×10−3μmol/cm2/s light intensity and a semi-continuous culture system. On the basis of the ARTP screening procedure, a mutant strain (Sp-A1) was successfully isolated, which showed astaxanthin production of 45.88±1.56μg/g, a 196% increase over that of the original wild type strain (15.50±1.52μg/g). The mutant strain accumulated higher content of chlorophyll a than that of the original wild type strain, whereas the β-carotene and polysaccharide contents as well as the superoxide dismutase (SOD) activity of the mutant strain were slightly lower. Under a single stress of 0.625g/L NaNO3, astaxanthin accumulation of mutant strain Sp-A1 reached 0.038±0.002μg/mL after 7days of culture, which was equivalent to 142.50±0.04μg/g of the astaxanthin content versus the dried S. platensis weight. This study demonstrates that ARTP is a novel powerful mutagenesis tool to generate S. platensis strains for increased yields of astaxanthin and may, therefore, play an important role in the enhanced expression of astaxanthin in microbial hosts.

High concentrations of biotechnologically produced astaxanthin by lowering pH in a Phaffia rhodozyma bioprocess

Astaxanthin additions to animal diets predominantly serve as colorization aid to satisfy consumer expectations and desire for a consistent product with familiar coloration, e.g. the characteristic pink colorization of the flesh of species being produced by aquaculture. The heterobasidiomycetous yeast Phaffia rhodozyma (Xanthophyllomyces dendrorhous) can be used as natural feed source of astaxanthin. However, currently, the majority of astaxanthin used for the feed market is produced by chemical synthesis. We present a further step in direction of a competitive production of natural astaxanthin in an optimized bioprocess with non-genetically modified Phaffia rhodozyma. After medium optimization AXJ-20, a mutant strain of P. rhodozyma wild-type strain ATCC 96594, was able to grow to a cell dry weight concentration of over 114 g per kg of culture broth in a fed-batch process. In this bioprocess, where pH was lowered from 5.5 to 3.5 during the maturation phase, AXJ-20 produced the highest value reported for astaxanthin production with P. rhodozyma up to now: 0.7 g astaxanthin per kg of culture broth with a space-time-yield of 3.3 mg astaxanthin per kg of culture broth per hour. Lowering the pH during the bioprocess and increasing trace element and vitamin concentrations prevented loss of cell dry weight concentration in the maturation phase and proved to be critical for astaxanthin concentration and purity.

Development of large-scale and economic pH control system for outdoor cultivation of microalgae Haematococcus pluvialis using industrial flue gas

The aim of this study was to develop the economic and effective buffer system for microalgae mass cultivation using industrial flue gas. Due to the continuous flue gas supplement, culture media acidified, therefore cell growth inhibited. Although buffering agent was added, this result increase in cost for overall culture process. Therefore combined buffer system of bicarbonate and phosphate (BP) for large-scale use was investigated. The bicarbonate buffer system generated from CO2 dissolution, additionally phosphate buffer system improves the buffer performance under the continuous CO2 supplementation from flue gas. The microalgae Haematococcus pluvialis was cultivated under autotrophic outdoor conditions using these buffer solutions. As a result, the autotrophic BP buffer system enhanced the biomass and astaxanthin productivity of H. pluvialis to 105% and 103%, respectively. The results confirm that the BP buffer system reduces the cost of microalgal CO2 conversion process, particularly for the outdoor mass cultivation.

Chromosome-level genome assembly and transcriptome of the green alga Chromochloris zofingiensis illuminates astaxanthin production

Microalgae have potential to help meet energy and food demands without exacerbating environmental problems. There is interest in the unicellular green alga Chromochloris zofingiensis, because it produces lipids for biofuels and a highly valuable carotenoid nutraceutical, astaxanthin. To advance understanding of its biology and facilitate commercial development, we present a C. zofingiensis chromosome-level nuclear genome, organelle genomes, and transcriptome from diverse growth conditions. The assembly, derived from a combination of short- and long-read sequencing in conjunction with optical mapping, revealed a compact genome of ∼58 Mbp distributed over 19 chromosomes containing 15,274 predicted protein-coding genes. The genome has uniform gene density over chromosomes, low repetitive sequence content (∼6%), and a high fraction of protein-coding sequence (∼39%) with relatively long coding exons and few coding introns. Functional annotation of gene models identified orthologous families for the majority (∼73%) of genes. Synteny analysis uncovered localized but scrambled blocks of genes in putative orthologous relationships with other green algae. Two genes encoding beta-ketolase (BKT), the key enzyme synthesizing astaxanthin, were found in the genome, and both were up-regulated by high light. Isolation and molecular analysis of astaxanthin-deficient mutants showed that BKT1 is required for the production of astaxanthin. Moreover, the transcriptome under high light exposure revealed candidate genes that could be involved in critical yet missing steps of astaxanthin biosynthesis, including ABC transporters, cytochrome P450 enzymes, and an acyltransferase. The high-quality genome and transcriptome provide insight into the green algal lineage and carotenoid production.

