Impact of methyl jasmonate on squalene biosynthesis in microalga Schizochytrium mangrovei

Bioprocess conditions and regulation factors to optimize squalene production in thraustochytrids

Squalene is a widely distributed natural triterpene, as it is a key precursor in the biosynthesis of all sterols. It is a compound of high commercial value worldwide because it has nutritional, medicinal, pharmaceutical, and cosmetic applications, due to its different biological properties. The main source of extraction has been shark liver oil, which is currently unviable on a larger scale due to the impacts of overexploitation. Secondary sources are mainly vegetable oils, although a limited one, as they allow low productive yields. Due to the diversity of applications that squalene presents and its growing demand, there is an increasing interest in identifying sustainable sources of extraction. Wild species of thraustochytrids, which are heterotrophic protists, have been identified to have the highest squalene content compared to bacteria, yeasts, microalgae, and vegetable sources. Several studies have been carried out to identify the bioprocess conditions and regulation factors, such as the use of eustressors that promote an increase in the production of this triterpene; however, studies focused on optimizing their productive yields are still in its infancy. This review includes the current trends that also comprises the advances in genetic regulations in these microorganisms, with a view to identify the culture conditions that have been favorable in increasing the production of squalene, and the influences that both bioprocess conditions and applied regulation factors partake at a metabolic level.

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.

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.

Microalgae as feedstock for bioactive polysaccharides

Due to the increase in industrial demand for new biosourced molecules (notably bioactive exopolysaccharides (EPS)), microalgae are gaining popularity because of their nutraceutical potential and benefits health. Such health effects are delivered by specific secondary metabolites, e.g., pigments, exopolysaccharides, polyunsaturated fatty acids, proteins, and glycolipids. These are suitable for the subsequent uses in cosmetic, nutraceutical, pharmaceutical, biofuels, biological waste treatment, animal feed and food fields. In this regard, a special focus has been given in this review to describe the various methods used for extraction and purification of polysaccharides. The second part of the review provides an up-to-date and comprehensive summary of parameters affecting the microalgae growth and insights to maximize the metabolic output by understanding the intricacies of algal development and polysaccharides production. In the ultimate part, the health and nutraceutical claims associated with marine algal bioactive polysaccharides, explaining their noticeable potential for biotechnological applications, are summarized and comprehensively discussed.

Microbial genetic engineering approach to replace shark livering for squalene

Squalene is generally sourced from the liver oil of deep sea sharks (Squalus spp.), in which it accounts for 40-70% of liver mass. To meet the growing demand for squalene because of its beneficial effects for human health, three to six million deep sea sharks are slaughtered each year, profoundly endangering marine ecosystems. To overcome this unsustainable practice, microbial sources of squalene might offer a viable alternative to plant- or animal-based squalene, although only a few microorganisms have been found that are capable of synthesizing up to 30% squalene of dry biomass by native biosynthetic pathways. These squalene biosynthetic pathways, on the other hand, can be genetically manipulated to transform microorganisms into 'cellular factories' for squalene overproduction.

Recent advances in the microbial production of squalene

Squalene is a triterpene hydrocarbon, a biochemical precursor for all steroids in plants and animals. It is a principal component of human surface lipids, in particular of sebum. Squalene has several applications in the food, pharmaceutical, and medical sectors. It is essentially used as a dietary supplement, vaccine adjuvant, moisturizer, cardio-protective agent, anti-tumor agent and natural antioxidant. With the increased demand for squalene along with regulations on shark-derived squalene, there is a need to find alternatives for squalene production which are low-cost as well as sustainable. Microbial platforms are being considered as a potential option to meet such challenges. Considerable progress has been made using both wild-type and engineered microbial strains for improved productivity and yields of squalene. Native strains for squalene production are usually limited by low growth rates and lesser titers. Metabolic engineering, which is a rational strain engineering tool, has enabled the development of microbial strains such as Saccharomyces cerevisiae and Yarrowia lipolytica, to overproduce the squalene in high titers. This review focuses on key strain engineering strategies involving both in-silico and in-vitro techniques. Emphasis is made on gene manipulations for improved precursor pool, enzyme modifications, cofactor regeneration, up-regulation of limiting reactions, and downregulation of competing reactions during squalene production. Process strategies and challenges related to both upstream and downstream during mass cultivation are detailed.

