Biorefinery of Dunaliella salina: Sustainable recovery of carotenoids, polar lipids and glycerol

Genetic Engineering and Innovative Cultivation Strategies for Enhancing the Lutein Production in Microalgae

Carotenoids, with their diverse biological activities and potential pharmaceutical applications, have garnered significant attention as essential nutraceuticals. Microalgae, as natural producers of these bioactive compounds, offer a promising avenue for sustainable and cost-effective carotenoid production. Despite the ability to cultivate microalgae for its high-value carotenoids with health benefits, only astaxanthin and β-carotene are produced on a commercial scale by Haematococcus pluvialis and Dunaliella salina, respectively. This review explores recent advancements in genetic engineering and cultivation strategies to enhance the production of lutein by microalgae. Techniques such as random mutagenesis, genetic engineering, including CRISPR technology and multi-omics approaches, are discussed in detail for their impact on improving lutein production. Innovative cultivation strategies are compared, highlighting their advantages and challenges. The paper concludes by identifying future research directions, challenges, and proposing strategies for the continued advancement of cost-effective and genetically engineered microalgal carotenoids for pharmaceutical applications.

Is the carotenoid production from Phaffia rhodozyma yeast genuinely sustainable? a comprehensive analysis of biocompatibility, environmental assessment, and techno-economic constraints

Microorganisms, such as yeasts, filamentous fungi, bacteria, and microalgae, have gained significant attention due to their potential in producing commercially valuable natural carotenoids. In recent years, Phaffia rhodozyma yeasts have emerged as intriguing non-conventional sources of carotenoids, particularly astaxanthin and β-carotene. However, the shift from academic exploration to effective industrial implementation has been challenging to achieve. This study aims to bridge this gap by assessing various scenarios for carotenoid production and recovery. It explores the use of ionic liquids (ILs) and bio-based solvents (ethanol) to ensure safe extraction. The evaluation includes a comprehensive analysis involving Life Cycle Assessment (LCA), biocompatibility assessment, and Techno-Economic Analysis (TEA) of two integrated technologies that utilize choline-based ILs and ethanol (EtOH) for astaxanthin (+β-carotene) recovery from P. rhodozyma cells. This work evaluates the potential sustainability of integrating these alternative solvents within a yeast-based bioeconomy.

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.

Challenges in Functional Food Products with the Incorporation of Some Microalgae

Much attention has been given to the use of microalgae to produce functional foods that have valuable bioactive chemicals, including essential amino acids, polyunsaturated fatty acids, vitamins, carotenoids, fiber, and minerals. Microalgal biomasses are increasingly being used to improve the nutritional values of foods because of their unique nutrient compositions that are beneficial to human health. Their protein content and amino acid composition are the most important components. The microalgal biomass used in the therapeutic supplement industry is dominated by bio-compounds like astaxanthin, β-carotene, polyunsaturated fatty acids like eicosapentaenoic acid and docosahexaenoic acid, and polysaccharides such as β-glucan. The popularity of microalgal supplements is growing because of the health benefits of their bioactive substances. Moreover, some microalgae, such as Dunaliella, Arthrospira (Spirulina), Chlorella, and Haematococcus, are commonly used microalgal species in functional food production. The incorporation of microalgal biomass leads not only to enhanced nutritional value but also to improved sensory quality of food products without altering their cooking or textural characteristics. Microalgae, because of their eco-friendly potential, have emerged as one of the most promising and novel sources of new functional foods. This study reviews some recent and relevant works, as well as the current challenges for future research, using different methods of chemical modification in foods with the addition of a few commercial algae to allow their use in nutritional and sensory areas. It can be concluded that the production of functional foods through the use of microalgae in foods has become an important issue.

