Carotenoids in algae: distributions, biosyntheses and functions

Multifaceted Applications of Microbial Pigments: Current Knowledge, Challenges and Future Directions for Public Health Implications

Microbial oddities such as versatile pigments are gaining more attention in current research due to their widely perceived applications as natural food colorants, textiles, antimicrobial activities, and cytotoxic activities. This indicates that the future generation will depend on microbial pigments over synthetic colorants for sustainable livelihood. Although several reviews have detailed the comprehensive applications of microbial pigments extensively, knowledge on several aspects of pigmented microbes is apparently missing and not properly reviewed anywhere. Thus, this review has been made to provide overall knowledge on biodiversity, distribution, pathogenicity, and ecological and industrial applications of microbial pigments as well as their challenges and future directions for food, industrial, and biomedical applications. Meticulously, this compendious review treatise on the pigments from bacteria, fungi, yeasts, and microalgae includes reports from the 1970s to 2018. A total of 261 pigment compounds produced by about 500 different microbial species are included, and their bioactive nature is described.

Promises and Challenges of Microalgal Antioxidant Production

The exploration of natural antioxidants for nutraceuticals and pharmaceuticals industries has recently increased. This communication aims to grasp the relevance of microalgae in the panorama of natural antioxidant molecules supply to industrial applications as alternatives and/or complements to those typically used from higher plants. Microalgal richness in antioxidant compounds and scavenging ability compared to higher plants is discussed in the context of microalgal biodiversity. We mainly focus on families of powerful antioxidant compounds that have been scarcely investigated in microalgae, such as phenolic compounds, sterols, or vitamins, discussing the promise and challenges of microalgae as providers of health benefits, for instance, through their use as functional food ingredients.

Raman Sensing and Its Multimodal Combination with Optoacoustics and OCT for Applications in the Life Sciences

Currently, many optical modalities are being investigated, applied, and further developed for non-invasive analysis and sensing in the life sciences. To befit the complexity of the study objects and questions in this field, the combination of two or more modalities is attempted. We review our work on multimodal sensing concepts for applications ranging from non-invasive quantification of biomolecules in the living organism to supporting medical diagnosis showing the combined capabilities of Raman spectroscopy, optical coherence tomography, and optoacoustics.

Construction of a pathway to C50-ε-carotene

Substrate tolerance of bacterial cyclases has been demonstrated in various contexts, but little is known about that of plant cyclases. Here, we tested two plant ε-cyclases to convert C₅₀-lycopene, which we previously established by rounds of directed evolution. Unlike bacterial β-cyclases, two-end cyclase from lettuce exhibited complete specificity against this molecule, indicating that this enzyme has some mechanism that exerts size-specificity. Arabidopsis one-end cyclase At-y2 showed detectable activity to C₅₀-lycopene. Interestingly, we found that it functions as a two-end cyclase in a C₅₀ context. Based on this observation, a possible model for substrate discrimination of this enzyme is proposed.

Effect of glyphosate on the growth, morphology, ultrastructure and metabolism of Scenedesmus vacuolatus

The effects of a commercial glyphosate formulation on the oxidative stress parameters and morphology (including the ultrastructure) of the phytoplanktonic green microalga Scenedesmus vacuolatus were evaluated. After 96 h of exposure to increasing herbicide concentrations (0, 4, 6, 8 mg L-1 active ingredient) with the addition of alkyl aryl polyglycol ether surfactant, the growth of the cultures decreased (96 h-IC50- 4.90 mg L-1) and metabolic and morphology alterations were observed. Significant increases in cellular volume (103-353%) and dry weight (105%) and a significant decrease in pigment content (41-48%) were detected. Oxidative stress parameters were significantly affected, showing an increase in the reactive oxygen species (ROS) and reduced glutathione (GSH) contents, oxidative damage to lipids and proteins and a decrease in the activities of the antioxidant enzymes superoxide dismutase (SOD) and catalase (CAT) and the detoxifying enzyme glutathione-S-transferase (GST). Cells exposed to glyphosate formulation were larger and showed an increase in vacuole size, bleaching, cell wall thickening and alteration of the stacking pattern of thylakoids. The results of this study showed the participation of oxidative stress in the mechanism of toxic action of the commercial glyphosate formulation on S. vacuolatus and the relation between the biochemical, morphological and ultrastructure alterations.

Carotenoid Production by Dunaliella salina under Red Light

The halotolerant photoautotrophic marine microalga Dunaliella salina is one of the richest sources of natural carotenoids. Here we investigated the effects of high intensity blue, red and white light from light emitting diodes (LED) on the production of carotenoids by strains of D. salina under nutrient sufficiency and strict temperature control favouring growth. Growth in high intensity red light was associated with carotenoid accumulation and a high rate of oxygen uptake. On transfer to blue light, a massive drop in carotenoid content was recorded along with very high rates of photo-oxidation. In high intensity blue light, growth was maintained at the same rate as in red or white light, but without carotenoid accumulation; transfer to red light stimulated a small increase in carotenoid content. The data support chlorophyll absorption of red light photons to reduce plastoquinone in photosystem II, coupled to phytoene desaturation by plastoquinol:oxygen oxidoreductase, with oxygen as electron acceptor. Partitioning of electrons between photosynthesis and carotenoid biosynthesis would depend on both red photon flux intensity and phytoene synthase upregulation by the red light photoreceptor, phytochrome. Red light control of carotenoid biosynthesis and accumulation reduces the rate of formation of reactive oxygen species (ROS) as well as increases the pool size of anti-oxidant.

Microalgae metabolites: A rich source for food and medicine

Microalgae are one of the important components in food chains of aquatic ecosystems and have been used for human consumption as food and as medicines. The wide diversity of compounds synthesized from different metabolic pathways of fresh and marine water algae provide promising sources of fatty acids, steroids, carotenoids, polysaccharides, lectins, mycosporine-like amino acids, halogenated compounds, polyketides, toxins, agar agar, alginic acid and carrageenan. This review discusses microalgae used to produce biological substances and its economic importance in food science, the pharmaceutical industry and public health.

