Enhanced production of fatty acids and astaxanthin in Aurantiochytrium sp. by the expression of Vitreoscilla hemoglobin

Thraustochytrids as a promising source of fatty acids, carotenoids, and sterols: bioactive compound biosynthesis, and modern biotechnology

Thraustochytrids are eukaryotes and obligate marine protists. They are increasingly considered to be a promising feed additive because of their superior and sustainable application in the production of health-benefiting bioactive compounds, such as fatty acids, carotenoids, and sterols. Moreover, the increasing demand makes it critical to rationally design the targeted products by engineering industrial strains. In this review, bioactive compounds accumulated in thraustochytrids were comprehensively evaluated according to their chemical structure, properties, and physiological function. Metabolic networks and biosynthetic pathways of fatty acids, carotenoids, and sterols were methodically summarized. Further, stress-based strategies used in thraustochytrids were reviewed to explore the potential methodologies for enhancing specific product yields. There are internal relationships between the biosynthesis of fatty acids, carotenoids, and sterols in thraustochytrids since they share some branches of the synthetic routes with some intermediate substrates in common. Although there are classic synthesis pathways presented in the previous research, the metabolic flow of how these compounds are being synthesized in thraustochytrids still remains uncovered. Further, combined with omics technologies to deeply understand the mechanism and effects of different stresses is necessary, which could provide guidance for genetic engineering. While gene-editing technology has allowed targeted gene knock-in and knock-outs in thraustochytrids, efficient gene editing is still required. This critical review will provide comprehensive information to benefit boosting the commercial productivity of specific bioactive substances by thraustochytrids.

Improvement of Astaxanthin Production in Aurantiochytrium limacinum by Overexpression of the Beta-Carotene Hydroxylase Gene

Aurantiochytrium limacinum is a heterotrophic eukaryotic microorganism that can accumulate high levels of commercial products such as astaxanthin and docosahexaenoic acid. Due to its rapid growth and relatively simple extraction method, A. limacinum is considered a promising astaxanthin resource to replace the conventional microalgal production. However, the astaxanthin biosynthetic process in A. limacinum remains incompletely understood, especially in those catalysed by β-carotene hydroxylase (CrtZ) and ketolase. In this study, we overexpressed a crtZ candidate gene to increase astaxanthin production and expand our understanding of the conversion from beta-carotene to astaxanthin. The resultant transformant AlcrtZ#10 cultivated for 5 days showed a significant increase in astaxanthin production per culture (2.8-fold) and per cell (4.5-fold) compared with that of the wild-type strain. Strikingly, longer light exposure increased astaxanthin production and decreased the beta-carotene content in the wild-type strain, suggesting that light exposure duration is important for astaxanthin production in A. limacinum. Among several predicted intermediates, furthermore, the cantaxanthin produced from β-carotene by ketolase activity were enhanced in the transformant AlcrtZ#10. Although the further investigation is needed, this result suggested that the main route of astaxanthin was via cantaxanthin. Thus, our findings will be valuable not only for its application, but also for understanding the astaxanthin biosynthetic process in A. limacinum.

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.

Biocolorants in food: Sources, extraction, applications and future prospects

Color of a food is one of the major factors influencing its acceptance by consumers. At presently synthetic dyes are the most commonly used food colorant in food industry by providing more esthetically appearance and as a means to quality control. However, the growing concern about health and environmental due to associated toxicity with synthetic food colorants has accelerated the global efforts to replace them with safer and healthy food colorants obtained from natural resources (plants, microorganisms, and animals). Further, many of these biocolorants not only provide myriad of colors to the food but also exert biological properties, thus they can be used as nutraceuticals in foods and beverages. In order to understand the importance of nature-derived pigments as food colorants, this review provides a thorough discussion on the natural origin of food colorants. Following this, different extraction methods for isolating biocolorants from plants and microbes were also discussed. Many of these biocolorants not only provide color, but also have many health promoting properties, for this reason their physicochemical and biological properties were also reviewed. Finally, current trends on the use of biocolorants in foods, and the challenges faced by the biocolorants in their effective utilization by food industry and possible solutions to these challenges were discussed.