Microbes of biotechnological importance in acidic saline lakes in the Yilgarn Craton, Western Australia

Acidic salt lakes are environments that harbor an array of biologically challenging conditions. Through 16S rRNA, 18S rRNA, and ITS amplicon sequencing of eight such lakes across the Yilgarn Craton of Western Australia, we aim to understand the microbial ecology of these lakes with a focus on iron- and sulfur-oxidizing and reducing microorganisms that have theoretical application in biomining industries. In spite of the biological challenges to life in these lakes, the microbial communities were highly diverse. Redundancy analysis of soil samples revealed sulfur, ammonium, organic carbon, and potassium were significant diversities of the microbial community composition. The most abundant microbes with a hypothetical application in biomining include the genus 9 M32 of the Acidithiobacillus family, Alicyclobacillus and Acidiphilium, all of which are possible iron- and/or sulfur-oxidizing bacteria. It is evident through this study that these lakes harbor multiple organisms with potential in biomining industries that should be exploited and studied further.

Using wastewater as a cultivation alternative for microalga Dunaliella salina: Potentials and challenges

Untreated or poorly treated wastewater still represents environmental issues world-widely. Wastewater, especially saline wastewater treatment, is still primarily associated with high costs from physical and chemical processes, as high salinity hinders biological treatment. One favourable way is to find the suitable biological pathways and organisms to improve the biological treatment efficiency. In this context, halophilic microorganisms could be strong candidates to address the economics and effectiveness of the saline wastewater treatment process. Dunaliella salina is a photoautotrophic microalga that grows in saline environments. It is known for producing marketable bio-compounds such as carotenoids, lipids, and proteins. A biological treatment based on D. salina cultivation offers the opportunity to treat saline wastewater, reducing the threat of possible eutrophication from inappropriate discharge. At the same time, D. salina cultivation could yield compounds of industrial relevance to turn saline wastewater treatment into a profitable and sustainable process. Most research on D. salina has primarily focused on bioproduct generation, leaving thorough reviews of its application in wastewater treatment inadequate. This paper discusses the future challenges and opportunities of using D. salina to treat wastewater from different sources. The main conclusions are (1) D. salina effectively recovers some heavy metals (driven by metal binding capacity and exposure time) and nutrients (driven by pH, their bioavailability, and functional groups in the cell); (2) salinity plays a significant role in bioproducts generation, and (3) wastewater can be combined with the generation of bioproducts.

In vivo neuroprotective capacity of a Dunaliella salina extract - comprehensive transcriptomics and metabolomics study

In this study, an exhaustive chemical characterization of a Dunaliella salina (DS) microalga extract obtained using supercritical fluids has been performed, and its neuroprotective capacity has been evaluated in vivo using an Alzheimer's disease (AD) transgenic model of Caenorhabditis elegans (strain CL4176). More than 350 compounds were annotated in the studied DS extract, with triacylglycerols, free fatty acids (FAs), carotenoids, apocarotenoids and glycerol being the most abundant. DS extract significantly protects C. elegans in a dose-dependent manner against Aβ-peptide paralysis toxicity, after 32 h, 53% of treated worms at 50 µg/mL were not paralyzed. This concentration was selected to further evaluate the transcriptomics and metabolomics changes after 26 h by using advanced analytical methodologies. The RNA-Seq data showed an alteration of 150 genes, mainly related to the stress and detoxification responses, and the retinol and lipid metabolism. The comprehensive metabolomics and lipidomics analyses allowed the identification of 793 intracellular metabolites, of which 69 were significantly altered compared to non-treated control animals. Among them, different unsaturated FAs, lysophosphatidylethanolamines, nucleosides, dipeptides and modified amino acids that have been previously reported as beneficial during AD progression, were assigned. These compounds could explain the neuroprotective capacity observed, thus, providing with new evidences of the protection mechanisms of this promising extract.