Non-endogenous ketocarotenoid accumulation in engineered Synechocystis sp. PCC 6803

The cyanobacterium Synechocystis sp. PCC 6803 is a model species commonly employed for biotechnological applications. It is naturally able to accumulate zeaxanthin (Zea) and echinenone (Ech), but not astaxanthin (Asx), which is the highest value carotenoid produced by microalgae, with a wide range of applications in pharmaceutical, cosmetics, food and feed industries. With the aim of finding an alternative and sustainable biological source for the production of Asx and other valuable hydroxylated and ketolated intermediates, the carotenoid biosynthetic pathway of Synechocystis sp. PCC 6803 has been engineered by introducing the 4,4' β-carotene oxygenase (CrtW) and 3,3' β-carotene hydroxylase (CrtZ) genes from Brevundimonas sp. SD-212 under the control of a temperature-inducible promoter. The expression of exogenous CrtZ led to an increased accumulation of Zea at the expense of Ech, while the expression of exogenous CrtW promoted the production of non-endogenous canthaxanthin and an increase in the Ech content with a concomitant strong reduction of β-carotene (β-car). When both Brevundimonas sp. SD-212 genes were coexpressed, significant amounts of non-endogenous Asx were obtained accompanied by a strong decrease in β-car content. Asx accumulation was higher (approximately 50% of total carotenoids) when CrtZ was cloned upstream of CrtW, but still significant (approximately 30%) when the position of genes was inverted. Therefore, the engineered strains constitute a useful tool for investigating the ketocarotenoid biosynthetic pathway in cyanobacteria and an excellent starting point for further optimisation and industrial exploitation of these organisms for the production of added-value compounds.

Risks and benefits of consuming edible seaweeds

Recent interest in seaweeds as a source of macronutrients, micronutrients, and bioactive components has highlighted prospective applications within the functional food and nutraceutical industries, with impetus toward the alleviation of risk factors associated with noncommunicable diseases such as obesity, type 2 diabetes, and cardiovascular disease. This narrative review summarizes the nutritional composition of edible seaweeds; evaluates the evidence regarding the health benefits of whole seaweeds, extracted bioactive components, and seaweed-based food products in humans; and assesses the potential adverse effects of edible seaweeds, including those related to ingestion of excess iodine and arsenic. If the potential functional food and nutraceutical applications of seaweeds are to be realized, more evidence from human intervention studies is needed to evaluate the nutritional benefits of seaweeds and the efficacy of their purported bioactive components. Mechanistic evidence, in particular, is imperative to substantiate health claims.

Influence of long term nitrogen limitation on lipid, protein and pigment production of Euglena gracilis in photoheterotrophic cultures

Nitrogen limitation is considered a good strategy for enhancement of algal lipid production while conversely N repletion has been shown to result in biomass rich in proteins. In this study, the influence of long-term N limitation on Euglena gracilis fatty acid (FA), protein, chlorophyll a, and carotenoid concentrations was studied in N limited cultures. Biomass composition was analyzed from three-time points from N starved late stationary phase cultures, exposed to three different initial N concentrations in the growth medium. Total lipid content increased under N limitation in ageing cultures, but the low N content and prolonged cultivation time resulted in the formation of a high proportion of saturated FAs. Furthermore, growth as well as the production of proteins, chlorophyll a and carotenoids were enhanced in higher N concentrations and metabolism of these cellular components stayed stable during the stationary growth phase. Our findings showed that a higher N availability and a shorter cultivation time is a good strategy for efficient E. gracilis biomass production, regardless of whether the produced biomass is intended for maximal recovery of polyunsaturated FAs, proteins, or photosynthetic pigments. Additionally, we showed an increase of neoxanthin, β-carotene, and diadinoxanthin as a response to higher N availability.

Sequencing and Phylogenetic Analysis of Chloroplast Genes in Freshwater Raphidophytes

The complex evolution of chloroplasts in microalgae has resulted in highly diverse pigment profiles. Freshwater raphidophytes, for example, display a very different pigment composition to marine raphidophytes. To investigate potential differences in the evolutionary origin of chloroplasts in these two groups of raphidophytes, the plastid genomes of the freshwater species Gonyostomum semen and Vacuolaria virescens were sequenced. To exclusively sequence the organelle genomes, chloroplasts were manually isolated and amplified using single-cell whole-genome-amplification. Assembled and annotated chloroplast genes of the two species were phylogenetically compared to the marine raphidophyte Heterosigma akashiwo and other evolutionarily more diverse microalgae. These phylogenetic comparisons confirmed the high relatedness of all investigated raphidophyte species despite their large differences in pigment composition. Notable differences regarding the presence of light-independent protochlorophyllide oxidoreductase (LIPOR) genes among raphidophyte algae were also revealed in this study. The whole-genome amplification approach proved to be useful for isolation of chloroplast DNA from nuclear DNA. Although only approximately 50% of the genomes were covered, this was sufficient for a multiple gene phylogeny representing large parts of the chloroplast genes.

Phytoene Accumulation in the Novel Microalga Chlorococcum sp. Using the Pigment Synthesis Inhibitor Fluridone

Carotenoids are lipophilic pigments found in plants and algae, as well as some bacteria, archaea, and fungi that serve two functions-(1) as light harvesting molecules-primary carotenoids, and (2) as antioxidants, acting against reactive oxygen species⁻secondary carotenoids. Because of their strong antioxidant properties, they are also valuable for the development of anti-aging and photo-protective cosmetic applications. Of particular interest is the carotenoid phytoene, for its colorless and UV absorption characteristics. In this study, we targeted a reduction of phytoene desaturase (PDS) activity with the pigment-inhibiting herbicide 1-methyl-3-phenyl-5-[3-(trifluoromethyl)phenyl]pyridin-4-one (fluridone), which leads to the over-accumulation of phytoene in the recently characterized microalgal strain Chlorococcum sp. (UTEX B 3056). After post-incubation with fluridone, phytoene levels were measured at ~33 ug/mg cell tissue, as opposed to non-detectable levels in control cultures. Hence, the novel microalga Chlorococcum sp. is a viable candidate for the production of the high-value carotenoid phytoene and subsequent applications in cosmeceuticals, as well as more obvious nutraceutical and pharmaceutical applications.