Effects of CO2 enrichment on primary photochemistry, growth and astaxanthin accumulation in the chlorophyte Haematococcus pluvialis

The atmospheric CO2 level is limiting for growth of phototrophic organisms such as microalgae, so CO2 enrichment boosts the growth and photosynthesis of microalgal cultures. Still, excessive CO2 injection might inhibit photosynthesis of microalgae. We investigated the effect of continuous sparging of the cultures of Haematococcus pluvialis BM 1 (IPPAS H-2018) (Chlorophyceae), the richest natural source of the value-added pigment astaxanthin. H. pluvialis cultures with CO2-enriched air-gas mixtures (with CO2 level from the atmospheric to 20%) on growth and astaxanthin accumulation in the microalga. Special attention was paid to photosynthetic activity and non-photochemical excited chlorophyll states quenching in the microalgal cells, which was monitored via chlorophyll fluorescence analysis. We also report on the capability of CO2 capture by H. pluvialis derived from direct measurements of its elemental carbon content. The beneficial effect of the moderately high (5%) CO2 levels on the culture growth and astaxanthin accumulation under stress results in a higher overall astaxanthin productivity. However, increase of the CO2 level to 10% or 20% was deteriorative for growth, photosynthesis and carbon assimilation. The results support the possibility of combining a traditional two-stage H. pluvialis cultivation with CO2 bio-capture although a dilution of the flue gas before its injection is required.

물리·화학적 돌연변이 유도를 통한 Paracoccus haeundaensis의 astaxanthin 생산량 증대

Carotenoid는 천연 지용성 색소이며, 세균, 조류, 식물 등이 생산한다. 세계 시장의 대부분을 차지하는 합성 염료의 대안으로서 현재는 조류나 세균, 갑각류 등의 원료로부터 아스타잔틴의 생산, 정제, 이용이 주목 받고 있다. 이 연구는 UV와 EMS를 이용하여 P. haeundaensis의 돌연변이를 유도하고, 결과적으로 astaxanthin을 과잉 생산하는 돌연변이주를 선별하고 특성을 확인하기 위해 다양한 배양 및 영양 조건을 이용하여 astaxanthin 생산량을 확인하였다. 실험 결과 UV 조사 시간이 증가하거나, EMS 농도가 증가할수록 균주의 생존율이 감소하였다. Astaxanthin 과잉 생산 돌연변이 균주의 경우 400 mM EMS와 UV 20분을 순차적으로 처리한 방법에서 선별된 변이주가 가장 높은 astaxanthin 생산량을 보이는 것을 확인하였으며, 이 균주의 이름을 PUE로 명명하였다. PUE의 최적 배양 조건은 <TEX>$25^{\circ}C$</TEX>, pH 7-8, 3% NaCl이며, 1% raffinose, 3% potassium nitrate 첨가 시 astaxanthin 생산량이 증가하는 것으로 밝혀졌다. PUE에서는 wild type 균주에 비해 astaxanthin 생산량이 1.58배 증가함을 확인할 수 있었다. 본 연구의 실험 결과, 돌연변이 유도에 의해 선별된 변이주는 astaxanthin의 산업적 생산에 활용 가능한 후보가 될 수 있을 것으로 사료된다. Carotenoids are natural lipid-soluble pigments, which are produced primarily by bacteria, algae, and plants. Many studies have focused on the identification, production, and utilization of natural sources of astaxanthin from algae, yeast, and crustacean byproducts as an alternative to the synthetic pigment, which is mostly used today. The aim of the present study was to identify a mutant of Paracoccus haeundaensis by exposure to UV and ethyl methanesulfonate (EMS). The mutant was then exposed to nutrient stress conditions to isolate an astaxanthin-hyperproducing strain, followed by characterization of the mutant. The survival rate decreased in accordance with an increase in the UV exposure time and an increase in the EMS concentration. A mutant of the original P. haeundaensis strain was identified that showed hyperproduction of astaxanthin following exposure to UV irradiation (20 min) and EMS treatment (0.4 M concentration). The optimal culture conditions for the PUE mutant were <TEX>$25^{\circ}C$</TEX>, pH 7-8, and 3% NaCl. The effects of various carbon and nitrogen sources on the growth and astaxanthin production of PUE were examined. The addition of 1% raffinose and 3% potassium nitrate influenced cell growth and astaxanthin production. The selected mutant exhibited an increase of 1.58 folds in astaxanthin content compared to initial wild type strain. A genetically stable mutant strain obtained using mutagen (UV irradiation and EMS treatment) may be a suitable candidate for further industrial scale production of astaxanthin.