Media Supplementation with Mannitol and Biotin Enhances Squalene Production of Thraustochytrium ATCC 26185 through Increased Glucose Uptake and Antioxidative Mechanisms

Media supplementation with exogenous chemicals is known to stimulate the accumulation of important lipids produced by microalgae and thraustochytrids. However, the roles of exogenous chemicals in promoting and preserving the terpenoids pool of thraustochytrids have been rarely investigated. Here, we realized the effects of two media supplements—mannitol and biotin—on the biomass and squalene production by a thraustochytrid strain (Thraustochytrium sp. ATCC 26185) and elucidated their mechanism of action. A significant change in the biomass was not evident with the exogenous addition of these supplements. However, with mannitol (1 g/L) supplementation, the ATCC 26185 culture achieved the best concentration (642 ± 13.6 mg/L) and yield (72.9 ± 9.6 mg/g) of squalene, which were 1.5-fold that of the control culture (non-supplemented). Similarly, with biotin supplementation (0.15 mg/L), the culture showed 459 ± 2.9 g/L and 55.7 ± 3.2 mg/g of squalene concentration and yield, respectively. The glucose uptake rate at 24 h of fermentation increased markedly with mannitol (0.31 g/Lh⁻¹) or biotin (0.26 g/Lh⁻¹) supplemented culture compared with non-supplemented culture (0.09 g/Lh⁻¹). In addition, the reactive oxygen species (ROS) level of culture supplemented with mannitol remained alleviated during the entire period of fermentation while it alleviated after 24 h with biotin supplementation. The ∆ROS with mannitol was better compared with biotin supplementation. The total antioxidant capacity (T-AOC) of the supplemented culture was more than 50% during the late stage (72–96 h) of fermentation. Our study provides the potential of mannitol and biotin to enhance squalene yield and the first lines of experimental evidence for their protective role against oxidative stress during the culture of thraustochytrids.

Genetic regulation and fermentation strategy for squalene production in Schizochytrium sp

Squalene, as an important terpenoid, is extensively used in the medicine and health care fields owing to its functions of anti-oxidation, blood lipid regulation and cancer prevention. The marine microalgae, Schizochytrium sp., which acts as an excellent strain with potential of high squalene production was selected as the starting strain. The overexpressed strain with sqs gene got the reduced biomass and lipid, while the squalene titer was increased by 79.6% ± 4.7% to 12.8 ± 0.2 mg/L. In order to further increase squalene production, the recombinant strain (HS strain) with sqs and hmgr gene co-overexpression was further constructed. The biomass and squalene titer of the HS strain were increased by 13.6% ± 1.2% and 88.8% ± 5.3%, respectively, which indicated the carbon flux of the mevalonate pathway was enhanced for squalene accumulation. Regarding the squalene synthesis is completely coupled with cell growth, fermentation strategy to prolong the logarithmic growth phase was conducive to improve squalene production. Under the condition of optimal composition and concentrated medium, the squalene titer of HS strain was 27.0 ± 1.3 mg/L, which was 2.0 times that of the basal medium condition (13.5 ± 0.4 mg/L). This study which combined the metabolic engineering and fermentation strategy provides a new strategy for squalene production in Schizochytrium sp. KEY POINTS: •The overexpression of sqs and hmgr genes promoted carbon metabolism for squalene. •The optimal and concentrated media can increase squalene yield.

Improving squalene production by blocking the competitive branched pathways and expressing rate-limiting enzymes in Rhodopseudomonas palustris

Squalene is a medically valuable bioactive compound that can be used as a raw material for fuels. Microbial fermentation is the preferred method for the squalene production. In this study, we employed several metabolic engineering strategies to increase squalene yield in Rhodopseudomonas palustris. A 57% increase in squalene titer was achieved by blocking the carotenoid pathway, thus directing more FPP into the squalene biosynthetic pathway. In order to cut down the conversion of squalene to haponoids, a recombinant strain R. palustris [Δshc, ΔcrtB] in which both carotenoid and haponoid pathways were blocked was then constructed, resulting in a 50-fold increase in squalene titer. Based on the expression of rate-limiting enzymes involved in the squalene pathway, the final squalene content reached 23.3 mg/g DCW, which was 178-times higher than that of the wild-type strain. In this study, several methods effective in improving squalene yield have been described and the potential of R. palustris for producing squalene has been demonstrated.

