Enhanced production of carotenoids using a Thraustochytrid microalgal strain containing high levels of docosahexaenoic acid-rich oil

High capacities of carbon capture and photosynthesis of a novel organic carbon-fixing microalgae in municipal wastewater: From mutagenesis, screening, ability evaluation to mechanism analysis

The development of wastewater treatment processes capable of reducing and fixing carbon is currently a hot topic in the wastewater treatment field. Microalgae possess a natural carbon-fixing advantage, and microalgae that can symbiotically coexist with indigenous bacteria in actual wastewater attract more significant attention. Ultraviolet (UV) mutagenesis and dissolved organic carbon (DOC) acclimation were applied to strengthen the carbon-fixing performance of microalgae in this study. The mechanisms associated with microalgal water purification ability, gene regulation at the molecular level and photosynthetic potential under different trophic modes resulting from carbon fixation and transformation were disclosed. The superior performance of Chlorella sp. MHQ2 was eventually screened out among a large number of mutants generated from 3 wild-type Chlorella strains. Results indicated that the dry cell weight of the optimal species Chlorella sp. HQ mutant MHQ2 was 1.91 times that of the wild strain in the pure algal system, more carbon from municipal wastewater (MW) were transferred to the microalgae and re-entered into the biological cycle through resource utilization. In addition, COD, NH3-N and TP removal efficiencies of MW by Chlorella sp. MHQ2 were found to increase to 95.8% (1.1-times), 96.4% (1.4-times), and 92.9% (1.2-times), respectively, under the extra DOC supply and the assistance of indigenous bacteria in the MW. In the transcriptome analysis of the logarithmic phase, the glycolytic pathway was inhibited, and the pentose phosphate pathway was mainly carried out for microalgal life activities, further promoting efficient energy utilization. Upon analysis of carbon capture capacity and photosynthetic potential in trophic mode, the addition of NaHCO3 increased the photosynthetic rate of Chlorella sp. MHQ2 in mixotrophy whereas it was attenuated in autotrophy. This study could provide a new perspective for the study of resource utilization and microalgae carbon- fixing mechanisms in the actual wastewater treatment process.

The Biosynthesis of Astaxanthin Esters in Schizochytrium sp. is Mediated by a Bifunctional Diacylglycerol Acyltransferase

Astaxanthin esters are a major form of astaxanthin found in nature. However, the exact mechanisms of the biosynthesis and storage of astaxanthin esters were previously unknown. We found that Schizochytrium sp. synthesized both astaxanthin and docosahexaenoic acid (DHA)-enriched lipids. The major type of astaxanthin produced was free astaxanthin along with astaxanthin-DHA monoester and other esterified forms. DHA accounted for 41.0% of the total fatty acids from astaxanthin monoesters. These compounds were deposited mainly in lipid droplets. The biosynthesis of the astaxanthin esters was mainly carried out by a novel diacylglycerol acyltransferase ScDGAT2-1, while ScDGAT2-2 was involved only in the production of triacylglycerol. We also identified astaxanthin ester synthases from the astaxanthin-producing algae Haematococcus pluvialis and Chromochloris zofingiensis, as well as a thraustochytrid Hondaea fermentalgiana with an unknown carotenoid profile. This investigation enlightens the application of thraustochytrids for the production of both DHA and astaxanthin and provides enzyme resources for the biosynthesis of astaxanthin esters in the engineered microbes.

Assessment of thraustochytrids potential for carotenoids, terpenoids and polyunsaturated fatty acids biorefinery

Heterotrophic fast-growing thraustochytrids have been identified as promising candidates for the bioconversion of organic sources into industrially important valuable products. Marine thraustochytrids exhibit remarkable potential for high-value polyunsaturated fatty acids (PUFAs) production however their potential is recently discovered for high-value carotenoids and terpenoids which also have a role as a dietary supplement and health promotion. Primarily, omega-3 and 6 PUFAs (DHA, EPA, and ARA) from thraustochytrids are emerging sources of nutrient supplements for vegetarians replacing animal sources and active pharmaceutical ingredients due to excellent bioactivities. Additionally, thraustochytrids produce reasonable amounts of squalene (terpenoid) and carotenoids which are also high-value products with great market potential. Hence, these can be coextracted as a byproduct with PUFAs under the biorefinery concept. There is still quite a few printed information on bioprocess conditions for decent (co)-production of squalene and carotenoid from selective protists such as lutein, astaxanthin, canthaxanthin, and lycopene. The current review seeks to provide a concise overview of the coproduction and application of PUFAs, carotenoids, and terpenoids from oleaginous thraustochytrids and their application to human health.

Metabolic engineering and synthetic biology strategies for producing high-value natural pigments in Microalgae

Microalgae are microorganisms capable of producing bioactive compounds using photosynthesis. Microalgae contain a variety of high value-added natural pigments such as carotenoids, phycobilins, and chlorophylls. These pigments play an important role in many areas such as food, pharmaceuticals, and cosmetics. Natural pigments have a health value that is unmatched by synthetic pigments. However, the current commercial production of natural pigments from microalgae is not able to meet the growing market demand. The use of metabolic engineering and synthetic biological strategies to improve the production performance of microalgal cell factories is essential to promote the large-scale production of high-value pigments from microalgae. This paper reviews the health and economic values, the applications, and the synthesis pathways of microalgal pigments. Overall, this review aims to highlight the latest research progress in metabolic engineering and synthetic biology in constructing engineered strains of microalgae with high-value pigments and the application of CRISPR technology and multi-omics in this context. Finally, we conclude with a discussion on the bottlenecks and challenges of microalgal pigment production and their future development prospects.