Overexpression of Shinorhizobium meliloti flavohemoglobin improves cell growth and fatty acid biosynthesis in oleaginous fungus Mucor circinelloides

Oxygen availability is a limiting factor for lipid biosynthesis in eukaryotic microorganisms. Two bacterial hemoglobins from Vitreoscilla sp. (VHb) and Shinorhizobium meliloti (SHb), which deliver oxygen to the respiratory chain to produce more ATP, were introduced into Mucor circinelloides to alleviate oxygen limitation, thereby improving cell growth and fatty acid production. The VHb and SHb genes were integrated into the M. circinelloides MU402 genome by homologous recombination. VHb and SHb protein expression was verified by carbon monoxide difference spectrum analysis. The biomass was increased by ~ 50% in the strain expressing SHb compared with VHb. The total fatty acid (TFA) content of the strain expressing SHb reached 15.7% of the dry cell weight (~ 40% higher than that of the control strain) during flask cultivation. The biomass and TFA content were markedly increased (12.1 g/L and 21.1% dry cell weight, respectively) in strains expressing SHb than strains expressing VHb during fermenter cultivation. VHb and SHb expression also increased the proportion of polyunsaturated fatty acids. Overexpressed bacterial hemoglobins, especially SHb, increased cell growth and TFA content in M. circinelloides at low and high aeration, suggesting that SHb improves fatty acid production more effectively than VHb in oleaginous microorganisms.

An emerging simple and effective approach to increase the productivity of thraustochytrids microbial lipids by regulating glycolysis process and triacylglycerols' decomposition

BACKGROUND

The oleaginous microorganism Schizochytrium sp. is widely used in scientific research and commercial lipid production processes. However, low glucose-to-lipid conversion rate (GLCR) and low lipid productivity of Schizochytrium sp. restrict the feasibility of its use.

RESULTS

Orlistat is a lipase inhibitor, which avoids triacylglycerols (TAGs) from hydrolysis by lipase. TAGs are the main storage forms of fatty acids in Schizochytrium sp. In this study, the usage of orlistat increased the GLCR by 21.88% in the middle stage of fermentation. Whereas the productivity of lipid increased 1.34 times reaching 0.73 g/L/h, the saturated fatty acid and polyunsaturated fatty acid yield increased from 21.2 and 39.1 to 34.9 and 48.5 g/L, respectively, indicating the advantages of using a lipase inhibitor in microbial lipids fermentation. Similarly, the system was also successful in Thraustochytrid Aurantiochytrium. The metabolic regulatory mechanisms stimulated by orlistat in Schizochytrium sp. were further investigated using transcriptomics and metabolomics. The results showed that orlistat redistributed carbon allocation and enhanced the energy supply when inhibiting the TAGs' degradation pathway. Therefore, lipase in Schizochytrium sp. prefers to hydrolyze saturated fatty acid TAGs into the β-oxidation pathway.

CONCLUSIONS

This study provides a simple and effective approach to improve lipid production, and makes us understand the mechanism of lipid accumulation and decomposition in Schizochytrium sp., offering new guidance for the exploitation of oleaginous microorganisms.

Vitreoscilla Haemoglobin: A Tool to Reduce Overflow Metabolism

Overflow metabolism is a phenomenon extended in nature, ranging from microbial to cancer cells. Accumulation of overflow metabolites pose a challenge for large-scale bioprocesses. Yet, the causes of overflow metabolism are not fully clarified. In this work, the underlying mechanisms, reasons and consequences of overflow metabolism in different organisms have been summarized. The reported effect of aerobic expression of Vitreoscilla haemoglobin (VHb) in different organisms are revised. The use of VHb to reduce overflow metabolism is proposed and studied through flux balance analysis in E. coli at a fixed maximum substrate and oxygen uptake rates. Simulations showed that the presence of VHb increases the growth rate, while decreasing acetate production, in line with the experimental measurements. Therefore, aerobic VHb expression is considered a potential tool to reduce overflow metabolism in cells.

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.