Mining of squalene as a value-added byproduct from DHA producing marine thraustochytrid cultivated on food waste hydrolysate

The commercial production of docosahexaenoic acid (DHA) from oleaginous microorganisms is getting more attention due to several advantages over fish oils. The processing cost became a major bottleneck for commercialization of DHA from microorganisms. The most of cost shares in the feedstock to cultivate the microorganisms and downstream processing. The cost of feedstock can be compensated with the utilization of substrate from waste stream whereas production of value-added chemicals boosts the economic viability of nutraceutical production. In the present study, the docosahexaenoic acid (DHA)-producing marine protist Aurantiochytrium sp. T66 was cultivated on post-consumption food waste hydrolysate for the mining of squalene. After 120 h of cultivation, cell dry weight was 14.7 g/L, of which 6.34 g/L (43.13%; w/w) were lipids. DHA accounted for 2.15 g/L (34.05%) of total extracted lipids or 0.15 g/g_CDW. Maximum squalene concentration and yield were 1.05 g/L and 69.31 mg/g_CDW, respectively. Hence, utilization of food waste represents an excellent low-cost strategy for cultivating marine oleaginous thraustochytrids and produce squalene as a byproduct of DHA.

Co-production of DHA and squalene by thraustochytrid from forest biomass

Omega-3 fatty acids, and specifically docosahexaenoic acid (DHA), are important and essential nutrients for human health. Thraustochytrids are recognised as commercial strains for nutraceuticals production, they are group of marine oleaginous microorganisms capable of co-synthesis of DHA and other valuable carotenoids in their cellular compartment. The present study sought to optimize DHA and squalene production by the thraustochytrid Schizochytrium limacinum SR21. The highest biomass yield (0.46 g/g_substrate) and lipid productivity (0.239 g/g_substrate) were observed with 60 g/L of glucose, following cultivation in a bioreactor, with the DHA content to be 67.76% w/w_{total lipids}. To reduce costs, cheaper feedstocks and simultaneous production of various value-added products for pharmaceutical or energy use should be attempted. To this end, we replaced pure glucose with organosolv-pretreated spruce hydrolysate and assessed the simultaneous production of DHA and squalene from S. limacinum SR21. After the 72 h of cultivation period in bioreactor, the maximum DHA content was observed to 66.72% w/w_{total lipids} that was corresponded to 10.15 g/L of DHA concentration. While the highest DHA productivity was 3.38 ± 0.27 g/L/d and squalene reached a total of 933.72 ± 6.53 mg/L (16.34 ± 1.81 mg/g_CDW). In summary, we show that the co-production of DHA and squalene makes S. limacinum SR21 appropriate strain for commercial-scale production of nutraceuticals.

The role of fluconazole in the regulation of fatty acid and unsaponifiable matter biosynthesis in Schizochytrium sp. MYA 1381

Background

Schizochytrium has been widely used in industry for synthesizing polyunsaturated fatty acids (PUFAs), especially docosahexaenoic acid (DHA). However, unclear biosynthesis pathway of PUFAs inhibits further production of the Schizochytrium. Unsaponifiable matter (UM) from mevalonate pathway is crucial to cell growth and intracellular metabolism in all higher eukaryotes and microalgae. Therefore, regulation of UM biosynthesis in Schizochytrium may have important effects on fatty acids synthesis. Moreover, it is well known that UMs, such as squalene and β-carotene, are of great commercial value. Thus, regulating UM biosynthesis may also allow for an increased valuation of Schizochytrium.

Results

To investigate the correlation of UM biosynthesis with fatty acids accumulation in Schizochytrium, fluconazole was used to block the sterols pathway. The addition of 60 mg/L fluconazole at 48 h increased the total lipids (TLs) at 96 h by 16% without affecting cell growth, which was accompanied by remarkable changes in UMs and NADPH. Cholesterol content was reduced by 8%, and the squalene content improved by 45% at 72 h, which demonstrated fluconazole’s role in inhibiting squalene flow to cholesterol. As another typical UM with antioxidant capacity, the β-carotene production was increased by 53% at 96 h. The increase of squalene and β-carotene could boost intracellular oxidation resistance to protect fatty acids from oxidation. The NADPH was found to be 33% higher than that of the control at 96 h, which meant that the cells had more reducing power for fatty acid synthesis. Metabolic analysis further confirmed that regulation of sterols was closely related to glucose absorption, pigment biosynthesis and fatty acid production in Schizochytrium.

Conclusion

This work first reported the effect of UM biosynthesis on fatty acid accumulation in Schizochytrium. The UM was found to affect fatty acid biosynthesis by changing cell membrane function, intracellular antioxidation and reducing power. We believe that this work provides valuable insights in improving PUFA and other valuable matters in microalgae.