Screening of a Thraustochytrid Strain Collection for Carotenoid and Squalene Production Characterized by Cluster Analysis, Comparison of 18S rRNA Gene Sequences, Growth Behavior, and Morphology

Carotenoids and squalene are important terpenes that are applied in a wide range of products in foods and cosmetics. Thraustochytrids might be used as alternative production organisms to improve production processes, but the taxon is rarely studied. A screening of 62 strains of thraustochytrids sensu lato for their potential to produce carotenoids and squalene was performed. A phylogenetic tree was built based on 18S rRNA gene sequences for taxonomic classification, revealing eight different clades of thraustochytrids. Design of experiments (DoE) and growth models identified high amounts of glucose (up to 60 g/L) and yeast extract (up to 15 g/L) as important factors for most of the strains. Squalene and carotenoid production was studied by UHPLC-PDA-MS measurements. Cluster analysis of the carotenoid composition partially mirrored the phylogenetic results, indicating a possible use for chemotaxonomy. Strains in five clades produced carotenoids. Squalene was found in all analyzed strains. Carotenoid and squalene synthesis was dependent on the strain, medium composition and solidity. Strains related to Thraustochytrium aureum and Thraustochytriidae sp. are promising candidates for carotenoid synthesis. Strains closely related to Schizochytrium aggregatum might be suitable for squalene production. Thraustochytrium striatum might be a good compromise for the production of both molecule groups.

Microalgae and Thraustochytrids are Sustainable Sources of Vegan EPA and DHA with Commercial Feasibility

Vegan diets preclude the availability of some of the essential fatty acids supplied by foods of animal origin. Significantly, eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids are long-chain (LC)-omega - 3 (n - 3) polyunsaturated fatty acids (PUFAs), widely known for preventing a variety of metabolic diseases. In addition to vegan-food supplements, there is increasing demand for infant foods and health foods from dietary sources of EPA and DHA from plant origin. Their demands are being met industrially by utilizing thraustochytrids (marine protists) and microalgae-based platforms. The importance of these organisms is highlighted for the sustainable production of biotechnologically derived specialty lipids for human health.

Developing algae as a sustainable food source

Current agricultural and food production practices are facing extreme stress, posed by climate change and an ever-increasing human population. The pressure to feed nearly 8 billion people while maintaining a minimal impact on the environment has prompted a movement toward new, more sustainable food sources. For thousands of years, both the macro (seaweed and kelp) and micro (unicellular) forms of algae have been cultivated as a food source. Algae have evolved to be highly efficient at resource utilization and have proven to be a viable source of nutritious biomass that could address many of the current food production issues. Particularly for microalgae, studies of their large-scale growth and cultivation come from the biofuel industry; however, this knowledge can be reasonably translated into the production of algae-based food products. The ability of algae to sequester CO₂ lends to its sustainability by helping to reduce the carbon footprint of its production. Additionally, algae can be produced on non-arable land using non-potable water (including brackish or seawater), which allows them to complement rather than compete with traditional agriculture. Algae inherently have the desired qualities of a sustainable food source because they produce highly digestible proteins, lipids, and carbohydrates, and are rich in essential fatty acids, vitamins, and minerals. Although algae have yet to be fully domesticated as food sources, a variety of cultivation and breeding tools exist that can be built upon to allow for the increased productivity and enhanced nutritional and organoleptic qualities that will be required to bring algae to mainstream utilization. Here we will focus on microalgae and cyanobacteria to highlight the current advancements that will expand the variety of algae-based nutritional sources, as well as outline various challenges between current biomass production and large-scale economic algae production for the food market.

Elucidation of sterol biosynthesis pathway and its co-regulation with fatty acid biosynthesis in the oleaginous marine protist Schizochytrium sp

Sterols constitute vital structural and regulatory components of eukaryotic cells. In the oleaginous microorganism Schizochytrium sp. S31, the sterol biosynthetic pathway primarily produces cholesterol, stigmasterol, lanosterol, and cycloartenol. However, the sterol biosynthesis pathway and its functional roles in Schizochytrium remain unidentified. Through Schizochytrium genomic data mining and a chemical biology approach, we first in silico elucidated the mevalonate and sterol biosynthesis pathways of Schizochytrium. The results showed that owing to the lack of plastids in Schizochytrium, it is likely to use the mevalonate pathway as the terpenoid backbone pathway to supply isopentenyl diphosphate for the synthesis of sterols, similar to that in fungi and animals. In addition, our analysis revealed a chimeric organization of the Schizochytrium sterol biosynthesis pathway, which possesses features of both algae and animal pathways. Temporal tracking of sterol profiles reveals that sterols play important roles in Schizochytrium growth, carotenoid synthesis, and fatty acid synthesis. Furthermore, the dynamics of fatty acid and transcription levels of genes involved in fatty acid upon chemical inhibitor-induced sterol inhibition reveal possible co-regulation of sterol synthesis and fatty acid synthesis, as the inhibition of sterol synthesis could promote the accumulation of fatty acid in Schizochytrium. Sterol and carotenoid metabolisms are also found possibly co-regulated, as the inhibition of sterols led to decreased carotenoid synthesis through down-regulating the gene HMGR and crtIBY in Schizochytrium. Together, elucidation of the Schizochytrium sterol biosynthesis pathway and its co-regulation with fatty acid synthesis lay the essential foundation for engineering Schizochytrium for the sustainable production of lipids and high-value chemicals.