Obtaining High-Purity Docosahexaenoic Acid Oil in Thraustochytrid Aurantiochytrium through a Combined Metabolic Engineering Strategy

High-purity docosahexaenoic acid (DHA) resources are insufficient in the pharmaceutical and food industries. Although many efforts have attempted to obtain the high-purity DHA production, few reports have been successful. Here, a combined metabolic engineering strategy was employed to increase the DHA purity in the oleaginous thraustochytrid Aurantiochytrium. The strategy includes both partial deactivation of the competing pathway of DHA biosynthesis, by disrupting one copy of the fatty acid synthase gene, and strengthening of substrate supply and triacylglycerol synthesis, by the overexpression of acetyl-CoA carboxylase and diacylglycerol acyltransferase. With this strategy, a final mutant was obtained with a DHA purity of 61% in total fatty acids and a content of 331 mg/g dry cell weight. This study provides an advanced strategy for sustainable high-purity DHA production and highlights the strategy for producing designer oils in industrial oleaginous microorganisms.

Recent Advances in the Physicochemical Properties and Biotechnological Application of Vitreoscilla Hemoglobin

Vitreoscilla hemoglobin (VHb), the first discovered bacterial hemoglobin, is a soluble heme-binding protein with a faster rate of oxygen dissociation. Since it can enhance cell growth, product synthesis and stress tolerance, VHb has been widely applied in the field of metabolic engineering for microorganisms, plants, and animals. Especially under oxygen-limited conditions, VHb can interact with terminal oxidase to deliver enough oxygen to achieve high-cell-density fermentation. In recent years, with the development of bioinformatics and synthetic biology, several novel physicochemical properties and metabolic regulatory effects of VHb have been discovered and numerous strategies have been utilized to enhance the expression level of VHb in various hosts, which greatly promotes its applications in biotechnology. Thus, in this review, the new information regarding structure, function and expressional tactics for VHb is summarized to understand its latest applications and pave a new way for the future improvement of biosynthesis for other products.

Improving Hypoxia Adaption Causes Distinct Effects on Growth and Bioactive Compounds Synthesis in an Entomopathogenic Fungus Cordyceps militaris

Cordyceps militaris is an entomopathogenic fungus producing a variety of bioactive compounds. To meet the huge demand for medicinal and edible products, industrialized fermentation of mycelia and cultivation of stromata have been widely developed in China. The content of bioactive metabolites of C. militaris, such as cordycepin, is higher when cultivated on silkworm pupae than on rice or in broth. However, compared with other cultivation methods, C. militaris grows more slowly and accumulates less biomass. The hypoxic environment in pupa hemocoel is one of environmental factor which is not existed in other cultivation methods. It is suggested that hypoxia plays an important role on the growth and the synthesis of bioactive compounds in C. militaris. Here, we demonstrated that the distinct effects on the growth and synthesis of bioactive compounds employing different strategies of improving hypoxia adaption. The introduction of Vitreoscilla hemoglobin enhanced growth, biomass accumulation, and crude polysaccharides content of C. militaris. However, cordycepin production was decreased to 9-15% of the control group. Meanwhile, the yield of adenosine was increased significantly. Nonetheless, when the predicted bHLH transcription factor of sterol regulatory element binding proteins (SREBPs) was overexpressed in C. militaris to improve the hypoxia adaption of fungal cells, cordycepin content was significantly increased more than two-fold. These findings reveal the role of SREBPs on growth and bioactive compounds synthesis. And it also provides a scientific basis for rationally engineering strains and optimization strategies of air supply in cultivation and fermentation.

