Primary Carotenoid Research Articles

Lutein and Zeaxanthin: Source, Extraction, Stability, Bioactivity, and Functional Food Applications.

Nature has been acknowledged as a fundamental source of diverse bioactive molecules. Among natural carotenoids, lutein, zeaxanthin, and their oxidative metabolites are specifically deposited in the macular region of living organisms. Lutein and zeaxanthin are carotenoids primarily found in green leafy vegetables, eggs, and various fruits. Lutein and zeaxanthin emerge as the primary carotenoids in the retina, playing a crucial role as photo-protectants to prevent retinal degeneration. The extraction of lutein and zeaxanthin from natural sources involves several techniques, including solvent extraction and supercritical fluid extraction, with an emphasis on optimizing efficiency and yield. Incorporating these carotenoids into functional foods-such as fortified dairy products, baked goods, and snacks-enhances their nutritional profiles and provides significant health benefits. This review examines the sources, stability, bioactivity, and various extraction methods for lutein and zeaxanthin, highlighting their potential for photoprotection, antioxidant activity, and antidiabetic effects. These attributes, combined with innovative extraction techniques, position lutein and zeaxanthin as promising ingredients for functional food applications.

Genetic and metabolic factors influencing skin yellowness in yellow-feathered broilers

The degree of yellowness of the skin is an important factor affecting the market popularity and sales price of yellow-feathered broilers. Despite its commercial importance, the specific pigments and genetic mechanisms involved remain unclear. This study identified lutein as the primary carotenoid in the skin and established serum lutein concentration as a molecular marker for predicting skin yellowness in carcasses. Through RNA sequencing of broilers with varying yellowness, we identified key genes like CYP26A1, CYP1B1, CYP2C18, CYP2W1, HSD17B2, AOX1, KMO, PLIN1, and RET, which may regulate carotenoid absorption and deposition. Additionally, a single nucleotide polymorphism in the CYP1A1 gene was significantly associated with skin yellowness in Ma-Huang chickens. Overall, this study examined the primary pigment types that influence the skin yellowness of yellow-feathered broilers, emphasizing that lutein can serve as a molecular marker for skin yellowness and providing insights into the regulatory factors that regulate skin yellowness. These findings provide essential theoretical support for the breeding of skin color traits in yellow-feathered broilers.

Optimizing pH and Light for Enhanced Carotenoid Synthesis and Antioxidant Properties in Sub-Aerial Cyanobacteria.

Carotenoid, natural pigments, synthesized by plants and microbes are now much favored in global markets due to the awareness of their putative health benefits, and a wide array of commercial applications. There is a diversity of natural and synthetic carotenoid, but only a few of them are commercially produced, including carotenes (β-carotene and lycopene) and xanthophylls (astaxanthin, canthaxanthin, lutein, zeaxanthin, and capsanthin). However, for commercial production, plants and algae are more favored than cyanobacteria because of their much less carotenoid synthesis than land plants; although they are well known for producing commercially important carotenoid. But with advances in optimization of their carotenoid production, cyanobacteria can be used as a potential source of carotenoid production in the future allowing us to exploit its various applications. Hence, this study investigated the effects of pH and light conditions on carotenoid production in the sub-aerial cyanobacterium Desertifilum dzianense ON358232.1. The results revealed that the highest carotenoid synthesis occurred under alkaline conditions (pH 9) and red-light exposure, significantly increasing compared to the control (pH 7.2, white light). UV-Vis and FTIR analyses confirmed the presence of β-carotene as the primary carotenoid, demonstrating strong antioxidant potential. The study's findings highlight the optimal environmental parameters for enhancing carotenoid yield, which can be applied for industrial and pharmaceutical uses due to their antioxidant properties.