Efficient Co-production of Docosahexaenoic Acid Oil and Carotenoids in Aurantiochytrium sp. Using a Light Intensity Gradient Strategy

Aurantiochytrium is a promising source of docosahexaenoic acid (DHA) and carotenoids, but their synthesis is influenced by environmental stress factors. In this study, the effect of different light intensities on the fermentation of DHA oil and carotenoids using Aurantiochytrium sp. TZ209 was investigated. The results showed that dark culture and low light intensity conditions did not affect the normal growth of cells, but were not conducive to the accumulation of carotenoids. High light intensity promoted the synthesis of DHA and carotenoids, but caused cell damage, resulting in a decrease of oil yield. To solve this issue, a light intensity gradient strategy was developed, which markedly improved the DHA and carotenoid content without reducing the oil yield. This strategy produced 30.16 g/L of microalgal oil with 15.11 g/L DHA, 221 µg/g astaxanthin, and 386 µg/g β-carotene. This work demonstrates that strain TZ209 is a promising DHA producer and provides an efficient strategy for the co-production of DHA oil together with carotenoids.

Modulating DHA-Producing Schizochytrium sp. toward Astaxanthin Biosynthesis via a Seamless Genome Editing System

Schizochytrium sp. is commercially used for the production of docosahexaenoic acid (DHA). Some strains of Schizochytrium sp. are also known to produce low amounts of carotenoids, including astaxanthin and β-carotene. In order to enhance the production of astaxanthin in Schizochytrium sp., we established a seamless genome editing system with a dual selection marker for rapid screening of positive transformants. By using this system, we strengthened the endogenous mevalonate pathway, enhanced the supply of geranylgeranyl diphosphate and β-carotene, upregulated endogenous β-carotene hydroxylase, and introduced the algal astaxanthin pathway. The highest astaxanthin production in the engineered Schizochytrium sp. was achieved at 8.1 mg/L (307.1 μg/g dry cell weight) under shake-flask conditions, which was 2.6-fold higher than that in the start strain. Meanwhile, the percentage of DHA to total fatty acids was not obviously affected. We then eliminated the dual selection marker by using the Cre-loxP recombination system, and the engineered strain was ready for iterative editing. The developed system could be applied to seamlessly engineer DHA-producing Schizochytrium sp. toward astaxanthin and other value-added terpenoids, which broadens the application of this strain.

Development and validation of reliable astaxanthin quantification from natural sources

Astaxanthin derived from natural sources occurs in the form of various esters and stereomers, which complicates its quantitative and qualitative analysis. To simplify and standardize astaxanthin measurement with high precision, an enzymolysis-based astaxanthin quantification method was developed to hydrolyze astaxanthin esters and determine free astaxanthin in all its diastereomeric forms. Astaxanthin standards and differently processed Haematococcus pluvialis biomass were investigated. Linear correlation of standards of all-E-astaxanthin was observed in a measurement range between extract concentrations of 1.0 μg/mL and 11.2 μg/mL with a coefficient of variation below 5%. The diastereomers 9Z-, and 13Z-astaxanthin, and two di-Z-forms were detected. In contrast to the measurement of standards, the observed measurement range was extended to 30 μg/mL in extracts from H. pluvialis. The nature of the sample had to be taken into account for measurement, as cell, respectively, sample composition altered the optimal concentration for astaxanthin determination. The measurement precision of all-E-astaxanthin quantification in dried H. pluvialis biomass (1.2-1.8 mg dried biomass per sample) was calculated with a coefficient of variation of maximum 1.1%, whereas it was below 10% regarding the diastereomers. Complete enzymolysis was performed with 1.0 to 2.0 units of cholesterol esterase in the presence of various solvents with up to 2.0 mg biomass (dry weight). The method was compared with other astaxanthin determination approaches in which astaxanthin is converted to acetone in a further step before measurement. The developed method resulted in a higher total astaxanthin recovery but lower selectivity of the diastereomers. The reliability of photometric astaxanthin estimations was assessed by comparing them with the developed chromatographic method. At later stages in the cell cycle of H. pluvialis, all methods yielded similar results (down to 0.1% deviation), but photometry lost precision at earlier stages (up to 31.5% deviation). To optimize sample storage, the shelf life of astaxanthin-containing samples was investigated. Temperatures below -20°C, excluding oxygen, and storing intact H. pluvialis cells instead of dried or disrupted biomass reduced astaxanthin degradation.

The Porifera microeukaryome: Addressing the neglected associations between sponges and protists

While bacterial and archaeal communities of sponges are intensively studied, given their importance to the animal's physiology as well as sources of several new bioactive molecules, the potential and roles of associated protists remain poorly known. Historically, culture-dependent approaches dominated the investigations of sponge-protist interactions. With the advances in omics techniques, these associations could be visualized at other equally important scales. Of the few existing studies, there is a strong tendency to focus on interactions with photosynthesizing taxa such as dinoflagellates and diatoms, with fewer works dissecting the interactions with other less common groups. In addition, there are bottlenecks and inherent biases in using primer pairs and bioinformatics approaches in the most commonly used metabarcoding studies. Thus, this review addresses the issues underlying this association, using the term "microeukaryome" to refer exclusively to protists associated with an animal host. We aim to highlight the diversity and community composition of protists associated with sponges and place them on the same level as other microorganisms already well studied in this context. Among other shortcomings, it could be observed that the biotechnological potential of the microeukaryome is still largely unexplored, possibly being a valuable source of new pharmacological compounds, enzymes and metabolic processes.