Biotechnological production of lipid and terpenoid from thraustochytrids

As fungus-like protists, thraustochytrids have been increasingly studied for their faster growth rates and high lipid content. In the 1990s, thraustochytrids were used as docosahexaenoic acid (DHA) producers for the first time. Thraustochytrids genera, such as Thraustochytrium, Schizochytrium, and Aurantiochytrium have been developed and patented as industrial strains for DHA production. The high DHA yield is attributed to its unique and efficient polyketide-like synthase (PKS) pathway. Moreover, thraustochytrids possess a completed mevalonate (MVA) pathway, so it can be used as host for terpenoid production. In order to improve strain performance, the metabolic engineering strategies have been applied to promote or disrupt intracellular metabolic pathways, such as genetic engineering and addition of chemical activators. However, it is difficult to realize industrialization only by improving strain performance. Various operation strategies were developed to enlarge the production quantities from the laboratory-scale, including two-stage cultivation strategies, scale-up technologies and bioreactor design. Moreover, an economical and effective downstream process is also an important consideration for the industrial application of thraustochytrids. Downstream costs accounts for 20-60% of the overall process costs, which represents an attractive target for increasing the cost-competitiveness of thraustochytrids, including how to improve the efficiency of lipid extraction and the further application of biomass residues. This review aims to overview the whole lipid biotechnology of thraustochytrids to provide the background information for researchers.

Yarrowia lipolytica as an Oleaginous Platform for the Production of Value-Added Fatty Acid-Based Bioproducts

The microbial fermentation process has been used as an alternative pathway to the production of value-added natural products. Of the microorganisms, Yarrowia lipolytica, as an oleaginous platform, is able to produce fatty acid-derived biofuels and biochemicals. Nowadays, there are growing progresses on the production of value-added fatty acid-based bioproducts in Y. lipolytica. However, there are fewer reviews performing the metabolic engineering strategies and summarizing the current production of fatty acid-based bioproducts in Y. lipolytica. To this end, we briefly provide the fatty acid metabolism, including fatty acid biosynthesis, transportation, and degradation. Then, we introduce the various metabolic engineering strategies for increasing bioproduct accumulation in Y. lipolytica. Further, the advanced progress in the production of fatty acid-based bioproducts by Y. lipolytica, including nutraceuticals, biofuels, and biochemicals, is summarized. This review will provide attractive thoughts for researchers working in the field of Y. lipolytica.

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.

Antioxidant Molecules from Marine Fungi: Methodologies and Perspectives

The marine environment represents a prosperous existing resource for bioprospecting, covering 70% of the planet earth, and hosting a huge biodiversity. Advances in the research are progressively uncovering the presence of unknown microorganisms, which have evolved unique metabolic and genetic pathways for the production of uncommon secondary metabolites. Fungi have a leading role in marine bioprospecting since they represent a prolific source of structurally diverse bioactive metabolites. Several bioactive compounds from marine fungi have already been characterized including antibiotics, anticancer, antioxidants and antivirals. Nowadays, the search for natural antioxidant molecules capable of replacing those synthetic currently used, is an aspect that is receiving significant attention. Antioxidants can inactivate reactive oxygen and nitrogen species, preventing the insurgence of several degenerative diseases including cancer, autoimmune disorders, cardiovascular and neurodegenerative diseases. Moreover, they also find applications in different fields, including food preservation, healthcare and cosmetics. This review focuses on the production of antioxidants from marine fungi. We begin by proposing a survey of the available tools suitable for the evaluation of antioxidants, followed by the description of various classes of marine fungi antioxidants together with their extraction strategies. In addition, a view of the future perspectives and trends of these natural products within the "blue economy" is also presented.

The strategies to reduce cost and improve productivity in DHA production by Aurantiochytrium sp.: from biochemical to genetic respects

The marine oleaginous protist Aurantiochytrium sp. (Schizochytrium sp.) is a well-known docosahexaenoic acid (DHA) producer and its different DHA products are the ideal substitute for the traditional fish oil resource. However, the cost of the DHA products derived from Aurantiochytrium sp. (Schizochytrium sp.) is still high, limiting their wide applications. In order to reduce the cost or improve the productivity of DHA from the microbial resource, many researches are focusing on exploring the renewable and low-cost materials as feedbacks, and/or the stimulators for biomass and DHA production. In addition, the genetic engineering is also being used in the Aurantiochytrium sp. (Schizochytrium sp.) system for further improvement. These break the bottleneck of the DHA production by Aurantiochytrium sp. (Schizochytrium sp.) in some degree. In this review, the strategies used currently to reduce cost and improve DHA productivity, mainly from the utilizations of low-cost materials and effective stimulators to the genetic engineering perspectives, are summarized, and the availabilities from the cost perspective are also evaluated. This review provides an overview about the strategies to revolve the production cost and yield of the DHA by Aurantiochytrium sp. (Schizochytrium sp.), a theoretical basis for genetic modification of Aurantiochytrium sp. (Schizochytrium sp.), and a practical basis for the development of DHA industry. KEY POINTS : • Utilizations of various low-cost materials for DHA production • Inducing the growth and DHA biosynthesis by the effective stimulators • Reducing cost and improving DHA productivity by genetic modification • The availability from cost perspective is evaluated.