Targeted metabolite and molecular profiling of carotenoids in rose petals: A step forward towards functional food applications

Given the increasing consumer demand for natural and functional foods, rose petals offer a promising novel ingredient for food innovation, especially yellow and orange rose petals rich in carotenoids, making them ideal for food processing and color retention. Despite their potential, the metabolic profile of carotenoids in roses has not yet been fully explored. Therefore, the present study aimed to provide a comprehensive analysis of carotenoid metabolism in rose petals during three developmental stages. The results revealed that orange rose petals had the highest carotenoid content of 488.85 μg/g, with xanthophylls being identified as the primary carotenoid constituents (70.40 %) in roses for the first time. Furthermore, two genes, RhBCH1 and RhCCD4, were identified to be involved in the regulation of carotenoid biosynthesis in roses. Overall, this study demonstrates the enormous potential of rose petals as functional food ingredients, providing a theoretical basis for breeding high-carotenoid rose varieties.

Enhancement of carotenogenesis by Blakeslea trispora in a mixed culture with bacteria.

Among carotenoids, ꞵ-carotene has the highest biological activity and is found as an all-trans isomer in many biological systems. Blakeslea trispora is a microorganism that is of interest to industries for the commercial production of ꞵ-carotene. This study investigated the effect of different bacteria on carotenogenesis in B. trispora. The B. trispora bisexual mold was cultured in a production medium, and different bacterial cells were added to it after 24 h. Then, the culture conditions and the culture medium were optimized in the presence of the selected bacteria using the experimental design. The percentage of carotenoids obtained from the mixed culture was determined using high-performance liquid chromatography (HPLC). Results showed that Kocuria rhizophila had the greatest effect on increasing the production of carotenoids in B. trispora. The highest content of carotenoids obtained during optimization was 770 ± 7.5 mg/L, a 6.8-fold increase compared to the control. HPLC analysis of carotenoids indicated the presence of two main peaks, ꞵ-carotene and γ-carotene, in which the primary carotenoid was ꞵ-carotene followed by γ-carotene with a lower content. Therefore, due to the importance of ꞵ-carotene in industry, the use of biostimulants is one of the appropriate strategies to increase the production of this pigment in industry.

Engineering Nannochloropsis oceanica for concurrent production of canthaxanthin and eicosapentaenoic acid

The marine alga Nannochloropsis oceanica can synthesize the high-value ketocarotenoid canthaxanthin yet at an extremely low level. Introducing a β-carotenoid ketolase from Chlamydomonas reinhardtii into the chloroplast for expression, enabled N. oceanica to synthesize substantial amounts of canthaxanthin and grow better under high light. Compared to wild type, the engineered strain had higher levels of primary carotenoids and chlorophyll a as well, and synthesized more eicosapentaenoic acid (EPA, an ω3 polyunsaturated fatty acids). Further metabolic engineering by enhancing the flux to carotenoids or suppressing competing pathways allowed for a considerable increase of canthaxanthin, reaching 4.7 mg g−1 dry weight. A fed-batch culture strategy with nitrate and phosphate replenishment was developed for the co-production of canthaxanthin and EPA, which within a 10-day period reached 37.6 and 268.8 mg/L, respectively. This study sheds light on manipulating the industrially relevant alga for efficient co-production of high-value biochemicals from CO2.

Reddening of the Unicellular Green Alga Euglena gracilis by Dried Bonito Stock and Intense Red Light Irradiation.

This study confirms for the first time that the significant red coloration of Euglena gracilis is induced by bonito stock (BS), a traditional Japanese food, and intense red light exposure (605~660 nm, 1000~1300 µmol photons/m2/s). Under the condition, excessive photosynthetic activity destroyed many chloroplasts, while carotenoids were maintained, resulting in the formation of reddened cells. The HPLC analysis revealed that diadinoxanthin was the primary carotenoid present in reddened cells. Additionally, an undefined xanthophyll, not produced under normal culture conditions, was synthesized and suggested to contain a C=O bond. While it has been reported that strong light stress can increase the total carotenoid content of cells, this study did not verify this claim, and it should be investigated further in future research. Under white light irradiation conditions (90 μmol photons/m2/s) in BS medium, no reddening of cells was observed, and good growth was achieved (over four times the cell density in CM medium on the seventh day). This cell suspension is considered to have a high nutritional value because it is composed of functional food, BS and E. gracilis. The fact that this method does not involve genetic modification suggests the possibility of industrial applications, including food use, even in reddened cells.

Carotenoids in maternal and cord blood, breast milk and their association with maternal dietary intake: a longitudinal study in Shanghai, China.

