High copy number integration into the ribosomal DNA of the yeast Phaffia rhodozyma

Omics-driven onboarding of the carotenoid producing red yeast Xanthophyllomyces dendrorhous CBS 6938

Transcriptomics is a powerful approach for functional genomics and systems biology, yet it can also be used for genetic part discovery. Here, we derive constitutive and light-regulated promoters directly from transcriptomics data of the basidiomycete red yeast Xanthophyllomyces dendrorhous CBS 6938 (anamorph Phaffia rhodozyma) and use these promoters with other genetic elements to create a modular synthetic biology parts collection for this organism. X. dendrorhous is currently the sole biotechnologically relevant yeast in the Tremellomycete class-it produces large amounts of astaxanthin, especially under oxidative stress and exposure to light. Thus, we performed transcriptomics on X. dendrorhous under different wavelengths of light (red, green, blue, and ultraviolet) and oxidative stress. Differential gene expression analysis (DGE) revealed that terpenoid biosynthesis was primarily upregulated by light through crtI, while oxidative stress upregulated several genes in the pathway. Further gene ontology (GO) analysis revealed a complex survival response to ultraviolet (UV) where X. dendrorhous upregulates aromatic amino acid and tetraterpenoid biosynthesis and downregulates central carbon metabolism and respiration. The DGE data was also used to identify 26 constitutive and regulated genes, and then, putative promoters for each of the 26 genes were derived from the genome. Simultaneously, a modular cloning system for X. dendrorhous was developed, including integration sites, terminators, selection markers, and reporters. Each of the 26 putative promoters were integrated into the genome and characterized by luciferase assay in the dark and under UV light. The putative constitutive promoters were constitutive in the synthetic genetic context, but so were many of the putative regulated promoters. Notably, one putative promoter, derived from a hypothetical gene, showed ninefold activation upon UV exposure. Thus, this study reveals metabolic pathway regulation and develops a genetic parts collection for X. dendrorhous from transcriptomic data. Therefore, this study demonstrates that combining systems biology and synthetic biology into an omics-to-parts workflow can simultaneously provide useful biological insight and genetic tools for nonconventional microbes, particularly those without a related model organism. This approach can enhance current efforts to engineer diverse microbes. KEY POINTS: • Transcriptomics revealed further insights into the photobiology of X. dendrorhous, specifically metabolic nodes that are transcriptionally regulated by light. • A modular genetic part collection was developed, including 26 constitutive and regulated promoters derived from the transcriptomics of X. dendrorhous. • Omics-to-parts can be applied to nonconventional microbes for rapid "onboarding".

Generation of stable homozygous transformants of diploid yeasts such as Xanthophyllomyces dendrorhous

The nonconventional yeast Xanthophyllomyces dendrorhous is an established platform for genetic pathway modification. A genetic tool box is available and can be used extensively to select from for different engineering strategies. Due to the diploid nature of X. dendrorhous, genetic transformation typically results in heterozygous lines. They are genetically unstable and lose their phenotypes caused by mitotic recombination. In addition, targeted integration for inactivation of genes of the carotenoid pathway resulted in an intermediary phenotype of incomplete pathway disruption. This issue is the main scope of this review. It is illustrated by using genetic modification of the carotenoid pathway of X. dendrorhous as a model system with a focus on the demonstration of how to solve these problems by generation of homozygous lines. They can be selected from heterozygous transformants after spontaneous mitotic recombination and selection or after induced meiotic recombination. Corresponding methods of how to proceed including the initiation of a sexual cycle are described. The selected segregated lines are stable in fermenter cultures without the need of selection pressure. This is an essential requirement for any industrial application. KEY POINTS: • Genetic interventions of diploid yeasts result in heterozygous transformants that are unstable without selection pressure. • This is due to mitotic recombination leading to the elimination of inserted DNA. • Stable homozygous lines can be obtained and selected after either meiotic or mitotic recombination.

PiggyBac transposase and transposon derivatives for gene transfer targeting the ribosomal DNA loci of CHO cells

Integrative non-viral vectors such as transposons engineered to mediate targeted gene transfer into safe harbor sites in the genome may be a promising approach for the production of therapeutic proteins or for gene therapy in an efficient and secure way. In this context, we designed and evaluated two strategies for targeting the nuclear ribosomal DNA (rDNA) loci. One approach relied on the co-location of the transposase and transposon near transcriptionally active rDNA copies using a nucleolar localization signal (NoLS). Another one consisted of targeting the 18S-coding region in the rDNA loci using a NoLS-FokI-dCas9 endonuclease to perform targeted transgene knock-in. We show that integration into the rDNA of Chinese hamster ovary (CHO) cells can be achieved at a high frequency using the piggyBac transposon system, indicating that the rDNA is highly accessible for transposition. Consistently, rDNA-targeted transposition events were most frequently obtained when both the piggyBac transposon DNA and the transposase were nucleoli-targeted, yielding cells displaying stable and homogeneous expression of the transgene. This approach thus provides an alternative strategy to improve targeted transgene delivery and protein expression using CHO cells.