A review on commercial-scale high-value products that can be produced alongside cellulosic ethanol

The demand for fossil derivate fuels and chemicals has increased, augmenting concerns on climate change, global economic stability, and sustainability on fossil resources. Therefore, the production of fuels and chemicals from alternative and renewable resources has attracted considerable and growing attention. Ethanol is a promising biofuel that can reduce the consumption of gasoline in the transportation sector and related greenhouse gas (GHG) emissions. Lignocellulosic biomass is a promising feedstock to produce bioethanol (cellulosic ethanol) because of its abundance and low cost. Since the conversion of lignocellulose to ethanol is complex and expensive, the cellulosic ethanol price cannot compete with those of the fossil derivate fuels. A promising strategy to lower the production cost of cellulosic ethanol is developing a biorefinery which produces ethanol and other high-value chemicals from lignocellulose. The selection of such chemicals is difficult because there are hundreds of products that can be produced from lignocellulose. Multiple reviews and reports have described a small group of lignocellulose derivate compounds that have the potential to be commercialized. Some of these products are in the bench scale and require extensive research and time before they can be industrially produced. This review examines chemicals and materials with a Technology Readiness Level (TRL) of at least 8, which have reached a commercial scale and could be shortly or immediately integrated into a cellulosic ethanol process.

Bio-based squalene production by Aurantiochytrium sp. through optimization of culture conditions, and elucidation of the putative biosynthetic pathway genes

Newly-isolated thraustochytrid strains from coastal waters of China were characterized as bioresource of squalene and the culture condition for the top producer was systematically optimized. Phylogenetic analysis revealed that eight squalene-producing isolates were closely related to genus Aurantiochytrium and one to genus Labyrinthula. The top producer, Aurantiochytrium sp. TWZ-97, produced squalene up to 188.6 mg/L at 28 °C in a 5-L bioreactor containing optimal medium (glucose: 40 g/L, monosodium glutamate: 3 g/L, yeast extract: 25 g/L, and NaCl: 6 g/L), which was 6-fold higher than that under unoptimized condition. Transcriptome analysis revealed for the first time the presence of seven key genes of mevalonate pathway for squalene biosynthesis in strain TWZ-97. Medium optimization yielded a 2.23-fold higher expression of the squalene synthase gene under optimal condition compared to unoptimized. This study provides a potential thraustochytrid strain TWZ-97 as bioresource of squalene and uncovers novel information about its squalene biosynthesis pathway for future strain improvement.

Improving squalene production by enhancing the NADPH/NADP+ ratio, modifying the isoprenoid-feeding module and blocking the menaquinone pathway in Escherichia coli

BACKGROUND

Squalene is currently used widely in the food, cosmetics, and medicine industries. It could also replace petroleum as a raw material for fuels. Microbial fermentation processes for squalene production have been emerging over recent years. In this study, to study the squalene-producing potential of Escherichia coli (E. coli), we employed several increasing strategies for systematic metabolic engineering. These include the expression of human truncated squalene synthase, the overexpression of rate-limiting enzymes in isoprenoid pathway, the modification of isoprenoid-feeding module and the blocking of menaquinone pathway.

RESULTS

Herein, human truncated squalene synthase was engineered in Escherichia coli to create a squalene-producing bacterial strain. To increase squalene yield, we employed several metabolic engineering strategies. A fivefold squalene titer increase was achieved by expressing rate-limiting enzymes (IDI, DXS, and FPS) involved in the isoprenoid pathway. Pyridine nucleotide transhydrogenase (UdhA) was then expressed to improve the cellular NADPH/NADP⁺ ratio, resulting in a 59% increase in squalene titer. The Embden-Meyerhof pathway (EMP) was replaced with the Entner-Doudoroff pathway (EDP) and pentose phosphate pathway (PPP) to feed the isoprenoid pathway, along with the overexpression of zwf and pgl genes which encode rate-limiting enzymes in the EDP and PPP, leading to a 104% squalene content increase. Based on the blocking of menaquinone pathway, a further 17.7% increase in squalene content was achieved. Squalene content reached a final 28.5 mg/g DCW and 52.1 mg/L.

CONCLUSIONS

This study provided novel strategies for improving squalene yield and demonstrated the potential of producing squalene by E. coli.

Simultaneous production of DHA and squalene from Aurantiochytrium sp. grown on forest biomass hydrolysates

BACKGROUND

Recent evidence points to the nutritional importance of docosahexaenoic acid (DHA) in the human diet. Thraustochytrids are heterotrophic marine oleaginous microorganisms capable of synthesizing high amounts of DHA, as well as other nutraceutical compounds such as squalene, in their cellular compartment. Squalene is a natural triterpene and an important biosynthetic precursor to all human steroids. It has a wide range of applications in the cosmetic and pharmaceutical industries, with benefits that include boosting immunity and antioxidant activity. Apart from its nutritional quality, it can also be utilized for high-grade bio-jet fuel by catalytic conversion.

