Recent advancements in astaxanthin production from microalgae: A review

Two years of outdoor cultivation in alternate climates produces little divergence in the productivity of Nannochloropsis

Local environmental conditions may act as driving forces of natural selection and lead to trait divergence through time in outdoor microalgae cultures. In addition, microalgae phenotypes expressed outdoors may be modulated by other organisms, including pests and associated microbial communities. The present work builds on the long-term cultivation of a Nanochloropsis strain, across four geographically distinct field sites. The strain showed enhanced productivity at a site in California and decreased productivity at a site in New Mexico. The goal of the present work was to determine if those trait differences, among others, were the result of natural selection and evolution, phenotypic plasticity, or changes due to the influence of local microbiomes. To accomplish this goal, we coupled an outdoor common garden experiment in which cultivars from all four sites were grown at a single site in New Mexico with analyses of the algal microbiome. Our work revealed no differences in biomass productivity or biomass composition across strains in a common garden, suggesting that the parent strain exhibits high phenotypic plasticity, allowing growth across a wide range of climatic conditions. With respect to the microbiome, community composition and richness differed across cultivation system scales, parent and replicate ponds, and with and without pest management - but not greatly within the common garden. Our findings suggest that Nannochloropsis plasticity was driving the variation in phenotypic productivity responses to site-specific conditions and disturbances. This study helps in understanding the phenotypic changes and microbial community dynamics over years of cultivation.

Astaxanthin biosynthesis for functional food development and space missions

Astaxanthin (AXT), a natural carotenoid, has strong antioxidant and anti-ageing effects and can reduce ultraviolet light-induced damage to cells and DNA, stimulate the immune system, and improve cardiovascular disease prognosis. Despite its wide applications in the: nutraceutical, cosmetic, aquaculture, and pharmaceutical industries, AXT industrial production and application are hindered by natural source scarcity, low production efficiency, and high requirements. This review compares the qualitative differences of AXT derived from different natural sources, evaluates the upstream procedures for AXT expression in different chassis organisms, and investigates synthetic biology- and cell factory-based strategies for the industrial production of natural AXT. Synthetic biology is a promising novel strategy for reprogramming plants or microorganisms to produce AXT. Additionally, genetic engineering using cell factories extends beyond terrestrial applications, as it may contribute to the long-term sustainability of human health during space exploration and migration endeavors. This review provides a theoretical basis for the efficient and accurate genetic engineering of AXT from the microalga Haematococcuspluvialis, providing a valuable reference for future research on the biomanufacturing of AXT and other biological metabolites.

Antihyperuricemia Bioactive Substances Derived from Marine Organisms

Hyperuricemia is a metabolic disorder attributed to dysregulated purine metabolism or insufficient uric acid excretion. With a high incidence rate and comorbidities burden, hyperuricemia brings enormous pressure to society and attracts much attention nowadays. Though several urate-lowering drugs (including xanthine oxidase inhibitors, uricosuric drugs, and recombinant uricase) are available in clinical practice, their use is often limited due to serious side effects or contraindications. The development of novel urate-lowering drugs and functional foods is in the spotlight. Regarded as an important source of bioactive substances, marine organisms, including seaweeds, animals, and microorganisms, have yielded a large number of bioactive substances with novel structures and unique pharmacological activities. Up to the present, numerous marine organisms-derived bioactive substances have shown potential in combating hyperuricemia. Thus, this review discusses the antihyperuricemia substances derived from marine organisms and summarizes their antihyperuricemia pharmacological properties, with the aim of providing new insights for the development of antihyperuricemia drugs or functional foods from marine organism resources.

Increasing the sustainability of photoautotrophic microalgae production by minimising freshwater requirements

There are now several companies that are producing microalgae such as Arthrospira platensis, Chlorella vulgaris, and Dunaliella salina, among others. They are cultivated mainly in large-scale raceway and tubular photobioreactors. Microalgae production represents a sustainable alternative to conventional biomass production. Microalgae can be used to manufacture agricultural products, animal feed, food and other commercial products. The water requirements for cultivating microalgae are significant, exceeding 1 m3·kg-1. This value varies depending on the production strategy. One of the main reasons for water loss is evaporation, which is influenced by the photobioreactor location, the season, and the operating conditions. Efforts are being made to reduce water requirements and make microalgae production economically viable and more environmentally friendly. Several strategies are being investigated for reducing freshwater use in microalgae cultivation; these include reusing the culture medium and producing microalgae using seawater or wastewater. Such strategies not only reduce water consumption, but also reduce nutrient consumption and costs while increasing sustainability.

Effective astaxanthin production from flocculated Haematococcus pluvialis via biofilm cultivation in a tri-layer tray bioreactor

Haematococcus pluvialis, renowned for its high astaxanthin content, is a prime candidate for commercial-scale production of natural astaxanthin. While biofilm cultivation shows potential for enhancing astaxanthin accumulation in H. pluvialis, it faces challenges in effectively harvesting green-vegetative H. pluvialis and mitigating the "dark zone" issue within the biofilm. Our study demonstrated that flocculation using a combination of chitosan and NaOH was an effective method for harvesting green-vegetative H. pluvialis, which surpasses centrifugation in both biomass and astaxanthin production. A tri-layer tray bioreactor was developed to enhance astaxanthin production via biofilm redistribution by using a rinsing method, and its effectiveness was further supported by a tray photobioreactor with an integrated automatic rinsing system. The biofilm method achieved an optimal specific light energy consumption for astaxanthin production of 9.42 kWh g-1 at the light intensity of 150 μmol m-2 s-1, presenting its potential for commercial-scale cultivation of H. pluvialis for astaxanthin production.

Pickering emulsion stabilized by salmon protein-fucoidan complex and its absorption promotion effect on astaxanthin

In this experiment, salmon protein-fucoidan complexes (SMP-FU) were used to stabilize Pickering emulsions encapsulating astaxanthin (AXT). The hydrophobic forces and hydrogen bonding between SMP and FU were revealed as the main interaction to form the SMP-FU complex. The addition of FU led to the increase of three-phase contact angle from 51.3° to 92.1°, and the best hydrophilic-hydrophobic balance was achieved with 2 % FU. The emulsions stabilized by SMP-FU became more homogeneous and denser with the increase of FU concentration, and the smallest droplet size was obtained in the emulsion stabilized by SMP-FU(2 %), which exhibited good rheological properties and acceptable stabilities under the heating, strong ionic strength and extreme acid-base conditions. AXT loaded Pickering emulsion (PEAs) stabilized by SMP-FU (SMP-FU-PEAs) provided better protection for AXT and improved the AXT retention rate under different storage condition, and displayed better gastric acid stability and higher AXT release rate (60.57 %) and bioaccessibility index (71.52 %) in than SMP-PEAs during in vitro digestion. The Caco-2 cell assay and in vivo experiments revealed a significant increase in the uptake rate of AXT embedded in SMP-FU-PEAs, which provided a feasible way to subsequently promote the uptake and utilization of the active substance.