Light induces carotenoids accumulation in a heterotrophic docosahexaenoic acid producing microalga, Crypthecodinium sp. SUN

In the present study, the effect of various light conditions on carotenoid accumulation in a novel heterotrophic microalga, Crypthecodinium sp. SUN was investigated. The results showed that C. sp. SUN mainly produced γ-carotene and β-carotene. The total carotenoid content could reach to 12.8 mg g^-1 dry weight under high light intensity (100 μmol m^-2 s^-1), which was >100-fold higher than that under dark condition. Besides, along with the light intensity increased, the ROS level in vivo was decreased at 48 h and 72 h. Further study showed that, light could efficiently promote the gene expression of PSY and LCYb, which explain the molecular mechanisms of carotenoids accumulation under light conditions. Meanwhile, slightly inhibited fatty acids accumulation could promote the carotenoids yield. The present work proposed that C. sp. SUN could be a potential carotenoid producer, and provided valuable insight for carotenoids biosynthesis.

Biological aspects and biotechnological potential of marine diatoms in relation to different light regimens

As major primary producers in marine environments, diatoms are considered a valuable feedstock of biologically active compounds for application in several biotechnological fields. Due to their metabolic plasticity, especially for light perception and use and in order to make microalgal production more environmentally sustainable, marine diatoms are considered good candidates for the large-scale cultivation. Among physical parameters, light plays a primary role. Even if sunlight is cost-effective, the employment of artificial light becomes a winning strategy if a high-value microalgal biomass is produced. Several researches on marine diatoms are designed to study the influence of different light regimens to increase biomass production enriched in biotechnologically high-value compounds (lipids, carotenoids, proteins, polysaccharides), or with emphasised photonic properties of the frustule.

Low Temperature Stress Alters the Expression of Phytoene Desaturase Genes (crtP1 and crtP2) and the ζ-Carotene Desaturase Gene (crtQ) Together with the Cellular Carotenoid Content of Euglena gracilis

Carotenoids participate in photosynthesis and photoprotection in oxygenic phototrophs. Euglena gracilis, a eukaryotic phytoflagellate, synthesizes several carotenoids: β-carotene, neoxanthin, diadinoxanthin and diatoxanthin. Temperature is one of the most striking external stimuli altering carotenoid production. In the present study, to elucidate the regulation of carotenoid synthesis of E. gracilis in response to environmental stimuli, we functionally identified phytoene desaturase genes (crtP1 and crtP2) and the ζ-carotene desaturase gene (crtQ) of this alga and analyzed expression of those genes and the composition of major carotenoids in cells grown under cold (20�C) and high-intensity light (HL; 240 �mol photon m-2 s-1) conditions. 20�C-HL treatment increased the transcriptional level of the phytoene synthase gene (crtB), and crtP1 and crtP2, whose products catalyze the early steps of carotenoid biosynthesis in this alga. Cultivation at 20�C under illumination at 55 �mol photon m-2 s-1 (low-intensity light; LL) decreased the cell concentration, Chl and total major carotenoid content by 61, 75 and 50%, respectively, relative to control (25�C-LL) cells. When grown at 20�C-HL, the cells showed a greater decrease in cell concentration and photosynthetic pigment contents than those in 20�C-LL. β-Carotene, neoxanthin and diadinoxanthin contents were decreased by more than half in 20�C-LL and 20�C-HL treatments. On the other hand, when subjected to 20�C-LL and 20�C-HL, the cells retained a diatoxanthin content comparable with control cells. Our findings suggested that diatoxanthin plays crucial roles in the acclimation to cold and intense light condition. To the best of our knowledge, this is the first report on a photosynthetic organism possessing dual crtP genes.

Enhancing production of microalgal biopigments through metabolic and genetic engineering

The versatile use of biopigments in food, feed, cosmetic, pharmaceutical and analytical industries emphasized to find different and renewable sources of biopigments. Microalgae, including cyanobacteria, are becoming a potential candidate for pigment production as these have fast-growing ability, high pigment content, highly variable and also have "Generally recognized as safe" status. These algal groups are known to produce different metabolites that include hormones, vitamins, biopolythene and biochemicals. We discuss here the potential use of microalgal biopigments in our daily life as well as in food and cosmetic industries. Pigment like carotenoids has many health benefits such as antioxidant, anti-inflammatory properties and also provide photo-protection against UV radiation. This review details the effect of various abiotic and biotic factors such as temperature, light, nutrition on maximizing the pigment content in the microalgal cell. This review also highlights the potential of microalgae, whether in present native or engineered strain including the many metabolic strategies which are used or can be used to produce a higher amount of these valuable biopigments. Additionally, future challenges in the context of pigment production have also been discussed.

In vitro studies of the neuroprotective activities of astaxanthin and fucoxanthin against amyloid beta (Aβ1-42) toxicity and aggregation

Amyloid beta (Aβ) can aggregate and form plaques, which are considered as one of the major hallmarks of Alzheimer's disease. This study aims to directly compare the neuroprotective activities in vitro of two marine-derived carotenoids astaxanthin and fucoxanthin that have shown a spectrum of biological activities, including neuroprotection. The in vitro neuroprotective activities were investigated against Aβ_1-42-mediated toxicity in pheochromocytoma (PC-12) neuronal cells using the MTT cell viability assay, anti-apoptotic, antioxidant and neurite outgrowth activities; as well as inhibition against Aβ_1-42 fibrillization in the Thioflavin T (ThT) assay of fibril kinetics and via transmission electron microscopic (TEM) evaluation of fibril morphology. The results demonstrated that both astaxanthin and fucoxanthin exhibited multi-neuroprotective effects favouring fucoxanthin over astaxanthin supporting neuroprotective roles of marine-derived carotenoids as potential novel dementia prevention or therapeutic strategies.