Microbial sources of polyunsaturated fatty acids (PUFAs) and the prospect of organic residues and wastes as growth media for PUFA-producing microorganisms

The discovery of non-fish sources of polyunsaturated fatty acids (PUFAs) is of great biotechnological importance. Although various oleaginous microalgae and fungi are able of accumulating storage lipids (single cell oils - SCOs) containing PUFAs, the industrial applications utilizing these organisms are rather limited due to the high-fermentation cost. However, combining SCO production with other biotechnological applications, including waste and by-product valorization, can overcome this difficulty. In the current review, we present the major sources of fungi (i.e. members of Mucoromycota, fungoid-like Thraustochytrids and genetically modified strains of Yarrowia lipolytica) and microalgae (e.g. Isochrysis, NannochloropsisandTetraselmis) that have come recently to the forefront due to their ability to produce PUFAs. Approaches adopted in order to increase PUFA productivity and the potential of using various residues, such as agro-industrial, food and aquaculture wastes as fermentation substrates for SCO production have been considered and discussed. We concluded that several organic residues can be utilized as feedstock in the SCO production increasing the competitiveness of oleaginous organisms against conventional PUFA producers.

Marine-Derived Compounds with Potential Use as Cosmeceuticals and Nutricosmetics

The cosmetic industry is among the fastest growing industries in the last decade. As the beauty concepts have been revolutionized, many terms have been coined to accompany the innovation of this industry, since the beauty products are not just confined to those that are applied to protect and enhance the appearance of the human body. Consequently, the terms such as cosmeceuticals and nutricosmetics have emerged to give a notion of the health benefits of the products that create the beauty from inside to outside. In the past years, natural products-based cosmeceuticals have gained a huge amount of attention not only from researchers but also from the public due to the general belief that they are harmless. Notably, in recent years, the demand for cosmeceuticals from the marine resources has been exponentially on the rise due to their unique chemical and biological properties that are not found in terrestrial resources. Therefore, the present review addresses the importance of marine-derived compounds, stressing new chemical entities with cosmeceutical potential from the marine natural resources and their mechanisms of action by which these compounds exert on the body functions as well as their related health benefits. Marine environments are the most important reservoir of biodiversity that provide biologically active substances whose potential is still to be discovered for application as pharmaceuticals, nutraceuticals, and cosmeceuticals. Marine organisms are not only an important renewable source of valuable bulk compounds used in cosmetic industry such as agar and carrageenan, which are used as gelling and thickening agents to increase the viscosity of cosmetic formulations, but also of small molecules such as ectoine (to promote skin hydration), trichodin A (to prevent product alteration caused by microbial contamination), and mytiloxanthin (as a coloring agent). Marine-derived molecules can also function as active ingredients, being the main compounds that determine the function of cosmeceuticals such as anti-tyrosinase (kojic acid), antiacne (sargafuran), whitening (chrysophanol), UV protection (scytonemin, mycosporine-like amino acids (MAAs)), antioxidants, and anti-wrinkle (astaxanthin and PUFAs).

