De novo synthesis of astaxanthin: From organisms to genes

Breeding triple-advantage cottonseed with higher yield, enhanced nutrition, and reduced toxicity by redirecting terpenoid metabolism to astaxanthin

Cottonseed is a valuable source of edible oil and protein, but its utilization is limited by high gossypol content. In this study, we engineered cotton (Gossypium hirsutum) to biosynthesize astaxanthin through both single-gene (CrBKT) and multi-gene (CrBKT, ZmPSY1, PaCrtI, HpCrtZ) expression strategies. Transgenic cotton plants exhibited significant astaxanthin accumulation across multiple tissues, with distinct red pigmentation observed in leaves, stems, reproductive organs, and cottonseeds. While single CrBKT expression was sufficient to redirect metabolic flux toward astaxanthin biosynthesis, multi-gene transformation did not necessarily lead to higher astaxanthin levels, suggesting that BKT is the key determinant of astaxanthin accumulation in cotton. Additionally, BKT-overexpressing plants produced larger cottonseeds, with increased seed weight and size, indicating a possible link between carotenoid metabolism and seed development. Importantly, gossypol content was significantly reduced in transgenic cottonseeds, likely due to the redistribution of terpene metabolism. The qRT-PCR analyses confirmed that the expression of key gossypol biosynthetic genes was downregulated, supporting a metabolic trade-off between astaxanthin and gossypol biosynthesis. These results demonstrate that cotton can serve as a biofactory for astaxanthin production, providing a scalable and cost-effective alternative to traditional sources. Furthermore, the dual benefits of enhanced nutrition and reduced toxicity significantly expand the potential applications of cottonseed in human food, animal feed, and functional ingredient markets.

Engineering tobacco for efficient astaxanthin production using a linker-free monocistronic dual-protein expression system and interspecific hybridization method

The high-value carotenoid astaxanthin is biosynthesized through a dual-enzyme-catalyzed cascade and is getting increased attention for engineered biosynthesis in plants. When developing astaxanthin-producing tobacco by expressing 2A-peptide-linked CBFD (carotenoid β-ring-4-dehydrogenase) and HBFD (carotenoid 4-hydroxy-β-ring-4-dehydrogenase) from Adonis aestivalis, this work discovered an in-enzyme splicing site at the N-terminus of HBFD that has potentials for multiple protein expression in plant using monocistronic cassette. Based on this finding, we generated astaxanthin-producing tobacco plants expressing a directly fused protein of CBFD and HBFD with a monocistronic cassette. Further integrated IP (immunoprecipitation) and LC-MS/MS assays revealed the presence of an in-enzyme splicing site at the N-terminus of HBFD. Nevertheless, the obtained astaxanthin-producing tobacco plants exhibited a growth retardation as observed by previous researches. Subsequent studies revealed that the astaxanthin-producing caused growth retardation of tobacco was correlated with chloroplast disruption and chlorophyll reduction, and it could be alleviated by expressing a chlorophyll biosynthetic enzyme identified by proteomics. Additionally, crossing the astaxanthin-producing tobacco with a variety having higher chlorophyll content also alleviated the growth retardation caused by astaxanthin production, and improved the total astaxanthin yield per plant by at least threefold along with the biomass increase. This work provides novel approaches for expressing multiple proteins in tobacco and for engineering efficient astaxanthin-producing tobacco.

Astaxanthin: a nature's versatile compound utilized for diverse applications and its therapeutic effects

Astaxanthin (ASTX), red-colored xanthophyll, also known as the "king of carotenoids" exhibits a strong antioxidant property that can be naturally found in green algae Haematococcus pluvialis, red yeast Phaffia rhodozyma, and various aquatic species including salmon, krill, trout, and fish eggs. Due to their strong antioxidant qualities, ASTX nanoparticles may be crucial in fighting against phytotoxicity caused by heavy metal ions. Similarly, it may also reduce the uptake of heavy metal, i.e. cadmium, and translocation by improving the morpho-physiological profiles of plants. Furthermore, it can also have the ability to scavenge free radicals, therefore, it can protect plants from reactive oxygen species (ROS). Implementing ASTX nanoparticles on crops can also help to achieve higher food production while minimizing toxic effects. Additionally, it can also possess several therapeutic activities including anti-cancerous, anti-diabetic, antioxidant, anti-aging, anti-inflammation, hepatoprotective, and cardiovascular, etc. that can be beneficial to treat various types of diseases in humans and animals. Recently, it has gained more interest in food, agriculture, aquaculture, neutraceuticals, and pharmaceutical industries due to its wide range of applications including food-coloring agents, food supplements, and strong antioxidant property that helps in skin protection, and boosts immune function. However, ASTX possesses poor water solubility and chemical stability so the implementation of ASTX on human health is facing various issues. Therefore, nanoencapsulation of ASTX is very crucial to improve its chemical stability and solubility, ultimately leading to its bioavailability and bioaccessibility. Recently, ASTX has been commercially available with specific dosages in the market mainly in the form of tablets, gels, powders, creams, syrups, etc. The current review mainly highlights the present state of ASTX nanoparticle applications in various fields explaining its natural and synthetic sources, extraction methods, chemical structure, stability, nanoformulations, nano encapsulation, and various commercial aspects.

Multi-Omics Analysis Provides Insights into a Mosaic-Leaf Phenotype of Astaxanthin-Producing Tobacco

In metabolically engineered plants, the target products are usually uniformly distributed in the whole plant or specific tissues. When engineering tobacco to produce astaxanthin, a ketocarotenoid with strong antioxidant activity and multiple bioactivities, a scattered distribution of astaxanthin-producing regions was observed in a small portion of astaxanthin-producing tobacco plants, which caused mosaic-like red and green spots on the leaves (ASTA-mosaic). A physiological assay showed that the non-astaxanthin green region (Mosaic_G) had relatively higher chlorophyll content and better chloroplast structure than the astaxanthin-producing red region (Mosaic_R). Then, metabolomics, proteomics, and small RNA transcriptomics were employed to analyze the uneven distribution of astaxanthin-producing regions in tobacco leaves. The results of metabolomics and proteomics revealed a decrease in carotenoid metabolism, chlorophyll biosynthesis, and chlorophyll degradation in the Mosaic_G region. Pheophorbide a, an intermediate of chlorophyll degradation, was found to be significantly reduced in the Mosaic_G region, which was accompanied by the attenuation of chlorophyllase and pheophytinase, which catalyze the formation of pheophorbide a in chlorophyll degradation. Reductions in photosynthetic antenna proteins and photosystem-associated proteins were observed in the Mosaic_R region, consistent with the better chloroplast structure of the Mosaic_G region. Small RNA transcriptomics showed that several small RNAs could target chlorophyll-degradative genes, but they were more effective in targeting the astaxanthin biosynthetic genes. This finding was supported by the fact that the Mosaic_G region can remain green up to the senescence of tobacco leaves. This work provides insights into the mechanism of the uneven distribution of astaxanthin-producing regions in tobacco leaves and may contribute to the specialized utilization of tobacco plants for metabolic engineering.