Physiological role of β-carotene monohydroxylase (CYP97H1) in carotenoid biosynthesis in Euglena gracilis

Some carotenoids are found in the Euglena gracilis, including β-carotene, diadinoxanthin, diatoxanthins, and neoxanthin as the major species; however, the molecular mechanism underlying carotenoid biosynthesis in E. gracilis is not well understood. To clarify the pathway and regulation of carotenoid biosynthesis in this alga, we functionally characterized the cytochrome P450 (CYP)-type carotene hydroxylase gene EgCYP97H1. Heterologous in vivo enzyme assay in E. coli indicated that EgCYP97H1 hydroxylated β-carotene to β-cryptoxanthin. E. gracilis cells suppressing EgCYP97H1 resulted in marked growth inhibition and reductions in total carotenoid and chlorophyll contents. Analysis of carotenoid composition revealed that suppression of EgCYP97H1 resulted in higher level of β-carotene, suggesting that EgCYP97H1 is physiologically essential for carotenoid biosynthesis and thus normal cell growth. To our knowledge, this is the first time EgCYP97H1 has been suggested to be β-carotene monohydroxylase, but not β-carotene dihydroxylase. Moreover, during light adaptation of dark-grown E. gracilis, transcript levels of the carotenoid biosynthetic genes (EgCYP97H1, geranylgeranyl pyrophosphate synthase EgcrtE, and phytoene synthase EgcrtB) remained virtually unchanged. In contrast, carotenoid accumulation in E. gracilis grown under the same conditions was inhibited by treatment with a translational inhibitor but not a transcriptional inhibitor, indicating that photo-responsive carotenoid biosynthesis is regulated post-transcriptionally in this alga.

A hypothesis about the origin of carotenoid lipid droplets in the green algae Dunaliella and Haematococcus

Hypercarotenogenesis in green algae evolved by mutation of PSY that increased its transcription at high light, disintegration of the eyespot in Dunaliella and acquisition of the capacity to export carotenoids from chloroplasts in Haematococcus. Carotenoids (Car) are lipid-soluble pigments synthesized in plants, algae, bacteria and fungi. Car have strong antioxidative properties and as such are utilized to reduce the danger of different diseases in humans. Two green microalgae are utilized as rich natural sources for Car: Dunaliella salina/bardawil accumulates 10% (w/w) β-carotene (βC), which is also pro-vitamin A, and Haematococcus pluvialis accumulates 4% (w/w) astaxanthin (Ast), the strongest antioxidant among Car. D. bardawil accumulates βC in plastoglobules within the chloroplast, whereas H. pluvialis deposits Ast in cytoplasmic lipid droplets (CLD). In this review we compare the hypercarotenogenic responses (HCR) in Dunaliella and in Haematococcus and try to outline hypothetical evolutionary pathways for its origin. We propose that a mutation in phytoene synthetase that increased its transcription level in response to high light stress had a pivotal role in the evolution of the HCR. Proteomic analyses indicated that in D. bardawil/salina the HCR evolved from dissociation and amplification of eyespot lipid globules. The more robust HCR in algae that accumulate carotenoids in CLD, such as H. pluvialis, required also acquisition of the capacity to export βC out of the chloroplast and its enzymatic conversion into Ast.

Differential gene expression for carotenoid biosynthesis in a green alga Ulva prolifera based on transcriptome analysis

BACKGROUND

Carotenoids are widely distributed in plants and algae, and their biosynthesis has attracted widespread interest. Carotenoid-related research has mostly focused on model species, and there is a lack of data on the carotenoid biosynthetic pathway in U. prolifera that is the main species leading to green tide, a harmful plague of floating green algae.

RESULTS

The carotenoid content of U. prolifera samples, that is the main species leading to green tide, a harmful plague of floating green algae at different temperatures revealed that its terpenoid was highest in the samples subjected to high temperature at 28 °C (H), followed by the samples subjected to low temperature at 12 °C (L). Its terpenoid was lowest in the samples subjected to medium temperature at 20 °C (M). We conducted transcriptome sequencing (148.5 million raw reads and 49,676 unigenes in total) of samples that were subjected to different temperatures to study the carotenoid biosynthesis of U. prolifera. There were 1125-3164 significant differentially expressed genes between L, M and H incubation temperatures, of which 11-672 genes were upregulated and 453-3102 genes were downregulated. A total of 3164 genes were significantly differentially expressed between H and M, of which 62 genes were upregulated and 3102 genes were downregulated. A total of 2669 significant differentially expressed genes were observed between L and H, of which 11 genes were upregulated and 2658 genes were downregulated. A total of 13 genes were identified to be involved in carotenoid biosynthesis in U. prolifera, and the expression levels of the majority were highest at H and lowest at M of incubation temperature. Both the carotenoid concentrations and the expression of the analysed genes were lowest in the normal temperature group, while low temperature and high temperature seemed to activate the biosynthesis of carotenoids in U. prolifera.

CONCLUSIONS

In this study, transcriptome sequencing provided critical information for understanding the accumulation of carotenoids and will serve as an important reference for the study of other metabolic pathways in U. prolifera.

Ocean warming and copper pollution: implications for metabolic compounds of the agarophyte Gelidium floridanum (Gelidiales, Rhodophyta)

Ocean warming is increasing and scientific predictions suggest a rise of up to 4°C in sea water temperatures. The combination of a polluted and warmer environment may be detrimental for aquatic species, especially for primary producers such as seaweeds. This study investigated the potential for interactive effects of an increased seawater temperature in a copper-rich environment on the photosynthetic pigments and metabolic compounds of the red seaweed Gelidium floridanum. Seaweed samples were cultivated in a factorial design with temperature (24°C and 30°C), copper (0 and 3 μM), and time (7 and 14 d). The exposure of G. floridanum to copper and 30°C for 7 d resulted in a lower concentration of chlorophyll a, smaller phycobiliprotein rods and lower concentration of soluble sugars. After 14 d of cultivation, a higher concentration of chlorophyll a and soluble sugars could be observed on seaweeds cultivated under 30°C. The accumulation of carotenoids and the release of phenolic compounds indicated specific protective mechanisms against temperature and copper, respectively. Overall, seaweeds grew less when exposed to copper 3 μM at 30°C.

Chemically-Induced Production of Anti-Inflammatory Molecules in Microalgae

Microalgae have been widely recognized as a valuable source of natural, bioactive molecules that can benefit human health. Some molecules of commercial value synthesized by the microalgal metabolism have been proven to display anti-inflammatory activity, including the carotenoids lutein and astaxanthin, the fatty acids EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid), and sulphated polysaccharides. These molecules can accumulate to a certain extent in a diversity of microalgae species. A production process could become commercially feasible if the productivity is high and the overall production process costs are minimized. The productivity of anti-inflammatory molecules depends on each algal species and the cultivation conditions, the latter being mostly related to nutrient starvation and/or extremes of temperature and/or light intensity. Furthermore, novel bioprocess tools have been reported which might improve the biosynthesis yields and productivity of those target molecules and reduce production costs simultaneously. Such novel tools include the use of chemical triggers or enhancers to improve algal growth and/or accumulation of bioactive molecules, the algal growth in foam and the surfactant-mediated extraction of valuable compounds. Taken together, the recent findings suggest that the combined use of novel bioprocess strategies could improve the technical efficiency and commercial feasibility of valuable microalgal bioproducts production, particularly anti-inflammatory compounds, in large scale processes.

