Screening of Structurally Distinct Lycopene β-Cyclases for Production of the Cyclic C40 Carotenoids β-Carotene and Astaxanthin by Corynebacterium glutamicum

Enhanced production of C50 carotenoid bacterioruberin by metabolically engineered Corynebacterium glutamicum

Bacterioruberin is a red-pigmented C50 carotenoid commonly found in halophilic archaea, known for its strong antioxidant properties. In this study, we demonstrate the complete biosynthesis of bacterioruberin in metabolically engineered Corynebacterium glutamicum overproducing lycopene. To investigate the function of the encoded enzymes, we genetically modified C. glutamicum to produce lycopene and constructed recombinant C. glutamicum strains expressing bacterioruberin biosynthetic genes. The carotenoids produced by the recombinant strains were then analyzed. The pathway comprising the bifunctional lycopene elongase and 1,2-hydratase (lyeJ), carotenoid 3,4-desaturase (crtD), and C50 carotenoid 2'',3''-hydratase (cruF) from "Haloferax marinum" was introduced into the C. glutamicum ΔcrtRYEb strain. The expression of each gene allowed for the identification of bacterioruberin, its known precursors, and previously unidentified precursors. In fed-batch fermentation, a carotenoid titer of 9.74 mg/L with a yield of 0.29 mg/g DCW and a productivity of 0.30 mg/L/h, was achieved. This study is the first to demonstrate that C. glutamicum can accumulate the non-native bacterioruberin instead of its native cyclic C50 carotenoid, decaprenoxanthin.

Comparative genomics and evolutionary insights into zeaxanthin biosynthesis in two novel Flavobacterium species

BACKGROUND

During the screening of pigment-producing microbes from domestic sources, 102 yellow- or orange-pigmented bacteria were isolated. Among these, two novel Flavobacterium strains, F. sedimentum SUN046T and F. fluvius SUN052T, were identified as zeaxanthin producers. A polyphasic taxonomic characterization, combined with comparative genomic analysis of 45 Flavobacterium species, was conducted to determine their taxonomic positions and explore potential evolutionary relationships in zeaxanthin biosynthesis.

RESULTS

Both strains utilized the mevalonic acid (MVA) pathway and possessed the crt gene cluster (crtB, crtI, crtY/crtYcd, and crtZ). Strain SUN046T exhibited unique features in the carotenoid biosynthesis pathway, notably the absence of HMG-CoA synthase (HMGCS) in the upper MVA pathway and the presence of the rare lycopene β-cyclase crtYcd, which is uncommon among bacteria. The CrtYcd in SUN046T possessed a single active site and direct lycopene-binding modes. Conversely, CrtY in SUN052T exhibited multiple active sites, which is flavin adenine dinucleotide (FAD) dependent. These structural differences has impacted catalytic efficiencies, as evidenced by zeaxanthin yields of 6.49 µg/mL in SUN046T and 13.23 µg/mL in SUN052T. Variations in carotenoid biosynthetic pathway among other Flavobacterium species were also observed.

CONCLUSION

These findings suggest that both strains represent valuable new resources for zeaxanthin production and provide foundational insights for biotechnological applications involving the genus Flavobacterium, highlighting the genetic and evolutionary complexity of microbial carotenoid biosynthesis.

Metabolic Engineering of Corynebacterium glutamicum for Producing Different Types of Triterpenoids