Chassis engineering of Escherichia coli for trans-4-hydroxy-l-proline production

Microbial production of trans-4-hydroxy-l-proline (Hyp) offers significant advantages over conventional chemical extraction. However, it is still challenging for industrial production of Hyp due to its low production efficiency. Here, chassis engineering was used for tailoring Escherichia coli cellular metabolism to enhance enzymatic production of Hyp. Specifically, four proline 4-hydroxylases (P4H) were selected to convert l-proline to Hyp, and the recombinant strain overexpressing DsP4H produced 32.5 g l^-1 Hyp with α-ketoglutarate addition. To produce Hyp without α-ketoglutarate addition, α-ketoglutarate supply was enhanced by rewiring the TCA cycle and l-proline degradation pathway, and oxygen transfer was improved by fine-tuning heterologous haemoglobin expression. In a 5-l fermenter, the engineered strain E. coliΔsucCDΔputA-VHb_(L) -DsP4H showed a significant increase in Hyp titre, conversion rate and productivity up to 49.8 g l^-1 , 87.4% and 1.38 g l^-1  h^-1 respectively. This strategy described here provides an efficient method for production of Hyp, and it has a great potential in industrial application.

Enhanced Coproduction of Cell-Bound Zeaxanthin and Secreted Exopolysaccharides by Sphingobium sp. via Metabolic Engineering and Optimized Fermentation

Zeaxanthin is a value-added carotenoid with wide applications. This study aims to manipulate a generally recognized as safe and carotenoid-producing bacterium, Sphingobium sp., for enhanced production of zeaxanthin and exopolysaccharides. First, whole-genome sequencing and analysis of pathway genes were applied to define the carotenoid pathway in Sphingobium sp. Second, a Sphingobium transformation system was established to engineer metabolite flux into zeaxanthin. By a combination of chemical mutagenesis and removal of bottlenecks of carotenoid biosynthesis via overexpression of three rate-limiting enzymes, the genetically modified Sphingobium DIZ strain produced 21.26 mg/g dry cell weight of zeaxanthin, which was about 4-fold higher than the wild type. Upon optimization of culture conditions, the DIZ strain produced 479.5 mg/L of zeaxanthin with the productivity of 4.99 mg/L/h and 21.9 g/L of exopolysaccharides using a fed-batch fermentation strategy. This study represents the first genetic manipulation of Sphingobium sp., a biotechnologically important bacterium, for high-yield production of value-added metabolites.

Enhanced production of individual ganoderic acids by integrating Vitreoscilla haemoglobin expression and calcium ion induction in liquid static cultures of Ganoderma lingzhi

Ganoderic acids produced by Ganoderma exhibit anticancer and antimetastatic activities. A novel approach by combining Vitreoscilla haemoglobin (VHb) expression and calcium ion induction was developed to enhance ganoderic acid (GA) production in liquid static cultures of G. lingzhi. The maximum contents of GA-O, GA-S and GA-Me were 1451.33 ± 67.50, 1431.23 ± 79.74 and 1283.81 ± 85.13 μg per 100 mg cell weight, respectively under the integrated approach, which are the highest contents as ever reported in Ganoderma. The contents of squalene and lanosterol were increased by 2.0- and 3.0-fold in this case compared with those in the control. The transcription levels of 3-hydroxy-3-methylglutaryl coenzyme A reductase, farnesyl-diphosphate synthase, squalene synthase and cytochrome P450 CYP5150L8 were upregulated by 2.56-, 3.31-, 2.59- and 6.12-fold respectively. Additionally, the expression of VHb improved the ratio of type I to type II GA in liquid static cultivation of G. lingzhi. The transcription levels of cyp512a2, cyp512v2 and cyp512a13, candidate cytochrome P450 genes involved in oxidative modification of the lanostane skeleton in GA biosynthesis, were also increased by 2.28-, 2.65- and 3.54-fold in the VHb-expressing strain respectively. Our results illustrated that the approach described here efficiently improved GA production in G. lingzhi fermentation.

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.

