The role of light and nitrogen in growth and carotenoid accumulation in Scenedesmus sp

Light Influences the Growth, Pigment Synthesis, Photosynthesis Capacity, and Antioxidant Activities in Scenedesmus falcatus

Light plays a significant role in microalgae cultivation, significantly influencing critical parameters, including biomass production, pigment content, and the accumulation of metabolic compounds. This study was intricately designed to optimize light intensities, explicitly targeting enhancing growth, pigmentation, and antioxidative properties in the green microalga, Scenedesmus falcatus (KU.B1). Additionally, the study delved into the photosynthetic efficiency in light responses of S. falcatus. The cultivation of S. falcatus was conducted in TRIS-acetate-phosphate medium (TAP medium) under different light intensities of 100, 500, and 1000 μmol photons m-2·s-1 within a photoperiodic cycle of 12 h of light and 12 h of dark. Results indicated a gradual increase in the growth of S. falcatus under high light conditions at 1000 μmol photons m-2·s-1, reaching a maximum optical density of 1.33 ± 0.03 and a total chlorophyll content of 22.67 ± 0.2 μg/ml at 120 h. Conversely, a slower growth rate was observed under low light at 100 μmol photons m-2·s-1. However, noteworthy reductions in the maximum quantum yield (Fv/Fm) and actual quantum yield (Y(II)) were observed under 1000 μmol photons m-2·s-1, reflecting a decline in algal photosynthetic efficiency. Interestingly, these changes under 1000 μmol photons m-2·s-1 were concurrent with a significant accumulation of a high amount of beta-carotene (919.83 ± 26.33 mg/g sample), lutein (34.56 ± 0.19 mg/g sample), and canthaxanthin (24.00 ± 0.38 mg/g sample) within algal cells. Nevertheless, it was noted that antioxidant activities and levels of total phenolic compounds (TPCs) decreased under high light at 1000 μmol photons m-2·s-1, with IC50 of DPPH assay recorded at 218.00 ± 4.24 and TPC at 230.83 ± 86.75 mg of GAE/g. The findings suggested that the elevated light intensity at 1000 μmol photons m-2·s-1 enhanced the growth and facilitated the accumulation of valuable carotenoid pigment in S. falcatus, presenting potential applications in the functional food and carotenoid industry.

Comprehensive Update on Carotenoid Colorants from Plants and Microalgae: Challenges and Advances from Research Laboratories to Industry

The substitution of synthetic food dyes with natural colorants continues to be assiduously pursued. The current list of natural carotenoid colorants consists of plant-derived annatto (bixin and norbixin), paprika (capsanthin and capsorubin), saffron (crocin), tomato and gac fruit lycopene, marigold lutein, and red palm oil (α- and β-carotene), along with microalgal Dunaliella β-carotene and Haematococcus astaxanthin and fungal Blakeslea trispora β-carotene and lycopene. Potential microalgal sources are being sought, especially in relation to lutein, for which commercial plant sources are lacking. Research efforts, manifested in numerous reviews and research papers published in the last decade, have been directed to green extraction, microencapsulation/nanoencapsulation, and valorization of processing by-products. Extraction is shifting from conventional extraction with organic solvents to supercritical CO2 extraction and different types of assisted extraction. Initially intended for the stabilization of the highly degradable carotenoids, additional benefits of encapsulation have been demonstrated, especially the improvement of carotenoid solubility and bioavailability. Instead of searching for new higher plant sources, enormous effort has been directed to the utilization of by-products of the fruit and vegetable processing industry, with the application of biorefinery and circular economy concepts. Amidst enormous research activities, however, the gap between research and industrial implementation remains wide.

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

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

Accessing the biotechnological potential of a novel isolated microalga from a semi-arid region of Brazil

