Driving into the Factory of Docosahexaenoic Acid (DHA), Microalgae

Abstract

Microalgae, with their rapid growth and cost-effective cultivation, have emerged as a potent source of bioactive compounds, including lipids. Docosahexaenoic acid (DHA), an omega-3 polyunsaturated fatty acid, is an important fraction of microalgal lipids, which holds a crucial place in human nutrition and health. This chapter underscores microalgae’s potential as a prolific factory for DHA production. Limited availability of conventional sources has stimulated interest in sustainable alternatives, with microalgae proving to be an effective solution. Microalgae can synthesize DHA de novo, eliminating the need for resource-intensive intermediaries. Optimization of cultivation conditions, including light intensity and nutrient availability, has boosted DHA production. Genetic engineering techniques enhance yields by overexpressing key biosynthetic genes, while innovative cultivation strategies such as mixotrophic and phototrophic modes increase biomass accumulation and DHA content. Biorefinery approaches utilize residual biomass for value-added product production, enhancing overall sustainability. By harnessing microalgae’s inherent capabilities through cultivation optimization, genetic manipulation, and innovative processing, a reliable and sustainable DHA source is established, promoting enhanced human health and nutrition to meet the growing demand for this essential nutrient.

1. Introduction

The essential fatty acids has garnered substantial attention due to their pivotal role in maintaining optimal health and well-being. Among these, docosahexaenoic acid (DHA), an omega-3 very-long-chain (VLC) fatty acid, has emerged as a compound of paramount importance with diverse physiological benefits [1, 2, 3]. As our knowledge of DHA advantages expands, the discrepancy between the recommended DHA dietary intake and its actual consumption gains more attention [4]. With the growing global population and occurrences of chronic diseases, the demand for DHA is set to increase [5]. This raises the need to explore innovative and sustainable sources for DHA production, especially considering the declining availability of traditional marine sources and the environmental concerns associated with overfishing [6]. In this context, microalgae have emerged as an intriguing and promising solution to bridge the gap between DHA demand and supply. Microalgae are unicellular photosynthetic organisms abundant in various aquatic ecosystems that possess a remarkable ability to synthesize and accumulate lipids rich in DHA [7]. This unique characteristic has attracted the attention of researchers and industries prompting a comprehensive exploration of their potential as a reliable and sustainable source of DHA.

The journey into DHA production from microalgae is a multidisciplinary endeavor. It involves the seamless integration of biology, biotechnology, engineering, and environmental science. Scientists delve into the intricate mechanisms within microalgae cells, deciphering the molecular basis and metabolic pathways responsible for DHA synthesis [8, 9]. This knowledge serves as the blueprint for enhancing DHA yields through genetic engineering and optimization of growth conditions. Moreover, the cultivation of microalgae occurs within controlled environments. These cultivation systems mimic the natural conditions necessary for optimal growth, ensuring that microalgae flourish and efficiently convert sunlight and nutrients into DHA. Combining advanced technology and ecological considerations transforms microalgae into miniature biorefineries, producing DHA while minimizing resource consumption and waste generation.

2. Potential of microalgae for sustainable lipid production

Lipids are significant chemical compounds produced by microalgae (up to 70%) [10, 11]. The accumulation of high levels of lipids with various and unique fatty acid cprofile in microalgae nominates them as a viable and sustainable source for valuable lipid production [12]. The world is currently facing the significant challenge of the population growth and paucity of food and eco-friendly fuel sources. Interest in the production of lipid or valuable fatty acids (FAs) from oleaginous microalgae as a potential stock is rooted in their higher lipid content and fast growth rate [13]. Microalgae have several other advantages including high efficiency in photosynthesis, carbon dioxide sequestration, simple growth requirements, efficient land utilization, ability to grow in wastewater, and the year-round harvest. Compared with the land food sources, microalgae do not require arable land or potable water for growth; this avoids the competition for limited resources [14, 15, 16]. Microalgae produce 10–400 times more energy per acre in comparison to land plants [16]. The lipids and fatty acids from microalgae are considered as energy storage boxes, involved in metabolic processes and cell membrane-related functions. Unlike traditional sources of lipids, such as vegetable oils and animal fats, microalgae produce lipids rich in highly unsaturated fatty acids (HUFAs). They are essential and valuable fatty acids not commonly synthesized in our body and needed to be obtained by diet.