RESULTS

In the present study, the potential of thraustochytrid strain Aurantiochytrium sp. T66 to produce DHA and squalene was evaluated. When the strain was cultivated on organosolv-pretreated birch hydrolysate (30 g/L glucose) in flask, it resulted in 10.39 g/L of cell dry weight and 4.98 g/L of total lipids, of which 25.98% was DHA. In contrast, when the strain was grown in a bioreactor, cell dry weight, total lipid, and DHA increased to 11.24 g/L, 5.90 g/L, and 35.76%, respectively. The maximum squalene yield was 69.31 mg/g_CDW (0.72 g/L) when the strain was cultivated in flask, but it increased to 88.47 mg/g_CDW (1.0 g/L), when cultivation shifted to a bioreactor.

CONCLUSIONS

This is the first report demonstrating the utilization of low cost non-edible lignocellulosic feedstock to cultivate the marine oleaginous microorganism Aurantiochytrium sp. for the production of nutraceutical vital compounds. Owing to the simultaneous generation of DHA and squalene, the strain is suitable for industrial-scale production of nutraceuticals.

Screening chemical modulators of benzoic acid derivatives to improve lipid accumulation in Schizochytrium limacinum SR21 with metabolomics analysis

BACKGROUND

Schizochytrium sp. is a marine fungus with great potential as an alternative commercial source of lipids rich in polyunsaturated fatty acids (PUFAs). To further increase lipid accumulation in Schizochytrium sp., the effect of exogenous additives has become one of the hotspots of current research. Although benzoic acid derivatives showed positive effects on lipid accumulation in Schizochytrium, the biochemical mechanism needs further investigation.

RESULTS

Four benzoic acid derivatives (sodium benzoate, p-aminobenzoic acid, p-methyl benzoic acid and folic acid) were screened and evaluated for their effect on lipid accumulation in Schizochytrium limacinum SR21. The lipid yield was increased by 56.84% with p-aminobenzoic acid (p-ABA) at a concentration of 200 mg/L among the four tested chemical modulators. The metabolomics analysis showed that 200 mg/L p-ABA was optimal for promoting glucose catabolism in glycolysis with an increase in the mevalonate pathway and a weakening of the tricarboxylic acid (TCA) cycle. Moreover, p-ABA increased NADPH generation by enhancing the pentose phosphate pathway (PPP), ultimately redirecting the metabolic flux to lipid synthesis. Fed-batch fermentation further proved that p-ABA could significantly increase the yield of lipid by 30.01%, reaching 99.67 g/L, and the lipid content was increased by 35.03%, reaching 71.12%. More importantly, the yields of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) were increased by 33.28% and 42.0%, respectively.

CONCLUSION

The addition of p-ABA could promote the synthesis of tetrahydrofolate, enhancing NADPH, which ultimately promoted the flow of carbon flux to lipid synthesis. These findings provide a valuable strategy for improving the lipid accumulation in Schizochytrium by additives.

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.

Screening of chemical modulators for lipid accumulation in Schizochytrium sp. S31

Schizochytrium sp. is a promising candidate for docosahexaenoic acid (DHA) production due to its high content of lipid and DHA proportions. To further enhance the lipid accumulation, seven chemical modulators were screened to evaluate their roles on lipid accumulation. Notably, among the seven tested chemical modulators, the addition of naphthoxyacetic acid (BNOA) or jasmonic acid (JA) was able to increase the lipid accumulation of Schizochytrium sp. S31. In addition, the effects of BNOA and JA were demonstrated dose-dependent and time-dependent, achieving a highest increase in lipid content by 11.16% and 12.71% when 2.0 mg/L of BNOA or 20 mg/L of JA was added into culture at 48 h after inoculation, respectively. In addition, the combination of 2 mg/L BNOA and 20 mg/L JA further increased lipid accumulation up to 16.79%. These results provided valuable strategy on promoting the lipid accumulation and DHA production by chemical modulators in Schizochytrium sp. S31.

Mining terpenoids production and biosynthetic pathway in thraustochytrids

Terpenoids are major bioactive compounds produced by microalgae and other eukaryotic microorganisms. Mining metabolic potential of marine microalgae for commercial production of terpenoids suggest thraustochytrids as one of the promising cell factories. The identification of potential thraustochytrid strains and relevant laboratory scale bioprocesses has been pursued largely. Further investigations in the improvement of terpenoids biosynthesis expect relevant molecular mechanisms to be understood directing metabolic engineering of the pathways. In this review, fermentative and mechanistic studies to identify key enzymes and pathways that are associated to terpenoids biosynthesis in thraustochytrids are discussed. Exploration of biosynthesis mechanisms in other model organisms facilitated identification of potential molecular targets for engineering terpenoids biosynthetic pathway in thraustochytrids. In addition, the preliminary genetic manipulation and in silico analysis in this review provides a platform for system-level metabolic engineering towards thraustochytrid strains improvement. Overall, the review contributes comprehensive information to allow better terpenoids productivity in thraustochytrids.

