Progress toward an Escherichia coli canthaxanthin bioprocess

Effects of high light exposure and heterologous expression of β-carotene ketolase on the metabolism of carotenoids in Chlamydomonas reinhardtii

Introduction

Stress from high light exposure and overexpression of β-carotene ketolase can have significant effects on the synthesis of carotenoids in Chlamydomonas reinhardtii. As a promising platform for carotenoid production, C. reinhardtii needs further research and technological innovation to address challenges, such as environmental interference, exogenous gene expression, and metabolic regulation, to achieve efficient and sustainable production of carotenoids.

Methods

Appropriate β-carotene ketolase were selected from different organisms and subjected for codon optimization based on the preferences of the nuclear genome of C. reinhardtii. After designation, including intron insertion and chloroplast transit peptide, expression vectors were constructed and used for nuclear transformation of C. reinhardtii CC849 by bead milling method. Subsequently, DNA-PCR and RT-PCR were used to identify positive transformants grown with antibiotic stress, LC-MS/MS and metabolic analysis were performed to evaluate the products of transformants.

Results

In this study, carotenoid metabolism regulation in C. reinhardtii was investigated in a time-dependent manner through high light exposure and heterologous expression of β-carotene ketolase. The results suggested that the stress from high light exposure (500 μmol/m2/s) negatively regulated the accumulation of β-carotene; positively induced the accumulation of zeaxanthin, echinenone, and canthaxanthin; and continuously promoted accumulation of zeaxanthin and canthaxanthin in C. reinhardtii. Metabolomics analysis suggested that high light exposure stress promoted biosynthesis of carotenoids, improved the intermediates associated with the astaxanthin synthesis pathway, and promoted conversion of β-carotene to downstream substances. Several strategies were implemented to improve canthaxanthin production in C. reinhardtii to achieve overexpression of β-carotene ketolase genes from different sources, including strong promoters, insertion introns, and chloroplast conduction peptides. It was found that β-carotene, echinenone, and canthaxanthin were all significantly increased in the transformed C. reinhardtii overexpressing β-carotene ketolase. Among these, the highest canthaxanthin content was found in pH124-CrtO, which was seven times that observed in the wild type. Moreover, the metabolomics analysis of carotenoids showed promotion of the abscisic acid and astaxanthin pathways in the transformed C. reinhardtii.

Discussion

The results of this study provide a new scheme for manipulating the metabolism of carotenoids and promoting the synthesis of high-value carotenoids in C. reinhardtii.

Arts, cultural heritage, sciences, and micro-/bio-/technology: Impact of biomaterials and biocolorants from antiquity till today!

Nature has inspired and provided humans with ideas, concepts, and thoughts on design, art, and performance for millennia. From early societies when humankind often took shelter in caves, until today, many materials and colorants to express feelings or communicate with one another were derived from plants, animals, or microbes. In this manuscript, an overview of these natural products used in the creation of art is given, from paintings on rocks to fashionable dresses made from bacterial cellulose. Besides offering many examples of art works, the origin and application of various biomaterials and colorants are discussed. While many facets of our daily lives have changed over millennia, one certainty has been that humans have an intrinsic need to conceptualize and create to express themselves. Driven by technological advances in the past decades and in the light of global warming, new and often more sustainable materials and colorants have been discovered and implemented. The impact of art on human societies remains relevant and powerful.

ONE-SENTENCE SUMMARY

This manuscript discusses the use of biomaterials and biocolorants in art from a historical perspective, spanning 37,000 bc until today.

Metabolic Engineering of Model Microorganisms for the Production of Xanthophyll

Xanthophyll is an oxidated version of carotenoid. It presents significant value to the pharmaceutical, food, and cosmetic industries due to its specific antioxidant activity and variety of colors. Chemical processing and conventional extraction from natural organisms are still the main sources of xanthophyll. However, the current industrial production model can no longer meet the demand for human health care, reducing petrochemical energy consumption and green sustainable development. With the swift development of genetic metabolic engineering, xanthophyll synthesis by the metabolic engineering of model microorganisms shows great application potential. At present, compared to carotenes such as lycopene and β-carotene, xanthophyll has a relatively low production in engineering microorganisms due to its stronger inherent antioxidation, relatively high polarity, and longer metabolic pathway. This review comprehensively summarized the progress in xanthophyll synthesis by the metabolic engineering of model microorganisms, described strategies to improve xanthophyll production in detail, and proposed the current challenges and future efforts needed to build commercialized xanthophyll-producing microorganisms.

Construction of Canthaxanthin-Producing Yeast by Combining Spatiotemporal Regulation and Pleiotropic Drug Resistance Engineering

The ketocarotenoid canthaxanthin has important applications in the feed industry. Its biosynthesis using microbial cell factories is an attractive alternative to the current chemical synthesis route. Canthaxanthin-producing Saccharomyces cerevisiae was constructed by introducing the β-carotene ketolase variant OBKTM29 into a β-carotene producer. Subcellular re-localization of OBKTM29 was explored, together with copy number adjustment both in the cytoplasm and on the periplasmic membrane, to accelerate the conversion of β-carotene to canthaxanthin. Moreover, pleiotropic drug resistance (PDR) regulators Pdr1 and Pdr3 were overexpressed to improve the stress tolerance of the yeast strain, leading to obviously enhanced canthaxanthin production. The synthetic pathway was then regulated by a temperature-responsive GAL system to separate product synthesis from cell growth. Finally, 1.44 g/L canthaxanthin was harvested in fed-batch fermentation. This work demonstrated the power of spatial and temporal regulation and the efficiency of PDR engineering in heterologous biosynthesis.

Canthaxanthin, a Red-Hot Carotenoid: Applications, Synthesis, and Biosynthetic Evolution

Carotenoids are a class of pigments with a biological role in light capture and antioxidant activities. High value ketocarotenoids, such as astaxanthin and canthaxanthin, are highly appealing for applications in human nutraceutical, cosmetic, and animal feed industries due to their color- and health-related properties. In this review, recent advances in metabolic engineering and synthetic biology towards the production of ketocarotenoids, in particular the red-orange canthaxanthin, are highlighted. Also reviewed and discussed are the properties of canthaxanthin, its natural producers, and various strategies for its chemical synthesis. We review the de novo synthesis of canthaxanthin and the functional β-carotene ketolase enzyme across organisms, supported by a protein-sequence-based phylogenetic analysis. Various possible modifications of the carotenoid biosynthesis pathway and the present sustainable cost-effective alternative platforms for ketocarotenoids biosynthesis are also discussed.