3. Heterogeneity of algal fatty acids

Tremendous species diversity in microalgae provides a rich reservoir with different characteristics of lipid composition and yield. There is a recent trend toward the evaluation of different microalgae and their lipidomic profiling. As befits their variable morphology and physiology, microalgae contain miscellaneous and unique acyl lipid composition [17]. Further, adaptation to adverse ecosystems and diverse habitats has reflected in exceptional variety of lipid patterns and unique fatty acid profile in microalgae [15, 17]. They synthesize a group of essential fatty acids that are not synthesized by other plants, animals, and humans [18].

Unlike traditional sources of lipids, such as vegetable oils and animal fats, microalgae produce lipids rich in highly unsaturated fatty acids (HUFAs). Fatty acids of HUFA as part of complex lipids might be involved in cellular metabolism and physiological responses such as energy maintenance and transport, cell membrane structure and thus cell activity, cell signaling, modification of transcription, mechanical protection and thermal as well as electrical insulation [19, 20].

HUFAs include polyunsaturated fatty acids (PUFAs) and omega-3 long-chain and very-long-chain PUFA (LC and VLC-PUFA) such as docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) [16, 18, 21]. Numerous health benefits are attributed to these fatty acids which makes them highly desirable in various industrial sectors of food additives and in cosmeceutical, nutraceuticals, pharmaceutical industries [22].

4. Architecture of microalgal lipid and fatty acids

Microalgal lipids are heterogeneous molecules with various structures ranging from short fatty acids (FAs) to more complex forms of phospholipids (PLs), triacylglycerols (TAGs), and sterols and their esters [20]. Complex lipids differ structurally according to the FA chain length along with the presence, location, and orientation of double bonds in their FAs; the branching of the hydrocarbon chain; the addition of polar groups; and glycosylation. The structural difference among FAs and lipids provides their functional differences upon cell and microalgal responses [19, 23, 24].

FAs are a series of hydrocarbon chains with a methyl (CH3) group on one end (methyl, ω or n terminal) and carboxylic acid (COOH) the opposite end of the molecule (acid or α terminal). The ω3 FAs contain multiple double bonds with one bond at the third carbon relative to the methyl end [25]. The systematic nomenclature for fatty acids may also imply the carboxyl group (Δ) [20]. In brief, when designated as ω-? or n-?, the location of the first double bond in reference to the methyl end is attended and when named as Δ-? the position relative to functional carboxylic acid end is considered. Further, the carbon immediately after the carboxyl end is named α, and the subsequent carbons are β and γ, respectively. The formulation below outlines the structure of fatty acids.

$$\underset{\omega }{C{H}_3}–\left(C{H}_2\right)n–\underset{\gamma }{C{H}_2}–\underset{\beta }{C{H}_2}–\underset{\alpha }{C{H}_2}–\underset{\Delta }{COOH}$$

The most abundant microalgal fatty acids are even-numbered, in straight-chain form, while odd-numbered and branched-chain FAs exist in respectively in ruminant tissues and bacteria [26]. The carbon number of fatty acids ranges from 2 to 30. Based on the chain length, fatty acids are classified as SCFA = short-chain fatty acids (C4–C13), MCFA = medium-chain fatty acids (C14–C17), LCFA = long-chain fatty acids (C18–C20), and VLCFA = Very-long-chain fatty acids (> C20) [27].

The lipid content in the microalgae is diverse; some produce SCFA and MCFA, while others synthesize VLCFAs. The enriched FA profile of SCFA, MCFA, and MUFA and lipid content of microalgae make them a possible source of biofuel [28]. In contrast, there are other microalgae that generally accumulate a large quantity of VLC-PUFAs as their major components that are of much current nutritional interest [17].

The unsaturation degree varies from 1 to ≥2 double bond(s), categorically referred to as monounsaturated fatty acids (MUFAs) and PUFAs, respectively. Apart from the position of the double bonds, cis or trans orientation of these bonds makes the lipid structure even more complex. These variation factors may pack FAs in lipid membranes by modifying its biological, biochemical, and biophysical properties. The majority of the naturally occurring unsaturated FA in microalgae are of cis type, trans configurations rarely occur [19, 29].

5. Current sources of DHA

The HUFAs were traditionally sourced from marine fish resources [30]. In fact microalgae are the original producers of n3 HUFAs and DHA that enters the food chain via consumption by the subsequent organism, fish [16, 18, 21]. Biocontamination by heavy metals, toxic and carcinogen pollutants, and bio-destruction by depletion of particular fish species and overfishing due to rising population have raised concerns about finding sustainable sources replacing fish that has the additional limitation of peculiar taste and odor [6]. This has drawn the attention toward evaluating the primary sources of microalgae [31].