Extremophiles: the species that evolve and survive under hostile conditions

Extremophiles possess unique cellular and molecular mechanisms to assist, tolerate, and sustain their lives in extreme habitats. These habitats are dominated by one or more extreme physical or chemical parameters that shape existing microbial communities and their cellular and genomic features. The diversity of extremophiles reflects a long list of adaptations over millions of years. Growing research on extremophiles has considerably uncovered and increased our understanding of life and its limits on our planet. Many extremophiles have been greatly explored for their application in various industrial processes. In this review, we focused on the characteristics that microorganisms have acquired to optimally thrive in extreme environments. We have discussed cellular and molecular mechanisms involved in stability at respective extreme conditions like thermophiles, psychrophiles, acidophiles, barophiles, etc., which highlight evolutionary aspects and the significance of extremophiles for the benefit of mankind.

Role of secondary metabolites in distressed microalgae

Proficient photosynthetic microalgae/cyanobacteria produce a remarkable amount of various biomolecules. Secondary metabolites (SM) represent high value products for global biotrend application. Production improvement can be achieved by nutritional, environmental, and physiological stress as a first line tools for their stimulation. In recent decade, an increasing interest in algal stress biology and omics techniques have deepened knowledge in this area. However, deep understanding and connection of specific stress elucidator are missing. Hence, the present review summarizes recent evidence with an emphasis on the carotenoids, phenolic, and less-discussed compounds (glycerol, proline, mycosporins-like amino acids). Even when they are synthesized at very low concentrations, it highlights the need to expand knowledge in this area using genome-editing tools and omics approaches.

Effect of culture conditions at lab-scale on metabolite composition and antibacterial and antibiofilm activities of Dunaliella tertiolecta

Dunaliella tertiolecta RCC6 was cultivated indoors in glass bubble column photobioreactors operated under batch and semi-continuous regimens and using two different conditions of light and temperature. Biomass was harvested by centrifugation, frozen, and then lyophilized. The soluble material was obtained by sequential extraction of the lyophilized biomass with solvents with a gradient of polarity (hexane, ethyl acetate, and methanol) and its metabolic composition was investigated through nuclear magnetic resonance (NMR) spectroscopy. The effect of light on chlorophyll biosynthesis was clearly shown through the relative intensities of the ¹ H NMR signals due to pheophytins. The highest signal intensity was observed for the biomasses obtained at lower light intensity, resulting in a lower light availability per cell. Under high temperature and light conditions, the ¹ H NMR spectra of the hexane extracts showed an incipient accumulation of triacylglycerols. In these conditions and under semi-continuous regimen, an enhancement of β-carotene and sterols production was observed. The antibacterial and antibiofilm activities of the extracts were also tested. Antibacterial activity was not detected, regardless of culture conditions. In contrast, the minimal biofilm inhibitory concentrations (MBICs) against Escherichia coli for the hexane extract obtained under semi-continuous regimen using high temperature and irradiance conditions was promising.

Progress towards a targeted biorefinery of Chromochloris zofingiensis: a review

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

Supplementary Information

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

Carotenoids: Dietary Sources, Extraction, Encapsulation, Bioavailability, and Health Benefits-A Review of Recent Advancements

Natural carotenoids (CARs), viz. β-carotene, lutein, astaxanthin, bixin, norbixin, capsanthin, lycopene, canthaxanthin, β-Apo-8-carotenal, zeaxanthin, and β-apo-8-carotenal-ester, are being studied as potential candidates in fields such as food, feed, nutraceuticals, and cosmeceuticals. CAR research is advancing in the following three major fields: (1) CAR production from natural sources and optimization of its downstream processing; (2) encapsulation for enhanced physical and chemical properties; and (3) preclinical, clinical, and epidemiological studies of CARs' health benefits. This review critically discusses the recent developments in studies of the chemistry and antioxidant activity, marketing trends, dietary sources, extraction, bioaccessibility and bioavailability, encapsulation methods, dietary intake, and health benefits of CARs. Preclinical, clinical, and epidemiological studies on cancer, obesity, type 2 diabetes (T2D), cardiovascular diseases (CVD), osteoporosis, neurodegenerative disease, mental health, eye, and skin health are also discussed.