Taxonomy, ecology and biotechnological applications of thraustochytrids: A review

Thraustochytrids were first discovered in 1934, and since the 1960's they have been increasingly studied for their beneficial and deleterious effects. This review aims to provide an enhanced understanding of these protists with a particular emphasis on their taxonomy, ecology and biotechnology applications. Over the years, thraustochytrid taxonomy has improved with the development of modern molecular techniques and new biochemical markers, resulting in the isolation and description of new strains. In the present work, the taxonomic history of thraustochytrids is reviewed, while providing an up-to-date classification of these organisms. It also describes the various biomarkers that may be taken into consideration to support taxonomic characterization of the thraustochytrids, together with a review of traditional and modern techniques for their isolation and molecular identification. The originality of this review lies in linking taxonomy and ecology of the thraustochytrids and their biotechnological applications as producers of docosahexaenoic acid (DHA), carotenoids, exopolysaccharides and other compounds of interest. The paper provides a summary of these aspects while also highlighting some of the most important recent studies in this field, which include the diversity of polyunsaturated fatty acid metabolism in thraustochytrids, some novel strategies for biomass production and recovery of compounds of interest. Furthermore, a detailed overview is provided of the direct and current applications of thraustochytrid-derived compounds in the food, fuel, cosmetic, pharmaceutical, and aquaculture industries and of some of the commercial products available. This review is intended to be a source of information and references on the thraustochytrids for both experts and those who are new to this field.

Isoprenoid biosynthesis in dandelion latex is enhanced by the overexpression of three key enzymes involved in the mevalonate pathway

BACKGROUND

Latex from the dandelion species Taraxacum brevicorniculatum contains many high-value isoprenoid end products, e.g. triterpenes and polyisoprenes such as natural rubber. The isopentenyl pyrophosphate units required as precursors for these isoprenoids are provided by the mevalonate (MVA) pathway. The key enzyme in this pathway is 3-hydroxy-methyl-glutaryl-CoA reductase (HMGR) and its activity has been thoroughly characterized in many plant species including dandelion. However, two enzymes acting upstream of HMGR have not been characterized in dandelion latex: ATP citrate lyase (ACL), which provides the acetyl-CoA utilized in the MVA pathway, and acetoacetyl-CoA thiolase (AACT), which catalyzes the first step in the pathway to produce acetoacetyl-CoA. Here we isolated ACL and AACT genes from T. brevicorniculatum latex and characterized their expression profiles. We also overexpressed the well-characterized HMGR, ACL and AACT genes from Arabidopsis thaliana in T. brevicorniculatum to determine their impact on isoprenoid end products in the latex.

RESULTS

The spatial and temporal expression profiles of T. brevicorniculatum ACL and AACT revealed their pivotal role in the synthesis of precursors necessary for isoprenoid biosynthesis in latex. The overexpression of A. thaliana ACL and AACT and HMGR in T. brevicorniculatum latex resulted in the accumulation of all three enzymes, increased the corresponding enzymatic activities and ultimately increased sterol levels by ~5-fold and pentacyclic triterpene and cis-1,4-isoprene levels by ~2-fold. Remarkably high levels of the triterpene precursor squalene were also detected in the triple-transgenic lines (up to 32 mg/g root dry weight) leading to the formation of numerous lipid droplets which were observed in root cross-sections.

CONCLUSIONS

We could show the effective expression of up to three transgenes in T. brevicorniculatum latex which led to increased enzymatic activity and resulted in high level squalene accumulation in the dandelion roots up to an industrially relevant amount. Our data provide insight into the regulation of the MVA pathway in dandelion latex and can be used as a basis for metabolic engineering to enhance the production of isoprenoid end products in this specialized tissue.

Stress responses of the oil-producing green microalga Botryococcus braunii Race B

Plants react to biotic and abiotic stresses with a variety of responses including the production of reactive oxygen species (ROS), which may result in programmed cell death (PCD). The mechanisms underlying ROS production and PCD have not been well studied in microalgae. Here, we analyzed ROS accumulation, biomass accumulation, and hydrocarbon production in the colony-forming green microalga Botryococcus braunii in response to several stress inducers such as NaCl, NaHCO₃, salicylic acid (SA), methyl jasmonate, and acetic acid. We also identified and cloned a single cDNA for the B. braunii ortholog of the Arabidopsis gene defender against cell death 1 (DAD1), a gene that is directly involved in PCD regulation. The function of B. braunii DAD1 was assessed by a complementation assay of the yeast knockout line of the DAD1 ortholog, oligosaccharyl transferase 2. Additionally, we found that DAD1 transcription was induced in response to SA at short times. These results suggest that B. braunii responds to stresses by mechanisms similar to those in land plants and other  organisms.