Recombinant Yarrowia lipolytica strains for the heterologous expression of multi-component enzyme systems: Expression of mammalian steroidogenic proteins

New Yarrowia lipolytica strains for the co-expression of steroidogenic mammalian proteins were obtained in this study. For this purpose, a two-step approach for constructing recombinant strains that permits the simple introduction of several expression cassettes encoding heterologous proteins into the yeast genome was successfully applied. This study tested two series of integrative multi-copy expression vectors containing cDNAs for the mature forms of P450scc system components (cytochrome P450scc (CYP11A1), adrenodoxin reductase, adrenodoxin, or fused adrenodoxin-P450scc) or for P45017α (CYP17A1) under the control of the isocitrate lyase promoter pICL1, which were constructed using the basic plasmids p64PT or p67PT (rDNA or the long terminal repeat (LTR) zeta of Ylt1 as integration targeting sequences and ura3d4 as a multi-copy selection marker). This study demonstrated the integration of up to three expression vectors containing different heterologous cDNA via their simultaneous transformation into haploid recipient strains. Additionally, further combinations of the different expression cassettes in one strain were obtained by subsequent diploidisation using selected haploid multi-copy transformants. Thus, recombinant strains containing three to five different expression cassettes were obtained, as demonstrated by Southern blotting. Expression of P450scc system proteins was identified by western blotting. The presented method for recombinant strain construction is a useful tool for the heterologous expression of multi-component enzyme systems in Y. lipolytica.

Xanthophyllomyces dendrorhous, a Versatile Platform for the Production of Carotenoids and Other Acetyl-CoA-Derived Compounds

Xanthophyllomyces dendrorhous (with Phaffia rhodozyma as its anamorphic state) is a basidiomycetous, moderately psychrophilic, red yeast belonging to the Cystofilobasidiales. Its red pigmentation is caused by the accumulation of astaxanthin, which is a unique feature among fungi. The present chapter reviews astaxanthin biosynthesis and acetyl-CoA metabolism in X. dendrorhous and describes the construction of a versatile platform for the production of carotenoids, such as astaxanthin, and other acetyl-CoA-derived compounds including fatty acids by using this fungus.

Systematical Engineering of Synthetic Yeast for Enhanced Production of Lycopene

Synthetic biology allows the re-engineering of biological systems and promotes the development of bioengineering to a whole new level, showing great potential in biomanufacturing. Here, in order to make the heterologous lycopene biosynthesis pathway compatible with the host strain YSy 200, we evolved YSy200 using a unique Synthetic Chromosome Rearrangement and Modification by LoxP-mediated Evolution (SCRaMbLE) system that is built in the Sc2.0 synthetic yeast. By inducing SCRaMbLE, we successfully identified a host strain YSy201 that can be served as a suitable host to maintain the heterologous lycopene biosynthesis pathway. Then, we optimized the lycopene biosynthesis pathway and further integrated into the rDNA arrays of YSy201 to increase its copy number. In combination with culturing condition optimization, we successfully screened out the final yeast strain YSy222, which showed a 129.5-fold increase of lycopene yield in comparison with its parental strain. Our work shows that, the strategy of combining the engineering efforts on both the lycopene biosynthesis pathway and the host strain can improve the compatibility between the heterologous pathway and the host strain, which can further effectively increase the yield of the target product.

Metabolic engineering of Saccharomyces cerevisiae for high-level production of gastrodin from glucose

BACKGROUND

The natural phenolic glycoside gastrodin is the major bioactive ingredient in the well-known Chinese herb Tianma and is widely used as a neuroprotective medicine in the clinic. Microbial production from sustainable resources is a promising method to replace plant extraction and chemical synthesis which were currently used in industrial gastrodin production. Saccharomyces cerevisiae is considered as an attractive host to produce natural plant products used in the food and pharmaceutical fields. In this work, we intended to explore the potential of S. cerevisiae as the host for high-level production of gastrodin from glucose.