Carotenoid Production from Microalgae: The Portuguese Scenario

Microalgae have an outstanding capacity to efficiently produce value-added compounds. They have been inspiring researchers worldwide to develop a blue biorefinery, supporting the development of the bioeconomy, tackling the environmental crisis, and mitigating the depletion of natural resources. In this review, the characteristics of the carotenoids produced by microalgae are presented and the downstream processes developed to recover and purify them are analyzed, considering their main applications. The ongoing activities and initiatives taking place in Portugal regarding not only research, but also industrialization under the blue biorefinery concept are also discussed. The situation reported here shows that new techniques must be developed to make microalgae production more competitive. Downstream pigment purification technologies must be developed as they may have a considerable impact on the economic viability of the process. Government incentives are needed to encourage a constructive interaction between academics and businesses in order to develop a biorefinery that focuses on high-grade chemicals.

Optimization of Extraction Conditions of Carotenoids from Dunaliella parva by Response Surface Methodology

Extraction conditions can exert a remarkable influence on extraction efficiency. The aim of this study was to improve the extraction efficiency of carotenoids from Dunaliella parva (D. parva). Dimethyl sulfoxide (DMSO) and 95% ethanol were used as the extraction solvents. The extraction time, extraction temperature and the proportions of mixed solvent were taken as influencing factors, and the experimental scheme was determined by Central Composite Design (CCD) of Design Expert 10.0.4.0 to optimize the extraction process of carotenoids from D. parva. The absorbance values of the extract at 665 nm, 649 nm and 480 nm were determined by a microplate spectrophotometer, and the extraction efficiency of carotenoids was calculated. Analyses of the model fitting degree, variance and interaction term 3D surface were performed by response surface analysis. The optimal extraction conditions were as follows: extraction time of 20 min, extraction temperature of 40 °C, and a mixed solvent ratio (DMSO: 95% ethanol) of 3.64:1. Under the optimal conditions, the actual extraction efficiency of carotenoids was 0.0464%, which was increased by 18.19% (the initial extraction efficiency of 0.03926%) with a lower extraction temperature (i.e., lower energy consumption) compared to the standard protocol.

Overview of Membrane Science and Technology in Portugal

Membrane research in Portugal is aligned with global concerns and expectations for sustainable social development, thus progressively focusing on the use of natural resources and renewable energy. This review begins by addressing the pioneer work on membrane science and technology in Portugal by the research groups of Instituto Superior Técnico-Universidade de Lisboa (IST), NOVA School of Science and Technology-Universidade Nova de Lisboa (FCT NOVA) and Faculdade de Engenharia-Universidade do Porto (FEUP) aiming to provide an historical perspective on the topic. Then, an overview of the trends and challenges in membrane processes and materials, mostly in the last five years, involving Portuguese researchers, is presented as a contribution to a more sustainable water-energy-material-food nexus.

Reuse of sea water reverse osmosis brine to produce Dunaliella salina based β-carotene as a valuable bioproduct: A circular bioeconomy perspective

Due to population growth and global warming, the use of the sea water reverse osmosis process to obtain freshwater is increasing rapidly. A sustainable method with low environmental impact is limited for the management of brine with a high salt content, which is released as a result of the process. Some microalgae species can grow in salty environments and produce β-carotene. This study aims to evaluate the commercial potential of β-carotene production from microalgae grown in sea water reverse osmosis brine from a bioeconomy perspective. Synthetic media are often used for the production of β-carotene from algae, the use of sea water reverse osmosis brine is not common and the commercial potential of this application has not been evaluated before. In terms of the development of the β-carotene market, the strengths and weaknesses of the process, opportunities, and threats are thoroughly examined in this report. Also, with the use of sea water reverse osmosis, a daily 750 tons of algal β-carotene can be produced. The biotechnological production of microalgal β-carotene and the reuse of salt water within the scope of circular bioeconomy are seen as a sustainable solution due to the fact that the strengths of the process are dominant, and the market value of natural β-carotene is increasing day by day.