Effect of Heterologous Expression of Key Enzymes Involved in Astaxanthin and Lipid Synthesis on Lipid and Carotenoid Production in Aurantiochytrium sp

Aurantiochytrium sp., a heterotrophic microorganism, has received increasing attention for its high production of polyunsaturated fatty acids and has been widely applied in various industries. This study intended to optimize the carotenoid synthesis pathway in Aurantiochytrium sp. by metabolic engineering to increase the carotenoid content. Multi-sourced key enzyme genes involved in lipid synthesis (LPAAT and DGAT) and astaxanthin synthesis (crtZ and crtW) were selected to construct single-gene expression vectors and transformed into Aurantiochytrium sp. The results showed that the overexpression of LPAAT of Phaeodactylum tricornutum in Aurantiochytrium sp. caused an increase of 39.3% in astaxanthin, 424.7% in β-carotene, 901.8% in canthaxanthin, and 575.9% in lutein, as well as a down-regulation of 15.3% in the fatty acid content. Transcriptomics analysis revealed enhanced expression of genes involved in purine and amino acid metabolism in the transformed strains, and the down-regulation of the citric acid cycle led to an increase in the source of acetyl coenzyme A for the production of fatty acids. This study provides strong experimental evidence to support the application of increasing carotenoid levels in Aurantiochytrium sp.

Advancements of astaxanthin production in Haematococcus pluvialis: Update insight and way forward

The global market demand for natural astaxanthin (AXT) is growing rapidly owing to its potential human health benefits and diverse industry applications, driven by its safety, unique structure, and special function. Currently, the alga Haematococcus pluvialis (alternative name H. lacustris) has been considered as one of the best large-scale producers of natural AXT. However, the industry's further development faces two main challenges: the limited cultivation areas due to light-dependent AXT accumulation and the low AXT yield coupled with high production costs resulting from complex, time-consuming upstream biomass culture and downstream AXT extraction processes. Therefore, it is urgently to develop novel strategies to improve the AXT production in H. pluvialis to meet industrial demands, which makes its commercialization cost-effective. Although several strategies related to screening excellent target strains, optimizing culture condition for high biomass yield, elucidating the AXT biosynthetic pathway, and exploiting effective inducers for high AXT content have been applied to enhance the AXT production in H. pluvialis, there are still some unsolved and easily ignored perspectives. In this review, firstly, we summarize the structure and function of natural AXT focus on those from the algal H. pluvialis. Secondly, the latest findings regarding the AXT biosynthetic pathway including spatiotemporal specificity, transport, esterification, and storage are updated. Thirdly, we systematically assess enhancement strategies on AXT yield. Fourthly, the regulation mechanisms of AXT accumulation under various stresses are discussed. Finally, the integrated and systematic solutions for improving AXT production are proposed. This review not only fills the existing gap about the AXT accumulation, but also points the way forward for AXT production in H. pluvialis.

Enhancing astaxanthin accumulation in immobilized Haematococcus pluvialis via alginate hydrogel membrane

Immobilized cultivation is anticipated to be effective for enhancing both biomass and astaxanthin accumulation in Haematococcus pluvialis (H. pluvialis). A novel fabrication method of alginate hydrogel membrane (AHM) was introduced for immobilized cultivation of H. pluvialis. This method incorporates cotton gauze into a hydrogel with a low sodium alginate (SA) concentration of 0.5 %, utilizing endogenous calcification. The optimized culture strategy achieved a peak astaxanthin productivity of 256.3 mg·m-2·d-1 with an inoculum of 16 g·m-2 under light irradiation of 300 μmol·m-2·s-1 on day 4, resulting in a 70.8 % increase in astaxanthin yield over the control group. Furthermore, a recovery method for H. pluvialis and SA from AHM was explored, using Na2CO3 to disintegrate AHM to recover all the microalgal cells and SA with a recovery rate of 88.7 %. Collectively, these findings suggest that immobilized cultivation using AHM is an effective strategy for boosting biomass and astaxanthin accumulation in H. pluvialis.

Microbial Astaxanthin Synthesis by Komagataella phaffii through Metabolic and Fermentation Engineering

Astaxanthin is a kind of carotenoid with a strong antioxidant ability, which has shown broad applications in the areas of healthcare, medicine, cosmetics, food additives, and aquaculture. With the increasing demand for natural products, the microbial production of astaxanthin has become a new hot spot. In this study, the astaxanthin synthesis pathway was first metabolically constructed in Komagataella phaffii (K. phaffii)(Pichia pastoris). By exploring the combination of different promoters, astaxanthin producers were obtained. Then, the key enzymes in the astaxanthin synthesis pathway were explored, and different enzyme assembly strategies and an increase in NADPH supply were used to improve the astaxanthin production. Furthermore, fermentation parameters including temperature, the concentration of the carbon source, nitrogen sources, metal ions, BHT (2,6-di-tert-butyl-4-methylphenol), and Tween-80 were comprehensively investigated for the microbial growth and astaxanthin synthesis. Finally, the astaxanthin production reached 716.13 mg/L by fed-batch fermentation in a 5 L bioreactor, which was the highest production of astaxanthin synthesized by K. phaffii.

Nano-enabled microalgae bioremediation: Advances in sustainable pollutant removal and value-addition

Microalgae-assisted bioremediation, enriched by nanomaterial integration, offers a sustainable approach to environmental pollution mitigation while harnessing microalgae's potential as a biocatalyst and biorefinery resource. This strategy explores the interaction between microalgae, nanomaterials, and bioremediation, advancing sustainability objectives. The potent combination of microalgae and nanomaterials highlights the biorefinery's promise in effective pollutant removal and valuable algal byproduct production. Various nanomaterials, including metallic nanoparticles and semiconductor quantum dots, are reviewed for their roles in inorganic and organic pollutant removal and enhancement of microalgae growth. Limited studies have been conducted to establish nanomaterial's (CeO2, ZnO, Fe3O4, Al2O3, etc.) role on microalgae in pollution remediation; most studies cover inorganic pollutants (heavy metals and nutrients) remediation, exhibited 50-300% bioremediation efficiency improvement; however, some studies cover antibiotics and toxic dyes removal efficiency with 19-95% improvement. These aspects unveil the complex mechanisms underlying nanomaterial-pollutant-microalgae interactions, focusing on adsorption, photocatalysis, and quantum dot properties. Strategies to enhance bioremediation efficiency are discussed, including pollutant uptake improvement, real-time control, tailored nanomaterial design, and nutrient recovery. The review assesses recent advancements, navigates challenges, and envisions a sustainable future for bioremediation, underlining the transformative capacity of nanomaterial-driven microalgae-assisted bioremediation. This work aligns with Sustainable Development Goals 6 (Clean Water and Sanitation) and 12 (Responsible Consumption and Production) by exploring nanomaterial-enhanced microalgae bioremediation for sustainable pollution management and resource utilization.

Marine vanadium pollution: Sources, ecological impacts and cutting-edge mitigation strategies

Vanadium (V) is a hazardous element with widespread environmental presence, particularly in marine environments, due to both natural and industrial sources. This review examines vanadium's impact on marine organisms, highlighting its disruption of metabolic processes in fish, microalgae, and crustaceans, leading to oxidative stress, impaired growth and reproduction. Vanadium accumulation in marine food chains poses risks to higher organisms, including humans. Conventional vanadium removal methods, e.g., filtering and reverse osmosis, are costly and energy-intensive. Alternatively, bioremediation offers a sustainable solution, particularly using microalgae and thraustochytrids. Microalgae can detoxify and immobilize vanadium through adsorption and biodegradation, contributing to carbon capture and producing value-added products. Advances in bioprocess engineering, including regulating key parameters such as temperature and pH during biomass harvesting and using chelating agents, have enhanced this bioremediation approach, making it a viable option for industrial-scale applications and aligning with Sustainable Development Goals by integrating environmental protection with renewable energy 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.