The use of microalgae as a source of food and pharmaceutical ingredients has garnered growing interest in recent years. Despite the rapid growth of the nutraceutical market, knowledge about the potential of bioactive molecules from microalgae remains insufficient. The present study aimed to investigate the biotechnological potential of the green microalga Desmodesmus armatus isolated from a semi-arid region of Brazil. The algal biomass was characterized in terms of gross biochemical composition, exopolysaccharide content, enzymatic inhibition capacity, and antioxidant, antibacterial, and hemolytic activities from solvents of different polarities (water, ethanol, acetone, and hexane). D armatus biomass had 40% of crude protein content, 25.94% of lipids, and 25.03% of carbohydrates. The prebiotic potential of exopolysaccharides from D armatus was demonstrated, which stimulated the growth of Lacticaseibacillus rhamnosus and Lactiplantibacillus plantarum bacteria strains. Moreover, the enzyme inhibition capacity for the proteases chymotrypsin (34.78%-45.8%) and pepsin (16.64%-27.27%), in addition to α-amylase (24.79%) and lipase (31.05%) was confirmed. The antioxidant potential varied between the different extracts, with 2,2-diphenyl-1-picrylhydrazyl sequestration values varying between 17.51% and 63.12%, and those of the 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) method between 6.82% and 22.89%. In the antibacterial activity test, only the ethanolic extract showed inhibition against Listeria sp. (at minimum inhibitory concentration [MIC] = 256 µg mL-1). This fraction also presented the highest significant levels of hemolysis (31.88%-52.45%). In summary, the data presented in the study suggest the presence of biocompounds with biotechnological and nutraceutical potential in the D armatus biomass. Future studies may evaluate the inclusion of this biomass in foods in order to increase their biological value.

Alternative microbial-based functional ingredient source for lycopene, beta-carotene, and polyunsaturated fatty acids

The acquisition of carotenoids and polyunsaturated fatty acids (PUFAs) from plants and animals for use as functional ingredients raises concerns regarding productivity and cost; utilization of microorganisms as alternative sources is an option. We proposed to evaluate the production of carotenoids and PUFAs by Rhodopseudomonas faecalis PA2 using different vegetable oils (rice bran oil, palm oil, coconut oil, and soybean oil) as carbon source, different concentrations of yeast extract as nitrogen source at different cultivation time to ensure the best production. Cultivation with soybean oil as source of carbon led to the most significant changes in the fatty acid profile. Compared to the initial condition, the strain cultivated in the optimal conditions (4% soybean oil, 0.35% yeast extract, and 14 days of incubation) showed an increase in μ_max, biomass, carotenoid productivity, and microbial lipids by 102.5%, 52.7%, 33.82%, and 34.78%, respectively. The unsaturated fatty acids content was raised with additional types of PUFAs; omega-3 [alpha-linolenic acid and eicosapentaenoic acid] and omega-6 [linoleic acid and eicosatrienoic acid] fatty acids were identified. The results of ultra high-performance liquid chromatography-electrospray ionization-quadrupole time of flight-mass spectrometry (UHPLC-ESI-QTOF-MS/MS) indicated the molecular formula and mass of bacterial metabolites were identical to those of lycopene and beta-carotene. The untargeted metabolomics revealed functional lipids and several physiologically bioactive compounds. The outcome provides scientific reference regarding carotenoids, PUFAs, and useful metabolites that have not yet been reported in the species Rhodopseudomonas faecalis for further use as a microbial-based functional ingredient.

Microalgal Carotenoids: Therapeutic Application and Latest Approaches to Enhance the Production

Microalgae are microscopic photosynthetic organisms frequently found in fresh and marine water ecosystems. Various microalgal species have been considered a reservoir of diverse health-value products, including vitamins, proteins, lipids, and polysaccharides, and are broadly utilized as food and for the treatment of human ailments such as cancer, cardiovascular diseases, allergies, and immunodeficiency. Microalgae-derived carotenoids are the type of accessory pigment that possess light-absorbing potential and play a significant role in metabolic functions. To date, nearly a thousand carotenoids have been reported, but a very less number of microalgae have been used for the commercial production of carotenoids. This review article briefly discussed the carotenoids of microalgal origin and their therapeutic application. In addition, we have briefly compiled the optimization of culture parameters used to enhance microalgal carotenoid production. In addition, the latest biotechnological approaches used to improve the yields of carotenoid has also been discussed.

Simultaneous 17β-estradiol degradation, carbon dioxide fixation, and carotenoid accumulation by Thermosynechococcus sp. CL-1

Thermosynechococcus sp. CL-1 (TCL-1) has a high potency to utilize CO₂ under extreme conditions including high temperature, alkaline condition, and the occurrence of 17β-estradiol (E2). In this study, TCL-1 cultivation with E2 addition in the range of 0-20 mg/L was combined with various growth arrangements (light intensity and dissolved inorganic nitrogen/DIN level). After 120 h cultivation, the 1.0 mg/L E2, 200 µmol photons/m²/s light intensity, and 5.8 mM available nitrogen performed the best growth with 4.58 ± 0.18 mg/L/h biomass productivity, 94.9 ± 3.3% total estrogen removal, and 11.41 ± 0.11 mg/L/h CO₂ fixation rate. Estrogen degradation was mainly carried out by biodegradation route which started from E2 conversion into estrone/E1 and with only 4-6% influence from the abiotic factors. Compared with the accumulated zeaxanthin, β-carotene was dominantly generated with a productivity of 0.043 ± 0.019 mg/L/h. Therefore, TCL-1 cultivation is an efficient strategy for simultaneous CO₂ fixation, estrogen removal, and carotenoid accumulation as valuable byproducts.