New strategies to study in depth the metabolic mechanism of astaxanthin biosynthesis in Phaffia rhodozyma

Astaxanthin, a ketone carotenoid known for its high antioxidant activity, holds significant potential for application in nutraceuticals, aquaculture, and cosmetics. The increasing market demand necessitates a higher production of astaxanthin using Phaffia rhodozyma. Despite extensive research efforts focused on optimizing fermentation conditions, employing mutagenesis treatments, and utilizing genetic engineering technologies to enhance astaxanthin yield in P. rhodozyma, progress in this area remains limited. This review provides a comprehensive summary of the current understanding of rough metabolic pathways, regulatory mechanisms, and preliminary strategies for enhancing astaxanthin yield. However, further investigation is required to fully comprehend the intricate and essential metabolic regulation mechanism underlying astaxanthin synthesis. Specifically, the specific functions of key genes, such as crtYB, crtS, and crtI, need to be explored in detail. Additionally, a thorough understanding of the action mechanism of bifunctional enzymes and alternative splicing products is imperative. Lastly, the regulation of metabolic flux must be thoroughly investigated to reveal the complete pathway of astaxanthin synthesis. To obtain an in-depth mechanism and improve the yield of astaxanthin, this review proposes some frontier methods, including: omics, genome editing, protein structure-activity analysis, and synthetic biology. Moreover, it further elucidates the feasibility of new strategies using these advanced methods in various effectively combined ways to resolve these problems mentioned above. This review provides theory and method for studying the metabolic pathway of astaxanthin in P. rhodozyma and the industrial improvement of astaxanthin, and provides new insights into the flexible combined use of multiple modern advanced biotechnologies.

Characterization of microalgal β-carotene and astaxanthin: exploring their health-promoting properties under the effect of salinity and light intensity

Microalgae are promising sources of valuable carotenoids like β-carotene and astaxanthin with numerous health benefits. This review summarizes recent studies on producing these carotenoids in microalgae under different salinity and light-intensity conditions, which are key factors influencing their biosynthesis. The carotenoid biosynthesis pathways in microalgae, involving the methylerythritol phosphate pathway in chloroplasts, are described in detail. The effects of high salinity and light stress on stimulating astaxanthin accumulation in species like Haematococcus pluvialis and Chromochloris zofingiensis and their synergistic impact are discussed. Similarly, the review covers how high light and salinity induce β-carotene production in Dunaliella salina and other microalgae. The diverse health-promoting properties of astaxanthin and β-carotene, such as their antioxidant, antiinflammatory, and anticancer activities, are highlighted. Strategies to improve carotenoid yields in microalgae through environmental stresses, two-stage cultivation, genetic engineering, and metabolic engineering approaches are evaluated. Overall, this review highlights advancements in β-carotene and astaxanthin production reporting the different microalgal capability to produce carotenoids under different stress level like 31.5% increase in β-carotene accumulation in Dunaliella salina and astaxanthin productivity reaching 18.1 mg/L/day in Haematococcus lacustris. It also explores novel biotechnological strategies, including CRISPR-Cas9, for enhancing carotenoid yield.

Chlamydomonas reinhardtii, Volvox carteri and related green algae accumulate ketocarotenoids not in vegetative cells but in zygospores

Zygospores of green alga such as Chlamydomonas reinhardtii, Volvox carteri or Dunaliella salina display a bright orange color indicative of carotenoids, yet there have been no reports on their pigment composition. The genomes of these algae contain genes for homologs of the β-carotene ketolase (BKT) from the well-known astaxanthin producer Haematococcus pluvialis, that were assumed to be pseudogenes, because none of these species has been reported to accumulate astaxanthin or other ketocarotenoids. Here, we show that C. reinhardtii and V. carteri synthesize ketocarotenoids specifically in zygospores. Contrary to the vegetative aplanospores of H. pluvialis, the major ketocarotenoid in zygospores of C. reinhardtii is not astaxanthin but 4-ketolutein. Moreover, the ketocarotenoids in maturing zygospores are not synthesized de novo but from carotenoids of the photosynthetic apparatus liberated by a massive breakdown of thylakoid membranes. In line with this conclusion, incubation of zygospores at 9°C instead of 22°C resulted in a reduced thylakoid breakdown and only low amounts of ketocarotenoids, while the accumulation of storage lipids was less affected. Furthermore, we show the full-length BKT from C. reinhardtii to catalyze the ketolation of both α-carotene and lutein in carotenogenic bacteria. We also detected putative BKT genes in the genomes of various other green algae not yet known to synthesize ketocarotenoids, suggesting a zygospore-specific accumulation of ketocarotenoids to be common among Chlamydomonadales. Our observation that zygospores of C. reinhardtii accumulate ketocarotenoids together with storage lipids sheds light on the physiology of a largely unexplored algal life stage crucial for survival and propagation.

Optimized separation of astaxanthin stereoisomers from microbial sources using chiral HPLC

Astaxanthin (AST) is a high-value antioxidant, and its efficient isolation and utilization are challenging owing to the presence of different stereoisomers from various sources. In the present study, a semi-preparative HPLC method for the efficient separation of AST stereoisomers using a Chiralpak IC chiral column with good loading capacity and chiral recognition ability was successfully developed. The mobile phase was methanol-methyl tert-butyl ether (90 : 10, v/v), with a flow rate of 3.06 mL min-1 and a maximum injection volume of 0.32 mg. The results indicated that the purity of all-trans AST was 97.9% for Haematococcus pluvialis and 97.5% for Phaffia rhodozyma. Additionally, molecular weights and fragmentation patterns analyzed using mass spectrometry were consistent with those of all-trans AST. Linearity validation and reproducibility experiments revealed that all calibration curves had coefficients of determination (R2) greater than 0.999 and a relative standard deviation (RSD) of <3.8%. This is because all-trans AST stereoisomers could undergo specific rotations or spins due to π-π interactions, hydrogen bonding, and inclusion interactions. This process allowed the successful separation of the three all-trans AST optical isomers and provides a theoretical basis for large-scale preparation of all-trans AST stereoisomers from different sources.