Continuous design and economic analysis of a Sargassum muticum biorefinery process

This work assesses scale effects in designing a biorefinery from Sargassum muticum seaweed by applying a detailed process modeling methodology. Two process conversion units were simulated: one considering anaerobic digestion steps for producing biogas and generating electricity (base project), and the other with residual seaweed solids sold as fertilizer (alternative project). A comprehensive economic analysis was performed to estimate the minimum selling price of the process's main product (fucoidan extract). Results indicated that capital expenditures are up to 12.7% times higher in the base project. Minimum selling prices of the fucoidan extract product demonstrate the biorefinery's economies of scale for both projects. Seaweed's low methane potential reduces the economic attractiveness of electricity generation from biogas in the base project. Conversely, organic fertilizer price was more influential in the alternative project. Nonetheless, risk analyses show similar results for both scenarios, mainly due to fucoidan extract selling price and CAPEX estimates uncertainties.

Microalgal secondary metabolite productions as a component of biorefinery: A review

The interest in developing microalgae for industrial use has been increasing because of concerns about the depletion of petroleum resources and securing sustainable energy sources. Microalgae have high biomass productivity and short culture periods. However, despite these advantages, various barriers need to be overcome for industrial applications. Microalgal cultivation has a high unit price, thus rendering industrial application difficult. It is indispensably necessary to co-produce their primary and secondary metabolites to compensate for these shortcomings. In this regard, this article reviews the following aspects, (1) co-production of primary and secondary metabolites in microalgae, (2) induction methods for the promotion of the biosynthesis of secondary metabolites, and (3) perspectives on the co-production and co-extraction of primary and secondary metabolites. This paper presents various approaches for producing useful metabolites from microalgae and suggests strategies that can be utilized for the co-production of primary and secondary metabolites.

Enhanced β-carotene and Biomass Production by Induced Mixotrophy in Dunaliella salina across a Combined Strategy of Glycerol, Salinity, and Light

Current mixotrophic culture systems for Dunaliella salina have technical limitations to achieve high growth and productivity. The purpose of this study was to optimize the mixotrophic conditions imposed by glycerol, light, and salinity that lead to the highest biomass and β-carotene yields in D. salina. The combination of 12.5 mM glycerol, 3.0 M salinity, and 50 μmol photons m⁻² s⁻¹ light intensity enabled significant assimilation of glycerol by D. salina and consequently enhanced growth (2.1 × 10⁶ cell mL⁻¹) and β-carotene accumulation (4.43 pg cell⁻¹). The saline and light shock induced the assimilation of glycerol by this microalga. At last stage of growth, the increase in light intensity (300 μmol photons m⁻² s⁻¹) caused the β-carotene to reach values higher than 30 pg cell⁻¹ and tripled the β-carotene values obtained from photoautotrophic cultures using the same light intensity. Increasing the salt concentration from 1.5 to 3.0 M NaCl (non-isosmotic salinity) produced higher growth and microalgal β-carotene than the isosmotic salinity 3.0 M NaCl. The mixotrophic strategy developed in this work is evidenced in the metabolic capability of D. salina to use both photosynthesis and organic carbon, viz., glycerol that leads to higher biomass and β-carotene productivity than that of an either phototrophic or heterotrophic process alone. The findings provide insights into the key role of exogenous glycerol with a strategic combination of salinity and light, which evidenced unknown roles of this polyol other than that in osmoregulation, mainly on the growth, pigment accumulation, and carotenogenesis of D. salina.

Comparative morphological, physiological, biochemical and genomic studies reveal novel genes of Dunaliella bioculata and D. quartolecta in response to salt stress

BACKGROUND

Salinity is an essential abiotic stress in plants. Dunaliella is a genus of high-salt-tolerant microalgae. The present study aimed to compare the characterizations of D. bioculata and D. quartolecta at different levels and investigate novel genes response to salt stress.