Differential Responses to UV-A Stress Recorded in Carotenogenic Microalgae Haematococcus rubicundus, Bracteacoccus aggregatus, and Deasonia sp

UV-A is the main ultraviolet component of natural (solar) radiation. Despite it, its effect on phototrophs is studied less than UV-B. Effects of UV-A on photosynthetic apparatus of three carotenoid-producing microalgae were elucidated. Photosynthetic activity was studied using chlorophyll fluorescence analysis. Cell extracts were evaluated by absorbance spectroscopy. On the one hand, there were some common features of three strains. In all cases the changes involved PSII primary photochemistry and antennae size. All strains accumulated UV-absorbing polar compounds. On the other hand, some responses were different. Upregulation of non-photochemical quenching was observed only in B. aggregatus BM5/15, whereas in other cases its level was low. H. rubicundus BM7/13 and Deasonia sp. NAMSU 934/2 accumulated secondary carotenoids, whereas B. aggregatus BM5/15 accumulated primary ones. Microscopic features of the cultures were also different. H. rubicundus BM7/13 and Deasonia sp. NAMSU 934/2 were represented mostly by solitaire cells or small cell clusters, lacking their green color; the cells of B. aggregatus BM5/15 formed aggregates from green cells. Cell aggregation could be considered as an additional UV-protecting mechanism. Finally, the strains differed by their viability. B. aggregatus BM5/15 was most resistant to UV-A, whereas massive cell death was observed in two other cultures.

Developing a Chromochloris zofingiensis Mutant for Enhanced Production of Lutein under CO2 Aeration

Microalgae are competitive and commercial sources for health-benefit carotenoids. In this study, a Chromochloris zofingiensis mutant (Cz-pkg), which does not shut off its photosystem and stays green upon glucose treatment, was generated and characterized. Cz-pkg was developed by treating the algal cells with a chemical mutagen as N-methyl-N’-nitro-N-nitrosoguanidine and followed by a color-based colony screening approach. Cz-pkg was found to contain a dysfunctional cGMP-dependent protein kinase (PKG). By cultivated with CO₂ aeration under mixotrophy, the mutant accumulated lutein up to 31.93 ± 1.91 mg L⁻¹ with a productivity of 10.57 ± 0.73 mg L⁻¹ day⁻¹, which were about 2.5- and 8.5-fold of its mother strain. Besides, the lutein content of Cz-pkg could reach 7.73 ± 0.52 mg g⁻¹ of dry weight, which is much higher than that of marigold flower, the most common commercial source of lutein. Transcriptomic analysis revealed that in the mutant Cz-pkg, most of the genes involved in the biosynthesis of lutein and chlorophylls were not down-regulated upon glucose addition, suggesting that PKG may regulate the metabolisms of photosynthetic pigments. This study demonstrated that Cz-pkg could serve as a promising strain for both lutein production and glucose sensing study.

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

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

Transcriptome-wide study in the green microalga Messastrum gracile SE-MC4 identifies prominent roles of photosynthetic integral membrane protein genes during exponential growth stage

The non-model microalga Messastrum gracile SE-MC4 is a potential species for biodiesel production. However, low biomass productivity hinders it from passing the life cycle assessment for biodiesel production. Therefore, the current study was aimed at uncovering the differences in the transcriptome profiles of the microalgae at early exponential and early stationary growth phases and dissecting the roles of specific differential expressed genes (DEGs) involved in cell division during M. gracile cultivation. The transcriptome analysis revealed that the photosynthetic integral membrane protein genes such as photosynthetic antenna protein were severely down-regulated during the stationary growth phase. In addition, the signaling pathways involving transcription, glyoxylate metabolism and carbon metabolism were also down-regulated during stationary growth phase. Current findings suggested that the coordination between photosynthetic integral membrane protein genes, signaling through transcription and carbon metabolism classified as prominent strategies during exponential growth stage. These findings can be applied in genetic improvement of M. gracile for biodiesel application.