Carotenoid profiling of five microalgae species from large-scale production

The carotenoid profiles of biomass from five eukaryotic microalgae, Porphyridium cruentum, Isochrysis galbana, Phaeodactylum tricornutum, Tetraselmis suecica and Nannochloropsis gaditana, produced at an industrial plant in outdoor photobioreactors, were investigated. Pigments were solvent-extracted after an ultrasonic pre-treatment and separated by HPLC-photodiode-array using a reversed-phase C18 column. Microalgae showed species-specific carotenoid profiles. Carotenoids were mostly in their free form, with a prevalence of xanthophylls over carotenes. Beta-carotene was the only carotenoid common to all species. The Rhodophyta P. cruentum exhibited the lowest total carotenoid content (167.2 mg 100 g^-1 dw) and the simplest profile, with (all-E)-zeaxanthin (94.2 mg 100 g^-1 dw, 56% of total carotenoids) and (all-E)-β- carotene (53.4 mg 100 g^-1 dw, 32% of total carotenoids) as the major carotenoids. The Haptophyta Isochrysis galbana and the Bacillariophyta Phaeodactylum tricornutum were the species with the highest total carotenoid content (1760 mg and 1022 mg 100 g^-1 dw, respectively). These species were characterized by similar carotenoid profiles, with (all-E)-fucoxanthin as the chief compound (1346 mg and 776.8 mg 100 g^-1 dw for I. galbana and P. tricornutum, respectively), accounting for about 76% of total carotenoids. The Chlorophyta Tetraselmis suecica was the species showing the greatest variety of carotenoids, with both α- carotene and β- carotene and their derivatives present. (All-E)-lutein (85.4 mg 100 g^-1 dw) and (all-E)-violaxanthin (81.8 mg 100 g^-1 dw) were the major pigments in this species. In the Ochrophyta Nannochloropsis gaditana, (all-E)-violaxanthin was the prevalent carotenoid (336.7 mg 100 g^-1 dw), followed by (all-E)-β-carotene (100.1 mg 100 g^-1 algal dw). The carotenoid content of the microalgal biomass studied compared favourably to that of major vegetable sources. Due to their characteristics, these microalgae, most of them currently finding their main application in aquaculture, may be also regarded as valuable sources of carotenoids to be used in the formulation of functional food and nutraceuticals.

Blue light reduces photosynthetic efficiency of cyanobacteria through an imbalance between photosystems I and II

Several studies have described that cyanobacteria use blue light less efficiently for photosynthesis than most eukaryotic phototrophs, but comprehensive studies of this phenomenon are lacking. Here, we study the effect of blue (450 nm), orange (625 nm), and red (660 nm) light on growth of the model cyanobacterium Synechocystis sp. PCC 6803, the green alga Chlorella sorokiniana and other cyanobacteria containing phycocyanin or phycoerythrin. Our results demonstrate that specific growth rates of the cyanobacteria were similar in orange and red light, but much lower in blue light. Conversely, specific growth rates of the green alga C. sorokiniana were similar in blue and red light, but lower in orange light. Oxygen production rates of Synechocystis sp. PCC 6803 were five-fold lower in blue than in orange and red light at low light intensities but approached the same saturation level in all three colors at high light intensities. Measurements of 77 K fluorescence emission demonstrated a lower ratio of photosystem I to photosystem II (PSI:PSII ratio) and relatively more phycobilisomes associated with PSII (state 1) in blue light than in orange and red light. These results support the hypothesis that blue light, which is not absorbed by phycobilisomes, creates an imbalance between the two photosystems of cyanobacteria with an energy excess at PSI and a deficiency at the PSII-side of the photosynthetic electron transfer chain. Our results help to explain why phycobilisome-containing cyanobacteria use blue light less efficiently than species with chlorophyll-based light-harvesting antennae such as Prochlorococcus, green algae and terrestrial plants.

Carotenoid Profiling of a Red Seaweed Pyropia yezoensis: Insights into Biosynthetic Pathways in the Order Bangiales

Carotenoids are natural pigments that contribute to light harvesting and photo-protection in photosynthetic organisms. In this study, we analyzed the carotenoid profiles, including mono-hydroxy and epoxy-carotenoids, in the economically valuable red seaweed Pyropia yezoensis, to clarify the detailed biosynthetic and metabolic pathways in the order Bangiales. P. yezoensis contained lutein, zeaxanthin, α-carotene, and β-carotene, as major carotenoids in both the thallus and conchocelis stages. Monohydroxy intermediate carotenoids for the synthesis of lutein with an ε-ring from α-carotene, α-cryptoxanthin (β,ε-caroten-3’-ol), and zeinoxanthin (β,ε-caroten-3-ol) were identified. In addition, β-cryptoxanthin, an intermediate in zeaxanthin synthesis from β-carotene, was also detected. We also identified lutein-5,6-epoxide and antheraxanthin, which are metabolic products of epoxy conversion from lutein and zeaxanthin, respectively, by LC-MS and ¹H-NMR. This is the first report of monohydroxy-carotenoids with an ε-ring and 5,6-epoxy-carotenoids in Bangiales. These results provide new insights into the biosynthetic and metabolic pathways of carotenoids in red seaweeds.

Blue-Red LED wavelength shifting strategy for enhancing beta-carotene production from halotolerant microalga, Dunaliella salina

In the present study, to improve the photosynthetic betacarotene productivity of Dunaliella salina, a blue-red LED wavelength-shifting system (B-R system) was investigated. Dunaliella salina under the B-R system showed enhanced density and beta-carotene productivity compared to D. salina cultivated under single light-emitting diode light wavelengths (blue, white, and red light-emitting diode). Additionally, we developed blue light-adapted D. salina (ALE-D. salina) using an adaptive laboratory evolution (ALE) approach. In combination with the B-R system applied to ALE-D. salina (ALE B-R system), the beta-carotene concentration (33.94 ± 0.52 μM) was enhanced by 19.7% compared to that observed for the non-ALE-treated wild-type of D. salina (intact D. salina) under the B-R system (28.34 ± 0.24 μM).