RESULTS

Here, we first identified the plant-derived glucosyltransferase AsUGT to convert 4-hydroxybenzyl alcohol to gastrodin with high catalytic efficiency in yeast. Then, we engineered de novo production of gastrodin by overexpressing codon-optimized AsUGT^syn, the carboxylic acid reductase gene CAR^syn from Nocardia species, the phosphopantetheinyl transferase gene PPTcg-1^syn from Corynebacterium glutamicum, the chorismate pyruvate-lyase gene UbiC^syn from Escherichia coli, and the mutant ARO4^K229L. Finally, we achieved an improved product titer by a chromosomal multiple-copy integration strategy and enhancement of metabolic flux toward the aglycon 4-hydroxybenzyl alcohol. The best optimized strain produced 2.1 g/L gastrodin in mineral medium with glucose as the sole carbon source by flask fermentation, which was 175 times higher than that of the original gastrodin-producing strain.

CONCLUSIONS

The de novo high-level production of gastrodin was first achieved. Instead of chemical synthesis or plants extraction, our work provides an alternative strategy for the industrial production of gastrodin by microbial fermentation from a sustainable resource.

Yeast-based vaccines: New perspective in vaccine development and application

In presently licensed vaccines, killed or attenuated organisms act as a source of immunogens except for peptide-based vaccines. These conventional vaccines required a mass culture of associated or related organisms and long incubation periods. Special requirements during storage and transportation further adds to the cost of vaccine preparations. Availability of complete genome sequence, well-established genetic, inherent natural adjuvant and non-pathogenic nature of yeast species viz. Saccharomyces cerevisiae, Pichia pastoris makes them an ideal model system for the development of vaccines both for public health and for on-farm consumption. In this review, we compile the work in this emerging field during last two decades with major emphases on S. cerevisiae and P. pastoris which are routinely used worldwide for expression of heterologous proteins with therapeutic value against infectious diseases along with possible use in cancer therapy. We also pointed towards the developments in use of whole recombinant yeast, yeast surface display and virus-like particles as a novel strategy in the fight against infectious diseases and cancer along with other aspects including suitability of yeast in vaccines preparations, yeast cell wall component as an immune stimulator or modulator and present status of yeast-based vaccines in clinical trials.

Functional characterization of thiolase-encoding genes from Xanthophyllomyces dendrorhous and their effects on carotenoid synthesis

BACKGROUND

The basidiomycetous yeast Xanthophyllomyces dendrorhous has been described as a potential biofactory for terpenoid-derived compounds due to its ability to synthesize astaxanthin. Functional knowledge of the genes involved in terpenoid synthesis would create opportunities to enhance carotenoid production. A thiolase enzyme catalyzes the first step in terpenoid synthesis.

RESULTS

Two potential thiolase-encoding genes were found in the yeast genome; bioinformatically, one was identified as an acetyl-CoA C-acetyltransferase (ERG10), and the other was identified as a 3-ketoacyl Co-A thiolase (POT1). Heterologous complementation assays in Saccharomyces cerevisiae showed that the ERG10 gene from X. dendrorhous could complement the lack of the endogenous ERG10 gene in S. cerevisiae, thereby allowing cellular growth and sterol synthesis. X. dendrorhous heterozygous mutants for each gene were created, and a homozygous POT1 mutant was also obtained. This mutant exhibited changes in pigment composition and higher ERG10 transcript levels than the wild type strain.

CONCLUSIONS

The results support the notion that the ERG10 gene in X. dendrorhous is a functional acetyl-CoA C-acetyltransferase essential for the synthesis of mevalonate in yeast. The POT1 gene would encode a functional 3-ketoacyl Co-A thiolase that is non-essential for cell growth, but its mutation indirectly affects pigment production.

Enhancement of astaxanthin production in Xanthophyllomyces dendrorhous by efficient method for the complete deletion of genes

Background

Red yeast, Xanthophyllomyces dendrorhous is the only yeast known to produce astaxanthin, an anti-oxidant isoprenoid (carotenoid) widely used in the aquaculture, food, pharmaceutical and cosmetic industries. The potential of this microorganism as a platform cell factory for isoprenoid production has been recognized because of high flux through its native terpene pathway. Recently, we developed a multiple gene expression system in X. dendrorhous and enhanced the mevalonate synthetic pathway to increase astaxanthin production. In contrast, the mevalonate synthetic pathway is suppressed by ergosterol through feedback inhibition. Therefore, releasing the mevalonate synthetic pathway from this inhibition through the deletion of genes involved in ergosterol synthesis is a promising strategy to improve isoprenoid production. An efficient method for deleting diploid genes in X. dendrorhous, however, has not yet been developed.