Carotenoids from fungi and microalgae: A review on their recent production, extraction, and developments

The demand for carotenoids from natural sources obtained by biological extraction methods is increasing with the development of biotechnology and the continued awareness of food safety. Natural plant-derived carotenoids have a relatively high production cost and are affected by the season, while microbial-derived carotenoids are favored due to their natural, high-efficiency, low production cost, and ease of industrialization. This article reviewed the following aspects of natural carotenoids derived from microorganisms: (1) the structures and properties of main carotenoids; (2) fungal and microalgal sources of the main carotenoids; (3) influencing factors and modes of improvement for carotenoids production; (4) efficient extraction methods for carotenoids; and (5) the commercial value of carotenoids. This review provided a reference and guidance for the development of natural carotenoids derived from microorganisms.

Combined Production of Astaxanthin and β-Carotene in a New Strain of the Microalga Bracteacoccus aggregatus BM5/15 (IPPAS C-2045) Cultivated in Photobioreactor

Carotenoids astaxanthin and β-carotene are widely used natural antioxidants. They are key components of functional food, cosmetics, drugs and animal feeding. They hold leader positions on the world carotenoid market. In current work, we characterize the new strain of the green microalga Bracteacoccus aggregatus BM5/15 and propose the method of its culturing in a bubble-column photobioreactor for simultaneous production of astaxanthin and β-carotene. Culture was monitored by light microscopy and pigment kinetics. Fatty acid profile was evaluated by tandem gas-chromatography-mass spectrometry. Pigments were obtained by the classical two-stage scheme of autotrophic cultivation. At the first, vegetative, stage biomass accumulation occurred. Maximum specific growth rate and culture productivity at this stage were 100-200 mg∙L^-1∙day^-1, and 0.33 day^-1, respectively. At the second, inductive, stage carotenoid synthesis was promoted. Maximal carotenoid fraction in the biomass was 2.2-2.4%. Based on chromatography data, astaxanthin and β-carotene constituted 48 and 13% of total carotenoid mass, respectively. Possible pathways of astaxanthin synthesis are proposed based on carotenoid composition. Collectively, a new strain B. aggregatus BM5/15 is a potential biotechnological source of two natural antioxidants, astaxanthin and β-carotene. The results give the rise for further works on optimization of B. aggregatus cultivation on an industrial scale.

Enhancement of astaxanthin accumulation using black light in Coelastrum and Monoraphidium isolated from Malaysia

Microalgae are important microorganisms which produce potentially valuable compounds. Astaxanthin, a group of xanthophyll carotenoids, is one of the most powerful antioxidants mainly found in microalgae, yeasts, and crustaceans. Environmental stresses such as intense light, drought, high salinity, nutrient depletion, and high temperature can induce the accumulation of astaxanthin. Thus, this research aims to investigate the effect of black light, also known as long-wave ultraviolet radiation or UV-A, as a stressor on the accumulation of astaxanthin as well as to screen the antioxidant property in two tropical green algal strains isolated from Malaysia, Coelastrum sp. and Monoraphidium sp. SP03. Monoraphidium sp. SP03 showed a higher growth rate (0.66 day^-1) compared to that of Coelastrum sp. (0.22 day^-1). Coelastrum sp. showed significantly higher accumulation of astaxanthin in black light (0.999 g mL culture^-1) compared to that in control condition (0.185 g mL^-1). Similarly, Monoraphidium sp. SP03 showed higher astaxanthin content in black light (0.476 g mL culture^-1) compared to that in control condition (0.363 g mL culture^-1). Coelastrum sp. showed higher scavenging activity (30.19%) when cultured in black light condition, indicating a correlation between the antioxidant activity and accumulation of astaxanthin. In this study, black light was shown to possess great potential to enhance the production of astaxanthin in microalgae.

Double-high in palmitic and oleic acids accumulation in a non-model green microalga, Messastrum gracile SE-MC4 under nitrate-repletion and -starvation cultivations

Bioprospecting for biodiesel potential in microalgae primarily involves a few model species of microalgae and rarely on non-model microalgae species. Therefore, the present study determined changes in physiology, oil accumulation, fatty acid composition and biodiesel properties of a non-model microalga Messastrum gracile SE-MC4 in response to 12 continuous days of nitrate-starve (NS) and nitrate-replete (NR) conditions respectively. Under NS, the highest oil content (57.9%) was achieved despite reductions in chlorophyll content, biomass productivity and lipid productivity. However, under both NS and NR, palmitic acid and oleic acid remained as dominant fatty acids thus suggesting high potential of M. gracile for biodiesel feedstock consideration. Biodiesel properties analysis returned high values of cetane number (CN 61.9-64.4) and degree of unsaturation (DU 45.3-57.4) in both treatments. The current findings show the possibility of a non-model microalga to inherit superior ability over model species in oil accumulation for biodiesel development.