Emerging prospects of microbial production of omega fatty acids: Recent updates

Healthy foods containing omega-3/omega-6 polyunsaturated fatty acids (PUFAs) have been in great demand because of their unique dietary and health properties. Reduction in chronic inflammatory and autoimmune diseases has shown their therapeutic and health-promoting effects when consumed under recommended ratio 1:1-1:4, however imbalanced ratios (>1:4, high omega-6) enhance these risks. The importance of omega-6 is apparent however microbial production favors larger production of omega-3. Current research focus is prerequisite to designing omega-6 production strategies for better application prospects, for which thraustochytrids could be promising due to higher lipid productivity. This review provides recent updates on essential fatty acids production from potential microbes and their application, especially major insights on omega research, also discussed the novel possible strategies to promote omega-3 and omega-6 accumulation via engineering and omics approaches. It covers strategies to block the conversion of omega-6 into omega-3 by enzyme inhibition, nanoparticle-mediated regulation and/or metabolic flux regulation, etc.

Production of Carotenoids and Phospholipids by Thraustochytrium sp. in Batch and Repeated-Batch Culture

The carotenogenic thraustochytrid Thraustochytrium sp. RT2316-16 was grown in batch and repeated-batch cultures using different feeds containing glucose, or glycerol, and yeast extract, for the production of lipids, phospholipids and carotenoids. RT2316-16 produced canthaxanthin, astaxanthin and β-carotene. The effects of biotin, ascorbic acid, light and temperature were evaluated in some of the experiments. In 2-day-old batch cultures, the combined mass percentage of eicosapentaenoic acid and docosahexaenoic acid in total lipids was between 16.5% (glycerol-based medium in the dark; biomass concentration = 4.2 ± 1.1 g L⁻¹) and 42.6% (glucose-based medium under light; biomass concentration = 3.3 ± 0.1 g L⁻¹), decreasing to 3.8% and 6.1%, respectively, after day 4. In repeated-batch cultures, the total lipids in the biomass increased after glucose or glycerol was fed alone, whereas the total carotenoids (168 ± 7 μg g⁻¹ dry weight (DW)) and phospholipids in the biomass increased after feeding with yeast extract. The biomass with the highest content of phospholipids (28.7 ± 4.3 mg g⁻¹ DW) was obtained using a feed medium formulated with glycerol, yeast extract and ascorbic acid. Glycerol was the best carbon source for the production of a biomass enriched with total lipids (467 ± 45 mg g⁻¹ DW). The composition of carotenoids depended strongly on the composition of the feed. Repeated-batch cultures fed with yeast extract contained canthaxanthin as the main carotenoid, whereas in the cultures fed only with glucose, the biomass contained mainly β-carotene.

Optimization of Astaxanthin Recovery in the Downstream Process of Haematococcus pluvialis

Astaxanthin derived from Haematococcus pluvialis is a valuable metabolite applied in a wide range of products. Its extraction depends on a sophisticated series of downstream process steps, including harvesting, disruption, drying, and extraction, of which some are dependent on each other. To determine the processes that yield maximum astaxanthin recovery, bead milling, high-pressure homogenization, and no disruption of H. pluvialis biomass were coupled with spray-drying, vacuum-drying, and freeze-drying in all possible combinations. Eventually, astaxanthin was extracted using supercritical CO2. Optimal conditions for spray-drying were evaluated through the design of experiments and standard least squares regression (feed rate: 5.8 mL/min, spray gas flow: 400 NL/h, inlet temperature: 180 °C). Maximal astaxanthin recoveries were yielded using high-pressure homogenization and lyophilization (85.4%). All combinations of milling or high-pressure homogenization and lyophilization or spray-drying resulted in similar recoveries. Bead milling and spray-drying repeated with a larger spray-dryer resulted in similar astaxanthin recoveries compared with the laboratory scale. Smaller astaxanthin recoveries after the extraction of vacuum-dried biomass were mainly attributed to textural changes. Evaluation of these results in an economic context led to a recommendation for bead milling and spray-drying prior to supercritical CO2 extraction to achieve the maximum astaxanthin recoveries.

Uncovering the Bioactivity of Aurantiochytrium sp.: a Comparison of Extraction Methodologies

Aurantiochytrium sp. is an emerging alternative source of polyunsaturated fatty acids (PUFAs), docosahexaenoic acid (DHA), and squalene, playing an important role in the phasing out of traditional fish sources for these compounds. Novel lipid extraction techniques with a focus on sustainability and low environmental footprint are being developed for this organism, but the exploration of other added-value compounds within it is still very limited. In this work, a combination of novel green extraction techniques (high hydrostatic pressure extraction (HPE) and supercritical fluid extraction (SFE)) and traditional techniques (organic solvent Soxhlet extraction and hydrodistillation (HD)) was used to obtain lipophilic extracts of Aurantiochytrium sp., which were then screened for antioxidant (DPPH radical reduction capacity and ferric-reducing antioxidant potential (FRAP) assays), lipid oxidation protection, antimicrobial, anti-aging enzyme inhibition (collagenase, elastase and hyaluronidase), and anti-inflammatory (inhibition of NO production) activities. The screening revealed promising extracts in nearly all categories of biological activity tested, with only the enzymatic inhibition being low in all extracts. Powerful lipid oxidation protection and anti-inflammatory activity were observed in most SFE samples. Ethanolic HPEs inhibited both lipid oxidation reactions and microbial growth. The HD extract demonstrated high antioxidant, antimicrobial, and anti-inflammatory activities making, it a major contender for further studies aiming at the valorization of Aurantiochytrium sp. Taken together, this study presents compelling evidence of the bioactive potential of Aurantiochytrium sp. and encourages further exploration of its composition and application.