Effects of Culture Medium Enrichment with Zinc on Astaxanthin Accumulation in a New Strain of the Microalga Dysmorphococcus globosus

High Zn2+ concentrations in microalgal cells that produce astaxanthin as a feed additive can reduce the symptoms of malnutrition in aquatic animals. Therefore, in this study, we analysed the effect of Zn2+ in the culture medium on the growth of a newly isolated microalgal strain Dysmorphococcus globosus ZY24. Zn2+ and white light stress altered the pigment content in microalgal cells. In addition, high Zn2+ concentrations in the culture medium altered cell morphology and chlorophyll fluorescence and also increased intracellular Zn2+ accumulation. Further, an optimal Zn2+ concentration in the culture medium promoted the synthesis of astaxanthin and other pigments. When the concentration of Zn2+ was 45.5 mg L-1, Dysmorphococcus globosus ZY24 produced 0.31 mg g-1 astaxanthin, whereas the total zinc content of the microalgae was 4337 mg kg-1. This study confirmed that microalgae have a high capacity for Zn2+ enrichment, providing a theoretical basis for studying Zn2+ enrichment in microalgae. Furthermore, Zn2+ supplementation to stimulate astaxanthin production in microalgae is a practical method to enhance their nutritional value.

Regulation Mechanism of Gibberellic Acid-3 for Astaxanthin Biosynthesis in Heterotrophic Growing Chromochloris zofingiensis

Chromochloris zofingiensis has been proven as a potential resource for large-scale astaxanthin production, but little information on phytohormones for its growth and astaxanthin accumulation could be obtained. This study explored the impact of gibberellic acid-3 (GA3) on growth and astaxanthin biosynthesis in heterotrophic C. zofingiensis. After 6 days of cultivation with GA3, biomass and astaxanthin yields in 7.5 L fermenters reached 268.5 g·L-1 and 0.34 g·L-1, respectively, which were 6% and 89% higher than those in the control. GA3 changed transcription levels of genes linked to carbon metabolism, lipid metabolism, astaxanthin production, and ABC transporters. Genes related to astaxanthin biosynthesis, such as phytoene synthase (PSY), phytoene desaturase (PDS), beta-carotenoid hydroxylase (CHYb), and beta-carotenoid ketolase (BKT), were up-regulated under GA3 induction. The enhancement of carbon metabolism and lipid metabolism led to elevated consumption of substrates and generation of reducing power, thus facilitating astaxanthin biosynthesis. By using GA3 and arginine together, the astaxanthin yield increased to 0.39 g·L-1, which was 18% higher than that obtained under GA3 induction. It could be concluded that GA3 showed significant effects on astaxanthin biosynthesis. This research proposed novel feasible approaches to enhance astaxanthin production in heterotrophic C. zofingiensis.

Targeting Synovial Macrophages with Astaxanthin-Loaded Liposomes for Antioxidant Treatment of Osteoarthritis

Osteoarthritis (OA) is a chronic joint disease highly associated with an imbalance in the network of inflammatory factors and typically characterized by oxidative stress and cartilage damage. Moreover, the specificity of the joint structure makes it difficult for drugs to achieve good penetration and effective enrichment in the joint cavity. Therefore, therapeutic strategies that increase the specific targeting of drugs to inflammatory joint and incorporate antioxidative stress effects are important to improve the efficacy of OA. Here, we developed a folic acid-modified liposomal nanoparticle (AST@Lip-FA) loaded with the antioxidant astaxanthin (AST) to enhance the water solubility and stability of AST and to target the delivery of AST to the site of OA, leading to a significant improvement in therapeutic efficacy. In vitro experiments demonstrated that, due to the recognition by FA of the receptor folate receptor β on the surface of activated macrophages, the cellular uptake efficiency of AST@Lip-FA was increased. Meanwhile, intracellularly overexpressed inflammatory mediators such as reactive oxygen species and nitric oxide were efficiently removed by AST@Lip-FA. In addition, in the ACLT-induced OA mouse model, AST@Lip-FA was precisely enriched in the inflamed joints and achieved long-term retention, fully utilizing the anti-inflammatory, antioxidant, and cartilage-protecting effects of AST to effectively alleviate the progression of OA. In summary, AST@Lip-FA has an important prospect as a potential and effective therapeutic strategy for OA.

Metabolic engineering of Mucor circinelloides to improve astaxanthin production

Astaxanthin is a bioactive natural pigment with antioxidant properties. It has extensive applications within the industrial sector as well as in human and animal health. Mucor circinelloides is a zygomycete fungus that accumulates β-carotene as the main carotenoid compound. M. circinelloides is a well-known model organism among Mucorales for studying carotenogenesis in fungi, which makes it a promising candidate for the biotechnological production of carotenoids. In this study, β-carotene hydroxylase (crtR-B) and ketolase (bkt) genes (codon-optimized) were coexpressed from Haematococcus pluvialis in M. circinelloides using two potent promoters gpd1 and zrt1 respectively to generate an astaxanthin-producing biofactory. Following 72 h of cultivation, the recombinant M. circinelloides Mc-57 obtained in this study produced 135 ± 8 µg/g of astaxanthin. This is the highest reported amount in M. circinelloides to date. The mRNA levels of crtR-B and bkt in Mc-57 were assayed using RT-qPCR. These levels showed a 5.7-fold increase at 72 h and a 5.5-fold increase at 24 h, respectively, compared to the control strain. This demonstrated the successful overexpression of both genes, which correlated with the production of astaxanthin in the Mc-57. Moreover, the addition of glutamate (2 g/L) and mevalonate (15 mM) resulted in an increase in astaxanthin production in the recombinant strain. The results showed that the combined addition of these metabolic precursors resulted in 281 ± 20 µg/g of astaxanthin, which is 2.08-fold higher than the control medium (135 ± 8 µg/g). The addition of metabolic precursors also positively impacted the biomass growth of Mc-57, reaching 11.2 ± 0.57 g/L compared to 9.1 ± 0.23 g/L (control medium). The study successfully addressed the challenge of balancing the accumulation of astaxanthin with biomass growth, which has been regarded as common bottleneck in the metabolic engineering of microbial cells. The development of a recombinant fungal strain of M. circinelloides not only increased astaxanthin content. Additionally, it provided a foundation for further improvement of the biotechnological production of astaxanthin in M. circinelloides.

Natural-based solutions to mitigate dietary microplastics side effects in fish

Dietary microplastics (MPs) can be consumed by fish, crossing through the gastrointestinal tract. MPs smaller than 20 μm can easily translocate to other organs, such as liver, commonly triggering oxidative stress in fish. Given the current unlikelihood of their short-term elimination, strategies to mitigate MPs-related issues on fish are of considerable interest to the scientific community. In the present study, to reduce both the dietary MPs-induced oxidative stress and the accumulation of MPs, the effectiveness of microencapsulated astaxanthin (ASX) was evaluated in zebrafish (Danio rerio). Specifically, zebrafish were reared from larvae to adults (6 months) and fed diets containing MPs different in range-size (polymer A: 1-5 μm; polymer B: 40-47 μm) at different concentrations (50 or 500 mg/kg). After this period, fish from each experimental group were divided in two sub-groups that were fed, for an additional month, with the previous diets or with the same diets containing implemented with microencapsulated ASX (7 g/kg), respectively. Results showed that microencapsulated ASX was able to counteract the negative effects caused by MPs different in size. Particularly, in zebrafish fed diets containing polymer B microbeads, microencapsulated astaxanthin was able to restore the intestinal epithelium, affected by the abrasive role of MPs during gut transit. Differently, in zebrafish fed diets containing polymer A microbeads, absorbed at intestinal level and translocated mainly to the liver, the microencapsulated ASX decreased the oxidative stress response and reduced the MPs accumulation in target organs due to the antioxidant and the coagulant properties of the ASX and microcapsules wall, respectively. Taken together, the results highlighted that the aquafeeds' implementation with microencapsulated astaxanthin is a prospective tool to prevent MPs-related issues in fish.