Carotenoids are important bioactive substances in breast milk, the profile of which is seldom studied. This study aimed to explore the profile of carotenoids in breast milk and maternal/cord plasma of healthy mother-neonate pairs in Shanghai, China, and their correlation with dietary intake. Maternal blood, umbilical cord blood and breast milk samples from five lactation stages (colostrum, transitional milk and early-, mid- and late-term mature milk) were collected. Carotenoid levels were analysed by HPLC. Carotenoid levels in breast milk changed as lactation progressed (P < 0·001). β-Carotene was the primary carotenoid in colostrum. Lutein accounted for approximately 50 % of total carotenoids in transitional milk, mature milk and cord blood. Positive correlations were observed between five carotenoids in umbilical cord blood and maternal blood (P all < 0·001). β-Carotene levels were also correlated between maternal plasma and three stages of breast milk (r = 0·605, P < 0·001; r = 0·456, P = 0·011, r = 0·446; P = 0·013, respectively). Dietary carotenoid intakes of lactating mothers also differed across lactation stages, although no correlation with breast milk concentrations was found. These findings suggest the importance of exploring the transport mechanism of carotenoids between mothers and infants and help guide the development of formulas for Chinese infants as well as the nutritional diets of lactating mothers.

Analysis of Carotenoids and Gene Expression in Apple Germplasm Resources Reveals the Role of MdCRTISO and MdLCYE in the Accumulation of Carotenoids.

Carotenoids play an important role in the coloring and nutritional value of apple (Malus spp.) fruits. Here, six carotenoids, including lutein, zeaxanthin, β-carotene, β-cryptoxanthin, violaxanthin, and neoxanthin, were detected in 105 fruits of apple germplasm resources, which showed a skewed distribution in both the peel and pulp. There were more carotenoids in the peel than in the pulp, and lutein and β-carotene were the primary carotenoids that were present. The expression levels of most carotenoid pathway genes in germplasm fruits during fruit development were higher in the fruits that had an abundance of carotenoids. A linear relationship analysis showed that the expression levels of MdCRTISO and MdLCYE were highly correlated with the content of carotenoids. The leaves accumulated the greatest number of carotenoids, while the roots had the lowest amount. MdCRTISO and MdLCYE were highly expressed in the fruits compared to other tissues. Transgenic calli and transiently transformed fruits confirmed that MdCRTISO and MdLCYE affected the biosynthesis of carotenoids owing to their effects on the expression of other genes for enzymes in the carotenoid pathway. Our findings will extend the understanding of carotenoid biosynthesis in apple and excavate apple germplasm resources with rich carotenoids to breed high-quality apples.

Carotenoid composition in twenty ulam species as potential halal active pharmaceutical ingredients

Ulam is a traditional Southeast Asian vegetable that has been consumed and practised by old folks for decades. Several studies have found that ulam has numerous benefits, including being high in natural antioxidants, antimicrobials, vitamins, and minerals and being used as an early illness preventive method. Even yet, many ulam have yet to be identified and documented. This study aimed to identify the carotenoid content and composition in a variety of ulam species as a potential halal active pharmaceutical ingredient. The individual carotenoid composition was examined in twenty ulam species with three groups of distinct parts: leaves, fruits, and rhizomes. Using HPLC analysis, neoxanthin, lutein, and β-carotene were the primary carotenoids discovered in the overall species. The results presented 12 species with 4 carotenoid pigments, 4 species with 3 carotenoid pigments, 2 species with 2 carotenoid pigments and 2 species with 1 carotenoid pigment. Mentha arvensis (51.38±0.24 µg/g DW) has substantially greater neoxanthin. In contrast, Manihot esculenta (1179±9.90 µg/g DW), (457±2.12 µg/g DW), and (2434.5±5.66 µg/g DW) had significantly higher β-carotene, lutein, and violaxanthin, respectively. Naturally available carotenoid sources as prospective components for halal pharmaceutical products will be discovered as a result of this research. These proven findings have also given communities the confidence to include ulam in their daily diets because it is a natural source with exceptional biological qualities.

An R-R-type MYB transcription factor promotes non-climacteric pepper fruit carotenoid pigment biosynthesis.