Dose and life stage-dependent effects of dietary beta-carotene supplementation on the growth and development of the Booroolong frog

Carotenoids are known for their antioxidant capacity and are considered to play an important role in vertebrate growth and development. However, evidence for their beneficial effects remains limited, possibly because very few studies have tested for dose effects across different life stages. The present study investigated the effect of various doses of dietary beta-carotene supplements on the growth and development of larval and post-metamorphic Booroolong frogs (Litoria booroolongensis). Larval and post-metamorphic basal diets (containing 0.015 and 0.005 mg g-1 total carotenoids, respectively) were supplemented with beta-carotene at one of four concentrations: 0 mg g-1, 0.1 mg g-1, 1 mg g-1 and 10 mg g-1. Each treatment included 72 replicate individuals, and individuals remained on the same diet treatment over both life stages (spanning 53 experimental weeks). Our results show that larvae receiving an intermediate (1 mg g-1) beta-carotene supplement dose grew faster than unsupplemented larvae (0 mg g-1), and metamorphosed earlier. After metamorphosis, there was no effect of the lowest supplement dose (0.1 mg g-1) on growth and development. However, juveniles fed the highest supplement dose (10 mg g-1) displayed significantly smaller body mass and lower body condition, compared to all other supplement doses, from 4-months through to sexual maturity (7-months). These findings indicate that beta-carotene supplementation has positive effects on growth and development, but only at intermediate doses, and only in the larval life stage. This knowledge may assist with amphibian conservation by expediting the rate that metamorphs can be generated in captive breeding programmes. More broadly, this is the first study to demonstrate both dose and life stage-dependent effects of dietary beta-carotene supplementation on vertebrate growth and development.

A Sweetpotato Auxin Response Factor Gene (IbARF5) Is Involved in Carotenoid Biosynthesis and Salt and Drought Tolerance in Transgenic Arabidopsis

Auxin response factors (ARFs) compose a family of transcription factors and have been found to play major roles in the process of plant growth and development. However, their roles in plant carotenoid biosynthesis and responses to abiotic stresses are rarely known to date. In the present study, we found that the IbARF5 gene from sweetpotato (Ipomoea batatas (L.) Lam.) line HVB-3 increased the contents of carotenoids and enhanced the tolerance to salt and drought in transgenic Arabidopsis. The transgenic Arabidopsis plants exhibited the increased abscisic acid (ABA) and proline contents and superoxide dismutase (SOD) activity and the decreased H₂O₂ content. Furthermore, it was found that IbARF5 positively regulated the genes associated with carotenoid and ABA biosynthesis and abiotic stress responses. These results suggest that IbARF5 is involved in carotenoid biosynthesis and salt and drought tolerance in transgenic Arabidopsis. This study provides a novel ARF gene for improving carotenoid contents and salt and drought tolerance of sweetpotato and other plants.

Hormonally active phytochemicals from macroalgae: A largely untapped source of ligands to deorphanize nuclear receptors in emerging marine animal models

Hormonally active phytochemicals (HAPs) are signaling molecules produced by plants that alter hormonal signaling in animals, due to consumption or environmental exposure. To date, HAPs have been investigated mainly in terrestrial ecosystems. To gain a full understanding of the origin and evolution of plant-animal interactions, it is necessary also to study these interactions in the marine environment, where the major photosynthetic lineages are very distant from the terrestrial plants. Here we focus on chemicals from red and brown macroalgae and point out their potential role as modulators of the endocrine system of aquatic animals through nuclear hormone receptors. We show that, regarding steroids and oxylipins, there are already some candidates available for further functional investigations of ligand-receptor interactions. Furthermore, several carotenoids, produced by cyanobacteria provide candidates that could be investigated with respect to their presence in macroalgae. Finally, regarding halogenated compounds, it is not clear yet which molecules could bridge the gap to explain the transition from lipid sensing to thyroid hormone high affinity binding among nuclear receptors.

Insights into carotenoid accumulation using VIGS to block different steps of carotenoid biosynthesis in petals of California poppy

Viral-induced gene silencing of selected biosynthetic genes decreased overall carotenoid accumulation in California poppy. Regulation of carotenogenesis was linked with pigment sequestration, not changes in biosynthetic gene expression. Genes of carotenogenesis are well described, but understanding how they affect carotenoid accumulation has proven difficult because of plant lethality when the pigments are lacking. Here, we used a Tobacco Rattle Virus-based virus-induced-gene-silencing (VIGS) approach in California poppy (Eschscholzia californica) to investigate how silencing of the carotenoid biosynthetic pathway genes affects carotenoid metabolite accumulation and RNA transcript abundance of the carotenoid biosynthetic pathway genes. VIGS of upstream (PDS and ZDS) and downstream (βOH and ZEP) genes reduced transcript abundance of the targeted genes in the poppy petals while having no effect on abundance of the other carotenogenesis genes. Silencing of PDS, ZDS, βOH and ZEP genes reduced total pigment concentration by 75-90% and altered petal colour. HPLC and LC-MS measurements suggested that petal colour changes were caused by substantially altered pigment profiles and quantity. Carotenoid metabolites were different to those normally detected in wild-type petals accumulated but overall carotenoid concentration was less, suggesting the chemical form of carotenoid was important for whether it could be stored at high amounts. In poppy petals, eschscholtzxanthin and retro-carotene-triol were the predominant carotenoids, present mainly as esters. Specific esterification enzymes for specific carotenoids and/or fatty acids appear key for enabling petal carotenoids to accumulate to high amounts. Our findings argue against a direct role for carotenoid metabolites regulating carotenogenesis genes in the petals of California poppy as transcript abundance of carotenogenesis genes studied was unchanged, while the petal carotenoid metabolite profile changed substantially.