Comparative metabolomic analysis of Haematococcus pluvialis during hyperaccumulation of astaxanthin under the high salinity and nitrogen deficiency conditions

Revealing the differences of metabolite profiles of H. pluvialis during hyperaccumulation of astaxanthin under the high salinity and nitrogen deficiency conditions was the key issues of the present study. To investigate the optimum NaCl and NaNO3 concentration and the corresponding metabolic characteristic related to the astaxanthin accumulation in H. pluvialis, a batch culture experiment was conducted. The results indicated that 7.5 g·L- 1 and 0 g·L- 1 (nitrogen deficiency) were the optimum NaCl and NaNO3 levels for the astaxanthin accumulation respectively, under which the highest astaxanthin contents reached up to 7.51mg·L- 1 and 5.60mg·L- 1. A total of 132 metabolites were identified using LC-MS/MS technique, among which 30 differential metabolites with statistical significance were highlighted. Subsequently, 18 and 10 differential metabolic pathways in the high salinity (HS) and nitrogen-deficient (ND) treatments were extracted and annotated respectively. The values of Fv/Fm, Yield and NPQ were all at the highest level in the ND group during the experiment. The levels of the metabolites in the ND group were almost lower than those both in the control (CK) and HS group, while which in the HS group were substantially at the higher or close levels compared to the CK group. Finally, 7 metabolic markers related to the astaxanthin accumulation were highlighted in the HS and ND group respectively. L-Proline, L-Aspartate, Uridine 5'-monophosphate (UMP), Succinate, L-2-Hydroxygluterate, L-Valine and Inosine 5'-monophosphate (IMP) were identified as the metabolic markers in the HS group, whose fold change were 0.85, 4.14, 0.31, 0.66, 3.10, 1.32 and 0.30. Otherwise, the metabolic markers were Glyceric acid, Thymine, sn-Glycerol 3-phosphate, Glycine, Allantoic acid, L-Valine and IMP in the ND group, with the fold change 0.23, 2.11, 0.38, 0.41, 0.50 and 2.96 respectively. The results provided the comparative metabolomic view of astaxanthin accumulation in H. pluvialis under the different cultivation conditions, moreover showed a novel insights into the astaxanthin production.

Selecting a preculture strategy for improving biomass and astaxanthin productivity of Chromochloris zofingiensis

Chromochloris zofingiensis is a potential source of natural astaxanthin; however, its rapid growth and astaxanthin enrichment cannot be achieved simultaneously. This study established autotrophic, mixotrophic, and heterotrophic preculture patterns to assess their ameliorative effect on the C. zofingiensis heterotrophic growth state. In comparison, mixotrophic preculture (MP) exhibited the best improving effect on heterotrophic biomass concentration of C. zofingiensis (up to 121.5 g L-1) in a 20 L fermenter, reaching the global leading level. The astaxanthin productivity achieved 111 mg L-1 day-1, 7.4-fold higher than the best record. The transcriptome and 13C tracer-based metabolic flux analysis were used for mechanism inquiry. The results revealed that MP promoted carotenoid and lipid synthesis, and supported synthesis preference of low unsaturated fatty acids represented by C18:1 and C16:0. The MP group maintained the best astaxanthin productivity via mastering the balance between increasing glucose metabolism and inhibition of carotenoid synthesis. The MP strategy optimized the physiological state of C. zofingiensis and realized its heterotrophic high-density growth for an excellent astaxanthin yield on a pilot scale. This strategy exhibits great application potential in the microalgae-related industry. KEY POINTS: • Preculture strategies changed carbon flux and gene expression in C. zofingiensis • C. zofingiensis realized a high-density culture with MP and fed-batch culture (FBC) • Astaxanthin productivity achieved 0.111 g L-1 day-1 with MP and FBC.

Extraction and Synthesis of Typical Carotenoids: Lycopene, β-Carotene, and Astaxanthin

Carotenoids are tetraterpene compounds acting as precursors to vitamin A, with functions that include protecting eyesight, enhancing immunity, promoting cell growth and differentiation, and providing antioxidative benefits. Lycopene, β-carotene, and astaxanthin are particularly critical for health and have diverse applications in food, health products, and medicine. However, natural carotenoids are encased within cell structures, necessitating mechanical methods to disrupt the cell wall for their extraction and purification-a process often influenced by environmental conditions. Thus, improving the efficiency of carotenoid extraction from natural resources is of great interest. This review delves into the research progress made on the extraction processes, structures, and biological functions of carotenoids, focusing on lycopene, β-carotene, and astaxanthin. Traditional extraction methods primarily involve organic solvent-assisted mechanical crushing. With deeper research and technological advancements, more environmentally friendly solvents, advanced machinery, and suitable methods are being employed to enhance the extraction and purification of carotenoids. These improvements have significantly increased extraction efficiency, reduced preparation time, and lowered production costs, laying the groundwork for new carotenoid product developments.

Effects of dietary astaxanthin on immune status and lipid metabolism in gilthead seabream (Sparus aurata)

Astaxanthin (AX) is a carotenoid known to have one of the highest documented antioxidant capacities and has attracted considerable scientific and commercial interest. The incorporation of AX into aquaculture practices has been associated with improved pigmentation, modulation of the immune and endocrine systems, stress reduction, reproductive efficiency and general fish health. This study describes the effects of dietary AX (0, control, 20, 100 and 500 mg kg-1 AX per kg of diet) for 15 and 30 days on growth performance, immune and antioxidant status, histology and gene expression in gilthead seabream (Sparus aurata). Fish fed diets enriched with 500 mg kg-1 of AX for 15 days decreased in skin mucus peroxidase activity while at 30 days of trial, fish fed a diet supplemented with 20 mg kg-1 AX increased the peroxidase activity in serum. In addition, bactericidal activity against Vibrio harveyi increased in the skin mucus of fish fed any of the AX supplemented diets. Regarding antioxidant activities in the liver, catalase and glutathione reductase were decreased and increased, respectively, in fish fed a diet supplemented with 500 mg kg-1 of AX. Finally, although the expression of up to 21 inflammatory and lipid metabolism-related genes was analysed in visceral adipose tissue, only the expression of the interleukin 6 (il6) gene was up-regulated in fish fed a diet supplemented with 20 mg kg-1 of AX. The present results provide a detailed insight into the potent antioxidant properties of AX and its possible modulatory effects on the immune status and lipid metabolism of seabream, which may be of interest to the aquaculture sector.

Astaxanthin induces plant tolerance against cadmium by reducing cadmium uptake and enhancing carotenoid metabolism for antioxidant defense in wheat (Triticum aestivum L.)

Soil cadmium (Cd) contamination poses a significant threat to global food security and the environment. Astaxanthin (AX), a potent biological antioxidant belonging to the carotenoid group, has been demonstrated to confer tolerance against diverse abiotic stresses in plants. This study investigated the potential of AX in mitigating Cd-induced damage in wheat seedlings. Morpho-physiological, ultrastructural, and biochemical analyses were conducted to evaluate the impact of AX on Cd-exposed wheat seedlings. Illumina-based gene expression profiling was employed to uncover the molecular mechanisms underlying the protective effects of AX. The addition of 100 μM AX alleviated Cd toxicity by enhancing various parameters: growth, photosynthesis, carotenoid content, and total antioxidant capacity (T-AOC), while reducing Cd accumulation, malondialdehyde (MDA), and hydrogen peroxide (H2O2) levels. RNA sequencing analysis revealed differentially expressed genes associated with Cd uptake and carotenoid metabolism, such as zinc/iron permease (ZIP), heavy metal-associated protein (HMA), 3-beta hydroxysteroid dehydrogenase/isomerase (3-beta-HSD), and thiolase. These findings suggest that AX enhances Cd tolerance in wheat seedlings by promoting the expression of detoxification and photosynthesis-related genes. This research offers valuable insights into the potential use of AX to address Cd contamination in agricultural systems, highlighting the significance of antioxidant supplementation in plant stress management.