Overexpression of Malonyl-CoA: ACP Transacylase in Schizochytrium sp. to Improve Polyunsaturated Fatty Acid Production

Polyunsaturated fatty acids (PUFAs) have been widely applied in the food and medical industry. In this study, malonyl-CoA: ACP transacylase (MAT) was overexpressed through homologous recombination to improve PUFA production in Schizochytrium. The results showed that the lipid and PUFA concentration were increased by 10.1 and 24.5% with MAT overexpression, respectively. Metabolomics analysis revealed that the intracellular tricarboxylic acid cycle was weakened and glucose absorption was accelerated in the engineered strain. In the mevalonate pathway, intracellular carotene content was decreased, and the carbon flux was then redirected toward PUFA synthesis. Furthermore, a glucose fed-batch fermentation was finally performed with the engineered Schizochytrium. The total lipid yield was further increased to 110.5 g/L, 39.6% higher than the wild strain. Docosahexaenoic acid and eicosapentaenoic acid yield were enhanced to 47.39 g/L and 1.65 g/L with an increase of 81.5 and 172.5%, respectively. This study provided an effective metabolic engineering strategy for industrial PUFA production.

Simultaneous cell disruption and lipid extraction of wet aurantiochytrium sp. KRS101 using a high shear mixer

Microalgae are regarded as a promising source of biofuels, and the concept of a microalgae-based biorefinery has attracted increasing attention in recent years. From an economic perspective, however, the process remains far from competitive with fossil fuels. This is particularly true of lipid extraction, due in part to the energy-intensive drying step. As a result, wet extraction methods have been studied as an economic alternative. In the present study, a novel extraction approach which utilizes high shear stress mixing was adopted and demonstrated for simultaneous lipid extraction and cell disruption to enable the retrieval of lipids directly from concentrated wet biomass. When a high shear mixer (HSM) was used to extract lipid from a dense biomass (> 350 g/L) of the oleaginous algae Aurantiochytrium sp., it exhibited a yield of esterifiable lipids which exceeded 80% in 10 min at 15,000 rpm with various solvent types. The HSM was found to improve the lipid yields substantially with solvents less miscible with either lipids or water, such that the range of Hansen solubility parameters for the usable solvents became 3.3 times wider (14.9-26.5 MPa^1/2). The HSM, which appeared effectively to loosen the water barrier that prevents solvent molecules from penetrating through the cell envelope, was found to be more efficient with hexane, hexane/isopropanol, and ethanol, all of which showed nearly identical lipid yields compared to the dry extraction process. The HSM can, indeed, offer a powerful mechanical means of lipid extraction with non-polar and less toxic solvents from wet biomass.

Enhanced bacterial cellulose production by Gluconacetobacter xylinus via expression of Vitreoscilla hemoglobin and oxygen tension regulation

Oxygen plays a key role during bacterial cellulose (BC) biosynthesis by Gluconacetobacter xylinus. In this study, the Vitreoscilla hemoglobin (VHb)-encoding gene vgb, which has been widely applied to improve cell survival during hypoxia, was heterologously expressed in G. xylinus via the pBla-VHb-122 plasmid. G. xylinus and G. xylinus-vgb ⁺ were statically cultured under hypoxic (10 and 15% oxygen tension in the gaseous phase), atmospheric (21%), and oxygen-enriched conditions (40 and 80%) to investigate the effect of oxygen on cell growth and BC production. Irrespective of vgb expression, we found that cell density increased with oxygen tension (10-80%) during the exponential growth phase but plateaued to the same value in the stationary phase. In contrast, BC production was found to significantly increase at lower oxygen tensions. In addition, we found that BC production at oxygen tensions of 10 and 15% was 26.5 and 58.6% higher, respectively, in G. xylinus-vgb ⁺ than that in G. xylinus. The maximum BC yield and glucose conversion rate, of 4.3 g/L and 184.7 mg/g, respectively, were observed in G. xylinus-vgb ⁺ at an oxygen tension of 15%. Finally, BC characterization suggested that hypoxic conditions enhance BC's mass density, Young's modulus, and thermostability, with G. xylinus-vgb ⁺ synthesizing softer BC than G. xylinus under hypoxia as a result of a decreased Young's modulus. These results will facilitate the use of static culture for the production of BC.