Dietary phytochemicals in breast cancer research: anticancer effects and potential utility for effective chemoprevention

Cancerous tissue transformation developing usually over years or even decades of life is a highly complex process involving strong stressors damaging DNA, chronic inflammation, comprehensive interaction between relevant molecular pathways, and cellular cross-talk within the neighboring tissues. Only the minor part of all cancer cases are caused by inborn predisposition; the absolute majority carry a sporadic character based on modifiable risk factors which play a central role in cancer prevention. Amongst most promising candidates for dietary supplements are bioactive phytochemicals demonstrating strong anticancer effects. Abundant evidence has been collected for beneficial effects of flavonoids, carotenoids, phenolic acids, and organosulfur compounds affecting a number of cancer-related pathways. Phytochemicals may positively affect processes of cell signaling, cell cycle regulation, oxidative stress response, and inflammation. They can modulate non-coding RNAs, upregulate tumor suppressive miRNAs, and downregulate oncogenic miRNAs that synergically inhibits cancer cell growth and cancer stem cell self-renewal. Potential clinical utility of the phytochemicals is discussed providing examples for chemoprevention against and therapy for human breast cancer. Expert recommendations are provided in the context of preventive medicine.

Analysis of functional components and radical scavenging activity of 21 algae species collected from the Japanese coast

The functional chemical substances and the antioxidant activity of lipids in 21 marine algae along the Japanese coast were investigated. Principal component analysis was performed to detect any correlation between the chemical substances and algae phylum. Chlorophyta contained a high level of β-carotene. Rhodophyta contained high amounts of cholesterol, β-sitosterol, and saturated fatty acids. Phaeophyta were rich in fucosterol, α-tocopherol, fucoxanthin, and polyphenol. Phaeophyta algae also showed the highest antioxidant activity compared with other phylum. This suggests that Phaeophyta has the greatest potential to be used as a functional food. Consumption of the beneficial Phaeophyta species, such as Eisenia arborea Areschoug and Ecklonia cava Kjellman should be encouraged as not only as food products but also as nutraceuticals and dietary supplements. These beneficial ingredients should be encouraged to be studied in depth with the possibility to develop specific formulated products target to special consumer's population with added nutritional value.

A lycopene β-cyclase gene, IbLCYB2, enhances carotenoid contents and abiotic stress tolerance in transgenic sweetpotato

Lycopene β-cyclase (LCYB) is an essential enzyme that catalyzes the conversion of lycopene into α-carotene and β-carotene in carotenoid biosynthesis pathway. However, the roles and underlying mechanisms of the LCYB gene in plant responses to abiotic stresses are rarely known. This gene has not been used to improve carotenoid contents of sweetpotato, Ipomoea batatas (L.) Lam.. In the present study, a new allele of the LCYB gene, named IbLCYB2, was isolated from the storage roots of sweetpotato line HVB-3. Its overexpression significantly increased the contents of α-carotene, β-carotene, lutein, β-cryptoxanthin and zeaxanthin and enhanced the tolerance to salt, drought and oxidative stresses in the transgenic sweetpotato (cv. Shangshu 19) plants. The genes involved in carotenoid and abscisic acid (ABA) biosynthesis pathways and abiotic stress responses were up-regulated in the transgenic plants. The ABA and proline contents and superoxide dismutase (SOD) activity were significantly increased, whereas malonaldehyde (MDA) and H₂O₂ contents were significantly decreased in the transgenic plants under abiotic stresses. The overall results indicate that the IbLCYB2 gene enhances carotenoid contents and abiotic stress tolerance through positive regulation of carotenoid and ABA biosynthesis pathways in sweetpotato. This gene has the potential to improve carotenoid contents and abiotic stress tolerance in sweetpotato and other plants.

Selected Methods of Extracting Carotenoids, Characterization, and Health Concerns: A Review

Carotenoids are the most powerful nutrients (medicine) on earth due to their potent antioxidant properties. The ability of these tetraterpenoids in obviating human chronic ailments like cancer, cardiovascular disease, osteoporosis, and diabetes has drawn public attention toward these novel compounds. Conventionally, carotenoids have been extracted from plant materials and agro-industrial byproduct using different solvents, but these procedures result in contaminating the target compound (carotenoids) with extraction solvents. Furthermore, some utilized solvents are not safe and hence are harmful to the environment. This has attracted criticism from consumers, ecologists, environmentalists, and public health workers. However, there is clear consumer preference for carotenoids from natural origin without traces of extracting solvent. Therefore, this review seeks to discuss methods for higher recovery of pure carotenoids without contamination from a solvent. Methods such as enzyme-based extraction, supercritical fluid extraction, microwave-assisted extraction, Soxhlet extraction, ultrasonic extraction, and postextraction treatment (saponification) are discussed. Merits and demerits of these methods along with health concerns during intake of carotenoids were also considered.

Exploring the Valuable Carotenoids for the Large-Scale Production by Marine Microorganisms

Carotenoids are among the most abundant natural pigments available in nature. These pigments have received considerable attention because of their biotechnological applications and, more importantly, due to their potential beneficial uses in human healthcare, food processing, pharmaceuticals and cosmetics. These bioactive compounds are in high demand throughout the world; Europe and the USA are the markets where the demand for carotenoids is the highest. The in vitro synthesis of carotenoids has sustained their large-scale production so far. However, the emerging modern standards for a healthy lifestyle and environment-friendly practices have given rise to a search for natural biocompounds as alternatives to synthetic ones. Therefore, nowadays, biomass (vegetables, fruits, yeast and microorganisms) is being used to obtain naturally-available carotenoids with high antioxidant capacity and strong color, on a large scale. This is an alternative to the in vitro synthesis of carotenoids, which is expensive and generates a large number of residues, and the compounds synthesized are sometimes not active biologically. In this context, marine biomass has recently emerged as a natural source for both common and uncommon valuable carotenoids. Besides, the cultivation of marine microorganisms, as well as the downstream processes, which are used to isolate the carotenoids from these microorganisms, offer several advantages over the other approaches that have been explored previously. This review summarizes the general properties of the most-abundant carotenoids produced by marine microorganisms, focusing on the genuine/rare carotenoids that exhibit interesting features useful for potential applications in biotechnology, pharmaceuticals, cosmetics and medicine.