Carotenoids are major accessory pigments in the chloroplast, and they also act as phytohormones and volatile compound precursors to influence plant development and confer characteristic colours, affecting both the aesthetic and nutritional value of fruits. Carotenoid pigmentation in ripening fruits is highly dependent on developmental trajectories. Transcription factors incorporate developmental and phytohormone signalling to regulate the biosynthesis process. By contrast to the well-established pathways regulating ripening-related carotenoid biosynthesis in climacteric fruit, carotenoid regulation in non-climacteric fruit is poorly understood. Capsanthin is the primary carotenoid of non-climacteric pepper (Capsicum) fruit; its biosynthesis is tightly associated with fruit ripening, and it confers red pigmentation to the ripening fruit. In the present study, using a coexpression analysis, we identified an R-R-type MYB transcription factor, DIVARICATA1, and demonstrated its role in capsanthin biosynthesis. DIVARICATA1 encodes a nucleus-localised protein that functions primarily as a transcriptional activator. Functional analyses showed that DIVARICATA1 positively regulates carotenoid biosynthetic gene (CBG) transcript levels and capsanthin levels by directly binding to and activating CBG promoter transcription. Furthermore, an association analysis revealed a significant positive association between DIVARICATA1 transcription level and capsanthin content. ABA promotes capsanthin biosynthesis in a DIVARICATA1-dependent manner. Comparative transcriptomic analysis of DIVARICATA1 in Solanaceae plants showed that its function likely differs among species. Moreover, the pepper DIVARICATA1 gene could be regulated by the ripening regulator MADS-RIN. The present study illustrates the transcriptional regulation of capsanthin biosynthesis and offers a target for breeding peppers with high red colour intensity.

Valuable pigments from microalgae: phycobiliproteins, primary carotenoids, and fucoxanthin.

Phycobiliproteins, carotenoids and fucoxanthin are photosynthetic pigments extracted from microalgae and cyanobacteria with great potential biotechnological applications, as healthy food colorants and cosmetics. Phycocyanin possesses a brilliant blue color, with fluorescent properties making it useful as a reagent for immunological essays. The most important source of phycocyanin is the cyanobacterium Arthrospira platensis, however, recently, the Rhodophyta Galdieria sulphuraria has also been identified as such. The main obstacle to the commercialization of phycocyanin is represented by its chemical instability, strongly reducing its shelf-life. Moreover, the high level of purity needed for pharmaceutical applications requires several steps which increase both the production time and cost. Microalgae (Chlorella, Dunaliella, Nannochloropsis, Scenedesmus) produce several light harvesting carotenoids, and are able to manage with oxidative stress, due to their free radical scavenging properties, which makes them suitable for use as source of natural antioxidants. Many studies focused on the selection of the most promising strains producing valuable carotenoids and on their extraction and purification. Among carotenoids produced by marine microalgae, fucoxanthin is the most abundant, representing more than 10% of total carotenoids. Despite the abundance and diversity of fucoxanthin producing microalgae only a few species have been studied for commercial production, the most relevant being Phaeodactylum tricornutum. Due to its antioxidant activity, fucoxanthin can bring various potential benefits to the prevention and treatment of lifestyle-related diseases. In this review, we update the main results achieved in the production, extraction, purification, and commercialization of these important pigments, motivating the cultivation of microalgae as a source of natural pigments.

Influence of vegetation on occurrence and color of snow algal blooms in Mt. Gassan, Yamagata Prefecture, Japan

ABSTRACT Snow algae are photosynthetic microbes growing on melting snow surfaces, the blooms of which are visible on alpine snowpacks in Japan during the melting season. We characterized the seasonal and altitudinal variations in algal blooms on Mount Gassan, Japan, to assess the influence of vegetation on the algal bloom. From May to July in 2019, we collected colored snow from lower deciduous forest to the upper alpine areas. In the lower forest area, chlorophyll-a concentration in colored snow samples increased concomitantly with deciduous tree budburst, whereas in the alpine area, chlorophyll-a increased from June to July, although at lower levels than in the forest area. The absorption spectra of algal pigments extracted from samples differed among study sites and seasons, with those obtained from forest sites mainly characterized by absorption of chlorophylls and primary carotenoids, whereas those from alpine sites showed an intense secondary carotenoid peak throughout the study period. Chemical solute analyses revealed a general abundance of phosphate in snow, which was significantly higher in forest than in alpine sites and positively correlated with chlorophyll-a concentration. These findings suggest that nutrient supply from the forest canopy largely controls the appearance of colored snow in this area.