Transcription activation of β-carotene biosynthetic genes at the initial stage of stresses as an indicator of the increased β-carotene accumulation in isolated Dunaliella salina strain GY-H13

β-carotene is an efficient antioxidant and its accumulation is an oxidative response to stressors. Dunaliella salina strain GY-H13 is rich in β-carotene under environmental stresses, which was selected as material to understand the molecular mechanism underlying β-carotene biosynthesis. Seven full length cDNA sequences in β-carotene biosynthesis pathway were cloned, including geranylgeranyl pyrophosphate synthase (GGPS), phytoene synthase (PSY), phytoene desaturase (PDS), 15-cis-zeta-carotene isomerase (ZISO), zeta-carotene desaturase (ZDS), prolycopene isomerase (CRTISO), lycopene beta-cyclase (LCYb). The seven protein sequences from the strain GY-H13 showed the highest similarity with other D. salina strains. Especially, PSY, PDS and LCYb protein sequences shared 100 % identity. Phylogenetic analysis indicated all proteins from GY-H13 firstly clustered with those from other D. salina strains with a bootstrap of 100 %. Multiple alignment indicated several distinct conserved motifs such as aspartate-rich domain (ARD), dinucleotide binding domain (DBD), and carotene binding domain (CBD). These motifs are located near ligand-binding pocket, which may be required for the activity of enzyme. Expression levels of these genes and β-carotene content were measured over 24-h cycle, showing clear daily dynamics. All genes were dramatically up-regulated in the morning but the highest accumulation of β-carotene was observed at noon, suggesting a lag-effect between gene transcription and biological response. Furthermore, the accumulation of β-carotene increased under nitrogen deficiency, Cd exposure and high light and decreased under high salinity in a time-dependent manner. No gene of β-carotene biosynthesis was up-regulated by high salinity while most genes were activated by the other stresses at the beginning stage of exposure. Growth inhibition and oxidative damage were also observed under high salinity. Overall, transcription activation of β-carotene biosynthetic genes at the initial stage of stress exposure is a determinant of the increased accumulation of β-carotene in microalgae, which help their survive under harsh environments. The newly isolated D. salina strain GY-H13 would be a promising microalgae model for investigating the molecular mechanism of stress-induced β-carotene biosynthesis.

HPLC-PDA-MS/MS as a strategy to characterize and quantify natural pigments from microalgae

Interest in pigment composition of microalgae species is growing as new natural pigments sources are being sought. However, we still have a limited number of species of microalgae exploited to obtain these compounds. Considering these facts, the detailed composition of carotenoids and chlorophylls of two species of green microalgae (Chlorella sorokiniana and Scenedesmus bijuga) were determined for the first time by high-performance liquid chromatography coupled to diode array and mass spectrometry detectors (HPLC-PDA-MS/MS). A total of 17 different carotenoids were separated in all the extracts. Most of the carotenoids present in the two microalgae species are xanthophylls. C. sorokiniana presented 11 carotenoids (1408.46 μg g⁻¹), and S. bijuga showed 16 carotenoids (1195.75 μg g⁻¹). The main carotenoids detected in the two microalgae were all-trans-lutein and all-trans-β-carotene. All-trans-lutein was substantially higher in C. sorokiniana (59.01%), whereas all-trans-β-carotene was detected in higher quantitative values in S. bijuga (13.88%). Seven chlorophyll compounds were identified in both strains with different proportions in each species. Concentrations of chlorophyll representing 7.6% and 10.2% of the composition of the compounds present in the biomass of C. sorokiniana and S. bijuga, respectively. Relevant chlorophyll compounds are reported for the first time in these strains. The data obtained provide significant insights for microalgae pigment composition databases.

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The carotenoids and chlorophylls profile by HPLC-PDA-MS of microalgae is reported.

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Microalgae showed species-specific pigments profiles.

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17 carotenoids and 7 chlorophylls were identified and quantified in details.

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The quantitative profile presented a prevalence of chlorophylls over carotenoids.

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Green microalgae are proposed as an interesting natural source of food pigments.