Metabolic engineering of Rhodopseudomonas palustris for squalene production

Squalene is a strong antioxidant used extensively in the food, cosmetic and medicine industries. Rhodopseudomonas palustris TIE-1 was used as the host because of its ability to grow photosynthetically using solar energy and carbon dioxide from atmosphere. The deletion of the shc gene resulted in a squalene production of 3.8 mg/g DCW, which was 27-times higher than that in the wild type strain. For constructing a substrate channel to elevate the conversion efficiency, we tried to fuse crtE gene with hpnD gene. By fusing the two genes, squalene content was increased to 12.6 mg/g DCW, which was 27.4 % higher than that resulted from the co-expression method. At last, the titer of squalene reached 15.8 mg/g DCW by co-expressing the dxs gene, corresponding to 112-fold increase relative to that for wild-type strain. This study provided novel strategies for improving squalene yield and demonstrated the potential of producing squalene by Rhodopseudomonas palustris.

Metabolomics analysis reveals 6-benzylaminopurine as a stimulator for improving lipid and DHA accumulation of Aurantiochytriumsp

BACKGROUND

Phytohormones are chemical messengers that have a positive effect on biodiesel production of microalgae at low concentrations. However, the effect of phytohormone 6-benzylaminopurine on lipid and docosahexaenoic acid (DHA) production in marine DHA-producer Aurantiochytrium has never been reported. In this study, a GC-MS-based metabolomics method combined with a multivariate analysis is applied to reveal the metabolic mechanism of 6-benzylaminopurine enhancing production of lipid and DHA in Aurantiochytrium sp.YLH70.

RESULTS

In total, 71 metabolites were identified by GC-MS. The PCA model revealed that 76.9% of metabolite variation was related to 6-benzylaminopurine treatment, and overall metabolomics profiles between the 6-benzylaminopurine and control groups were clearly discriminated. Forty-six metabolites identified by the PLS-DA model were responsible for responding to 6-benzylaminopurine. Metabolic analysis showed that 6-benzylaminopurine could accelerate the rate of utilization of glucose in Aurantiochytrium sp. YLH70, and the metabolic flux from glycolysis, TCA cycle and mevalonate pathway to fatty acids biosynthesis was promoted. Moreover, the anti-stress mechanism in Aurantiochytrium sp.YLH70 might be induced by 6-benzylaminopurine.

CONCLUSION

Metabolomics is a suitable tool to discover the metabolic mechanism for improving lipid and DHA accumulation in a microorganism. 6-benzylaminopurine has the potential to stimulate lipid and DHA production of Aurantiochytrium sp.YLH70 for industrial purposes. © 2015 The Authors. Journal of Chemical Technology & Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

A review (research and patents) on jasmonic acid and its derivatives

In medicinal chemistry there is a growing interest in using small molecules, including plant stress hormones. Jasmonic acid (JA) and its volatile methyl ester (MJ), collectively termed jasmonates, are lipid-derived cyclopentanone compounds that occur ubiquitously and exclusively in the plant kingdom. This review covers the synthesis, usage, and biological activities of JA and its derivatives. A brief overview of the available information on JA and its features is given, followed by a detailed review of JA and its derivatives as drugs and prodrugs; the properties in plants and the synthesis in recent patents are described. This review shows the direction of long-term drug/nutraceutical safety trials and provides insights for future research in this area. Research on JA continues to be of major interest. Recent innovations offer hope for the development of new therapeutics in related fields. It is anticipated that several analogs can be advanced to preclinical and clinical studies.

Enhancement of ganoderic acid accumulation by overexpression of an N-terminally truncated 3-hydroxy-3-methylglutaryl coenzyme A reductase gene in the basidiomycete Ganoderma lucidum

Ganoderic acids produced by Ganoderma lucidum, a well-known traditional Chinese medicinal mushroom, exhibit antitumor and antimetastasis activities. Genetic modification of G. lucidum is difficult but critical for the enhancement of cellular accumulation of ganoderic acids. In this study, a homologous genetic transformation system for G. lucidum was developed for the first time using mutated sdhB, encoding the iron-sulfur protein subunit of succinate dehydrogenase, as a selection marker. The truncated G. lucidum gene encoding the catalytic domain of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) was overexpressed by using the Agrobacterium tumefaciens-mediated transformation system. The results showed that the mutated sdhB successfully conferred carboxin resistance upon transformation. Most of the integrated transfer DNA (T-DNA) appeared as a single copy in the genome. Moreover, deregulated constitutive overexpression of the HMGR gene led to a 2-fold increase in ganoderic acid content. It also increased the accumulation of intermediates (squalene and lanosterol) and the upregulation of downstream genes such as those of farnesyl pyrophosphate synthase, squalene synthase, and lanosterol synthase. This study demonstrates that transgenic basidiomycete G. lucidum is a promising system to achieve metabolic engineering of the ganoderic acid pathway.

