Multiple promoters driving the expression of astaxanthin biosynthesis genes can enhance free-form astaxanthin production

Molecular approaches to enhance astaxanthin biosynthesis; future outlook: engineering of transcription factors in Haematococcus pluvialis

Microalgae are the preferred species for producing astaxanthin because they pose a low toxicity risk than chemical synthesis. Astaxanthin has multiple health benefits and is being used in: medicines, nutraceuticals, cosmetics, and functional foods. Haematococcus pluvialis is a model microalga for astaxanthin biosynthesis; however, its natural astaxanthin content is low. Therefore, it is necessary to develop methods to improve the biosynthesis of astaxanthin to meet industrial demands, making its commercialization cost-effective. Several strategies related to cultivation conditions are employed to enhance the biosynthesis of astaxanthin in H. pluvialis. However, the mechanism of its regulation by transcription factors is unknown. For the first time, this study critically reviewed the studies on identifying transcription factors, progress in H. pluvialis genetic transformation, and use of phytohormones that increase the gene expression related to astaxanthin biosynthesis. In addition, we propose future approaches, including (i) Cloning and characterization of transcription factors, (ii) Transcriptional engineering through overexpression of positive regulators or downregulation/silencing of negative regulators, (iii) Gene editing for enrichment or deletion of transcription factors binding sites, (iv) Hormonal modulation of transcription factors. This review provides considerable knowledge about the molecular regulation of astaxanthin biosynthesis and the existing research gap. Besides, it provides the basis for transcription factors mediated metabolic engineering of astaxanthin biosynthesis in H. pluvialis.

The bioproduction of astaxanthin: A comprehensive review on the microbial synthesis and downstream extraction

Astaxanthin is a valuable orange-red carotenoid with wide applications in agriculture, food, cosmetics, pharmaceuticals and nutraceuticals areas. At present, the biological synthesis of astaxanthin mainly relies on Haematococcus pluvialis and Xanthophyllomyces dendrorhous. With the rapid development of synthetic biology, more recombinant microbial hosts have been genetically constructed for astaxanthin production including Escherichia coli, Saccharomyces cerevisiae and Yarrowia lipolytica. As multiple genes (15) were involved in the astaxanthin synthesis, it is particularly important to adopt different strategies to balance the metabolic flow towards the astaxanthin synthesis. Furthermore, astaxanthin is a fat-soluble compound stored intracellularly, hence efficient extraction methods are also essential for the economical production of astaxanthin. Several efficient and green extraction methods of astaxanthin have been reported in recent years, including the superfluid extraction, ionic liquid extraction and microwave-assisted extraction. Accordingly, this review will comprehensively introduce the advances on the astaxanthin production and extraction by using different microbial hosts and strategies to improve the astaxanthin synthesis and extraction efficiency.

Biotechnological strategies overcoming limitations to H. pluvialis-derived astaxanthin production and Morocco's potential

Haematococcus pluvialis is the richest source of natural astaxanthin, but the production of H. pluvialis-derived astaxanthin is usually limited by its slow cell proliferation and astaxanthin accumulation. Efforts to enhance biomass productivity, astaxanthin accumulation, and extraction are ongoing. This review highlights different approaches that have previously been studied in microalgal species for enhanced biomass productivity, as well as optimized methods for astaxanthin accumulation and extraction, and how these methods could be combined to bypass the challenges limiting natural astaxanthin production, particularly in H. pluvialis, at all stages (biomass production, and astaxanthin accumulation and extraction). Biotechnological approaches, such as overexpressing low CO2 inducible genes, utilizing complementary carbon sources, CRISPR-Cas9 bioengineering, and the use of active compounds, for biomass productivity are outlined. Direct astaxanthin extraction from H. pluvialis zoospores and Morocco's potential for microalgal-based astaxanthin production are equally discussed. This review emphasizes the need to engineer an optimized H. pluvialis-derived astaxanthin production system combining two or more of these strategies for increased growth, and astaxanthin productivity, to compete in the larger, lower-priced market in aquaculture and nutraceutical sectors.

Production of Astaxanthin Using CBFD1/HFBD1 from Adonis aestivalis and the Isopentenol Utilization Pathway in Escherichia coli

Astaxanthin is a powerful antioxidant and is used extensively as an animal feed additive and nutraceutical product. Here, we report the use of the β-carotene hydroxylase (CBFD1) and the β-carotene ketolase (HBFD1) from Adonis aestivalis, a flowering plant, to produce astaxanthin in E. coli equipped with the P. agglomerans β-carotene pathway and an over-expressed 4-methylerythritol-phosphate (MEP) pathway or the isopentenol utilization pathway (IUP). Introduction of the over-expressed MEP pathway and the IUP resulted in a 3.2-fold higher carotenoid content in LB media at 36 h post-induction compared to the strain containing only the endogenous MEP. However, in M9 minimal media, the IUP pathway dramatically outperformed the over-expressed MEP pathway with an 11-fold increase in total carotenoids produced. The final construct split the large operon into two smaller operons, both with a T7 promoter. This resulted in slightly lower productivity (70.0 ± 8.1 µg/g·h vs. 53.5 ± 3.8 µg/g·h) compared to the original constructs but resulted in the highest proportion of astaxanthin in the extracted carotenoids (73.5 ± 0.2%).