Triterpenoids widely exist in nature with diverse structures and possess various functional properties and biological effects. However, research on triterpenoids biosynthesis in Corynebacterium glutamicum is still limited to squalene, which restricts the development of C. glutamicum to produce high-value triterpenoids. In this study, C. glutamicum was developed as an efficient and flexible platform for the biosynthesis of different types of triterpenoids. Squalene was synthesized and the titer was improved to 400.1 mg/L in flask combining strategies of metabolic engineering and fermentation optimization. Particularly, intracellular squalene accounted for more than 97%, addressing the problem of leaking squalene in C. glutamicum, which may restrict the subsequent synthesis of other triterpenoids derived from squalene. Furthermore, 201.9 mg/L (3S)-2,3-oxidosqualene (SQO) and 264.9 mg/L (3S,22S)-2,3,22,23-dioxidosqualene (SDO) were successfully synthesized in strains harboring heterogeneous squalene epoxidase from Arabidopsis thaliana with different expression strengths. Therefore, a platform for de novo triterpenoids synthesis based on SQO or SDO was constructed in C. glutamicum. For instance, biosynthesis of α-amyrin and α-onocerin was achieved for the first time by introducing oxidosqualene cyclases in SQO- and SDO-producing C. glutamicum strains, respectively. After optimization, the titer of α-amyrin and α-onocerin was improved to 65.3 and 136.85 mg/L, respectively. Furthermore, ursolic acid, derived from α-amyrin, was synthesized after expressing cytochrome P450 enzyme and its compatible cytochrome P450 reductases with a titer of 486 μg/L. For the first time, reactions of epoxidation, cyclization, and oxidation from squalene were achieved in C. glutamicum, leading to the production of different types of triterpenoids. Our study provides a new platform for the production of triterpenoids, which will be helpful for the large-scale production of triterpenoids employing C. glutamicum as a chassis strain.

Response surface-based media optimization for astaxanthin production in Corynebacterium glutamicum

Introduction

Astaxanthin is a C40 carotenoid that is used in animal feeds or cosmetics. Due to its high antioxidant property it is used for, e.g., anti-aging formulations and due to its intense red color it is used, e.g., in animal feed. While about 95% of commercial astaxanthin is currently chemically synthesized from fossil sources, the interest in natural and sustainable astaxanthin is growing. Corynebacterium glutamicum, an attractive host used in large-scale processes, e.g., industrial amino acid production, has been engineered for astaxanthin production.

Methods

Here, a design of experiment (DoE) approach was applied to optimize the standard minimal medium for astaxanthin production. The concentrations of carbon, nitrogen and phosphorus sources, magnesium, calcium, the iron chelator protocatechuic acid, the vitamin biotin, and the trace metals were varied and astaxanthin production was evaluated.

Results and discussion

By increasing the concentration of iron and decreasing that of manganese especially, it was possible to increase astaxanthin titers from 7.9 mg L-1-39.6 mg L-1 in a micro cultivation system and from 62 mg L-1-176 mg L-1 in a fed-batch fermentation.

Distribution, Biosynthesis, and Function of Carotenoids in Oxygenic Phototrophic Algae

For photosynthesis, oxygenic phototrophic organisms necessarily contain not only chlorophylls but also carotenoids. Various carotenoids have been identified in algae and taxonomic studies of algae have been conducted. In this review, the relationship between the distribution of chlorophylls and carotenoids and the phylogeny of sea and freshwater oxygenic phototrophs, including cyanobacteria, red algae, brown algae, and green algae, is summarized. These phototrophs contain division- or class-specific chlorophylls and carotenoids, such as fucoxanthin, peridinin, diadinoxanthin, and siphonaxanthin. The distribution of β-carotene and its derivatives, including β-carotene, zeaxanthin, violaxanthin, neoxanthin, diadinoxanthin, fucoxanthin, and peridinin (β-branch carotenoids), are limited to divisions of a part of Rhodophyta, Cryptophyta, Heterokontophyta, Haptophyta, and Dinophyta. Meanwhile, the distribution of α-carotene and its derivatives, such as lutein, loroxanthin, and siphonaxanthin (α-branch carotenoids), are limited to divisions of a part of Rhodophyta (macrophytic type), Cryptophyta, Euglenophyta, Chlorarachniophyta, and Chlorophyta. In addition, carotenogenesis pathways are also discussed based on the chemical structures of carotenoids and the known characteristics of carotenogenesis enzymes in other organisms. The specific genes and enzymes for carotenogenesis in algae are not yet known. Most carotenoids bind to membrane-bound pigment-protein complexes, such as reaction centers and light-harvesting complexes. Some carotenoids function in photosynthesis and are briefly summarized. Water-soluble peridinin-chlorophyll a-protein (PCP) and orange carotenoid protein (OCP) have also been characterized. This review is a summary and update from the previous review on the distribution of major carotenoids, primary carotenogenesis pathways, and the characteristics of carotenogenesis enzymes and genes.