The accumulation of a diverse array of FAs in the microalgae brings them forwards as the main HUFA including DHA source. This would revolutionize biotechnology in the fields of nutrition, aquaculture, nutraceutical, and pharmaceutical industry [32] benefiting human health, global marketing, and the environment [33]. Since microalgal DHA + EPA is comparable with fish, replacing the fish oil with microalgal oil can be viable and sustainable [34]. This will thereby minimize the pressure of ocean fisheries and preserve the biodiversity [35]. Table 1 shows the fatty acid profile of some microalgal species.

Species	∑SFA	∑MUFA	∑PUFA	∑n3 PUFA	∑n6 PUFA	n3: n6	UFA:SFA	DHA	EPA	TFA	References
Aurantiochytrium BL10	35	1	65				2	40	5	73	[36]
Crypthecodinium cohnii	47.3	0.81	51.9				1.12	51.12	—	15.2	[37]
Tisochrysis lutea	28.9	19.8	50.8				2.4	13	—	21	[38]
Monodus subterraneus	29	29	41.4				2.4	—	32	17	[39]
D. salina	34.8	32.2	33.1				1.9	15.4	—	27.1	[39]
D. tertiolecta	37.8	1.2	60.9				1.6	0.01	0.1		[40]
Volvox carteri	34.1	54.7	8				1.8	—	—		[41]
Chlamydomonas reinhardtii	27	15	58	29	29	1	2.7	—	—		[42]
Spirulina platensis	34.3	39.3	25.1	7.9	17.2	0.5	1.9	3.51	1.9	8.03	[43]
Isochrisis galbana	43.3	30	24.4	21.7	2.8	7.9	1.3	18.8	3.2	17.2	[44]
Chlorella vulgaris	22.2	35.4	38.9	29.2	9.7	3	3.4	20.9	2.9	13.3	[44]
D. sp. ABRIINW-I1	12	10	78	54	24	2.3	7.3	23.8	1.2	20	[45]

Table 1.

Comparison of fatty acid profile in different microalgal species. TFA is represented as percent of biomass dry weight and all others are as percent of TFA.

Currently, the major genera of omega 3 HUFA commercial microalgae belong to Chromista, of which the families Crypthecodiniaceae and Thraustochytriaceae are known as DHA producers [46, 47]. Crypthecodinium cohnii as the source of VLC-PUFA as well as DHA holds the primary place in commercialization [48, 49, 50]. The DHASCOT oil from Crypthecodinium cohnii (with 45% w/w DHA content) is marketed as the infant product.

6. DHA as essential bioactive fatty acids

A significant portion of human food, including plants and animals, contains n6 lacking n3 PUFAs [46]. Further, land plants mainly include shorter chain (16–18 carbon) n3 PUFAs such as α-linolenic acid (ALA). The n6 PUFA, linoleic acid (LA), can be converted to fatty acids with longer chains, and conversion of n3 ALA leads to synthesis of EPA and DHA. However, in human body, the conversion is not efficient and its rate is trivial (1 to 10%). Thus, these n3 HUFAs are very crucial part of the human diet and need to be supplied through regular daily intake of 0.2–0.3 g day⁻¹ [51].

The n3 fatty acids render an array of profound benefits in human health including normal growth, development of specific and nonspecific immunity, optimal fetal, ocular, cardiovascular, neurological and cognitive development, and functioning [1]. DHA and EPA are linked to alleviate and reduce the risk of asthma, arthritis, depression, psoriasis, autoimmune disorders, coronary cardiac disease, hypertension, inflammation, premenstrual tension, various atopic disorders, diabetes, skin disease, hypertonia, hyperlipidemia, atherosclerosis, thrombosis, Alzheimer, and cancer [52, 53, 54]. Moreover, DHA and EPA function as natural antimicrobials, anti-inflammatories and antioxidants [54, 55, 56, 57, 58, 59, 60, 61]. They constitute membrane phospholipids in certain tissues and provide the viscosity of cell membranes [62, 63, 64, 65]. DHA, the prominent fraction of the membrane phospholipids in neural and retinal systems, is more imperative for cell signaling, brain function, and vision [66]. Fetal neurodevelopment and infant cognitive development and visual acuity are especially attributed to DHA intake during early life [67, 68]. Lower intelligence quotients are determined in formula-fed than breastfed infants due to the rich DHA content of human milk [69]. Compared to EPA, DHA is reported to more effectively act on controlling the blood pressure and regulating the heart rate [70]. DHA is also implicated to be more efficient on treating neural system disorders (multiple sclerosis, Alzheimer’s, and Parkinson) [71] and preventing the onset of cancerous growths than EPA [72]. In the human body, dietary DHA might be retro-converted to EPA, while the production of DHA from EPA is not observed [73]. The detailed essentiality and health claims of DHA have been comprehensively discussed in some studies by Oscarsson and Hurt-Camejo [74], Horrocks and Yeo [2, 73], Sijtsma and De Swaaf [75], Li, Pora [3, 76].