Effects of dietary nanoliposome-coated astaxanthin on haematological parameters, immune responses and the antioxidant status of rainbow trout (Oncorhynchus mykiss)

BACKGROUND

Astaxanthin is the most prevalent carotenoid in the marine environment and is widely used as an additive in formulated aquafeeds.

OBJECTIVES

A 60-day feeding trial was conducted to consider the effect of dietary nanoliposome-coated astaxanthin (NA) on haematological parameters, serum antioxidant activities and immune responses of rainbow trout, Oncorhynchus mykiss.

METHODS

A total of 450 healthy fish weighing 31.00 ± 2.09 g were randomly assigned in triplicate (30 fish per replicate) to 5 dietary treatments: 0 (control), 25.00, 50.00, 75.00, and 100.00 mg kg-1 NA.

RESULTS

Fish fed the diet supplemented with 50.00 mg kg-1 NA exhibited the highest values of red blood cells, white blood cells, haemoglobin and haematocrit of 1.64 ± 0.01 × 106 mm-3, 5.54 ± 0.21 × 103 mm-3, 8.73 ± 0.24 g dL-1 and 46.67% ± 0.88%, respectively, which were significantly higher than those fed the basal diet (p < 0.05). The lowest and highest percentages of lymphocytes (67.67% ± 0.33%) and neutrophils (27.33% ± 1.20%) were also obtained in fish fed 50.00 mg kg-1 NA compared to those fed the basal diet (p < 0.05). Fish receiving diet supplemented with 50.00 mg kg-1 NA revealed the highest serum activity in superoxide dismutase, catalase, glutathione peroxidase, lysozyme and alternative complement and the lowest level of total cholesterol, cortisol, aspartate aminotransferase and alanine aminotransferase than fish receiving the basal diet (p < 0.05). Serum immunoglobulin (Ig) and ACH50 contents significantly increased with increasing dietary NA supplementation to the highest values of 43.17 ± 1.46 and 293.33 ± 2.03 U mL-1, respectively, in fish fed diet supplemented with 50 mg kg-1 NA (p < 0.05).

CONCLUSIONS

Supplementation of NA in rainbow trout diet at 50 mg kg-1 exhibited a positive effect on haematological parameters, antioxidant capacity and immune responses. Administration of such dosage can enhance rainbow trout immune responses against unfavourable or stressful conditions, for example disease outbreaks, hypoxic condition, thermal stress and sudden osmotic fluctuations, which usually happen in an intensive culture system.

Microbiome-based classification models for fresh produce safety and quality evaluation

Small sample sizes and loss of sequencing reads during the microbiome data preprocessing can limit the statistical power of differentiating fresh produce phenotypes and prevent the detection of important bacterial species associated with produce contamination or quality reduction. Here, we explored a machine learning-based k-mer hash analysis strategy to identify DNA signatures predictive of produce safety (PS) and produce quality (PQ) and compared it against the amplicon sequence variant (ASV) strategy that uses a typical denoising step and ASV-based taxonomy strategy. Random forest-based classifiers for PS and PQ using 7-mer hash data sets had significantly higher classification accuracy than those using the ASV data sets. We also demonstrated that the proposed combination of integrating multiple data sets and leveraging a 7-mer hash strategy leads to better classification performance for PS and PQ compared to the ASV method but presents lower PS classification accuracy compared to the feature-selected ASV-based taxonomy strategy. Due to the current limitation of generating taxonomy using the 7-mer hash strategy, the ASV-based taxonomy strategy with remarkably less computing time and memory usage is more efficient for PS and PQ classification and applicable for important taxa identification. Results generated from this study lay the foundation for future studies that wish and need to incorporate and/or compare different microbiome sequencing data sets for the application of machine learning in the area of microbial safety and quality of food.

IMPORTANCE

Identification of generalizable indicators for produce safety (PS) and produce quality (PQ) improves the detection of produce contamination and quality decline. However, effective sequencing read loss during microbiome data preprocessing and the limited sample size of individual studies restrain statistical power to identify important features contributing to differentiating PS and PQ phenotypes. We applied machine learning-based models using individual and integrated k-mer hash and amplicon sequence variant (ASV) data sets for PS and PQ classification and evaluated their classification performance and found that random forest (RF)-based models using integrated 7-mer hash data sets achieved significantly higher PS and PQ classification accuracy. Due to the limitation of taxonomic analysis for the 7-mer hash, we also developed RF-based models using feature-selected ASV-based taxonomic data sets, which performed better PS classification than those using the integrated 7-mer hash data set. The RF feature selection method identified 480 PS indicators and 263 PQ indicators with a positive contribution to the PS and PQ classification.

Astaxanthin from microalgae: A review on structure, biosynthesis, production strategies and application

Astaxanthin is a red-colored secondary metabolite with excellent antioxidant properties, typically finds application as foods, feed, cosmetics, nutraceuticals, and medications. Astaxanthin is usually produced synthetically using chemicals and costs less as compared to the natural astaxanthin obtained from fish, shrimps, and microorganisms. Over the decades, astaxanthin has been naturally synthesized from Haematococcus pluvialis in commercial scales and remains exceptional, attributed to its higher bioactive properties as compared to synthetic astaxanthin. However, the production cost of algal astaxanthin is still high due to several bottlenecks prevailing in the upstream and downstream processes. To that end, the present study intends to review the recent trends and advancements in astaxanthin production from microalgae. The structure of astaxanthin, sources, production strategies of microalgal astaxanthin, and factors influencing the synthesis of microalgal astaxanthin were discussed while detailing the pathway involved in astaxanthin biosynthesis. The study also discusses the relevant downstream process used in commercial scales and details the applications of astaxanthin in various health related issues.

Assessment of thraustochytrids potential for carotenoids, terpenoids and polyunsaturated fatty acids biorefinery

Heterotrophic fast-growing thraustochytrids have been identified as promising candidates for the bioconversion of organic sources into industrially important valuable products. Marine thraustochytrids exhibit remarkable potential for high-value polyunsaturated fatty acids (PUFAs) production however their potential is recently discovered for high-value carotenoids and terpenoids which also have a role as a dietary supplement and health promotion. Primarily, omega-3 and 6 PUFAs (DHA, EPA, and ARA) from thraustochytrids are emerging sources of nutrient supplements for vegetarians replacing animal sources and active pharmaceutical ingredients due to excellent bioactivities. Additionally, thraustochytrids produce reasonable amounts of squalene (terpenoid) and carotenoids which are also high-value products with great market potential. Hence, these can be coextracted as a byproduct with PUFAs under the biorefinery concept. There is still quite a few printed information on bioprocess conditions for decent (co)-production of squalene and carotenoid from selective protists such as lutein, astaxanthin, canthaxanthin, and lycopene. The current review seeks to provide a concise overview of the coproduction and application of PUFAs, carotenoids, and terpenoids from oleaginous thraustochytrids and their application to human health.