METHODS AND RESULTS

High chlorophyll contents were detected in D. bioculata on the 35^th d of salt stress, while high lipid and carotenoid contents were detected in D. quartolecta via morphological and biochemical analyses. Physiological analysis showed that D. quartolecta cells had a smaller increase in osmotic potential, a smaller decrease in the Na+/K+ ratio and photochemical efficiency (Fv/Fm), and a lower relative conductivity than D. bioculata cells. The genomic lengths of D. quartolecta and D. bioculata were 396,013,629 bp (scaffold N50 = 1954 bp) and 427,667,563 bp (scaffold N50 = 3093 bp) via high-throughput sequencing and de novo assembly, respectively. Altogether, 25,751 and 26,620 genes were predicted in their genomes by annotation analysis with various biodatabases. The D. bioculata genome showed more segmental duplication events via collinearity analysis. More single nucleotide polymorphisms and insertion-deletion variants were detected in the D. bioculata genome. Both algae, which showed a close phylogenetic relationship, may undergo positive selection via bioinformatics analysis. A total of 382 and 85 novel genes were screened in D. bioculata and D. quartolecta, with 138 and 51 enriched KEGG pathways, respectively. Unlike the novel genes adh1, hprA and serA, the relative expression of livF and phbB in D. bioculata was markedly downregulated as salinity increased, as determined by qPCR analysis. The relative expression of leuB, asd, pstC and proA in D. quartolecta was markedly upregulated with the same salinity increase.

CONCLUSION

Dunaliella quartolecta is more halophilic than D. bioculata, with more effective responses to high salt stress based on the multiphase comparative data.

Beta-carotene and its protective effect on gastric cancer

Beta-carotene is an important natural pigment that is very beneficial to human health. It is widely found in vegetables and fruits. The three main functions are antioxidant effects, cell gap junction-related functions and immune-related functions. Because of its diverse functions, beta-carotene is believed to prevent and treat many chronic diseases. Gastric cancer is one of the most important diseases it can treat. Gastric cancer is a type of cancer with a high incidence. Its etiology varies, and the pathogenesis is complex. Gastric cancer seriously affects human health. The role of beta-carotene, a natural nutrient, in gastric cancer has been explored by many researchers, including molecular mechanisms and epidemiological studies. Molecular studies have mainly focused on oxidative stress, cell cycle, signal transduction pathways and immune-related mechanisms of beta-carotene in gastric cancer. Many epidemiological surveys and cohort studies of patients with gastric cancer have been conducted, and the results of these epidemiological studies vary due to the use of different research methods and analysis of different regions. This paper will summarize the results of these studies, mainly in terms of molecular mechanisms and epidemiological research results, which will provide a systematic basis for future studies of the treatment and prognosis of gastric cancer. This paper will help researchers identify new research directions.

Transcriptomic sequencing reveals the response of Dunaliella salina to copper stress via the increased photosynthesis and carbon mechanism

Copper (Cu) is one of the essential microelements for plants and algae. It can stimulate growth and photosynthesis at low concentration but inhibit them at higher concentration. The knowledge of molecular response mechanisms to copper stress in green algae is still limited. The responses of the green algae Dunaliella salina to Cu stress were studied using the physiochemical indexes and RNA-seq analysis. The physiochemical indexes such as growth rate, the content of chlorophyll and soluble sugar, photosynthesis and peroxidase activity were all changed in D. salina under Cu stress. In addition, a total of 3799 differentially expressed genes (DEGs) were identified between the control and Cu-treated group. Among these, 2350 unigenes were up-regulated whereas 1449 were down-regulated. Here, the DEGs encoding proteins relevant to photosynthesis, carbon assimilation and carbohydrate mechanism were significantly up-regulated in the Cu-treated group. In addition, the unigenes encoding proteins involved in the antioxidant system and heat shock proteins were also up-regulated, and these were consistent with the expression patterns based on TPM (transcripts per million) values. This study shows that the enhanced growth and photosynthesis and carbon mechanism in D. salina can be triggered by copper, which will lay a firm foundation for future breeding and carotenoid production, further highlighting the underlying application of D. salina as a functional food.