7. Bioengineering of microalgal DHA production

Large-scale production of lipid from microalgae entails delicate bioengineering approaches [77] in either genetic or non-genetic tailoring form [78]. To optimize lipid production, several factors might be considered, such as the cultivation conditions, the microalgal strain and its biological properties, and the harvesting and extraction methods [79].

Cultivation and growth parameters including temperature, light, and nutrients significantly impact lipid content and composition [80]. Cultivation conditions might be complex as different strains may respond differently to the same conditions due to different molecular adjustment mechanisms to various stimuli [55]. This highlights the importance of comprehensive experimental analyses, unique to each strain, prior to embarking optimization programs. Accordingly, optimal condition favoring HUFA production is a fatty acid-, species-, or strain-specific property [55, 81]. Selection of a suitable microalgal strain is critical for achieving high lipid yields. Screening of a hyperproducer strain, optimization of physical conditions, breeding, and biochemical or metabolic engineering are the approaches to enhance lipid or valuable FA yield [81, 82]. The co-cultivation of microalgae species has been explored as a strategy for simultaneous production of EPA and DHA. Thurn, Stock [83] studied the photoautotrophic co-cultivation of Tisochrysis lutea and Microchloropsis salina, which resulted in the production of appropriate balance of EPA and DHA in the studied microalgae. Overall, metabolic engineering of microalgae holds great potential for enhancing DHA production.

While the role of organic carbon sources in the biosynthetic pathways of PUFAs remains unclear, Villanova, Fortunato [84] demonstrated an elevated EPA and DHA content in Phaeodactylum tricornutum when cultivated under mixotrophic conditions using the carbon source of glycerol. DHA synthesis was also examined in Tisochrysis lutea CCMP1324 cultures using autotrophic (with glucose and acetate as the carbon source), mixotrophic, and heterotrophic approaches (with glycerol). The mixotrophic conditions demonstrated the highest DHA production and productivity [85]. Mixotrophic growth also led to an increase in TFA content in the dry weight and TFA production in the medium. Specific extraction methods are also essential for maximizing DHA yields. Traditional methods, such as centrifugation and solvent extraction, can be time-consuming and energy-intensive. Newer technologies, such as organic solvents-water-organic solvents, flocculation, and membrane filtration, offer more efficient and sustainable alternatives [86, 87]. In a study on Crypthecodinium cohnii, cultivation was carried out in fed-batch conditions using cost-effective industrial by-products such as raw glycerol and corn steep liquor [88]. The fermentation resulted in an appropriate lipid content and productivity. The subsequent saponification extracting reaction followed by fractionation process at different temperatures yielded a PUFA rich fraction.

8. Biochemical engineering for DHA production

In order to develop an optimized microalgal platform, administering a varied range of environmental factors to an individual isolate may contribute to outreach the desired fatty acid content [89, 90]. Biochemical engineering is the strategy of enhancing the microalgal lipid/FA production via controlling the culture and nutritional conditions. During biochemical engineering, the metabolic fluxes generated in photobiosynthesis are channeled into the biosynthesis of lipids or the desired FAs [46, 91, 92].

Several studies have been conducted to identify the main factors and the conditions that might enhance DHA production in numerous microorganisms including Schizochytrium and Aurantiochytrium [93, 94, 95, 96, 97]. Once the microalga Crythecodinium cohnii was cultured in the salinity of 1.5 M NaCl, total DHA content was augmented up to 56.9% of TFA [16]. These were achieved via optimizing the concentration of fructose and monosodium glutamate (MSG) as well as agitation speed. Zhu et al. highlighted the importance of optimizing the medium and culture conditions for the growth and DHA production of Schizochytrium [98]. They emphasized that the data on the cultivation factors of Schizochytrium affecting its biomass and DHA production is limited but essential for industrial-scale DHA production. To improve the DHA production and prevent lipid peroxidation, Sun et al. developed a cooperative adaptive-evolution method in Schizochytrium sp. [99] to develop strains with high DHA production capacity and strong antioxidant defenses. This approach resulted in strains with improved DHA production and stability.