Isolation, Identification, and Antibacterial Properties of Prodigiosin, a Bioactive Product Produced by a New Serratia marcescens JSSCPM1 Strain: Exploring the Biosynthetic Gene Clusters of Serratia Species for Biological Applications

Prodigiosin pigment has high medicinal value, so exploring this compound is a top priority. This report presents a prodigiosin bioactive compound isolated from Serratia marcescens JSSCPM1, a new strain. The purification process of this compound involves the application of different chromatographic methods, including UV-visible spectroscopy, high-performance liquid chromatography (HPLC), and liquid chromatography-mass spectrometry (LC/MS). Subsequent analysis was performed using nuclear magnetic resonance (NMR) to achieve a deeper understanding of the compound's structure. Finally, through a comprehensive review of the existing literature, the structural composition of the isolated bioactive compound was found to correspond to that of the well-known compound prodigiosin. The isolated prodigiosin compound was screened for antibacterial activity against both Gram-positive and Gram-negative bacteria. The compound inhibited the growth of Gram-negative bacterial strains compared with Gram-positive bacterial strains. It showed a maximum minimum inhibitory concentration against Escherichia coli NCIM 2065 at a 15.9 ± 0.31 μg/mL concentration. The potential binding capabilities between prodigiosin and the OmpF porin proteins (4GCS, 4GCP, and 4GCQ) were determined using in silico studies, which are generally the primary targets of different antibiotics. Comparative molecular docking analysis indicated that prodigiosin exhibits a good binding affinity toward these selected drug targets.

Microfluidic fabrication of size-controlled nanocarriers with improved stability and biocompatibility for astaxanthin delivery

Improving the stability of astaxanthin (AST) is a vital way to enhance its oral bioavailability. In this study, a microfluidic strategy for the preparation of astaxanthin nano-encapsulation system was proposed. Thanks to the precise control of microfluidic and the rapid preparation ability of the Mannich reaction, the resulting astaxanthin nano-encapsulation system (AST-ACNs-NPs) was obtained with average sizes of 200 nm, uniform spherical shape and high encapsulation rate of 75%. AST was successfully doped into the nanocarriers, according to the findings of the DFT calculation, fluorescence spectrum, Fourier transform spectroscopy, and UV-vis absorption spectroscopy. Compared with free AST, AST-ACNs-NPs showed better stability under the conditions of high temperature, pH and UV light with<20% activity loss rate. The nano-encapsulation system containing AST could significantly reduce the hydrogen peroxide produced by reactive oxygen species, keep the potential of the mitochondrial membrane at a healthy level, and improve the antioxidant ability of H₂O₂-induced RAW 264.7 cells. These results indicated that microfluidics-based astaxanthin delivery system is an effective solution to improve the bioaccessibility of bioactive substances and has potential application value in food industry.

Rhodotorula sp. as a cell factory for production of valuable biomolecules

Rhodotorula sp. are well-known for their ability to biosynthesize a diverse range of valuable biomolecules, including carotenoids, lipids, enzymes, and polysaccharides. Despite the high number of studies conducted using Rhodotorula sp. at the laboratory scale, most of these do not address all processual aspects necessary for scaling up these processes for industrial applications. This chapter explores the potential of Rhodotorula sp. as a cell factory for the production of distinct biomolecules, with a particular emphasis on exploring their use from a biorefinery perspective. Through in-depth discussions of the latest research and insights into non-conventional applications, we aim to provide a comprehensive understanding of Rhodotorula sp.'s ability to produce biofuels, bioplastics, pharmaceuticals, and other valuable biochemicals. This book chapter also examines the fundamentals and challenges associated with the optimizing upstream and downstream processing of Rhodotorula sp-based processes. We believe that through this chapter, readers with different levels of expertise will gain insights into strategies for enhancing the sustainability, efficiency, and effectiveness of producing biomolecules using Rhodotorula sp.

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

BACKGROUND

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

RESULTS

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

CONCLUSION

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

Engineering Nutritionally Improved Edible Plant Oils

In contrast to traditional breeding, which relies on the identification of mutants, metabolic engineering provides a new platform to modify the oil composition in oil crops for improved nutrition. By altering endogenous genes involved in the biosynthesis pathways, it is possible to modify edible plant oils to increase the content of desired components or reduce the content of undesirable components. However, introduction of novel nutritional components such as omega-3 long-chain polyunsaturated fatty acids needs transgenic expression of novel genes in crops. Despite formidable challenges, significant progress in engineering nutritionally improved edible plant oils has recently been achieved, with some commercial products now on the market.

Unveiling the Mechanism of Alleviating Ischemia Reperfusion Injury via a Layered Double Hydroxide-Based Nanozyme

Oxidative stress after ischemia reperfusion can cause irreversible brain damage. Thus, it is vital to timely consume excessive reactive oxygen species (ROS) and conduct molecular imaging monitoring on the brain injury site. However, previous studies have focused on how to scavenge ROS while ignoring the mechanism of relieving the reperfusion injury. Herein, we reported a layered double hydroxide (LDH)-based nanozyme (denoted as ALDzyme), which was fabricated by the confinement of astaxanthin (AST) with LDH. This ALDzyme can mimic natural enzymes, which include superoxide dismutase (SOD) and catalase (CAT). Furthermore, the SOD-like activity of ALDzyme is 16.3 times higher than that of CeO₂ (a typical ROS scavenger). Based on these enzyme-mimicking properties, this one-of-a-kind ALDzyme offers strong anti-oxidative properties as well as high biocompatibility. Importantly, this unique ALDzyme can establish an efficient magnetic resonance imaging platform, thus guiding the in vivo details. As a result, the infarct area can be reduced by 77% after reperfusion therapy, and the neurological impairment score can be lowered from 3-4 to 0-1. Density functional theory computations can reveal more about the mechanism of this ALDzyme's significant ROS consumption. These findings provide a method for unraveling the neuroprotection application process in ischemia reperfusion injury using an LDH-based nanozyme as a remedial nanoplatform.

Recent advancements in astaxanthin production from microalgae: A review

Microalgae have emerged as the best source of high-value astaxanthin producers. Algal astaxanthin possesses numerous bioactivities hence the rising demand for several health applications and is broadly used in pharmaceuticals, aquaculture, health foods, cosmetics, etc. Among several low-priced synthetic astaxanthin, natural astaxanthin is still irreplaceable for human consumption and food-additive uses. This review highlights the recent development in production enhancement and cost-effective extraction techniques that may apply to large-scale astaxanthin biorefinery. Primarily, the biosynthetic pathway of astaxanthin is elaborated with the key enzymes involved in the metabolic process. Moreover, discussed the latest astaxanthin enhancement strategies mainly including chemicals as product inducers and byproducts inhibitors. Later, various physical, chemical, and biological cell disruption methods are compared for cell disruption efficiency, and astaxanthin extractability. The aim of this review is to provide a comprehensive review of advancements in astaxanthin research covering scalable upstream and downstream astaxanthin bioproduction aspects.