Accumulation and conversion of β-carotene and astaxanthin induced by abiotic stresses in Schizochytrium sp

Astaxanthin is a kind of ketone carotenoid belonging to tetraterpenoids with an excellent antioxidant activity and it is widely used in nutrition and health-care industries. This study aimed to explore the effect of different abiotic stresses on carotenoid production in Schizochytrium sp. Firstly, the characteristics of carotenoid accumulation were studied in Schizochytrium sp. by monitoring the change of carotenoid yields and gene expressions. Then, different abiotic stresses were systematically studied to regulate the carotenoid accumulation. Results showed that low temperature could advance the astaxanthin accumulation, while ferric ion could stimulate the conversion from carotene to astaxanthin. The glucose and monosodium glutamate ratio of 100:5 was helpful for the accumulation of β-carotene. In addition, micro-oxygen supply conditions could increase the yield of β-carotene and astaxanthin by 25.47% and 14.92%, respectively. This study provided the potential regulation strategies for carotenoid production which might be used in different carotenoid-producing strains.

Biotechnological Enhancement of Probiotics through Co-Cultivation with Algae: Future or a Trend?

The diversity of algal species is a rich source of many different bioactive metabolites. The compounds extracted from algal biomass have various beneficial effects on health. Recently, co-culture systems between microalgae and bacteria have emerged as an interesting solution that can reduce the high contamination risk associated with axenic cultures and, consequently, increase biomass yield and synthesis of active compounds. Probiotic microorganisms also have numerous positive effects on various aspects of health and represent potent co-culture partners. Most studies consider algae as prebiotics that serve as enhancers of probiotics performance. However, the extreme diversity of algal organisms and their ability to produce a plethora of metabolites are leading to new experimental designs in which these organisms are cultivated together to derive maximum benefit from their synergistic interactions. The future success of these studies depends on the precise experimental design of these complex systems. In the last decade, the development of high-throughput approaches has enabled a deeper understanding of global changes in response to interspecies interactions. Several studies have shown that the addition of algae, along with probiotics, can influence the microbiota, and improve gut health and overall yield in fish, shrimp, and mussels aquaculture. In the future, such findings can be further explored and implemented for use as dietary supplements for humans.

Saccharification of lignocellulosic biomass using an enzymatic cocktail of fungal origin and successive production of butanol by Clostridium acetobutylicum

A multistep approach was undertaken for biobutanol production targeting valorization of agricultural waste. Optimum production of lignocellulolytic enzymes [CMCase (3822.93U/mg), FPase (3640.93U/mg), β-glucosidase (3873.92U/mg), xylanase (3460.24U/mg), pectinase (3359.57U/mg), α-amylase (4136.54U/mg), and laccase (3863.16U/mg)] was accomplished through solid-substrate fermentation of pretreated mixed substrates (wheat bran, sugarcane bagasse and orange peel) by Aspergillus niger SKN1 and Trametes hirsuta SKH1. Partially purified enzyme cocktail was employed for saccharification of the said substrate mixture into fermentable sugar (69.23 g/L, product yield of 24% w/w). The recovered sugar with vegetable extract supplements was found as robust fermentable medium that supported 16.51 g/L biobutanol production by Clostridium acetobutylicum ATCC824. The sequential bioprocessing of low-priced substrates and exploitation of vegetable extract as growth factor for microbial butanol production will open a new vista in biofuel research.

Production of polyunsaturated fatty acids by Schizochytrium (Aurantiochytrium) spp

Diverse health benefits are associated with dietary consumption of omega-3 long-chain polyunsaturated fatty acids (ω-3 LC-PUFA), particularly docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). Traditionally, these fatty acids have been obtained from fish oil, but limited supply, variably quality, and an inability to sustainably increase production for a rapidly growing market, are driving the quest for alternative sources. DHA derived from certain marine protists (heterotrophic thraustochytrids) already has an established history of commercial production for high-value dietary use, but is too expensive for use in aquaculture feeds, a much larger potential market for ω-3 LC-PUFA. Sustainable expansion of aquaculture is prevented by its current dependence on wild-caught fish oil as the source of ω-3 LC-PUFA nutrients required in the diet of aquacultured animals. Although several thraustochytrids have been shown to produce DHA and EPA, there is a particular interest in Schizochytrium spp. (now Aurantiochytrium spp.), as some of the better producers. The need for larger scale production has resulted in development of many strategies for improving productivity and production economics of ω-3 PUFA in Schizochytrium spp. Developments in fermentation technology and metabolic engineering for enhancing LC-PUFA production in Schizochytrium spp. are reviewed.

Formulation of New Media from Dairy and Brewery Wastes for a Sustainable Production of DHA-Rich Oil by Aurantiochytrium mangrovei

Mozzarella stretching water (MSW) is a dairy effluent generated from mozzarella cheese production that does not have a real use and is destined to disposal, causing environmental problems and representing a high disposal cost for dairy producers. Spent brewery yeast (SBY) is another promising food waste produced after brewery manufacturing that could be recycled in new biotechnological processes. Aurantiochytrium mangrovei is an aquatic protist known as producer of bioactive lipids such as omega 3 long chain polyunsaturated fatty acids (ω3 LC-PUFA), in particular docosahexaenoic acid (DHA). In this work MSW and SBY have been used to formulate new sustainable growth media for A. mangrovei cultivation and production of DHA in an attempt to valorize these effluents. MSW required an enzymatic hydrolysis to enhance the biomass production. The new media obtained from hydrolysed MSW was also optimized using response surface methodologies, obtaining 10.14 g L^-1 of biomass in optimized medium, with a DHA content of 1.21 g L^-1.