Of different environmental parameters, temperature is a crucial factor for DHA production [78]. Bindea, Rusu [100] highlighted the importance of finding the optimum temperature that balances increased DHA production and cell growth. They found that low temperature favors DHA production but it limits the cell growth. Therefore, the temperature should be optimized in a way that maximizes DHA as well as biomass production.

The highest DHA yield in Schizochytrium sp. was obtained in GM media containing glycerol. Glycerol in addition to proteose peptone as respectively carbon and nitrogen carbon sources, in combination with ethanol, improved DHA production [101]. Chalima et al. [97] optimized DHA production of the cells in terms of cultivation factors of nutrients and temperature. Based on the results, microalgal growth was remarkably improved with the application of ammonium as nitrogen source.

Non-genetic tailoring offer some advantages including cost-effectiveness and the use of available resources. However, the inherited shortcoming of this method is that it is time-consuming procedure. Another drawback is that the abiotic stress inevitably accompanies reduced biomass yield [78]. The physiological stress required for high lipid content coincides with microalgal growth cessation [79, 102, 103]. Achieving the appropriate balance between the optimal biomass and lipid volumetric productivity of microalgae relies on various biotic and abiotic factors [104]. Therefore, various stresses should be meticulously programmed to reach the concurrent production of biomass and DHA.

Hosseinzadeh et al. [45] introduced an isolate Dunaliella sp. ABRIINW-I1 from Urmia lake as DHA hyperproductive microalga. Their data revealed that the combination of salinity, light, and temperature significantly increased the production of biomass, TFA, and DHA. The maximum growth and DHA level were achieved at 0.5 M NaCl, 25°C, and 200 μmol photon m⁻² s⁻¹. The highest DHA production in Dunaliella sp. ABRIINW-I1 was in the same range as commercial Thraustochytrids [45].

9. Metabolic engineering for DHA production

Apart from the biochemical engineering, another promising approach for higher production of targeted substances in the microalgae is metabolic engineering. It deals with genetic, transcriptomic, and regulatory processes within cells. In parallel, omics technology including genomics, transcriptomics, proteomics, metabolomics, and lipidomics explores the mechanisms underneath the cell responses toward stressors [53, 105]. Developing improved strains accumulating large quantities of the desired FAs requires providing a deep insight into microalgal biology, including its genetic, transcriptomic, and metabolic information.

Wang et al. used metabolic engineering techniques to improve the synthesis of DHA and fatty acids of odd chains in a strain of Schizochytrium sp. [106]. They achieved the significant improvements in the contents and titers of DHA and odd-chain fatty acids, leading to a decrease in the total fatty acid production cost. One approach to optimize DHA production is through the reconstruction and analysis of genome-scale metabolic models (GSMMs). Ye et al. reconstructed a GSMM of Schizochytrium limacinum SR21 and used it to predict the requirements for DHA production [107]. They identified six amino acids, malate, and citrate as potential supplements to enhance DHA production. Additionally, they used a Minimization of Metabolic Adjustment algorithm to identify 30 genes as potential targets for DHA over-production. Utilization of response surface methodology (RSM) is an effective approach used for the enhancement of DHA production. Nazir et al. applied RSM for cultivation conditions of Aurantiochytrium SW1 to optimize its biomass, TFA, and DHA production [108].

Manipulating the metabolic pathways through genetic modification is one of the strategies in metabolic engineering. Efforts have been undertaken to augment the EPA and DHA production by altering the metabolic pathways in microalgae [109]. For example, once the endogenous type 2 diacylglycerol acyltransferase (DGAT2B) was overexpressed in the Phaeodactylum tricornutum, higher lipid yields were resulted with enhanced levels of DHA in triacylglycerols (TAG) [110]. In addition to genetic manipulation, other approaches have been explored to optimize DHA production in microalgae. For instance, the addition of stimulators such as 2-phenylacetic acid (PAA) improves the growth, DHA, and the relevant transcriptome in Aurantiochytrium sp. [111]. This method is considered practical and efficient without any need to comprehensive understanding of the molecular targets.