A crosswalk on the genetic and conventional strategies for enhancing astaxanthin production in Haematococcus pluvialis

Astaxanthin is a naturally occurring xanthophyll with powerful: antioxidant, antitumor, and antibacterial properties that are widely employed in food, feed, medicinal and nutraceutical industries. Currently, chemical synthesis dominates the world's astaxanthin market, but the increasing demand for natural products is shifting the market for natural astaxanthin. Haematococcus pluvialis (H. pluvialis) is the factory source of natural astaxanthin when grown in optimal conditions. Currently, various strategies for the production of astaxanthin have been proposed or are being developed in order to meet its market demand. This up-to-date review scrutinized the current approaches or strategies that aim to increase astaxanthin yield from H. pluvialis. We have emphasized the genetic and environmental parameters that increase astaxanthin yield. We also looked at the transcriptomic dynamics caused by environmental factors (phytohormones induction, light, salt, temperature, and nutrient starvation) on astaxanthin synthesizing genes and other metabolic changes. Genetic engineering and culture optimization (environmental factors) are effective approaches to producing more astaxanthin for commercial purposes. Genetic engineering, in particular, is accurate, specific, potent, and safer than conventional random mutagenesis approaches. New technologies, such as CRISPR-Cas9 coupled with omics and emerging computational tools, may be the principal strategies in the future to attain strains that can produce more astaxanthin. This review provides accessible data on the strategies to increase astaxanthin accumulation natively. Also, this review can be a starting point for new scholars interested in H. pluvialis research.

Recent Advances in Astaxanthin as an Antioxidant in Food Applications

In recent years, astaxanthin as a natural substance has received widespread attention for its potential to replace traditional synthetic antioxidants and because its antioxidant activity exceeds that of similar substances. Based on this, this review introduces the specific forms of astaxanthin currently used as an antioxidant in foods, both in its naturally occurring forms and in artificially added forms involving technologies such as emulsion, microcapsule, film, nano liposome and nano particle, aiming to improve its stability, dispersion and bioavailability in complex food systems. In addition, research progress on the application of astaxanthin in various food products, such as whole grains, seafood and poultry products, is summarized. In view of the characteristics of astaxanthin, such as insolubility in water and sensitivity to light, heat, oxygen and humidity, the main research trends of astaxanthin-loaded systems with high encapsulation efficiency, good stability, good taste masking effect and cost-effectiveness are also pointed out. Finally, the possible sensory effects of adding astaxanthin to food aresummarized, providing theoretical support for the development of astaxanthin-related food.

Mitigating Dietary Microplastic Accumulation and Oxidative Stress Response in European Seabass (Dicentrarchus labrax) Juveniles Using a Natural Microencapsulated Antioxidant

Aquafeed's contamination by microplastics can pose a risk to fish health and quality since they can be absorbed by the gastrointestinal tract and translocate to different tissues. The liver acts as a retaining organ with the consequent triggering of oxidative stress response. The present study aimed to combine the use of natural astaxanthin with natural-based microcapsules to counteract these negative side effects. European seabass juveniles were fed diets containing commercially available fluorescent microplastic microbeads (1-5 μm; 50 mg/kg feed) alone or combined with microencapsulated astaxanthin (AX) (7 g/kg feed; tested for half or whole feeding trial-30 or 60 days, respectively). Fish from the different dietary treatments did not evidence variations in survival and growth performance and did not show pathological alterations at the intestinal level. However, the microplastics were absorbed at the intestinal level with a consequent translocation to the liver, leading, when provided solely, to sod1, sod2, and cat upregulation. Interestingly, the dietary implementation of microencapsulated AX led to a mitigation of oxidative stress. In addition, the microcapsules, due to their composition, promoted microplastic coagulation in the fish gut, limiting their absorption and accumulation in all the tissues analyzed. These results were supported by in vitro tests, which demonstrated that the microcapsules promoted microplastic coagula formation too large to be absorbed at the intestinal level and by the fact that the coagulated microplastics were released through the fish feces.

The Microalgae Chlamydomonas for Bioremediation and Bioproduct Production

The extensive metabolic diversity of microalgae, coupled with their rapid growth rates and cost-effective production, position these organisms as highly promising resources for a wide range of biotechnological applications. These characteristics allow microalgae to address crucial needs in the agricultural, medical, and industrial sectors. Microalgae are proving to be valuable in various fields, including the remediation of diverse wastewater types, the production of biofuels and biofertilizers, and the extraction of various products from their biomass. For decades, the microalga Chlamydomonas has been widely used as a fundamental research model organism in various areas such as photosynthesis, respiration, sulfur and phosphorus metabolism, nitrogen metabolism, and flagella synthesis, among others. However, in recent years, the potential of Chlamydomonas as a biotechnological tool for bioremediation, biofertilization, biomass, and bioproducts production has been increasingly recognized. Bioremediation of wastewater using Chlamydomonas presents significant potential for sustainable reduction in contaminants and facilitates resource recovery and valorization of microalgal biomass, offering important economic benefits. Chlamydomonas has also established itself as a platform for the production of a wide variety of biotechnologically interesting products, such as different types of biofuels, and high-value-added products. The aim of this review is to achieve a comprehensive understanding of the potential of Chlamydomonas in these aspects, and to explore their interrelationship, which would offer significant environmental and biotechnological advantages.

Advances in microbial astaxanthin production

This work explores astaxanthin (AXT), a valuable xanthophyll ketocarotenoid pigment with significant health benefits and diverse applications across various industries. It discusses the prevalence of synthetic AXT, and the development of natural-based alternatives derived from microorganisms such as microalgae, bacteria, and yeast. The chapter examines the potential of microbial AXT production, highlighting the advantages and challenges associated with natural AXT. Key microorganisms like Haematococcus pluvialis, Paracoccus carotinifaciens, and Phaffia rhodozyma are emphasized for their role in commercially producing this valuable ketocarotenoid. The narrative covers the complexities and opportunities in microbial AXT production, from cell structure implications to downstream processing strategies. Additionally, the chapter addresses current applications, commercialization trends, and market dynamics of natural microbial AXT, emphasizing the importance of cost-effective production, regulatory compliance, and technological advancements to reduce the market cost of the final product. As demand for natural microbial-based AXT rises, this chapter envisions a future where research, innovation, and collaboration drive sustainable and competitive microbial AXT production, fostering growth in this dynamic market.