'Altruistic' cooperation among the prokaryotic community of Atlantic salterns assessed by metagenomics

Hypersaline environments are extreme habitats with a limited prokaryotic diversity, mainly restricted to halophilic or halotolerant archaeal and bacterial taxa adapted to highly saline conditions. This study attempts to analyze the taxonomic and functional diversity of the prokaryotes that inhabit a solar saltern located at the Atlantic Coast, in Isla Cristina (Huelva, Southwest Spain), and the influence of salinity on the diversity and metabolic potential of these prokaryotic communities, as well as the interactions and cooperation among the individuals within that community. Brine samples were obtained from different saltern ponds, with a salinity range between 19.5 % and 39 % (w/v). Total prokaryotic DNA was sequenced using the Illumina shotgun metagenomic strategy and the raw sequence data were analyzed using supercomputing services following the MetaWRAP and SqueezeMeta protocols. The most abundant phyla at moderate salinities (19.5-22 % [w/v]) were Methanobacteriota (formerly "Euryarchaeota"), Pseudomonadota and Bacteroidota, followed by Balneolota and Actinomycetota and Uroviricota in smaller proportions, while at high salinities (36-39 % [w/v]) the most abundant phylum was Methanobacteriota, followed by Bacteroidota. The most abundant genera at intermediate salinities were Halorubrum and the bacterial genus Spiribacter, while the haloarchaeal genera Halorubrum, Halonotius, and Haloquadratum were the main representatives at high salinities. A total of 65 MAGs were reconstructed from the metagenomic datasets and different functions and pathways were identified in them, allowing to find key taxa in the prokaryotic community able to synthesize and supply essential compounds, such as biotin, and precursors of other bioactive molecules, like β-carotene, and bacterioruberin, to other dwellers in this habitat, lacking the required enzymatic machinery to produce them. This work shed light on the ecology of aquatic hypersaline environments, such as the Atlantic Coast salterns, and on the dynamics and factors affecting the microbial populations under such extreme conditions.

The TolC and Lipopolysaccharide-Specific Escherichia coli Bacteriophage TLS-the Tlsvirus Archetype Virus

Introduction

TLS is a virulent bacteriophage of Escherichia coli that utilizes TolC and lipopolysaccharide as its cell surface receptors.

Methods

The genome was reannotated using the latest online resources and compared to other T1-like phages.

Results

The TLS genome consists of 49,902 base pairs, encoding 86 coding sequences that display considerable sequence similarity with the T1 phage genome. It also contains 18 intergenic 21-base long repeats, each of them upstream of a predicted start codon and in the direction of transcription. Data revealed that DNA packaging occurs through the pac site-mediated headful mechanism.

Conclusions

Based on sequence analysis of its genome, TLS belongs to the Drexlerviridae family and represents the type member of the Tlsvirus genus.

Expanding the CRISPR Toolbox for Engineering Lycopene Biosynthesis in Corynebacterium glutamicum

Lycopene represents one of the central compounds in the carotenoid pathway and it exhibits a potent antioxidant ability with wide potential applications in medicine, food, and cosmetics. The microbial production of lycopene has received increasing concern in recent years. Corynebacterium glutamicum (C. glutamicum) is considered to be a safe and beneficial industrial production platform, naturally endowed with the ability to produce lycopene. However, the scarcity of efficient genetic tools and the challenge of identifying crucial metabolic genes impede further research on C. glutamicum for achieving high-yield lycopene production. To address these challenges, a novel genetic editing toolkit, CRISPR/MAD7 system, was established and developed. By optimizing the promoter, ORI and PAM sequences, the CRISPR/MAD7 system facilitated highly efficient gene deletion and exhibited a broad spectrum of PAM sites. Notably, 25 kb of DNA from the genome was successfully deleted. In addition, the CRISPR/MAD7 system was effectively utilized in the metabolic engineering of C. glutamicum, allowing for the simultaneous knockout of crtEb and crtR genes in one step to enhance the accumulation of lycopene by blocking the branching pathway. Through screening crucial genes such as crtE, crtB, crtI, idsA, idi, and cg0722, an optimal carotenogenic gene combination was obtained. Particularly, cg0722, a membrane protein gene, was found to play a vital role in lycopene production. Therefore, the CBIEbR strain was obtained by overexpressing cg0722, crtB, and crtI while strategically blocking the by-products of the lycopene pathway. As a result, the final engineered strain produced lycopene at 405.02 mg/L (9.52 mg/g dry cell weight, DCW) in fed-batch fermentation, representing the highest reported lycopene yield in C. glutamicum to date. In this study, a powerful and precise genetic tool was used to engineer C. glutamicum for lycopene production. Through the modifications between the host cell and the carotenogenic pathway, the lycopene yield was stepwise improved by 102-fold as compared to the starting strain. This study highlights the usefulness of the CRISPR/MAD7 toolbox, demonstrating its practical applications in the metabolic engineering of industrially robust C. glutamicum.