Molecular cloning and expression of squalene synthase and 2,3-oxidosqualene cyclase genes in persimmon (Diospyros kaki L.) fruits

Oleanolic acid (OA) and ursolic acid (UA) are the main triterpene acids in persimmon fruit, and squalene synthase and 2,3-oxidosqualene cyclases are important enzymes in pentacyclic triterpene biosynthesis. In order to study their relationship, DkSQS and DkOSC were cloned from persimmon fruits in the present study. The full-length cDNA of DkSQS was 1647 bp, containing an open reading frame (ORF) of 1245 bp that encoded a peptide of 415 amino acids (AA). The 3'-end of DkOSC cDNA fragment contained 522 bp, including a partial ORF of 298 bp, a full poly A tail that encoded 98 AA. Two cultivars of persimmon, i.e. cv. Nishimurawase and cv. Niuxinshi, were used to study the content of OA and UA and the related gene expression. Results showed that OA and UA contents changed in both cultivars during fruit development, the difference in cv. Nishimurawase was greater than that in cv. Niuxinshi. The expression of DkSQS and DkOSC had no obvious correlation with the biosynthesis of OA and UA in the flesh. There may be two main reasons. Firstly, different enzymes involved in the biosynthesis of triterpenes and mutual adjustment were existed in different gene expressions. Secondly, it was not clear that the DkOSC cloned in this research belonged to which subfamily. Therefore, the real relationship between triterpenes and DkSQS and DkOSC in persimmon fruits is still to be revealed.

Enhanced squalene production by wild-type Saccharomyces cerevisiae strains using safe chemical means

Interest is increasing in establishing renewable sources for squalene, a functional lipid, as the conventional ones are limited. In the present study, squalene production was achieved in a wild-type laboratory Saccharomyces cerevisiae strain by two safe chemical means using terbinafine (0.05-0.55 mM) and methyl jasmonate (MJ) (0-1.00 mM). Bioprocess kinetics optimized by response surface methodology and monitored by high-performance liquid chromatography revealed a clear dependence of growth and squalene content (SQC) and yield (SQY) on the above regulators. Maximum SQC (10.02±0.53 mg/g dry biomass) and SQY (20.70±1.00 mg/L) were achieved using 0.442 mM terbinafine plus 0.044 mM MJ after 28 h and 0.300 mM terbinafine after 30 h, respectively. A 10-fold increase in SQY was achieved in comparison to that in the absence of regulator. The ruggedness of optimum conditions for SQY was verified for five industrial strains. The cellular lipid fraction (∼12% of dry biomass) was rich in squalene (12-13%). Results are encouraging toward bioprocess scale up.

Enhanced production of squalene in the thraustochytrid Aurantiochytrium mangrovei by medium optimization and treatment with terbinafine

Squalene is an effective chemopreventive agent in reducing the incident of coronary heart disease and cancer. It is also a strong antioxidant used extensively in the food and cosmetic industries. Microbial sources of squalene are being explored in recent years. The objective of this study is to increase the squalene content and yield in the thraustochytrid, Aurantiochytrium mangrovei FB3 through medium optimization and the treatment with terbinafine, an inhibitor of squalene monooxygenase in the sterol biosynthetic pathway. The highest biomass concentration of 21.2 g l(-1) was obtained at a glucose concentration of 60 g l(-1), while the highest specific growth rate of 0.077 h(-1) and the growth yield coefficient of 0.44 g g(-1) based on glucose were achieved at a lower glucose concentration (30 g l(-1)). The addition of terbinafine led to a slight inhibition of cell growth whereas an obvious increase in squalene content was observed at terbinafine concentrations of 10 and 100 mg l(-1), which corresponded to an increase of 36 and 40% in squalene content, respectively compared to the control. The addition of terbinafine was thus effective in inducing the accumulation of squalene in A. mangrovei. This study not only demonstrated the production potential of squalene by A. mangrovei, but also provided novel information on the accumulation effect of terbinafine on the biosynthesis of an essential intermediate involved in sterol metabolic pathway.