Enhancing astaxanthin accumulation through the expression of the plant-derived astaxanthin biosynthetic pathway in Dunaliella salina

Dunaliella salina, a microalga that thrives under high-saline conditions, is notable for its high β-carotene content and the absence of a polysaccharide cell wall. These unique characteristics render it a prime candidate as a cellular platform for astaxanthin production. In this study, our initial tests in an E. coli revealed that β-ring-4-dehydrogenase (CBFD) and 4-hydroxy-β-ring-4-dehydrogenase (HBFD) genes from Adonis aestivalis outperformed β-carotene hydroxylase (BCH) and β-carotene ketolase (BKT) from Haematococcus pluvialis counterparts by two-fold in terms of astaxanthin biosynthesis efficiency. Subsequently, we utilized electroporation to integrate either the BKT gene or the CBFD and HBFD genes into the genome of D. salina. In comparison to wild-type D. salina, strains transformed with BKT or CBFD and HBFD exhibited inhibited growth, underwent color changes to shades of red and yellow, and saw a nearly 50% decline in cell density. HPLC analysis confirmed astaxanthin synthesis in engineered D. salina strains, with CBFD + HBFD-D. salina yielding 134.88 ± 9.12 μg/g of dry cell weight (DCW), significantly higher than BKT-D. salina (83.58 ± 2.40 μg/g). This represents the largest amount of astaxanthin extracted from transgenic D. salina, as reported to date. These findings have significant implications, opening up new avenues for the development of specialized D. salina-based microcell factories for efficient astaxanthin production.

Readily Available Oral Prebiotic Protein Reactive Oxygen Species Nanoscavengers for Synergistic Therapy of Inflammation and Fibrosis in Inflammatory Bowel Disease

A significant gap exists in the demand for safe and effective drugs for inflammatory bowel disease (IBD), and its associated intestinal fibrosis. As oxidative stress plays a central role in the pathogenesis of IBD, astaxanthin (AST), a good antioxidant with high safety, holds promise for treating IBD. However, the application of AST is restricted by its poor solubility and easy oxidation. Herein, different protein-based nanoparticles (NPs) are fabricated for AST loading to identify an oral nanovehicle with potential clinical applicability. Through systematic validation via molecular dynamics simulation and in vitro characterization of properties, whey protein isolate (WPI)-driven NPs using a simple preparation method without the need for cross-linking agents or emulsifiers were identified as the optimal carrier for oral AST delivery. Upon oral administration, the WPI-driven NPs, benefiting from the intrinsic pH sensitivity and mucoadhesive properties, effectively shielded AST from degradation by gastric juices and targeted release of AST at intestinal lesion sites. Additionally, the AST NPs displayed potent therapeutic efficacy in both dextran sulfate sodium (DSS)-induced acute colitis and chronic colitis-associated intestinal fibrosis by ameliorating inflammation, oxidative damage, and intestinal microecology. In conclusion, the AST WPI NPs hold a potential therapeutic value in treating inflammation and fibrosis in IBD.

Development in health-promoting essential polyunsaturated fatty acids production by microalgae: a review

Polyunsaturated fatty acids (PUFAs) found in microalgae, primarily omega-3 (ω-3) and omega-6 (ω-6) are essential nutrients with positive effects on diseases such as hyperlipidemia, atherosclerosis, and coronary risk. Researchers still seek improvement in PUFA yield at a large scale for better commercial prospects. This review summarizes advancements in microalgae PUFA research for their cost-effective production and potential applications. Moreover, it discusses the most promising cultivation modes using organic and inorganic sources. It also discusses biomass hydrolysates to increase PUFA production as an alternative and sustainable organic source. For cost-effective PUFA production, heterotrophic, mixotrophic, and photoheterotrophic cultivation modes are assessed with traditional photoautotrophic production modes. Also, mixotrophic cultivation has fascinating sustainable attributes over other trophic modes. Furthermore, it provides insight into growth phase (stage I) improvement strategies to accumulate biomass and the complementing effects of other stress-inducing strategies during the production phase (stage II) on PUFA enhancement under these cultivation modes. The role of an excessive or limiting range of salinity, nutrients, carbon source, and light intensity were the most effective parameter in stage II for accumulating higher PUFAs such as ω-3 and ω-6. This article outlines the commercial potential of microalgae for omega PUFA production. They reduce the risk of diabetes, cardiovascular diseases (CVDs), cancer, and hypertension and play an important role in their emerging role in healthy lifestyle management.

Advancement of Carotenogenesis of Astaxanthin from Haematococcus pluvialis: Recent Insight and Way Forward

The demand for astaxanthin has been increasing for many health applications ranging from pharmaceuticals, food, cosmetics, and aquaculture due to its bioactive properties. Haematococcus pluvialis is widely recognized as the microalgae species with the highest natural accumulation of astaxanthin, which has made it a valuable source for industrial production. Astaxanthin produced by other sources such as chemical synthesis or fermentation are often produced in the cis configuration, which has been shown to have lower bioactivity. Additionally, some sources of astaxanthin, such as shrimp, may denature or degrade when exposed to high temperatures, which can result in a loss of bioactivity. Producing natural astaxanthin through the cultivation of H. pluvialis is presently a demanding and time-consuming task, which incurs high expenses and restricts the cost-effective industrial production of this valuable substance. The production of astaxanthin occurs through two distinct pathways, namely the cytosolic mevalonate pathway and the chloroplast methylerythritol phosphate (MEP) pathway. The latest advancements in enhancing product quality and extracting techniques at a reasonable cost are emphasized in this review. The comparative of specific extraction processes of H. pluvialis biological astaxanthin production that may be applied to large-scale industries were assessed. The article covers a contemporary approach to optimizing microalgae culture for increased astaxanthin content, as well as obtaining preliminary data on the sustainability of astaxanthin production and astaxanthin marketing information.

The combination of uridine and nitrogen-deprivation promotes the efficient formation of astaxanthin-rich motile cells in Haematococcus pluvialis

Astaxanthin accumulation in Haematococcus pluvialis typically occurs alongside the formation of secondary cell wall (SCW), hindering astaxanthin extraction and bio-accessibility. A potential solution lies in cultivating astaxanthin-rich motile cells lacking SCW. This study explored the influence and underlying mechanism of nitrogen-deprivation (ND) on SCW formation and established a connection between pyrimidine metabolism and SCW development. Then, various pyrimidine and ND combinations were examined to cultivate astaxanthin-rich motile cells. The results indicated that, compared to the nitrogen-replete group, the combination of uridine and ND increased the proportion of motile cells by 25-33 times, achieving 95 %, and enhanced astaxanthin yield by 26.52 %. Moreover, the efficiency of astaxanthin extraction from intact, wet motile cells was 91 % - 95 %, which was 5.6-9.0 times that from non-motile cells. This study not only presents a promising method for producing astaxanthin-rich motile cells in H. pluvialis but also provides insights into the relationship between pyrimidine metabolism and SCW development.

Fine-tuning of key parameters to enhance biomass and nutritional polyunsaturated fatty acids production from Thraustochytrium sp

The escalating demand for long-chain polyunsaturated fatty acids (PUFAs) due to their vital health effects has deepened the exploration of sustainable sources. Thraustochytrium sp. stands out as a promising platform for omega-3 and 6 PUFA production. This research strategically optimizes key parameters: temperature, salinity, pH, and G:Y:P ratio and the optimized conditions for maximum biomass, total lipid, and DHA enhancement were 28 °C, 50 %, 6, and 10:1:2 respectively. Process optimization enhanced 32.30 and 31.92 % biomass (9.88 g/L) and lipid (6.57 g/L) yield. Notably, DHA concentration experienced a substantial rise of 69.91 % (1.63 g/L), accompanied by notable increases in EPA and DPA by 82.69 % and 31.47 %, respectively. MANOVA analysis underscored the statistical significance of the optimization process (p < 0.01), with all environmental factors significantly influencing biomass and lipid data (p < 0.05), particularly impacting DHA production. Thraustochytrium sp. can be a potential source of commercial DHA production with the fine-tuning of these key process parameters.