Thraustochytrids of Mangrove Habitats from Andaman Islands: Species Diversity, PUFA Profiles and Biotechnological Potential

Thraustochytrids are the most promising microbial source for the commercial production of docosahexaenoic acid (DHA) for its application in the human health, aquaculture, and nutraceutical sectors. The present study isolated 127 thraustochytrid strains from mangrove habitats of the south Andaman Islands, India to study their diversity, polyunsaturated fatty acids (PUFAs), and biotechnological potential. The predominant strains were identified as belonging to two major genera (Thraustochytrium, Aurantiochytrium) based on morphological and molecular characteristics. The strain ANVKK-06 produced the maximum biomass of 5.42 g·L^-1, while ANVKK-03 exhibited the maximum total lipid (71.03%). Omega-3 PUFAs such as eicosapentaenoic acid (EPA) accumulated up to 11.03% in ANVKK-04, docosapentaenoic acid (DPA) up to 8.65% in ANVKK-07, and DHA up to 47.19% in ANVKK-06. ANVKK-06 showed the maximum scavenging activity (84.79 ± 2.30%) while ANVKK-03 and ANVKK-10 displayed the highest antibacterial activity against human and fish pathogens, S. aureus (18.69 ± 1.2 mm) and V. parahaemolyticus (18.31 ± 1.0 mm), respectively. All strains were non-toxic as evident by negative blood agar hemolysis, thus, the thraustochytrids are suggested to be a potential source of DHA for application in the health care of human and fish.

Method Development Progress in Genetic Engineering of Thraustochytrids

Thraustochytrids are unicellular, heterotrophic marine eukaryotes. Some species are known to store surplus carbon as intracellular lipids, and these also contain the long-chain polyunsaturated fatty acid docosahexaenoic acid (DHA). Most vertebrates are unable to synthesize sufficient amounts of DHA, and this fatty acid is essential for, e.g., marine fish, domesticated animals, and humans. Thraustochytrids may also produce other commercially valuable fatty acids and isoprenoids. Due to the great potential of thraustochytrids as producers of DHA and other lipid-related molecules, a need for more knowledge on this group of organisms is needed. This necessitates the ability to do genetic manipulation of the different strains. Thus far, this has been obtained for a few strains, while it has failed for other strains. Here, we systematically review the genetic transformation methods used for different thraustochytrid strains, with the aim of aiding studies on strains not yet successfully transformed. The designs of transformation cassettes are also described and compared. Moreover, the potential problems when trying to establish transformation protocols in new thraustochytrid species/strains are discussed, along with suggestions utilized in other organisms to overcome similar challenges. The approaches discussed in this review could be a starting point when designing protocols for other non-model organisms.

Antarctic Thraustochytrids as Sources of Carotenoids and High-Value Fatty Acids

Eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and carotenoids are needed as human dietary supplements and are essential components in commercial feeds for the production of aquacultured seafood. Microorganisms such as thraustochytrids are potential natural sources of these compounds. This research reports on the lipid and carotenoid production capacity of thraustochytrids that were isolated from coastal waters of Antarctica. Of the 22 isolates, 21 produced lipids containing EPA+DHA, and the amount of these fatty acids exceeded 20% of the total fatty acids in 12 isolates. Ten isolates were shown to produce carotenoids (27.4-63.9 μg/g dry biomass). The isolate RT2316-16, identified as Thraustochytrium sp., was the best producer of biomass (7.2 g/L in five days) rich in carotenoids (63.9 μg/g) and, therefore, became the focus of this investigation. The main carotenoids in RT2316-16 were β-carotene and canthaxanthin. The content of EPA+DHA in the total lipids (34 ± 3% w/w in dry biomass) depended on the stage of growth of RT2316-16. Lipid and carotenoid content of the biomass and its concentration could be enhanced by modifying the composition of the culture medium. The estimated genome size of RT2316-16 was 44 Mb. Of the 5656 genes predicted from the genome, 4559 were annotated. These included genes of most of the enzymes in the elongation and desaturation pathway of synthesis of ω-3 polyunsaturated fatty acids. Carotenoid precursors in RT2316-16 were synthesized through the mevalonate pathway. A β-carotene synthase gene, with a different domain organization compared to the gene in other thraustochytrids, explained the carotenoid profile of RT2316-16.

Isolation and Optimization of Culture Conditions of Thraustochytrium kinnei for Biomass Production, Nanoparticle Synthesis, Antioxidant and Antimicrobial Activities

This work deals with the identification of a predominant thraustochytrid strain, the optimization of culture conditions, the synthesis of nanoparticles, and the evaluation of antioxidant and antimicrobial activities in biomass extracts and nanoparticles. Thraustochytrium kinnei was identified as a predominant strain from decomposing mangrove leaves, and its culture conditions were optimized for maximum biomass production of 13.53 g·L−1, with total lipids of 41.33% and DHA of 39.16% of total fatty acids. Furthermore, the strain was shown to synthesize gold and silver nanoparticles in the size ranges of 10–85 nm and 5–90 nm, respectively. Silver nanoparticles exhibited higher total antioxidant and DPPH activities than gold nanoparticles and methanol extract of the strain. The silver nanoparticles showed higher antimicrobial activity than gold nanoparticles and petroleum ether extract of the strain. Thus, Thraustochytrium kinnei is proven to be promising for synthesis of silver nanoparticles with high antioxidant and antimicrobial activity.