Citrus β-carotene hydroxylase 2 (BCH2) participates in xanthophyll synthesis by catalyzing the hydroxylation of β-carotene and compensates for BCH1 in citrus carotenoid metabolism.

As an essential horticultural crop, Citrus has carotenoid diversity, which affects its aesthetic and nutritional values. β,β-Xanthophylls are the primary carotenoids accumulated in citrus fruits, and non-heme di-iron carotene hydroxylase (BCH) enzymes are mainly responsible for β,β-xanthophyll synthesis. Previous studies have focused on the hydroxylation of BCH1, but the role of its paralogous gene in citrus, BCH2, remains largely unknown. In this study, we revealed the β-hydroxylation activity of citrus BCH2 (CsBCH2) for the first time through the functional complementation assay using Escherichia coli, although CsBCH2 exhibited a lower activity in hydroxylating β-carotene into β-cryptoxanthin than citrus BCH1 (CsBCH1). Our results showed that overexpression of CsBCH2 in citrus callus increased xanthophyll proportion and plastoglobule size with feedback regulation of carotenogenic gene expression. This study revealed the distinct expression patterns and functional characteristics of two paralogous genes, CsBCH1 and CsBCH2, and illustrated the backup compensatory role of CsBCH2 for CsBCH1 in citrus xanthophyll biosynthesis. The independent function of CsBCH2 and its cooperative function with CsBCH1 in β-cryptoxanthin biosynthesis suggested the potential of CsBCH2 to be employed for expanding the synthetic biology toolkit in carotenoid engineering.

Interdependence of fucoxanthin biosynthesis and fucoxanthin-chlorophyll a/c binding proteins in Phaeodactylum tricornutum under different light intensities

Fucoxanthin (FX), a primary carotenoid, is associated with the fucoxanthin-chlorophyll a/c binding protein (FCP) complex integrated into the thylakoid membrane (TM) which functions as a light-harvesting complex in the diatom Phaeodactylum tricornutum. Here, we aimed to elucidate the FX production regulated by different light intensities via the correlation of FX biosynthesis and apoproteins composing of FCP complex. High light (HL) accelerated P. tricornutum growth more than low light (LL). The maximum values of FX content and productivity obtained under LL (1.7 mg g−1 and 2.12 mg L−1 day−1, respectively) were substantially higher than those obtained under HL (0.54 mg g−1 and 0.79 mg L−1 day−1, respectively). Notably, proteome and photosynthetic pigment analyses revealed the enrichment of FCP antennae in the LL culture TM fractions but not the HL culture. Semi-quantification of FCP antenna protein using LC–MS/MS and RNA transcriptome analyses revealed that PtLhcf5 and PtLhcf8 played crucial roles in FCP biosynthesis under LL. P. tricornutum cultured under light transition exhibited FCP formation only in the early growth stage to meet the increased photosynthetic activity requirements under LL. Meanwhile, FCP degradation could be triggered by HL throughout the cultivation period. Therefore, FX production was highly correlated with FCP formation, and LL conditions in the early growth stage were critical for higher FX productivity.

Tissue Lycopene Accumulation in Transgenic Mice Lacking One or Both Carotenoid Cleaving Enzymes