Melatonin, a phytohormone for enhancing the accumulation of high-value metabolites and stress tolerance in microalgae: Applications, mechanisms, and challenges

High-value metabolites, such as carotenoids, lipids, and proteins, are synthesized by microalgae and find applications in various fields, including food, health supplements, and cosmetics. However, the potential of the microalgal industry to serve these sectors is constrained by low productivity and high energy consumption. Environmental stressors can not only stimulate the accumulation of secondary metabolites in microalgae but also induce oxidative stress, suppressing cell growth and activity, thereby resulting in a decrease in overall productivity. Using melatonin (MT) under stressful conditions is an effective approach to enhance the productivity of microalgal metabolites. This review underscores the role of MT in promoting the accumulation of high-value metabolites and enhancing stress resistance in microalgae under stressful and wastewater conditions. It discusses the underlying mechanisms whereby MT enhances metabolite synthesis and improves stress resistance. The review also offers new perspectives on utilizing MT to improve microalgal productivity and stress resistance in challenging environments.

Advances in oligosaccharides production from brown seaweeds: extraction, characterization, antimetabolic syndrome, and other potential applications

Brown seaweeds are a promising source of bioactive substances, particularly oligosaccharides. This group has recently gained considerable attention due to its diverse cell wall composition, structure, and wide-spectrum bioactivities. This review article provides a comprehensive update on advances in oligosaccharides (OSs) production from brown seaweeds and their potential health applications. It focuses on advances in feedstock pretreatment, extraction, characterization, and purification prior to OS use for potential health applications. Brown seaweed oligosaccharides (BSOSs) are extracted using various methods. Among these, enzymatic hydrolysis is the most preferred, with high specificity, mild reaction conditions, and low energy consumption. However, the enzyme selection and hydrolysis conditions need to be optimized for desirable yield and oligosaccharides composition. Characterization of oligosaccharides is essential to determine their structure and properties related to bioactivities and to predict their most suitable application. This is well covered in this review. Analytical techniques such as high-performance liquid chromatography (HPLC), gas chromatography (GC), and nuclear magnetic resonance (NMR) spectroscopy are commonly applied to analyze oligosaccharides. BSOSs exhibit a range of biological properties, mainly antimicrobial, anti-inflammatory, and prebiotic properties among others. Importantly, BSOSs have been linked to possible health advantages, including metabolic syndrome management. Metabolic syndrome is a cluster of conditions, such as obesity, hypertension, and dyslipidemia, which increase the risk of cardiovascular disease and type 2 diabetes. Furthermore, oligosaccharides have potential applications in the food and pharmaceutical industries. Future research should focus on improving industrial-scale oligosaccharide extraction and purification, as well as researching their potential utility in the treatment of various health disorders.[Figure: see text].

Microalgal lutein: Advancements in production, extraction, market potential, and applications

Lutein, a bioactive xanthophyll, has recently attracted significant attention for numerous health benefits, e.g., protection of eye health, macular degeneration, and acute and chronic syndromes etc. Microalgae have emerged as the best platform for high-value lutein production with high productivity, lutein content, and scale-up potential. Algal lutein possesses numerous bioactivities, hence widely used in pharmaceuticals, nutraceuticals, aquaculture, cosmetics, etc. This review highlights advances in upstream lutein production enhancement and feasible downstream extraction and cell disruption techniques for a large-scale lutein biorefinery. Besides bioprocess-related advances, possible solutions for existing production challenges in microalgae-based lutein biorefinery, market potential, and emerging commercial scopes of lutein and its potential health applications are also discussed. The key enzymes involved in the lutein biosynthesizing Methyl-Erythritol-phosphate (MEP) pathway have been briefly described. This review provides a comprehensive updates on lutein research advancements covering scalable upstream and downstream production strategies and potential applications for researchers and industrialists.

Enhancement of astaxanthin production, recovery, and bio-accessibility in Haematococcus pluvialis through taurine-mediated inhibition of secondary cell wall formation under high light conditions

This study explored the use of taurine in enhancing the production and bio-accessibility of astaxanthin in Haematococcus pluvialis, which typically forms a secondary cell wall hindering astaxanthin extraction. The biomass of taurine-treated group significantly increased by 18%, and astaxanthin yield surged by 34% in comparison to the control group. Without cell disruption, astaxanthin recovery from thin-walled cells in the taurine-treated group, using dimethyl sulfoxide and ethanol as extraction reagents, was 97% and 75%, respectively, which were 30-fold higher than those of thick-walled cells in the control group. Additionally, the cell fragmentation rate increased by 86% in taurine-treated group relative to the control group. Comparative transcriptome analysis identified taurine-induced upregulation of genes involved in the astaxanthin biosynthesis pathway and downregulation of those associated with secondary cell wall synthesis. This study thus offers an innovative taurine-based strategy to enhance astaxanthin production and bio-accessibility while shedding light on the mechanisms driving this process.

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.

Application of Nanomaterials in the Production of Biomolecules in Microalgae: A Review

Nanomaterials (NMs) are becoming more commonly used in microalgal biotechnology to empower the production of algal biomass and valuable metabolites, such as lipids, proteins, and exopolysaccharides. It provides an effective and promising supplement to the existing algal biotechnology. In this review, the potential for NMs to enhance microalgal growth by improving photosynthetic utilization efficiency and removing reactive oxygen species is first summarized. Then, their positive roles in accumulation, bioactivity modification, and extraction of valuable microalgal metabolites are presented. After the application of NMs in microalgae cultivation, the extracted metabolites, particularly exopolysaccharides, contain trace amounts of NM residues, and thus, the impact of these residues on the functional properties of the metabolites is also evaluated. Finally, the methods for removing NM residues from the extracted metabolites are summarized. This review provides insights into the application of nanotechnology for sustainable production of valuable metabolites in microalgae and will contribute useful information for ongoing and future practice.

Astaxanthin attenuated cigarette smoke extract-induced apoptosis via decreasing oxidative DNA damage in airway epithelium

Chronic obstructive pulmonary disease (COPD) is a lung inflammatory disease that is associated with environmental allergic component exposure. Cigarette smoke is an environmental toxicant that induces lung malfunction leading to various pulmonary diseases. Astaxanthin (AST) is a carotenoid that shows antioxidant and anti-inflammatory activities which might be a promising candidate for COPD therapy. In this study, we released that AST could attenuate cigarette smoke-induced DNA damage and apoptosis in vivo and in vitro. AST administration ameliorated cigarette smoke extract (CSE)-induced activation of Caspase-3 and apoptosis. Pretreated mice with AST significantly decrease CSE-induced DNA damage which shows lower nuclear γ-H2AX level. AST treatment also dramatically reduces the production of intracellular reactive oxygen species (ROS) by suppressing the expression of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase enzyme 4 (NOX4) and dual oxidase 1 (DUOX1). Taken together, this study suggested that AST can decrease CSE-induced DNA damage and apoptosis by inhibiting NOX4/DUOX1 expression that promotes ROS generation. AST may be a potential protective agent against CSE-associated lung disease that is worth in-depth investigation.