Research progress of engineering microbial cell factories for pigment production

Pigments are widely used in people's daily life, such as food additives, cosmetics, pharmaceuticals, textiles, etc. In recent years, the natural pigments produced by microorganisms have attracted increased attention because these processes cannot be affected by seasons like the plant extraction methods, and can also avoid the environmental pollution problems caused by chemical synthesis. Synthetic biology and metabolic engineering have been used to construct and optimize metabolic pathways for production of natural pigments in cellular factories. Building microbial cell factories for synthesis of natural pigments has many advantages, including well-defined genetic background of the strains, high-density and rapid culture of cells, etc. Until now, the technical means about engineering microbial cell factories for pigment production and metabolic regulation processes have not been systematically analyzed and summarized. Therefore, the studies about construction, modification and regulation of synthetic pathways for microbial synthesis of pigments in recent years have been reviewed, aiming to provide an up-to-date summary of engineering strategies for microbial synthesis of natural pigments including carotenoids, melanins, riboflavins, azomycetes and quinones. This review should provide new ideas for further improving microbial production of natural pigments in the future.

Metabolite analysis of soybean oil on promoting astaxanthin production of Phaffia rhodozyma

BACKGROUND

Astaxanthin is a carotenoid with strong antioxidant property. In addition, it has anti-cancer, anti-tumor, anti-inflammatory and many other functions. The micro-organisms that mainly produce astaxanthin are Haematococcus pluvialis and Phaffia rhodozyma. Compared with H. pluvialis, P. rhodozyma has shorter fermentation cycle and easier to control culture conditions, but the yield of astaxanthin in P. rhodozyma is low. This article studied how to improve the astaxanthin production of P. rhodozyma.

RESULTS

The results showed that when 10 mL L^-1 soybean oil was added to the culture medium, astaxanthin production increased significantly, reaching 7.35 mg L^-1 , which was 1.4 times that of the control group, and lycopene and β-carotene contents also increased significantly. Through targeted metabolite analysis, the fatty acids in P. rhodozyma significantly increased under the soybean oil stimulation, especially the fatty acids closely related to the formation of astaxanthin esters, included palmitic acid (C16:0), stearic acid (C18:0), oleic acid (C18:1n9), linoleic acid (C18:2n6), α-linolenic acid (C18:3n3) and γ-linolenic acid (C18:3n6), thereby increasing the astaxanthin esters content.

CONCLUSION

It showed that the addition of soybean oil can promote the accumulation of astaxanthin by promoting the increase of astaxanthin ester content. © 2022 Society of Chemical Industry.

Spatiotemporal Regulation of Astaxanthin Synthesis in S. cerevisiae

As a high-valued antioxidant, astaxanthin biosynthesis using microbial cell factories has attracted increasing attention. However, its lipophilic nature conflicts with the limited storage capacity for lipophilic substances of model microorganisms such as Saccharomyces cerevisiae. Expansion of lipid droplets by enhancing lipid synthesis provides more storage room while diverting the metabolic flux from the target pathway. Therefore, proper spatial regulation is required. In this study, a library of genes related to lipid metabolism were screened using the trifunctional CRISPR system, identifying opi3 and hrd1 as new engineering targets to promote astaxanthin synthesis by moderately rather than excessively upregulating lipid synthesis. The astaxanthin yield reached 9.79 mg/g DCW after lipid engineering and was further improved to 10.21 mg/g DCW by balancing the expression of β-carotene hydroxylase and ketolase. Finally, by combining spatial regulation through lipid droplet engineering and temporal regulation via temperature-responsive pathway expression, 446.4 mg/L astaxanthin was produced in fed-batch fermentation.