ObjectivesTo evaluate the impact of gender and ablation of β-carotene oxygenase 1 (BCO1), β-carotene oxygenase 2(BCO2) or both on tissue accumulation of lycopene dosed transgenic mice. Previous work from our laboratories suggests that BCO2 appears to be the primary carotenoid cleavage enzyme for lycopene in vivo. MethodsThree-week old C57BL/6 male and female mice (wild type [WT], Bco1-/-, Bco2-/-, Bco1-/- X Bco2-/- double knock out [DKO]) were divided into groups based on genotype (n = 8 per group/per gender) and fed a powdered AIN 93G diet for 2 weeks. The mice were gavaged daily for 2 weeks with 1 mg of lycopene dissolved in cottonseed oil after which they were fasted and sacrificed. Liver, serum, and extra-hepatic tissues were harvested. Lycopene concentration was measured with high-performance liquid chromatography. Data analyses were performed using one-way ANOVA. ResultsOn a concentration basis, liver, duodenum and adrenal lycopene were higher than other tissues. Serum and tissues of DKO mice accumulated the highest lycopene. DKO mice had significantly higher lycopene than Bco1-/- mice in the liver (P < .002), heart (P < .004), adipose (P < .03), and the testes (P < .004). Compared to Bco2-/- mice, DKO mice had greater accumulation in the serum (P < .001), intestine (P < .04), heart (P < .0001), kidneys (P < .0001), adipose (P < .04), and testes (P < .0001). Liver (P < .007) and adrenal (ns) tissues in Bco2-/- mice had higher levels of lycopene than Bco1-/- mice whereas Bco1-/- mice had significantly higher levels in the kidneys (P < .001) and tended to have greater accumulation in other tissues. ConclusionsAccumulation of lycopene in tissues depended upon gender, genotype and tissue type. The abolition of both enzymes and mice of a female sex generated a higher accumulation. We are probing whether tissue-specific expression levels of BCO1, BCO2 or carotenoid transport proteins explain differential tissue accumulation across genotypes. Funding SourcesN/A.

Spatial and Temporal Variations in Pigment and Species Compositions of Snow Algae on Mt. Tateyama in Toyama Prefecture, Japan.

Snow algae are photosynthetic microbes that inhabit the melting snow surface in alpine and polar regions. We analyzed the pigment and species composition of colored snow collected on Mt. Tateyama in Japan during the melting seasons of 2015 and 2016. High-performance liquid chromatographic analyses of the pigments extracted from the colored snow showed that their composition varied within the study area and were classified into four types: Type A (astaxanthin-monoester dominant), Type B (medium astaxanthin-monoester content), Type C (abundant primary carotenoids and free-astaxanthin), and Type D (abundant primary carotenoids and astaxanthin diesters). Types A and B were most commonly observed in the study area, whereas Types C and D appeared only at specific sites. Analysis of the 18S ribosomal RNA (18S rRNA) gene revealed six major amplicon sequence variants (ASVs) of snow algae, belonging to the Sanguina, Chloromonas, and Chlainomonas groups. The relative abundance of the algal ASVs showed that Sanguina was dominant (>48%) in both Types A and B, suggesting that the difference in astaxanthin abundance between the two types was caused by the production of pigments in the algal cells. The algal community structures of Types C and D differed from those of Types A and B, indicating that the primary carotenoids and astaxanthin diesters were derived from certain algal species in these types. Therefore, astaxanthin-rich Sanguina algae mostly induced the red snow that appeared widely in this alpine area; however, they were partially dominated by Chloromonas or Chlainomonas algae, causing different pigment compositions.

Reactive oxygen species derived from NADPH oxidase regulate astaxanthin and total fatty acid accumulation in Chromochloris zofingiensis

Many abiotic stresses can promote astaxanthin and total fatty acid (TFA) accumulation in microalgae, but their signal molecules remain undetermined. The reactive oxygen species (ROS) derived from NADPH oxidase has been reported to act as signals and regulate many cellular responses in cell responses to biotic and abiotic stresses in higher plants. The present study explored the regulatory effects of NADPH oxidase derived ROS on astaxanthin and TFA accumulation in the green alga Chromochloris zofingiensis under nitrogen starvation. Diphenylene iodonium (DPI) inhibition of NADPH oxidase significantly decreased the cellular ROS level under nitrogen starvation. This was accompanied with the decreasing of astaxanthin and secondary carotenoids content, and the increasing of primary carotenoids content. Molecular studies showed that DPI depressed the expression of PSY, LCYb, and BKT, but elevated that of LCYe, which were coordinated with carotenoids content. Meanwhile, the TFA and neutral lipid contents, and the expression of their key biosynthesis genes, ACCase and PDAT, were also reduced in the DPI-treated cells. Additionally, the addition of ROS scavenger, N-acetylcysteine (NAC), decreased the astaxanthin and TFA contents. Taken together, our results revealed that NADPH oxidase-derived ROS was the key regulator in astaxanthin and fatty acid accumulation under nitrogen starvation.