Sustainable mixotrophic microalgae refinery of astaxanthin and lipid from Chlorella zofingiensis

Microalgal astaxanthin possesses numerous bioactivities and has several health applications. The current research focuses on designing and optimizing the two-stage mixotrophic bioprocess by Chlorella zofingiensis for astaxanthin production. Gradual increase in light intensity (4-8k-lux) and 3x micronutrient concentration were the key parameters for maximizing biomass yield of 2.5 g/L during 15 days of stage I. Furthermore, stress conditions (excessive CO2, light, salinity, etc.) enhanced astaxanthin yield at stage II. 20k lux light, 3x nutrients, and 5% CO2 were the best ranges for maximum astaxanthin production. Maximum biomass yield and astaxanthin content were 3.3 g/L and 16.7 mg/g, respectively, after 29 days of bioprocess. Astaxanthin biosynthesis was also affected by salinity, but less than other parameters. Astaxanthin bioprocess resulted in enhanced lipid yields of 35-37%, which could be used for biodiesel. This study shows promising scale-up potential with attractive sustainability features of Chlorella zofingiensis model for commercial astaxanthin-lipid biorefinery.

Enhanced mixotrophic production of lutein and lipid from potential microalgae isolate Chlorella sorokiniana C16

The current work aims to isolate high lutein-producing microalgae and maximize lutein production under a sustainable lutein-lipid biorefinery scheme. Lutein reduces retinitis, macular degeneration risk and improves eye health. An effective bioprocess design optimized nutrients, temperature, light, and salinity for biomass and lutein yield enhancement. 3X macro/micronutrients maximally enhanced biomass and lutein yields, 5.2 g/Land 71.13 mg/L. Temperature 32 °C exhibited maximum 17.4 mg/g lutein content and 10 k lux was most favorable for growth and lutein yield (15.47 mg/g). A 25% seawater addition led maximum of 21-27% lipid that could be used for biodiesel. Isolate was identified as Chlorella sorokiniana C16, which exhibited one of the highest lutein yields reported among recent studies, positioning it as a promising candidate for commercial lutein production. This study provides valuable insights into an effective bioprocess design and highlights the C16 strain potential as a sustainable platform for high-value lutein production under a biorefinery scheme.

Advances in oligosaccharides production from algal sources and potential applications

In recent years, algal-derived glycans and oligosaccharides have become increasingly important in health applications due to higher bioactivities than plant-derived oligosaccharides. The marine organisms have complex, and highly branched glycans and more reactive groups to elicit greater bioactivities. However, complex and large molecules have limited use in broad commercial applications due to dissolution limitations. In comparison to these, oligosaccharides show better solubility and retain their bioactivities, hence, offering better applications opportunity. Accordingly, efforts are being made to develop a cost-effective method for enzymatic extraction of oligosaccharides from algal polysaccharides and algal biomass. Yet detailed structural characterization of algal-derived glycans is required to produce and characterize the potential biomolecules for improved bioactivity and commercial applications. Some macroalgae and microalgae are being evaluated as in vivo biofactories for efficient clinical trials, which could be very helpful in understanding the therapeutic responses. This review discusses the recent advancements in the production of oligosaccharides from microalgae. It also discusses the bottlenecks of the oligosaccharides research, technological limitations, and probable solutions to these problems. Furthermore, it presents the emerging bioactivities of algal oligosaccharides and their promising potential for possible biotherapeutic application.

Therapeutic Potentials of Microalgae and Their Bioactive Compounds on Diabetes Mellitus

Diabetes mellitus is a metabolic disorder characterized by hyperglycemia due to impaired insulin secretion, insulin resistance, or both. Oxidative stress and chronic low-grade inflammation play crucial roles in the pathophysiology of diabetes mellitus. There has been a growing interest in applying natural products to improve metabolic derangements without the side effects of anti-diabetic drugs. Microalgae biomass or extract and their bioactive compounds have been applied as nutraceuticals or additives in food products and health supplements. Several studies have demonstrated the therapeutic effects of microalgae and their bioactive compounds in improving insulin sensitivity attributed to their antioxidant, anti-inflammatory, and pancreatic β-cell protective properties. However, a review summarizing the progression in this topic is lacking despite the increasing number of studies reporting their anti-diabetic potential. In this review, we gathered the findings from in vitro, in vivo, and human studies to discuss the effects of microalgae and their bioactive compounds on diabetes mellitus and the mechanisms involved. Additionally, we discuss the limitations and future perspectives of developing microalgae-based compounds as a health supplement for diabetes mellitus. In conclusion, microalgae-based supplementation has the potential to improve diabetes mellitus and be applied in more clinical studies in the future.

Microalgae, Seaweeds and Aquatic Bacteria, Archaea, and Yeasts: Sources of Carotenoids with Potential Antioxidant and Anti-Inflammatory Health-Promoting Actions in the Sustainability Era

Carotenoids are a large group of health-promoting compounds used in many industrial sectors, such as foods, feeds, pharmaceuticals, cosmetics, nutraceuticals, and colorants. Considering the global population growth and environmental challenges, it is essential to find new sustainable sources of carotenoids beyond those obtained from agriculture. This review focuses on the potential use of marine archaea, bacteria, algae, and yeast as biological factories of carotenoids. A wide variety of carotenoids, including novel ones, were identified in these organisms. The role of carotenoids in marine organisms and their potential health-promoting actions have also been discussed. Marine organisms have a great capacity to synthesize a wide variety of carotenoids, which can be obtained in a renewable manner without depleting natural resources. Thus, it is concluded that they represent a key sustainable source of carotenoids that could help Europe achieve its Green Deal and Recovery Plan. Additionally, the lack of standards, clinical studies, and toxicity analysis reduces the use of marine organisms as sources of traditional and novel carotenoids. Therefore, further research on the processing of marine organisms, the biosynthetic pathways, extraction procedures, and examination of their content is needed to increase carotenoid productivity, document their safety, and decrease costs for their industrial implementation.

Metabolic Engineering of Model Microorganisms for the Production of Xanthophyll

Xanthophyll is an oxidated version of carotenoid. It presents significant value to the pharmaceutical, food, and cosmetic industries due to its specific antioxidant activity and variety of colors. Chemical processing and conventional extraction from natural organisms are still the main sources of xanthophyll. However, the current industrial production model can no longer meet the demand for human health care, reducing petrochemical energy consumption and green sustainable development. With the swift development of genetic metabolic engineering, xanthophyll synthesis by the metabolic engineering of model microorganisms shows great application potential. At present, compared to carotenes such as lycopene and β-carotene, xanthophyll has a relatively low production in engineering microorganisms due to its stronger inherent antioxidation, relatively high polarity, and longer metabolic pathway. This review comprehensively summarized the progress in xanthophyll synthesis by the metabolic engineering of model microorganisms, described strategies to improve xanthophyll production in detail, and proposed the current challenges and future efforts needed to build commercialized xanthophyll-producing microorganisms.