Ecological and Biotechnological Aspects of Pigmented Microbes: A Way Forward in Development of Food and Pharmaceutical Grade Pigments

Microbial pigments play multiple roles in the ecosystem construction, survival, and fitness of all kinds of organisms. Considerably, microbial (bacteria, fungi, yeast, and microalgae) pigments offer a wide array of food, drug, colorants, dyes, and imaging applications. In contrast to the natural pigments from microbes, synthetic colorants are widely used due to high production, high intensity, and low cost. Nevertheless, natural pigments are gaining more demand over synthetic pigments as synthetic pigments have demonstrated side effects on human health. Therefore, research on microbial pigments needs to be extended, explored, and exploited to find potential industrial applications. In this review, the evolutionary aspects, the spatial significance of important pigments, biomedical applications, research gaps, and future perspectives are detailed briefly. The pathogenic nature of some pigmented bacteria is also detailed for awareness and safe handling. In addition, pigments from macro-organisms are also discussed in some sections for comparison with microbes.

Isolation and optimization of a novel thraustochytrid strain for DHA rich and astaxanthin comprising biomass as aquafeed supplement

A marine organism, belonging to the Thraustochytrids family was isolated from mangroves of Mumbai, India. The isolated strain was identified as Aurantiochytrium limacinum by internal transcribed spacer sequence analysis. Optimization of process parameters yielded 14.47 g/L dry cell weight containing 55-58% oil in 3.5 days' cultivation on glucose, yeast extract, and peptone in the bioreactor. Docosahexaenoic acid (DHA) was found to be the dominant long-chain polyunsaturated fatty acid, accounting for 32-35% of total fatty acid content. The process parameter was tweaked to simultaneously synthesize astaxanthin along with DHA. The concurrent synthesis of DHA and astaxanthin-containing biomass establishes the isolated strain as a perfect choice for aquafeed. Accession number: NCBI accession number MN046792.

Sustainable production of food grade omega-3 oil using aquatic protists: Reliability and future horizons

Biotechnological production of omega-3 polyunsaturated fatty acids (PUFAs) has become a commercial alternative to fish oil in the past twenty years. Compared to PUFA production by fatty fishes, that from microorganisms has increased due to its promising sustainability and high product safety and to increasing awareness in the expanding vegan market. Although autotrophic production by microalgae seems to be more sustainable in the long term, to date most of the microbial production of omega-3 is carried out under heterotrophic conditions using conventional fermentation technologies. The present review critically analyzes the main reasons for this discrepancy and reports on the recent advances and the most promising approaches for its future development in the context of sustainability and circular economy.

Reprogramming microorganisms for the biosynthesis of astaxanthin via metabolic engineering

There is an increasing demand for astaxanthin in food, feed, cosmetics and pharmaceutical applications because of its superior anti-oxidative and coloring properties. However, naturally produced astaxanthin is expensive, mainly due to low productivity and limited sources. Reprogramming of microorganisms for astaxanthin production via metabolic engineering is a promising strategy. We primarily focus on the application of synthetic biology, enzyme engineering and metabolic engineering in enhancing the synthesis and accumulation of astaxanthin in microorganisms in this review. We also discuss the biosynthetic pathways of astaxanthin within natural producers, and summarize the achievements and challenges in reprogramming microorganisms for enhancing astaxanthin production. This review illuminates recent biotechnological advances in microbial production of astaxanthin. Future perspectives on utilization of new technologies for boosting microbial astaxanthin production are also discussed.

Diverse Enzymes With Industrial Applications in Four Thraustochytrid Genera

Thraustochytrids are heterotrophic fungus-like protists that can dissolve organic matters with enzymes. Four strains, AP45, ASP1, ASP2, and ASP4, were isolated from the coastal water of Taiwan, and respectively identified as Aurantiochytrium sp., Schizochytrium sp., Parietichytrium sp., and Botryochytrium sp. based on 18S rRNA sequences. Transcriptome datasets of these four strains at days 3-5 were generated using Next Generation Sequencing technology, and screened for enzymes with potential industrial applications. Functional annotations based on KEGG database suggest that many unigenes of all four strains were related to the pathways of industrial enzymes. Most of all four strains contained homologous genes for 15 out of the 17 targeted enzymes, and had extra- and/or intra-cellular enzymatic activities, including urease, asparaginase, lipase, glucosidase, alkaline phosphatase and protease. Complete amino sequences of the first-time identified L-asparaginase and phytase in thraustochytrids were retrieved, and respectively categorized to the Type I and BPPhy families based on phylogenetic relationships, protein structural modeling and active sites. Milligram quantities of highly purified, soluble protein of urease and L-asparaginase were successfully harvested and analyzed for recombinant enzymatic activities. These analytical results highlight the diverse enzymes for wide-range applications in thraustochytrids.

Effects of Supplementation of Microalgae (Aurantiochytrium sp.) to Laying Hen Diets on Fatty Acid Content, Health Lipid Indices, Oxidative Stability, and Quality Attributes of Meat

The present study is conducted to investigate the effects of dietary docosahexaenoic acid (DHA)-rich microalgae (MA, Aurantiochytrium sp.) on health lipid indices, stability, and quality properties of meat from laying hens. A total of 450 healthy 50-wk-old Hy-Line Brown layers were randomly allotted to 5 groups (6 replicates of 15 birds each), which received diets supplemented with 0, 0.5, 1.0, 1.5, and 2.0% MA for 15 weeks. Fatty acid contents and quality properties of breast and thigh muscles from two randomly selected birds per replicate (n = 12) were measured. The oxidative stability of fresh, refrigerated, frozen, and cooked meat was also determined. Results indicated that supplemental MA produced dose-dependent enrichments of long-chain n-3 polyunsaturated fatty acids (n-3 LC-PUFA), predominantly DHA, in breast and thigh muscles, with more health-promoting n-6/n-3 ratios (1.87-5.27) and favorable lipid health indices (p < 0.05). MA supplementation did not affect tenderness (shear force) and color (L*, a*, and b* values) of hen meat nor muscle endogenous antioxidant enzymes and fresh meat oxidation (p > 0.05). However, the n-3 LC-PUFA deposition slightly increased lipid oxidation in cooked and stored (4 °C) meat (p < 0.05). In conclusion, MA supplementation improves the nutritional quality of hen meat in terms of lipid profile without compromising meat quality attributes. Appropriate antioxidants are required to mitigate oxidation when such DHA-enriched meat is subjected to cooking and storage.