Advances in the synthesis of three typical tetraterpenoids including β-carotene, lycopene and astaxanthin

Carotenoids are natural pigments that widely exist in nature. Due to their excellent antioxidant, anticancer and anti-inflammatory properties, carotenoids are commonly used in food, medicine, cosmetic and other fields. At present, natural carotenoids are mainly extracted from plants, algae and microorganisms. With the rapid development of metabolic engineering and molecular biology as well as the continuous in-depth study of carotenoids synthesis pathways, industrial microorganisms have showed promising applications in the synthesis of carotenoids. In this review, we introduced the properties of several carotenoids and their biosynthetic metabolism process. Then, the microorganisms synthesizing carotenoids through the natural and non-natural pathways and the extraction methods of carotenoids were summarized and compared. Meanwhile, the influence of substrates on the carotenoids production was also listed. The methods and strategies for achieving high carotenoid production are categorized to help with future research.

Advances in plastid transformation for metabolic engineering in higher plants

The plastid (chloroplast) genome of higher plants is an appealing target for metabolic engineering via genetic transformation. Although the bacterial-type plastid genome is small compared with the nuclear genome, it can accommodate large quantities of foreign genes that precisely integrate through homologous recombination. Engineering complex metabolic pathways in plants often requires simultaneous and concerted expression of multiple transgenes, the possibility of stacking several transgenes in synthetic operons makes the transplastomic approach amazing. The potential for extraordinarily high-level transgene expression, absence of epigenetic gene silencing and transgene containment due to the exclusion of plastids from pollen transmission in most angiosperm species further add to the attractiveness of plastid transformation technology. This minireview describes recent advances in expanding the toolboxes for plastid genome engineering, and highlights selected high-value metabolites produced using transplastomic plants, including artemisinin, astaxanthin and paclitaxel.

Progress towards a targeted biorefinery of Chromochloris zofingiensis: a review

Biorefinery approaches offer the potential to improve the economics of the microalgae industry by producing multiple products from a single source of biomass. Chromochloris zofingiensis shows great promise for biorefinery due to high biomass productivity and a diverse range of products including secondary carotenoids, predominantly astaxanthin; lipids such as TAGs; carbohydrates including starch; and proteins and essential amino acids. Whilst this species has been demonstrated to accumulate multiple products, the development of an integrated downstream process to obtain these is lacking. The objective of this review paper is to assess the research that has taken place and to identify the steps that must be taken to establish a biorefinery approach for C. zofingiensis. In particular, the reasons why C. zofingiensis is a promising species to target for biorefinery are discussed in terms of cellular structure, potential products, and means to accumulate desirable components via the alteration of culture conditions. Future advances and the challenges that lie ahead for successful biorefinery of this species are also reviewed along with potential solutions to address them.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13399-022-02955-7.

Optimization of microbial cell factories for astaxanthin production: Biosynthesis and regulations, engineering strategies and fermentation optimization strategies

The global market demand for natural astaxanthin is rapidly increasing owing to its safety, the potential health benefits, and the diverse applications in food and pharmaceutical industries. The major native producers of natural astaxanthin on industrial scale are the alga Haematococcus pluvialis and the yeast Xanthopyllomyces dendrorhous. However, the natural production via these native producers is facing challenges of limited yield and high cost of cultivation and extraction. Alternatively, astaxanthin production via metabolically engineered non-native microbial cell factories such as Escherichia coli, Saccharomyces cerevisiae and Yarrowia lipolytica is another promising strategy to overcome these limitations. In this review we summarize the recent scientific and biotechnological progresses on astaxanthin biosynthetic pathways, transcriptional regulations, the interrelation with lipid metabolism, engineering strategies as well as fermentation process control in major native and non-native astaxanthin producers. These progresses illuminate the prospects of producing astaxanthin by microbial cell factories on industrial scale.

Production of High Levels of 3S,3'S-Astaxanthin in Yarrowia lipolytica via Iterative Metabolic Engineering

Astaxanthin is a highly value-added keto-carotenoid compound. The astaxanthin 3S,3'S-isomer is more desirable for food additives, cosmetics, and pharmaceuticals due to health concerns about chemically synthesized counterparts with a mixture of three isomers. Biosynthesis of 3S,3'S-astaxanthin suffers from limited content and productivity. We engineered Yarrowia lipolytica to produce high levels of 3S,3'S-astaxanthin. We first assessed various β-carotene ketolases (CrtW) and β-carotene hydroxylases (CrtZ) from two algae and a plant. HpCrtW and HpCrtZ from Haematococcus pluvialis exhibited the strongest activity in converting β-carotene into astaxanthin in Y. lipolytica. We then fine-tuned the HpCrtW and HpCrtZ transcriptional expression by increasing the rounds of gene integration into the genome and applied a modular enzyme assembly of HpCrtW and HpCrtZ simultaneously. Next, we rescued leucine biosynthesis in the engineered Y. lipolytica, leading to a five-fold increase in biomass. The astaxanthin production achieved from these strategies was 3.3 g/L or 41.3 mg/g dry cell weight under fed-batch conditions, which is the highest level reported in microbial chassis to date. This study provides the potential for industrial production of 3S,3'S-astaxanthin, and this strategy empowers us to build a sustainable biorefinery platform for generating other value-added carotenoids in the future.

Accumulation and conversion of β-carotene and astaxanthin induced by abiotic stresses in Schizochytrium sp

Astaxanthin is a kind of ketone carotenoid belonging to tetraterpenoids with an excellent antioxidant activity and it is widely used in nutrition and health-care industries. This study aimed to explore the effect of different abiotic stresses on carotenoid production in Schizochytrium sp. Firstly, the characteristics of carotenoid accumulation were studied in Schizochytrium sp. by monitoring the change of carotenoid yields and gene expressions. Then, different abiotic stresses were systematically studied to regulate the carotenoid accumulation. Results showed that low temperature could advance the astaxanthin accumulation, while ferric ion could stimulate the conversion from carotene to astaxanthin. The glucose and monosodium glutamate ratio of 100:5 was helpful for the accumulation of β-carotene. In addition, micro-oxygen supply conditions could increase the yield of β-carotene and astaxanthin by 25.47% and 14.92%, respectively. This study provided the potential regulation strategies for carotenoid production which might be used in different carotenoid-producing strains.