Carotenoids from Marine Organisms: Biological Functions and Industrial Applications

As is the case for terrestrial organisms, carotenoids represent the most common group of pigments in marine environments. They are generally biosynthesized by all autotrophic marine organisms, such as bacteria and archaea, algae and fungi. Some heterotrophic organisms also contain carotenoids probably accumulated from food or partly modified through metabolic reactions. These natural pigments are divided into two chemical classes: carotenes (such as lycopene and α- and β-carotene) that are composed of hydrogen and carbon; xanthophylls (such as astaxanthin, fucoxanthin and lutein), which are constituted by hydrogen, carbon and oxygen. Carotenoids, as antioxidant compounds, assume a key role in the protection of cells. In fact, quenching of singlet oxygen, light capture and photosynthesis protection are the most relevant biological functions of carotenoids. The present review aims at describing (i) the biological functions of carotenoids and their benefits for human health, (ii) the most common carotenoids from marine organisms and (iii) carotenoids having large success in pharmaceutical, nutraceutical and cosmeceutical industries, highlighting the scientific progress in marine species cultivation for natural pigments production.

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.

Applications for Marine Resources in Cosmetics

Marine resources represent an interesting source of active ingredients for the cosmetics industry. Algae (macro and micro) are rich in proteins, amino acids, carbohydrates, vitamins (A, B, and C) and oligo-elements such as copper, iron and zinc. All those active principles play roles in hydration, firming, slimming, shine and protection. Marine organisms inhabit a wide spectrum of habitats. Photo-protective compounds can be obtained from organisms subjected to strong light radiation, such as in tropical systems or in shallow water. In the same way, molecules with antioxidant potential can be obtained from microorganisms inhabiting extreme systems such as hydrothermal vents. For example, marine bacteria collected around deep-sea hydrothermal vents produce complex and innovative polysaccharides in the laboratory which are useful in cosmetics. There are many properties that will be put forward by the cosmetic industries.

Expression of Vitreoscilla hemoglobin enhances production of arachidonic acid and lipids in Mortierella alpina

BACKGROUND

Arachidonic acid (ARA, C20:4, n-6), which belongs to the omega-6 series of polyunsaturated fatty acids and has a variety of biological activities, is commercially produced in Mortierella alpina. Dissolved oxygen or oxygen utilization efficiency is a critical factor for Mortierella alpina growth and arachidonic acid production in large-scale fermentation. Overexpression of the Vitreoscilla hemoglobin gene is thought to significantly increase the oxygen utilization efficiency of the cells.

RESULTS

An optimized Vitreoscilla hemoglobin (VHb) gene was introduced into Mortierella alpina via Agrobacterium tumefaciens-mediated transformation. Compared with the parent strain, the VHb-expressing strain, termed VHb-20, grew faster under both limiting and non-limiting oxygen conditions and exhibited dramatic changes in cell morphology. Furthermore, VHb-20 produced 4- and 8-fold higher total lipid and ARA yields than those of the wild-type strain under a microaerobic environment. Furthermore, ARA production of VHb-20 was also 1.6-fold higher than that of the wild type under normal conditions. The results demonstrated that DO utilization was significantly increased by expressing the VHb gene in Mortierella alpina.

CONCLUSIONS

The expression of VHb enhances ARA and lipid production under both lower and normal dissolved oxygen conditions. This study provides a novel strategy and an engineered strain for the cost-efficient production of ARA.

Marine Microbial-Derived Molecules and Their Potential Use in Cosmeceutical and Cosmetic Products

The oceans encompass a wide range of habitats and environmental conditions, which host a huge microbial biodiversity. The unique characteristics of several marine systems have driven a variety of biological adaptations, leading to the production of a large spectrum of bioactive molecules. Fungi, fungi-like protists (such as thraustochytrids) and bacteria are among the marine organisms with the highest potential of producing bioactive compounds, which can be exploited for several commercial purposes, including cosmetic and cosmeceutical ones. Mycosporines and mycosporine-like amino acids, carotenoids, exopolysaccharides, fatty acids, chitosan and other compounds from these microorganisms might represent a sustainable, low-cost and fast-production alternative to other natural molecules used in photo-protective, anti-aging and skin-whitening products for face, body and hair care. Here, we review the existing knowledge of these compounds produced by marine microorganisms, highlighting the marine habitats where such compounds are preferentially produced and their potential application in cosmetic and cosmeceutical fields.