Enhanced Production of Astaxanthin without Decrease of DHA Content in Aurantiochytrium limacinum by Overexpressing Multifunctional Carotenoid Synthase Gene

Aurantiochytrium limacinum produces both docosahexaenoic acid (DHA) and astaxanthin, respectively. Organisms that produce these industrially important materials more efficiently than microalgae are currently needed. In this study, we overexpressed a putative homolog of CarS, which is involved in synthesizing the astaxanthin precursor, β-carotene, in A. limacinum to increase carotenoid synthesis with the goal of obtaining strains that produce large amounts of both DHA and carotenoids. AlCarS transformants #1 and #18 produced significantly increased amounts of astaxanthin as assessed according to culture (up to 5.8-fold) and optical density (up to 9.3-fold). The improved astaxanthin production of these strains did not affect their DHA productivity. Additionally, their CarS expression levels were higher than those of the wild-type strain, suggesting that CarS overexpression enhanced β-carotene production, which in turn improved astaxanthin productivity. Although cell yields were slightly decreased, these features will be valuable in health food, medical care, and animal feed fields.

The lipid metabolism in thraustochytrids

Thraustochytrids are unicellular heterotrophic marine protists of the Stramenopile group, often considered as non-photosynthetic microalgae. They have been isolated from a wide range of habitats including deep sea, but are mostly present in waters rich in sediments and organic materials. They are abundant in mangrove forests where they are major colonizers, feeding on decaying leaves and initiating the mangrove food web. Discovered 80 years ago, they have recently attracted considerable attention due to their biotechnological potential. This interest arises from their fast growth, their specific lipid metabolism and the improvement of the genetic tools and transformation techniques. These organisms are particularly rich in ω3-docosahexaenoic acid (DHA), an 'essential' fatty acid poorly encountered in land plants and animals but required for human health. To produce their DHA, thraustochytrids use a sophisticated system different from the classical fatty acid synthase system. They are also a potential source of squalene and carotenoids. Here we review our current knowledge about the life cycle, ecophysiology, and metabolism of these organisms, with a particular focus on lipid dynamics. We describe the different pathways involved in lipid and fatty acid syntheses, emphasizing their specificity, and we report on the recent efforts aimed to engineer their lipid metabolism.

Illustrating and Enhancing the Biosynthesis of Astaxanthin and Docosahexaenoic Acid in Aurantiochytrium sp. SK4

The marine thraustochytrids are a promising source of docosahexaenoic acid (DHA) and the ketocarotenoid astaxanthin. In this study, the biosynthetic pathways of these two important metabolites in Aurantiochytrium sp. SK4 was illustrated by the analyses of the genome, transcriptome, key enzymes, and pathway products. Two sets of genes were involved in two pathways for the biosynthesis of fatty acids. The absence of Δ-15 desaturase genes and the presence of docosapentaenoic acid (DPA), up to 12% of total fatty acids suggest that Aurantiochytrium sp. SK4 may synthesize DHA mainly via a polyketide synthase (PKS) pathway. Three enzymes, namely geranyl diphosphate synthase (GPPS), farnysyl diphosphate synthase (FPPS), and geranylgeranyle diphosphate synthase (GGPPS) were found to be involved in the formation of GGPP that was subsequently catalyzed to β-carotene by a trifunctional CrtIBY enzyme. β-Carotene might be ketolated and then hydroxylated into astaxanthin based on the carotenoid profiles. The formation of GGPP was proposed to be the limiting steps for carotenoid production. Overexpression of the Archaeoglobus GPS together with the Escherichia coli isopentenyl pyrophosphate isomerase, and Vitreoscilla hemoglobin resulted in not only 1.85- and 5.02-fold increases of total carotenoids and astaxanthin, but also 2.40- and 2.74-fold increases of total fatty acids and DHA. This study provides insights into the biosynthesis of carotenoids and fatty acids in Aurantiochytrium.

Prospects on the Use of Schizochytrium sp. to Develop Oral Vaccines

Although oral subunit vaccines are highly relevant in the fight against widespread diseases, their high cost, safety and proper immunogenicity are attributes that have yet to be addressed in many cases and thus these limitations should be considered in the development of new oral vaccines. Prominent examples of new platforms proposed to address these limitations are plant cells and microalgae. Schizochytrium sp. constitutes an attractive expression host for vaccine production because of its high biosynthetic capacity, fast growth in low cost culture media, and the availability of processes for industrial scale production. In addition, whole Schizochytrium sp. cells may serve as delivery vectors; especially for oral vaccines since Schizochytrium sp. is safe for oral consumption, produces immunomodulatory compounds, and may provide bioencapsulation to the antigen, thus increasing its bioavailability. Remarkably, Schizochytrium sp. was recently used for the production of a highly immunoprotective influenza vaccine. Moreover, an efficient method for transient expression of antigens based on viral vectors and Schizochytrium sp. as host has been recently developed. In this review, the potential of Schizochytrium sp. in vaccinology is placed in perspective, with emphasis on its use as an attractive oral vaccination vehicle.