Astaxanthin production from sewage of traditional Thai rice vermicelli

This research aimed to investigate an optimal condition for astaxanthin production by Phaffia rhodozyma TISTR 5730 in two different media: synthetic YM medium and the medium added with coconut water and diluted with sewage from Thai traditional rice vermicelli plant (coconut water: sewage of 1:0, 1:1, 1:3 and 1:5 ration respectively). The basic medium formulation was composed of 10 g/L glucose, 3 g/L yeast extract, 0.1 g/L K2HPO4, 0.01 g/L NaCl, 0.01 g/L MgSO4 and 0.01 g/L CaCl2 with initial pH 5.5. The cultures were cultivated on 200 rpm shaking bath at 50 °C for 120 hr. It was found that P. rhodozyma TISTR 5370 grew optimally when cultivated in a mixture of coconut water and Thai rice vermicelli sewage (ratio of 1:3), with growth of 3.23 g dry biomass/L and specific astaxanthin production of 680 μg/g dry cell respectively. When fan palm sugar was added to increase reducing sugar from 10 to 15, 20 and 25 g/L, it was demonstrated that the 15 g/L formulation produced highest both dry cell weight (9.66 g/L) and astaxanthin (810 μg/g dry cell weight). Furthermore, when 0.5, 1.0 and 1.5 g/L citric acid was added as supplement, it was found that 1.0-g/L citric acid formulation gave the best result: 10.30 g/L dried cell weight and 930 μg/g dry cell weight astaxanthin. This study provides a promising alternative method of sewage reduction and valorization of wastewater from Thai traditional rice vermicelli plant.

Engineering of β-carotene hydroxylase and ketolase for astaxanthin overproduction in Saccharomyces cerevisiae

The conversion of β-carotene to astaxanthin is a complex pathway network, in which two steps of hydroxylation and two steps of ketolation are catalyzed by β-carotene hydroxylase (CrtZ) and β-carotene ketolase (CrtW) respectively. Here, astaxanthin biosynthesis pathway was constructed in Saccharomyces cerevisiae by introducing heterologous CrtZ and CrtW into an existing high β-carotene producing strain. Both genes crtZ and crtW were codon optimized and expressed under the control of constitutive promoters. Through combinatorial expression of CrtZ and CrtW from diverse species, nine strains in dark red were visually chosen from thirty combinations. In all the selected strains, strain SyBE_Sc118060 with CrtW from Brevundimonas vesicularis DC263 and CrtZ from Alcaligenes sp. strain PC-1 achieved the highest astaxanthin yield of 3.1 mg/g DCW. Protein phylogenetic analysis shows that the shorter evolutionary distance of CrtW is, the higher astaxanthin titer is. Further, when the promoter of crtZ in strain SyBE_Sc118060 was replaced from FBA1p to TEF1p, the astaxanthin yield was increased by 30.4% (from 3.4 to 4.5 mg/g DCW). In the meanwhile, 33.5-fold increase on crtZ transcription level and 39.1-fold enhancement on the transcriptional ratio of crtZ to crtW were observed at early exponential phase in medium with 4% (w/v) glucose. Otherwise, although the ratio of crtZ to crtW were increased at mid-, late-exponential phases in medium with 2% (w/v) glucose, the transcription level of both crtZ and crtW were actually decreased during the whole time course, consequently leading to no significant improvement on astaxanthin production. Finally, through high cell density fed-batch fermentation using a carbon source restriction strategy, the production of astaxanthin in a 5-L bioreactor reached to 81.0 mg/L, which was the highest astaxanthin titer reported in yeast. This study provides a reference to greatly enhance desired compounds accumulation by employing the key enzyme(s) in microbes. Open image in new window

Nitrogen-doped carbon dots prepared from bovine serum albumin to enhance algal astaxanthin production

The aim of this work was to use green and simply synthesized nitrogen-doped carbon dots (N@CDs) based on carbonized bovine serum albumin (BSA) to boost the accumulation of astaxanthin in microalgae. The BSA carbon dots revealed a high blue emission having a quantum yield of up to 44%, which is superior to all previously reported carbon dots. By directly adding the N@CDs at low concentrations (1mgL−1) to the algal culture of Haematococcus pluvialis, astaxanthin production increased more than two-fold (66mgL−1), compared to the control (29mgL−1), in a shorter time of 1week instead of 2weeks at the reddening stage. After 1month of continuous irradiation, the HRTEM images and fluorescence spectra of N@CDs looked similar to as-prepared N@CDs, suggesting their photostability and reusability. Our novel N@CDs could be a promising tool for the future industry of natural astaxanthin and other value-added products from microalgae.