Carotenoid Production from Microalgae: Biosynthesis, Salinity Responses and Novel Biotechnologies

Microalgae are excellent biological factories for high-value products and contain biofunctional carotenoids. Carotenoids are a group of natural pigments with high value in social production and human health. They have been widely used in food additives, pharmaceutics and cosmetics. Astaxanthin, β-carotene and lutein are currently the three carotenoids with the largest market share. Meanwhile, other less studied pigments, such as fucoxanthin and zeaxanthin, also exist in microalgae and have great biofunctional potentials. Since carotenoid accumulation is related to environments and cultivation of microalgae in seawater is a difficult biotechnological problem, the contributions of salt stress on carotenoid accumulation in microalgae need to be revealed for large-scale production. This review comprehensively summarizes the carotenoid biosynthesis and salinity responses of microalgae. Applications of salt stress to induce carotenoid accumulation, potentials of the Internet of Things in microalgae cultivation and future aspects for seawater cultivation are also discussed. As the global market share of carotenoids is still ascending, large-scale, economical and intelligent biotechnologies for carotenoid production play vital roles in the future microalgal economy.

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

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

Dietary astaxanthin: an excellent carotenoid with multiple health benefits

Astaxanthin is a carotenoid widely found in marine organisms and microorganisms. With extensive use in nutraceuticals, cosmetics, and animal feed, astaxanthin will have the largest share in the global market for carotenoids in the near future. Owing to its unique molecular features, astaxanthin has excellent antioxidant activity and holds promise for use in biochemical studies. This review focuses on the observed health benefits of dietary astaxanthin, as well as its underlying bioactivity mechanisms. Recent studies have increased our understanding of the role of isomerization and esterification in the structure-function relationship of dietary astaxanthin. Gut microbiota may involve the fate of astaxanthin during digestion and absorption; thus, further knowledge is needed to establish accurate recommendations for dietary intake of both healthy and special populations. Associated with the regulation of redox balance and multiple biological mechanisms, astaxanthin is proposed to affect oxidative stress, inflammation, cell death, and lipid metabolism in humans, thus exerting benefits for skin condition, eye health, cardiovascular system, neurological function, exercise performance, and immune response. Additionally, preclinical trials predict its potential effects such as intestinal flora regulation and anti-diabetic activity. Therefore, astaxanthin is worthy of further investigation for boosting human health, and wide applications in the food industry.

Characterization of fatty acid desaturases reveals stress-induced synthesis of C18 unsaturated fatty acids enriched in triacylglycerol in the oleaginous alga Chromochloris zofingiensis

BACKGROUND

The green microalga Chromochloris zofingiensis is capable of producing high levels of triacylglycerol rich in C18 unsaturated fatty acids (UFAs). FA desaturation degree is regulated by FA desaturases (FADs). Nevertheless, it remains largely unknown regarding what FADs are involved in FA desaturations and how these FADs collaborate to contribute to the high abundance of C18 UFAs in triacylglycerol in C. zofingiensis.

RESULTS

To address these issues, we firstly determined the transcription start sites of 11 putative membrane-bound FAD-coding genes (CzFADs) and updated their gene models. Functional validation of these CzFADs in yeast and cyanobacterial cells revealed that seven are bona fide FAD enzymes with distinct substrates. Combining the validated functions and predicted subcellular compartments of CzFADs and the FA profiles of C. zofingiensis, the FA desaturation pathways in this alga were reconstructed. Furthermore, a multifaceted lipidomic analysis by systematically integrating thin-layer chromatography, gas chromatography-mass spectrometry and liquid chromatography-mass spectrometry techniques was conducted, unraveling profiles of polar membrane lipids in C. zofingiensis and major desaturation steps occurring in these lipids. By correlating transcriptional patterns of CzFAD genes and changes of lipids upon abiotic stress conditions, our results highlighted collaboration of CzFADs for C18 UFA synthesis and supported that both de novo FA synthesis and membrane lipid remodeling contributed C18 UFAs to triacylglycerol for storage.

CONCLUSIONS

Taken together, our study for the first time elucidated the pathways of C18 FA desaturations and comprehensive profiles of polar membrane lipids in C. zofingiensis and shed light on collaboration of CzFADs for the synthesis and enrichment of C18 UFAs in triacylglycerol.

Biosynthesis and extraction of high-value carotenoid from algae

Algae possess a considerable potential as bio-refinery for the scale-up production of high-value natural compounds like-carotenoids. Carotenoids are accessory pigments in the light-harvesting apparatus and also act as antioxidants and photo-protectors in green cells. They play important roles for humans, like-precursors of vitamin A, reduce the risk of some cancers, helps in the prevention of age-related diseases, cardiovascular diseases, improve skin health, and stimulates immunity. To date, about 850 types of natural carotenoid compounds have been reported and they have approximated 1.8 billion US$ of global market value. In comparison to land plants, there are few reports on biosynthetic pathways and molecular level regulation of algal carotenogenesis. Recent advances of algal genome sequencing, data created by high-throughput technologies and transcriptome studies, enables a better understanding of the origin and evolution of de novo carotenoid biosynthesis pathways in algae. Here in this review, we focused on, the biochemical and molecular mechanism of carotenoid biosynthesis in algae. Additionally, structural features of different carotenoids are elaborated from a chemistry point of view. Furthermore, current understandings of the techniques designed for pigment extraction from algae are reviewed. In the last section, applications of different carotenoids are elucidated and the growth potential of the global market value of carotenoids are also discussed.

High-level production of microbial prodigiosin: A review

Prodigiosin is a natural red pigment derived primarily from secondary metabolites of microorganisms, especially Serratia marcescens. It can also be chemically synthesized. Prodigiosin has been proven to have antitumor, antibacterial, antimalaria, anti-insect, antialgae, and immunosuppressive activities, and is gaining increasing important in the global market because of its great potential application value in clinical medicine development, environmental treatment, preparation of food additives, and so on. Due to the low efficiency of prodigiosin chemical synthesis, high-level prodigiosin of production by microorganisms are necessary for prodigiosin applications. In this paper, the production of prodigiosin by microorganism in recent decades is reviewed. The methods and strategies for increasing the yield of prodigiosin are discussed from the aspects of medium composition, additives, factors affecting production conditions, strain modification, and fermentation methods.

Astaxanthin for the Food Industry

Xanthophyll astaxanthin, which is commonly used in aquaculture, is one of the most expensive and important industrial pigments. It is responsible for the pink and red color of salmonid meat and shrimp. Due to having the strongest anti-oxidative properties among carotenoids and other health benefits, natural astaxanthin is used in nutraceuticals and cosmetics, and in some countries, occasionally, to fortify foods and beverages. Its use in food technology is limited due to the unknown effects of long-term consumption of synthetic astaxanthin on human health as well as few sources and the high cost of natural astaxanthin. The article characterizes the structure, health-promoting properties, commercial sources and industrial use of astaxanthin. It presents the possibilities and limitations of the use of astaxanthin in food technology, considering its costs and food safety. It also presents the possibilities of stabilizing astaxanthin and improving its bioavailability by means of micro- and nanoencapsulation.