Enhancing astaxanthin biosynthesis and pathway expansion towards glycosylated C40 carotenoids by Corynebacterium glutamicum

Astaxanthin, a versatile C40 carotenoid prized for its applications in food, cosmetics, and health, is a bright red pigment with powerful antioxidant properties. To enhance astaxanthin production in Corynebacterium glutamicum, we employed rational pathway engineering strategies, focused on improving precursor availability and optimizing terminal oxy-functionalized C40 carotenoid biosynthesis. Our efforts resulted in an increased astaxanthin precursor supply with 1.5-fold higher β-carotene production with strain BETA6 (18 mg g-1 CDW). Further advancements in astaxanthin production were made by fine-tuning the expression of the β-carotene hydroxylase gene crtZ and β-carotene ketolase gene crtW, yielding a nearly fivefold increase in astaxanthin (strain ASTA**), with astaxanthin constituting 72% of total carotenoids. ASTA** was successfully transferred to a 2 L fed-batch fermentation with an enhanced titer of 103 mg L-1 astaxanthin with a volumetric productivity of 1.5 mg L-1 h-1. Based on this strain a pathway expansion was achieved towards glycosylated C40 carotenoids under heterologous expression of the glycosyltransferase gene crtX. To the best of our knowledge, this is the first time astaxanthin-β-D-diglucoside was produced with C. glutamicum achieving high titers of microbial C40 glucosides of 39 mg L-1. This study showcases the potential of pathway engineering to unlock novel C40 carotenoid variants for diverse industrial applications.

Astaxanthin Isomers: A Comprehensive Review of Isomerization Methods and Analytic Techniques

The presence of multiple conjugated double bonds and chiral carbon atoms endows astaxanthin with geometric and optical isomers, and these isomers widely exist in biological sources, food processing, and in vivo absorption. However, there remains no systematic summary of astaxanthin isomers regarding isomerization methods and analytic techniques. To address this need, this Review focuses on a comprehensive analysis of Z-isomerization methods of astaxanthin, including solvent system, catalyst, and heat treatment. Comparatively, high-efficiency and health-friendly methods are more conducive to put into practical use, such as food-grade solvents and food-component catalysts. In addition, we outline the recent advances in analysis techniques of astaxanthin isomers, as well as the structural characteristics reflected by various methods (e.g., HPLC, NMR, FTIR, and RS). Furthermore, we summarized the related research on the safety evaluation of astaxanthin isomers. Finally, future trends and barriers in Z-transformation and analysis of astaxanthin isomers are also discussed.

Extraction and Purification of Highly Active Astaxanthin from Corynebacterium glutamicum Fermentation Broth

The marine carotenoid astaxanthin is one of the strongest natural antioxidants and therefore is used in a broad range of applications such as cosmetics or nutraceuticals. To meet the growing market demand, the natural carotenoid producer Corynebacterium glutamicum has been engineered to produce astaxanthin by heterologous expression of genes from the marine bacterium Fulvimarina pelagi. To exploit this promising source of fermentative and natural astaxanthin, an efficient extraction process using ethanol was established in this study. Appropriate parameters for ethanol extraction were identified by screening ethanol concentration (62.5-97.5% v/v), temperature (30-70 °C) and biomass-to-solvent ratio (3.8-19.0 mgCDW/mLsolvent). The results demonstrated that the optimal extraction conditions were: 90% ethanol, 60 °C, and a biomass-to-solvent ratio of 5.6 mgCDW/mLsolvent. In total, 94% of the cellular astaxanthin was recovered and the oleoresin obtained contained 9.4 mg/g astaxanthin. With respect to other carotenoids, further purification of the oleoresin by column chromatography resulted in pure astaxanthin (100%, HPLC). In addition, a 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay showed similar activities compared to esterified astaxanthin from microalgae and a nine-fold higher antioxidative activity than synthetic astaxanthin.