Fermentative production of astaxanthin from sorghum distillery residue by an indigenous Aurantiochytrium sp. CJ6 strain using a continuous-feeding fed-batch process

In this study, Aurantiochytrium sp. CJ6 was cultivated heterotrophically on a waste resource, sorghum distillery residue (SDR) hydrolysate without adding any nitrogen sources. Mild sulfuric acid treatment released sugars that supported the growth of CJ6. Optimal operating parameters (salinity, 2.5%; pH, 7.5; with light exposure) determined using batch cultivation attained biomass concentration and astaxanthin content of 3.72 g/L and 69.32 µg/g dry cell weight (DCW), respectively. Using continuous-feeding fed-batch (CF-FB) fermentation, the biomass concentration of CJ6 increased to 6.3 g/L with biomass productivity and sugar utilization rate of 0.286 mg/L/d and 1.26 g/L/d, respectively. Meanwhile, CJ6 obtained maximum astaxanthin content (93.9 µg/g DCW) and astaxanthin concentration (0.565 mg/L) after 20-day cultivation. Thus, the CF-FB fermentation strategy seems to have a high potential for the cultivation of thraustochytrids to produce the high-value product (astaxanthin) using SDR as the feedstock to achieve circular economy.

A sustainable vanadium bioremediation strategy from aqueous media by two potential green microalgae

Globally, environmental concerns are rapidly growing due to increasing pollution levels. Vanadium is a hazardous heavy metal that poses health issues with an exposure concentration of about 2 ppm. It is regularly discharged by some industries and poses an environmental challenge. There are no sustainable green treatment methods for discharged effluents to mitigate vanadium threats to humans and the environment. In this study, the goal was to develop a green, sustainable method for removing vanadium and to utilize the produced biomass for biofuels, thus offsetting the treatment cost. Microalgae Chlorella sorokiniana SU1 and Picochlorum oklahomensis were employed for vanadium (III) treatment. The maximum removal was 25.5 mg L^-1 with biomass and lipid yields of 3.0 g L^-1 and 884.4 mg L^-1 respectively after 14 days of treatment. The vanadium removal capacity by microalgae was further enhanced up to 2-2.7 folds while optimizing the key parameters, pH, and temperature before removing biomass from the liquid phase. FTIR is used to analyse the reactive groups in algal cell walls to confirm vanadium adsorption and to understand the dominant and quantitative interactions. Zeta potential analysis helps to find out the most suitable pH range to facilitate the ionic bonding of biomass and thus maximum vanadium adsorption. This study addresses regulating external factors for enhancing the removal performance during microalgal biomass harvesting, which significantly enhances the removal of vanadium (III) from the aqueous phase. This strategy aims to improve the removal efficiency of microalgal treatment at an industrial scale for the bioremediation of vanadium and other inorganic pollutants.

Genome engineering via gene editing technologies in microalgae

CRISPR-Cas has revolutionized genetic modification with its comparative simplicity and accuracy, and it can be used even at the genomic level. Microalgae are excellent feedstocks for biofuels and nutraceuticals because they contain high levels of fatty acids, carotenoids, and other metabolites; however, genome engineering for microalgae is not yet as developed as for other model organisms. Microalgal engineering at the genetic and metabolic levels is relatively well established, and a few genomic resources are available. Their genomic information was used for a "safe harbor" site for stable transgene expression in microalgae. This review proposes further genome engineering schemes including the construction of sgRNA libraries, pan-genomic and epigenomic resources, and mini-genomes, which can together be developed into synthetic biology for carbon-based engineering in microalgae. Acetyl-CoA is at the center of carbon metabolic pathways and is further reviewed for the production of molecules including terpenoids in microalgae.

Extraction of Valuable Biomolecules from the Microalga Haematococcus pluvialis Assisted by Electrotechnologies

The freshwater microalga Haematococcus pluvialis is well known as the cell factory for natural astaxanthin, which composes up to 4-7% of its total dry weight. The bioaccumulation of astaxanthin in H. pluvialis cysts seems to be a very complex process that depends on different stress conditions during its cultivation. The red cysts of H. pluvialis develop thick and rigid cell walls under stress growing conditions. Thus, the biomolecule extraction requires general cell disruption technologies to reach a high recovery rate. This short review provides an analysis of the different steps in H. pluvialis's up and downstream processing including cultivation and harvesting of biomass, cell disruption, extraction and purification techniques. Useful information on the structure of H. pluvialis's cells, biomolecular composition and properties and the bioactivity of astaxanthin is collected. Special emphasis is given to the recent progress in application of different electrotechnologies during the growth stages and for assistance of the recovery of different biomolecules from H. pluvialis.

Bioprocess development to enhance biomass and lutein production from Chlorella sorokiniana Kh12

Present study focused on optimizing bioprocess condition for microalgal lutein production. From previous baseline yields of biomass (3.46 g/L) and lutein (13.7 mg/g), this study examined few key parameters. The 3X:3X ratio macro- and micronutrients was the most affecting parameter with highest biomass and lutein yields of 4.61 g/L and 14.3 mg/g. Temperature 30 °C enhanced the lutein up to 17.3 mg/g but reduced the biomass to 3 g/L. The light effects study showed 10 k lux was most effective for lutein up to 14 mg/g, and effect of increasing salinity (25-75 %) was detrimental. All the above parameters' optimization resulted in a lipid content of 22.5-26.5 %. A maximum lutein productivity and yield of 0.451 mg/L/d and 65.74 mg/L with a 3X:3X macro- and micronutrient ratio was achieved. The Chlorella sorokiniana Kh12 strain exhibited one of the highest yields among recent reports; hence it could be a source for commercial lutein production.

A review of natural astaxanthin production in a circular bioeconomy context using Paracoccus carotinifaciens

Astaxanthin (AXT) is a ketocarotenoid with several properties, including antioxidant, antidiabetic and anticancer with a wide range of applications in cosmeceutical, feed, food and pharmaceuticals sectors. The large fraction of AXT available in the market is obtained by chemical route, but the consumers preference for natural products are changing the global market of AXT, and due to that several companies are looking for potential alternative sources such as Gram-negative bacteria Paracoccus carotinifaciens (P. carotinifaciens) to obtain natural AXT. The aim of this critical review is to provide a comprehensive overview of the latest AXT research findings and characteristics of the hyperproducer-AXT P. carotinifaciens. Moreover, a brief description of the potential application of P. carotinifaciens for the production of natural AXT at industrial scale for commercial purposes and the latest advancements in the upstream and downstream procedures following the biorefinery and circular economy percepts are considered.

Pigments of aminophenoxazinones and viridomycins produced by termite-associated Streptomyces tanashiensis BYF-112

Termite-associated Streptomyces tanashiensis BYF-112 was found as a potential source for yellow and green pigments, which were stable under the tested temperature, light and metal ions. Eight metabolites (1-8), including four new natural yellow pigments aminophenoxazinones (1-4), and two rarely iron dependent green pigments viridomycin A and F (9-10) were isolated from BYF-112 cultured in YMS and YMS treated with FeSO₄, respectively. The metabolites 2-4 displayed a significant safety performance on the normal liver cell line L-02, while the metabolite 1 showed weak cytotoxicity against the L-02 and several cancer cells. Especially, in the filter paper disc tests, the compound 1 possessed strong antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA) with the zone of inhibition (ZOI) of 15.3 mm, which was equal to that of referenced levofloxacin (ZOI = 15.2 mm). And the metabolite 1 also showed moderate antibacterial activities against Micrococcus teragenus and S. aureus, with the ZOI values of 15.3 and 17.2 mm. In addition, by the minimum inhibitory concentration (MIC) assay, the compound 1 displayed potential antibacterial activities against M. teragenus, S. aureus and MRSA, with the MIC values of 12.5, 12.5, and 25.0 μg/ml, respectively. The present results indicate that BYF-112 may be a promising source for safe and bioactive pigments, which can be used for further development and industrial applications.