Strategies for enhancing terpenoids accumulation in microalgae

Terpenoids represent one of the largest class of chemicals in nature, which play important roles in food and pharmaceutical fields due to diverse biological and pharmacological activities. Microorganisms are recognized as a promising source of terpenoids due to its short growth cycle and sustainability. Importantly, microalgae can fix inorganic carbon through photosynthesis for the growth of themselves and the biosynthesis of various terpenoids. Moreover, microalgae possess effective biosynthesis pathways of terpenoids, both the eukaryotic mevalonic acid (MVA) pathway and the prokaryotic methyl-D-erythritol 4-phosphate (MEP) pathway. In recent years, various genetic engineering strategies have been applied to increase target terpenoid yields, including overexpression of the rate-limited enzymes and inhibition of the competing pathways. However, since gene-editing tools are only built in some model microalgae, fermentation strategies that are easier to be operated have been widely successful in promoting the production of terpenoids, such as changing culture conditions and addition of chemical additives. In addition, an economical and effective downstream process is also an important consideration for the industrial production of terpenoids, and the solvent extraction and the supercritical fluid extraction method are the most commonly used strategies, especially in the industrial production of β-carotene and astaxanthin from microalgae. In this review, recent advancements and novel strategies used for terpenoid production are concluded and discussed, and new insights to move the field forward are proposed. KEY POINTS: • The MEP pathway is more stoichiometrically efficient than the MVA pathway. • Advanced genetic engineering and fermentation strategies can increase terpene yield. • SFE has a higher recovery of carotenoids than solvent extraction.

Algae as an attractive source for cosmetics to counter environmental stress

In recent times, a considerable amount of evidence has come to light regarding the effect that air pollution has on skin conditions. The human skin is the chief protection we have against environmental harm, whether biological, chemical, or physical. The stress from these environmental factors, along with internal influences, can be a cause of skin aging and enlarged pores, thinner skin, skin laxity, wrinkles, fine lines, dryness, and a more fragile dermal layer. This knowledge has led to greater demand for skin cosmetics and a requirement for natural raw ingredients with a high degree of safety and efficiency in combating skin complications. Recent developments in green technology have made the employment of naturally occurring bioactive compounds more popular, and novel extraction methods have ensured that the use of these compounds has greater compatibility with sustainable development principles. Thus, there is a demand for investigations into efficient non-harmful naturally occurring raw ingredients; compounds derived from algae could be beneficial in this area. Algae, both macroalgae and microalgae, consists of waterborne photosynthetic organisms that are potentially valuable as they have a range of bioactive compounds in their composition. Several beneficial metabolites can be obtained from algae, such as antioxidants, carotenoids, mycosporine-like amino acids (MAA), pigments, polysaccharides, and scytonemin. Various algae strains are now widely employed in skincare products for various purposes, such as a moisturizer, anti-wrinkle agent, texture-enhancing agents, or sunscreen. This research considers the environmental stresses on human skin and how they may be mitigated using cosmetics created using algae; special attention will be paid to external factors, both generally and specifically (amongst them light exposure and pollutants).

Current developments on the application of microbial carotenoids as an alternative to synthetic pigments

Microbial carotenoids have attracted rising interest from several industries as a sustainable alternative to substitute the synthetic ones. Traditionally, carotenoids available in the market are obtained by the chemical route using nonrenewable sources (petrochemicals), revealing the negative impact on the environment and consumers. The most promising developments in the upstream and downstream processes of microbial carotenoids are reviewed in this work. The use of agro-based raw materials for bioproduction, and alternative solvents such as biosolvents, deep eutectic solvents, and ionic liquids for the recovery/polishing of microbial carotenoids were also reviewed. The principal advances in the field, regarding the biorefinery and circular economy concepts, were also discussed for a better understanding of the current developments. This review provides comprehensive overview of the hot topics in the field besides an exhaustive analysis of the main advantages/drawbacks and opportunities regarding the implementation of microbial carotenoids in the market.