Effects of enhanced ultraviolet-B radiation, water deficit, and their combination on UV-absorbing compounds and osmotic adjustment substances in two different moss species

A simulation experiment was conducted to explore the influence of enhanced ultraviolet-B (UV-B) radiation, water deficit, and their combination on UV-absorbing compounds and osmotic adjustment substances of mosses Bryum argenteum and Didymodon vinealis isolated from biological soil crusts (BSCs) growing in a revegetated area of the Tengger Desert, China. Four levels of UV-B radiation and two gradients of water regime were employed. Compared with their controls, amounts of total flavonoids, chlorophyll, carotenoids, soluble sugars, and soluble proteins significantly decreased (p < 0.05), but proline content significantly increased (p < 0.05), when exposed to either enhanced UV-B or water deficit. The negative effects of enhanced UV-B were alleviated when water deficit was applied. There were increases in UV-absorbing compounds and osmotic adjustment substances when exposed to a combination of enhanced UV-B and water deficit compared with single stresses, except for the proline content in D. vinealis. In addition, our results also indicated interspecific differences in response to enhanced UV-B, water deficit, and their combination. Compared with B. argenteum, D. vinealis was more resistant to enhanced UV-B and water deficit singly and in combination. These results suggest that the damage of enhanced UV-B on both species might be alleviated by water deficit. This alleviation is important for understanding the response of BSCs to UV-B radiation in future global climate change. This also provides novel insights into assessment damages of UV-B to BSC stability in arid and semiarid regions.

A global perspective on carotenoids: Metabolism, biotechnology, and benefits for nutrition and health

Carotenoids are lipophilic isoprenoid compounds synthesized by all photosynthetic organisms and some non-photosynthetic prokaryotes and fungi. With some notable exceptions, animals (including humans) do not produce carotenoids de novo but take them in their diets. In photosynthetic systems carotenoids are essential for photoprotection against excess light and contribute to light harvesting, but perhaps they are best known for their properties as natural pigments in the yellow to red range. Carotenoids can be associated to fatty acids, sugars, proteins, or other compounds that can change their physical and chemical properties and influence their biological roles. Furthermore, oxidative cleavage of carotenoids produces smaller molecules such as apocarotenoids, some of which are important pigments and volatile (aroma) compounds. Enzymatic breakage of carotenoids can also produce biologically active molecules in both plants (hormones, retrograde signals) and animals (retinoids). Both carotenoids and their enzymatic cleavage products are associated with other processes positively impacting human health. Carotenoids are widely used in the industry as food ingredients, feed additives, and supplements. This review, contributed by scientists of complementary disciplines related to carotenoid research, covers recent advances and provides a perspective on future directions on the subjects of carotenoid metabolism, biotechnology, and nutritional and health benefits.

Chemical profiling of edible seaweed (Ochrophyta) extracts and assessment of their in vitro effects on cell-free enzyme systems and on the viability of glutamate-injured SH-SY5Y cells

Neurodegenerative processes involve numerous and closely related events that ultimately culminate in neuronal cell injury. The aim of this study was (i) to assess, for the first time, the neuroprotective potential of acetone extracts of six edible species of Ochrophyta, by evaluating their cholinesterase and lipoxygenase inhibitory activity in cell-free assays, as well as their capacity to attenuate glutamate-induced toxicity in neuronal (SH-SY5Y) cells, and (ii) to try to relate the chemical composition of the extracts with their biological activity, evaluating also the effect of the main compounds thereof. In spite of a modest cholinesterase inhibition, a dose-dependent response towards lipoxygenase was found for all macroalgae extracts. At non-cytotoxic concentrations, the extracts from Fucus serratus Linnaeus and Saccharina latissima (Linnaeus) C.E. Lane, C. Mayes, Druehl & G.W. Saunders were able to improve the viability of glutamate-insulted SH-SY5Y cells. These results encourage further studies for a more detailed understanding of the mechanisms beyond the documented biological activities, and point to the potential interest of the selected seaweed species and their extracts as promising candidates for in vivo studies.

A Possible Trifunctional β-Carotene Synthase Gene Identified in the Draft Genome of Aurantiochytrium sp. Strain KH105

Labyrinthulomycetes have been regarded as a promising industrial source of xanthophylls, including astaxanthin and canthaxanthin, polyunsaturated fatty acids such as docosahexaenoic acid and docosapentaenoic acid, ω-3 oils, and terpenic hydrocarbons, such as sterols and squalene. A Thraustochytrid, Aurantiochytrium sp. KH105 produces carotenoids, including astaxanthin, with strong antioxidant activity. To gain genomic insights into this capacity, we decoded its 97-Mbp genome and characterized genes for enzymes involved in carotenoid biosynthesis. Interestingly, all carotenogenic genes, as well as other eukaryotic genes, appeared duplicated, suggesting that this strain is diploid. In addition, among the five genes involved in the pathway from geranylgeranyl pyrophosphate to astaxanthin, geranylgeranyl phytoene synthase (crtB), phytoene desaturase (crtI) and lycopene cyclase (crtY) were fused into single gene (crtIBY) with no internal stop codons. Functionality of the trifunctional enzyme, CrtIBY, to catalyze the reaction from geranylgeranyl diphosphate to β-carotene was confirmed using a yeast assay system and mass spectrometry. Furthermore, analyses of differential gene expression showed characteristic up-regulation of carotenoid biosynthetic genes during stationary and starvation phases under these culture conditions. This suggests genetic engineering events to promote more efficient production of carotenoids. We also showed an occurrence of crtIBY in other Thraustochytrid species.

Genetic and metabolic engineering in diatoms

Diatoms have attracted considerable attention due to their success in diverse environmental conditions, which probably is a consequence of their complex origins. Studies of their metabolism will provide insight into their adaptation capacity and are a prerequisite for metabolic engineering. Several years of investigation have led to the development of the genome engineering tools required for such studies, and a profusion of appropriate tools is now available for exploring and exploiting the metabolism of these organisms. Diatoms are highly prized in industrial biotechnology, due to both their richness in natural lipids and carotenoids and their ability to produce recombinant proteins, of considerable value in diverse markets. This review provides an overview of recent advances in genetic engineering methods for diatoms, from the development of gene expression cassettes and gene delivery methods, to cutting-edge genome-editing technologies. It also highlights the contributions of these rapid developments to both basic and applied research: they have improved our understanding of key physiological processes; and they have made it possible to modify the natural metabolism to favour the production of specific compounds or to produce new compounds for green chemistry and pharmaceutical applications.This article is part of the themed issue 'The peculiar carbon metabolism in diatoms'.