The authors of this chapter have analyzed the expression of lipid synthesis genes in the native microalga Dunaliella under the stress conditions. Based on their results, under high TFA production, in the first 24 hours, all the glycerolipid and FA synthesis genes were up-regulated yielding in improved TAG synthesis. The fatty acid elongation genes, during the time span of 4 to 24 h, were up-regulated in all the conditions. The over-expression of the VLCFA elongase as well as Δ5, Δ7, Δ8, Δ9, Δ12, Δ15, ω3, ω6, and long-chain FA desaturase genes in high TFA samples suggested the increased elongation and desaturation toward VLC-PUFA and highly unsaturated fatty acids synthesis. Regarding DHA production pathway, the main genes involved in the recently discovered alternative pathway of polyketide synthase (PKS) were enriched (data not published).

The Δ6-desaturase, Δ4-desaturase, and Δ5-elongase were determined as rate-limiting enzymes in enhancement of DHA production in microalgae. The expression of Δ5-desaturase in Phaeodactylum tricornutum UTEX646 leads to 8 times increase of DHA production compared to the native strain [112].

10. Perspective

At present, with elevated fried- and fast-food consumption, the balance between omega-3 and omega-6 fatty acids has been disrupted and this has been linked to increased prevalence of chronic diseases [113, 114]. While dietary recommendations for EPA and DHA range from 250 to 1000 mg/day for adults, the actual consumption is around 163 mg/day [115]. Further, a significant portion of the population consumes less than 100 mg/day [116]. For a global population of around seven billion in 2019, meeting a daily dosage of 500 mg per person would reveal a DHA deficit of 0.4–1.0 million tons/year. A detailed overview of the widening discrepancy between DHA availability and the quantities required to meet optimal dietary intake has been discussed by Tocher et al. [4]. Addressing the challenge of filling the gap between DHA supply and demand has become an immediate and future imperative. As the global population grows and ages, there is mounting requirements for EPA/DHA to combat escalating chronic diseases.

Direct incorporation of microalgal-derived EPA/DHA into human foods and supplements circumvents the reliance on fish farming with the relevant limitations. Moreover, microalgae offer the advantage of remediating water pollution during intensified aquaculture through wastewater recycling, establishing ecological equilibrium and circular economy where microalgae support fish growth while mitigating pollutants [117].

In strain selection, only a few members out of the broad microalgal community has been qualified in terms of food-grade lipids and fatty acids [118]. Certain species have become favorite experimental organisms and most of the studies have been performed on them, leaving the local isolates unexplored. The studies should include a broad range of microalgal strains other than the model microalgae. By persistent isolation, screening and investigating the indigenous isolates from the immediate environment, a wide array of microalgal origins with exploitable potential will be available [16].

Modern techniques such as riboswitches, RNAi technology for posttranscriptional downregulation of specific genes, and coupling nuclear promoters for gene regulation may have a great contribution to the field of genetic engineering [119]. Genetically modified microalgae generated by genetic engineering technique would aid in exploring the underlying biology and achieving valuable biomolecules including DHA. The transgenes associated with the overproduction of with specific post-translation modifications should be activated within microalgal chloroplasts which are free of unwanted glycosylation [120].

11. Conclusion

In the realm of enhancing the global health, microalgae exhibit the potential to become a primary source of DHA, surpassing traditional methods. The remarkable ability of microalgae to synthesize DHA, coupled with advancements in cultivation techniques, metabolic engineering, and downstream processing, offers a sustainable and innovative solution to address the increasing DHA demand. The pivotal role of DHA in human health underscores the urgency to bridge the gap between DHA supply and the recommended dietary intake. With the global population expanding and chronic diseases on the rise, the demand for DHA is growing. Microalgae offer a versatile platform to fulfill this demand, not only by producing DHA but also by promoting sustainable practices through nutrient recycling and wastewater bioremediation. Furthermore, the versatility of microalgae as biorefineries presents a multifaceted advantage. Microalgae yield not only DHA but also a spectrum of other valuable compounds, including proteins, carotenoids, and biofuels.

However, challenges remain, including scaling up production, cost-effectiveness, and integrating microalgal-based DHA into mainstream markets. Rigorous research is essential to optimize growth conditions, genetic modifications, and cultivation strategies to achieve consistent and economically viable DHA production.