Improving Fucoxanthin Production in Mixotrophic Culture of Marine Diatom Phaeodactylum tricornutum by LED Light Shift and Nitrogen Supplementation.

Fucoxanthin (Fx), a kind of primary carotenoids in brown seaweeds and diatoms, has attractive efficacy in human’s healthcare including loss weight, the prevention of diabetes and Alzheimer’s disease. Marine diatom Phaeodactylum tricornutum is now realized as a promising producer for commercial Fx production due to its higher content of Fx than brown seaweeds with easily artificial cultivation and Fx extraction. In the present study, to improve Fx production in P. tricornutum, the mixotrophic cultures were applied to optimize initial cell density, light intensity, light regime and nitrogen supplementation. The results showed that the higher initial cell density (1 × 107 cells mL–1) and lower light intensity (20 μmol m–2 s–1) were favorable for biomass production and Fx accumulation. The maximal Fx content [16.28 mg g–1 dry weight (DW)] could be achieved under blue light (BL), but the highest biomass concentration (5.53 g L–1) could be attained under red: blue light (R: B, 6:1) in the batch culture. A novel two-phase culture approach was developed to increase the biomass concentration to the highest value (6.52 g L–1) with the maximal productivity of Fx (8.22 mg L–1 d–1) through light shift from R:B ratio (6:1) in phase 1 to R:B ratio (5:1) by enhancing BL and tryptone addition in phase 2. The content and intracellular amount of Fx were also increased 8% and 12% in phase 2 compared to phase 1. The expression levels analysis revealed that genes encoding phytoene synthase (PSY), zeaxanthin epoxidase (ZEP), and fucoxanthin-chlorophyll-protein b (FCPb) were upregulated significantly, with downregulation of the gene encoding violaxanthin de-epoxidase (VDE), leading to the improvement of Fx in phase 2. The present study demonstrated the two-phase culture strategy could promote Fx productivity through enhancing biomass production and increasing Fx content, indicating that strengthening BL coupled with adding tryptone were effective to facilitate Fx production by mixotrophic cultivation of marine diatom P. tricornutum.

High light boosts salinity stress-induced biosynthesis of astaxanthin and lipids in the green alga Chromochloris zofingiensis

Chromochloris zofingiensis, an astaxanthin-producing oleaginous green alga, is emerging as a model for studying carotenogenesis and lipogenesis. While the stimulated biosynthesis of secondary carotenoids and storage lipids by abiotic stresses has long been perceived in C. zofingiensis, the underlying mechanisms particularly under combinatorial stresses remain to be explored. In the present study, the synthesis of carotenoids and lipids was comparatively investigated in C. zofingiensis under high light (HL), salinity stress (SS) and the combinatorial HL and SS (HL + SS) conditions. While HL or SS alone enhanced astaxanthin and lipids moderately, HL + SS had synergistic effect and promoted these compounds considerably. HL + SS also gave rise to the highest productivities. Carotenoid profiling and transcriptional analysis supported the diversion of carotenoid flux from primary carotenoids to secondary carotenoids particularly astaxanthin and violaxanthin cycle that produces zeaxanthin likely contributed to astaxanthin synthesis. Lipid profiling and transcriptional analysis, on the other hand, suggested that both de novo fatty acid synthesis and membrane lipid turnover contributed fatty acyls for supporting triacylglycerol assembly via the acyl CoA-dependent and acyl CoA-independent routes. Astaxanthin and triacylglycerol that share common carbon precursors were induced to synthesize in a coordinated way regulated at the transcriptional level, yet the carbon flux was allocated predominantly to the latter. Taken together, our results demonstrated the beneficial effect of combinatorial stresses on both astaxanthin and triacylglycerol production, identified critical genes involved in carotenogenesis and lipogenesis, and provided new insights into algal astaxanthin biosynthesis.