Alleviation of metabolic bottleneck by combinatorial engineering enhanced astaxanthin synthesis in Saccharomyces cerevisiae.

Highly efficient biosynthesis of the commercially valuable carotenoid astaxanthin by microbial cells is an attractive alternative to chemical synthesis and microalgae extraction. With the goal of enhancing heterologous astaxanthin production in Saccharomyces cerevisiae, metabolic engineering and protein engineering were integrated to improve both the expression and activity of rate-limiting enzymes. Firstly, to increase the supply of β-carotene as a key precursor for astaxanthin, a positive mutant of GGPP synthase (CrtE03M) was overexpressed together with three other rate-limiting enzymes tHMG1, CrtI and CrtYB. Subsequently, to accelerate the conversion of β-carotene to astaxanthin, a color screening system was developed and adopted for directed evolution of β-carotene ketolase (OBKT), generating a triple mutant OBKTM (H165R/V264D/F298Y) with 2.4-fold improved activity. After adjusting copy numbers of the above-mentioned rate-limiting enzymes to further balance the metabolic flux, a diploid strain YastD-01 was generated by mating two astaxanthin-producing haploid strains carrying the same carotenogenic pathway. Finally, further overexpression of OCrtZ and OBKTM in YastD-01 resulted in accumulation of 8.10mg/g DCW (47.18mg/l) of (3S, 3'S)-astaxanthin in shake-flask cultures. This combinatorial strategy might be also applicable for alleviation of metabolic bottleneck in biosynthesis of other value-added products, especially colored metabolites.

Astaxanthin production from Haematococcus pluvialis: effects of light wavelength and salinity

Astaxanthin production from Haematococcus pluvialis: effects of light wavelength and salinity

Effects of selenite on green microalga Haematococcus pluvialis: Bioaccumulation of selenium and enhancement of astaxanthin production

Algae are at a low trophic level and play a crucial role in aquatic food webs. They can uptake and accumulate the trace element selenium (Se), which can be either essential or toxic to algal growth depending on the dosage and species. Se toxicity and algae resistance varied across different organisms. In order to investigate the effects of Se on the unicellular green alga Haematococcus pluvialis, an important industrial resource for natural astaxanthin, the algal growth rate, chlorophyll content, and fluorescence parameters were derived from experimental treatment with different concentrations of selenite. The results showed that the EC50 for the algal growth rate was 24mg/L, and that a low dosage of selenite (3mg/L) may not hinder H. pluvialis cell growth, but selenite at levels higher than 13mg/L do restrain cell growth. Bioaccumulation experiments showed that H. pluvialis accumulated up to 646μg/g total Se and 380μg/g organic Se, dry weight. However, treatment with high concentrations of selenite significantly increased intracellular hydrogen peroxide levels, antioxidant enzyme activity, and the production of astaxanthin, suggesting that Se bioaccumulation might be toxic to H. pluvialis.

Biofilm cultivation of Haematococcus pluvialis enables a highly productive one-phase process for astaxanthin production using high light intensities

State-of-the-art commercial cultivation of Haematococcus pluvialis for astaxanthin production is exclusively based on two-phase processes, separating a vegetative “green” phase for cell multiplication from an astaxanthin producing “red” phase consisting of resting stages. We report the continuous co-production of H. pluvialis biomass and astaxanthin in a one-phase process at high light intensities. By means of a Twin-Layer biofilm photobioreactor, H. pluvialis was grown immobilized under illuminations up to 1015μmolphotonsm−2s−1 and supplementary CO2 in the range of 1% to 10%, reaching a maximal dry biomass productivity of 19.4gm−2day−1 and a final standing crop of 213gm−2 growth area after 16days of cultivation. During the cultivation period, astaxanthin productivity increased with increasing light intensity to values of 0.39gm−2day−1 and a final amount of 3.4gm−2, representing an astaxanthin content of about 2.5% in the dry biomass. Compared to a two-phase process using the same photobioreactor, the one-phase approach resulted in a similar total astaxanthin amount per growth area in half the cultivation period. As a one-phase process, it also simplifies cultivation of H. pluvialis compared to the established two phase suspension-based systems for astaxanthin production.