Biotechnological advances for improving natural pigment production: a state-of-the-art review

In current years, natural pigments are facing a fast-growing global market due to the increase of people's awareness of health and the discovery of novel pharmacological effects of various natural pigments, e.g., carotenoids, flavonoids, and curcuminoids. However, the traditional production approaches are source-dependent and generally subject to the low contents of target pigment compounds. In order to scale-up industrial production, many efforts have been devoted to increasing pigment production from natural producers, via development of both in vitro plant cell/tissue culture systems, as well as optimization of microbial cultivation approaches. Moreover, synthetic biology has opened the door for heterologous biosynthesis of pigments via design and re-construction of novel biological modules as well as biological systems in bio-platforms. In this review, the innovative methods and strategies for optimization and engineering of both native and heterologous producers of natural pigments are comprehensively summarized. Current progress in the production of several representative high-value natural pigments is also presented; and the remaining challenges and future perspectives are discussed.

Toward improved terpenoids biosynthesis: strategies to enhance the capabilities of cell factories

Terpenoids form the most diversified class of natural products, which have gained application in the pharmaceutical, food, transportation, and fine and bulk chemical industries. Extraction from naturally occurring sources does not meet industrial demands, whereas chemical synthesis is often associated with poor enantio-selectivity, harsh working conditions, and environmental pollutions. Microbial cell factories come as a suitable replacement. However, designing efficient microbial platforms for isoprenoid synthesis is often a challenging task. This has to do with the cytotoxic effects of pathway intermediates and some end products, instability of expressed pathways, as well as high enzyme promiscuity. Also, the low enzymatic activity of some terpene synthases and prenyltransferases, and the lack of an efficient throughput system to screen improved high-performing strains are bottlenecks in strain development. Metabolic engineering and synthetic biology seek to overcome these issues through the provision of effective synthetic tools. This review sought to provide an in-depth description of novel strategies for improving cell factory performance. We focused on improving transcriptional and translational efficiencies through static and dynamic regulatory elements, enzyme engineering and high-throughput screening strategies, cellular function enhancement through chromosomal integration, metabolite tolerance, and modularization of pathways.

Measurement of lactose concentration in milk by using engineered bacteria producing lycopene

Lycopene is an orange-red carotenoid, which confers a visual phenotype to assess genetic transformation of microorganisms. In this study, the lycopene synthesis pathway was constructed in engineered Escherichia coli BL21 (DE3) by transforming plasmid pET-15b-crtBEI, wherein crtB, crtE, and crtI could be expressed under the control of T7 promoter and LacO operator gene, and lycopene could be accumulated in the engineered bacteria upon induction of lactose. A good linear relationship was observed between the lycopene content in engineered bacterial culture and lactose concentration in the range of 4-52 g/L; using this relation, the lactose concentration in milk could be determined. This method could be used to overcome several limitations of the high-performance liquid chromatography (HPLC) method for lactose detection, such as cumbersome sample preparation and expensive detection equipment. Moreover, this method required only a clean bench, shaker, and spectrophotometer for lactose analysis. Additionally, no significant difference was observed between this method and HPLC in terms of lactose measurement in milk, indicating that this method is reasonable and simple.

Astaxanthin from Haematococcus pluvialis: processes, applications, and market

Astaxanthin is a xanthophyll carotenoid widely used in aquaculture and nutraceutical industries. Among natural sources, the microalga Haematococcus pluvialis is the non-genetically modified organism with the greatest capacity to accumulate astaxanthin. Therefore, it is important to understand emerging strategies in upstream and downstream processing of astaxanthin from this microalga. This review covers all aspects regarding the production and the market of natural astaxanthin from H. pluvialis. Astaxanthin biosynthesis, metabolic pathways, and nutritional metabolisms from the green vegetative motile to red hematocyst stage were reviewed in detail. Also, traditional and emerging techniques on biomass harvesting and astaxanthin recovery were presented and evaluated. Moreover, the global market of astaxanthin was discussed, and guidelines for sustainability increasing of the production chain of astaxanthin from H. pluvialis were highlighted, based on biorefinery models. This review can serve as a baseline on the current knowledge of H. pluvialis and encourage new researchers to enter this field of research.

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.

A Comparison of Constitutive and Inducible Non-Endogenous Keto-Carotenoids Biosynthesis in Synechocystis sp. PCC 6803

The model cyanobacterium Synechocystis sp. PCC 6803 has gained significant attention as an alternative and sustainable source for biomass, biofuels and added-value compounds. The latter category includes keto-carotenoids, which are molecules largely employed in a wide spectrum of industrial applications in the food, feed, nutraceutical, cosmetic and pharmaceutical sectors. Keto-carotenoids are not naturally synthesized by Synechocystis, at least in any significant amounts, but their accumulation can be induced by metabolic engineering of the endogenous carotenoid biosynthetic pathway. In this study, the accumulation of the keto-carotenoids astaxanthin and canthaxanthin, resulting from the constitutive or temperature-inducible expression of the CrtW and CrtZ genes from Brevundimonas, is compared. The benefits and drawbacks of the two engineering approaches are discussed.