Integrated valorization system for simultaneous high strength organic wastewater treatment and astaxanthin production from Haematococcus pluvialis

High-strength organic wastewater, e.g., potato juice wastewater, exerts high stress on the environment. This study proposes an integrated system for simultaneous high-strength organic wastewater treatment and nutrients upcycling for astaxanthin production by the combination of anaerobic processes and microalgae (Haematococcus pluvialis) cultivation. The potato juice wastewater was pretreated by either acidification or methanation. The effluents of both pretreatments achieved higher biomass yields of H. pluvialis compared to cultivation in standard culture media (control). The high acetate and potassium concentrations of the acidification effluents resulted in significantly higher astaxanthin production (24.5-27.9 mg g^-1, 3 days) compared to the control (14.7 mg g^-1, 12 days) in a shorter period. The integrated system contributed to a final removal efficiency of 51.3-75.8%, 86.5-98.3%, and 69.4-83.4% for COD, phosphorus, and ammonia, respectively. This study presents a promising two-stage process for simultaneous efficient methane and astaxanthin production, as well as remediation of high-strength organic wastewater.

Synthesis of cembratriene-ol and cembratriene-diol in yeast via the MVA pathway

Background

Cembranoids are one kind of diterpenoids with multiple biological activities. The tobacco cembratriene-ol (CBT-ol) and cembratriene-diol (CBT-diol) have high anti-insect and anti-fungal activities, which is attracting great attentions for their potential usage in sustainable agriculture. Cembranoids were supposed to be formed through the 2-C-methyl-d-erythritol-4-phosphate (MEP) pathway, yet the involvement of mevalonate (MVA) pathway in their synthesis remains unclear. Exploring the roles of MVA pathway in cembranoid synthesis could contribute not only to the technical approach but also to the molecular mechanism for cembranoid biosynthesis.

Results

We constructed vectors to express cembratriene-ol synthase (CBTS1) and its fusion protein (AD-CBTS1) containing an N-terminal GAL4 AD domain as a translation leader in yeast. Eventually, the modified enzyme AD-CBTS1 was successfully expressed, which further resulted in the production of CBT-ol in the yeast strain BY-T20 with enhanced MVA pathway for geranylgeranyl diphosphate (GGPP) production but not in other yeast strains with low GGPP supply. Subsequently, CBT-diol was also synthesized by co-expression of the modified enzyme AD-CBTS1 and BD-CYP450 in the yeast strain BY-T20.

Conclusions

We demonstrated that yeast is insensitive to the tobacco anti-fungal compound CBT-ol or CBT-diol and could be applied to their biosynthesis. This study further established a feasibility for cembranoid production via the MVA pathway and provided an alternative bio-approach for cembranoid biosynthesis in microbes.

Importance of Downstream Processing of Natural Astaxanthin for Pharmaceutical Application

Astaxanthin (ASX) is a xanthophyll pigment considered as a nutraceutical with high antioxidant activity. Several clinical trials have shown the multiple health benefits of this molecule; therefore, it has various pharmaceutical industry applications. Commercial astaxanthin can be produced by chemical synthesis or through biosynthesis within different microorganisms. The molecule produced by the microorganisms is highly preferred due to its zero toxicity and superior therapeutic properties. However, the biotechnological production of the xanthophyll is not competitive against the chemical synthesis, since the downstream process may represent 70–80% of the process production cost. These operations denote then an opportunity to optimize the process and make this alternative more competitive. Since ASX is produced intracellularly by the microorganisms, high investment and high operational costs, like centrifugation and bead milling or high-pressure homogenization, are mainly used. In cell recovery, flocculation and flotation may represent low energy demanding techniques, whereas, after cell disruption, an efficient extraction technique is necessary to extract the highest percentage of ASX produced by the cell. Solvent extraction is the traditional method, but large-scale ASX production has adopted supercritical CO2 (SC-CO2), an efficient and environmentally friendly technology. On the other hand, assisted technologies are extensively reported since the cell disruption, and ASX extraction can be carried out in a single step. Because a high-purity product is required in pharmaceuticals and nutraceutical applications, the use of chromatography is necessary for the downstream process. Traditionally liquid-solid chromatography techniques are applied; however, the recent emergence of liquid-liquid chromatography like high-speed countercurrent chromatography (HSCCC) coupled with liquid-solid chromatography allows high productivity and purity up to 99% of ASX. Additionally, the use of SC-CO2, coupled with two-dimensional chromatography, is very promising. Finally, the purified ASX needs to be formulated to ensure its stability and bioavailability; thus, encapsulation is widely employed. In this review, we focus on the processes of cell recovery, cell disruption, drying, extraction, purification, and formulation of ASX mainly produced in Haematococcus pluvialis, Phaffia rhodozyma, and Paracoccus carotinifaciens. We discuss the current technologies that are being developed to make downstream operations more efficient and competitive in the biotechnological production process of this carotenoid.

Reprogramming microorganisms for the biosynthesis of astaxanthin via metabolic engineering

There is an increasing demand for astaxanthin in food, feed, cosmetics and pharmaceutical applications because of its superior anti-oxidative and coloring properties. However, naturally produced astaxanthin is expensive, mainly due to low productivity and limited sources. Reprogramming of microorganisms for astaxanthin production via metabolic engineering is a promising strategy. We primarily focus on the application of synthetic biology, enzyme engineering and metabolic engineering in enhancing the synthesis and accumulation of astaxanthin in microorganisms in this review. We also discuss the biosynthetic pathways of astaxanthin within natural producers, and summarize the achievements and challenges in reprogramming microorganisms for enhancing astaxanthin production. This review illuminates recent biotechnological advances in microbial production of astaxanthin. Future perspectives on utilization of new technologies for boosting microbial astaxanthin production are also discussed.

Dietary Supplementation of Astaxanthin Improved the Growth Performance, Antioxidant Ability and Immune Response of Juvenile Largemouth Bass (Micropterus salmoides) Fed High-Fat Diet

High-fat diet (HFD) usually induces oxidative stress and astaxanthin is regarded as an excellent anti-oxidant. An 8-week feeding trial was conducted to investigate the effects of dietary astaxanthin supplementation on growth performance, lipid metabolism, antioxidant ability, and immune response of juvenile largemouth bass (Micropterus salmoides) fed HFD. Four diets were formulated: the control diet (10.87% lipid, C), high-fat diet (18.08% lipid, HF), and HF diet supplemented with 75 and 150 mg kg^-1 astaxanthin (HFA1 and HFA2, respectively). Dietary supplementation of astaxanthin improved the growth of fish fed HFD, also decreased hepatosomatic index and intraperitoneal fat ratio of fish fed HFD, while having no effect on body fat. Malondialdehyde content and superoxide dismutase activity were increased in fish fed HFD, astaxanthin supplementation in HFD decreased the oxidative stress of fish. The supplementation of astaxanthin in HFD also reduced the mRNA levels of Caspase 3, Caspase 9, BAD, and IL15. These results suggested that dietary astaxanthin supplementation in HFD improved the growth performance, antioxidant ability and immune response of largemouth bass.