Toward the Enhancement of Microalgal Metabolite Production through Microalgae-Bacteria Consortia

Engineered mutualistic consortia of microalgae and bacteria may be a means of assembling a novel combination of metabolic capabilities with potential biotechnological advantages. Microalgae are promising organisms for the sustainable production of metabolites of commercial interest, such as lipids, carbohydrates, pigments, and proteins. Several studies reveal that microalgae growth and cellular storage of these metabolites can be enhanced significantly by co-cultivation with growth-promoting bacteria. This review summarizes the state of the art of microalgae-bacteria consortia for the production of microalgal metabolites. We discuss the current knowledge on microalgae-bacteria mutualism and the mechanisms of bacteria to enhance microalgae metabolism. Furthermore, the potential routes for a microalgae-bacteria biorefinery are outlined in an attempt to overcome the economic failures and negative energy balances of the existing production processes.

Microalgae Encapsulation Systems for Food, Pharmaceutical and Cosmetics Applications

Microalgae are microorganisms with a singular biochemical composition, including several biologically active compounds with proven pharmacological activities, such as anticancer, antioxidant and anti-inflammatory activities, among others. These properties make microalgae an interesting natural resource to be used as a functional ingredient, as well as in the prevention and treatment of diseases, or cosmetic formulations. Nevertheless, natural bioactives often possess inherent chemical instability and/or poor solubility, which are usually associated with low bioavailability. As such, their industrial potential as a health-promoting substance might be severely compromised. In this context, encapsulation systems are considered as a promising and emerging strategy to overcome these shortcomings due to the presence of a surrounding protective layer. Diverse systems have already been reported in the literature for natural bioactives, where some of them have been successfully applied to microalgae compounds. Therefore, this review focuses on exploring encapsulation systems for microalgae biomass, their extracts, or purified bioactives for food, pharmaceutical, and cosmetic purposes. Moreover, this work also covers the most common encapsulation techniques and types of coating materials used, along with the main findings regarding the beneficial effects of these systems.

Effects of different abiotic stresses on carotenoid and fatty acid metabolism in the green microalga Dunaliella salina Y6

Purpose

Under different abiotic-stress conditions, the unicellular green microalga Dunaliella salina accumulates large amounts of carotenoids which are accompanied by fatty acid biosynthesis. Carotenoids and fatty acids both possess long carbon backbones; however, the relationship between carotenoid and fatty acid metabolism is controversial and remains poorly understood in microalgae.

Methods

In this study, we investigated the growth curves and the β-carotene, lutein, lipid, and fatty acid contents of D. salina Y6 grown under different abiotic-stress conditions, including high light, nitrogen depletion, and high salinity.

Results

Both high-salinity and nitrogen-depleted conditions significantly inhibited cell growth. Nitrogen depletion significantly induced β-carotene accumulation, whereas lutein production was promoted by high light. The accumulation of lipids did not directly positive correlate with β-carotene and lutein accumulation under the three tested abiotic-stress conditions, and levels of only a few fatty acids were increased under specific conditions.

Conclusion

Our data indicate that cellular β-carotene accumulation in D. salina Y6 positive correlates with accumulation of specific fatty acids (C16:0, C18:3n3, C14:0, and C15:0) rather than with total fatty acid content under different abiotic stress conditions.

100 Years Later, What Is New in Glycerol Bioproduction?

Industrial production of glycerol by yeast, which began during WWI in the so-called Neuberg fermentation, was the first example of metabolic engineering. However, this process, based on bisulfite addition to fermentation liquid, has many drawbacks and was replaced by other methods of glycerol production. Osmotolerant yeasts and other microorganisms that do not require addition of bisulfite to steer cellular metabolism towards glycerol synthesis have been discovered or engineered. Because the glycerol market is expected to reach 5 billion US$ by 2024, microbial fermentation may again become a promising way to produce glycerol. This review summarizes some problems and perspectives on the production of glycerol by natural or engineered eukaryotic and prokaryotic microorganisms.