Results

Xanthophyllomyces dendrorhous was cultivated under gradually increasing concentrations of antibiotics following the introduction of antibiotic resistant genes to be replaced with target genes. Using this method, double CYP61 genes encoding C-22 sterol desaturases relating to ergosterol biosynthesis were deleted sequentially. This double CYP61 deleted strain showed decreased ergosterol biosynthesis compared with the parental strain and single CYP61 disrupted strain. Additionally, this double deletion of CYP61 genes showed increased astaxanthin production compared with the parental strain and the single CYP61 knockout strain. Finally, astaxanthin production was enhanced by 1.4-fold compared with the parental strain, although astaxanthin production was not affected in the single CYP61 knockout strain.

Conclusions

In this study, we developed a system to completely delete target diploid genes in X. dendrorhous. Using this method, we deleted diploid CYP61 genes involved in the synthesis of ergosterol that inhibits the pathway for mevalonate, which is a common substrate for isoprenoid biosynthesis. The resulting decrease in ergosterol biosynthesis increased astaxanthin production. The efficient method for deleting diploid genes developed in this study has the potential to improve industrial production of various isoprenoids in X. dendrorhous.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-016-0556-x) contains supplementary material, which is available to authorized users.

Genetic Dissection of Sexual Reproduction in a Primary Homothallic Basidiomycete

In fungi belonging to the phylum Basidiomycota, sexual compatibility is usually determined by two genetically unlinked MAT loci, one of which encodes one or more pheromone receptors (P/R) and pheromone precursors, and the other comprehends at least one pair of divergently transcribed genes encoding homeodomain (HD) transcription factors. Most species are heterothallic, meaning that sexual reproduction requires mating between two sexually compatible individuals harboring different alleles at both MAT loci. However, some species are known to be homothallic, one individual being capable of completing the sexual cycle without mating with a genetically distinct partner. While the molecular underpinnings of the heterothallic life cycles of several basidiomycete model species have been dissected in great detail, much less is known concerning the molecular basis for homothallism. Following the discovery in available draft genomes of the homothallic basidiomycetous yeast Phaffia rhodozyma of P/R and HD genes, we employed available genetic tools to determine their role in sexual development. Two P/R clusters, each harboring one pheromone receptor and one pheromone precursor gene were found in close vicinity of each other and were shown to form two redundant P/R pairs, each receptor being activated by the pheromone encoded by the most distal pheromone precursor gene. The HD locus is apparently genetically unlinked to the P/R locus and encodes a single pair of divergently transcribed HD1 and HD2 transcription factors, both required for normal completion of the sexual cycle. Given the genetic makeup of P. rhodozyma MAT loci, we postulate that it is a primarily homothallic organism and we propose a model for the interplay of molecular interactions required for sexual development in this species. Phaffia rhodozyma is considered one of the most promising microbial source of the carotenoid astaxanthin. Further development of this yeast as an industrial organism will benefit from new insights regarding its sexual reproduction system.

Some fungi are capable of sexual reproduction without the need for a sexually compatible partner, a behavior called homothallism. For some of these fungi, it was observed that they carried in a single individual all the genes normally determining sexual identity in two distinct sexually compatible individuals, but in most cases the role of these genes is still unclear. Here we examined in detail the homothallic sexual cycle of the yeast Phaffia rhodozyma that belongs to the Basidiomycota, which is the fungal lineage that also includes the mushrooms. Phaffia rhodozyma produces astaxanthin, a pigment with antioxidant properties used in the food and cosmetic industries and is accessible to genetic modifications, so far aimed mainly at improving astaxanthin production. Here we harnessed these genetic tools to dissect the self-fertile life cycle of this yeast and found that all genes normally involved in two-partner sexual reproduction are also required for self-fertile sex in P. rhodozyma and propose a model describing molecular interactions required to trigger sexual development. We also generated preferably outcrossing strains, which are potentially useful for further improvement of P. rhodozyma as an industrial organism.

The genome of the basal agaricomycete Xanthophyllomyces dendrorhous provides insights into the organization of its acetyl-CoA derived pathways and the evolution of Agaricomycotina

Background

Xanthophyllomyces dendrorhous is a basal agaricomycete with uncertain taxonomic placement, known for its unique ability to produce astaxanthin, a carotenoid with antioxidant properties. It was the aim of this study to elucidate the organization of its CoA-derived pathways and to use the genomic information of X. dendrorhous for a phylogenomic investigation of the Basidiomycota.

Results

The genome assembly of a haploid strain of Xanthophyllomyces dendrorhous revealed a genome of 19.50 Megabases with 6385 protein coding genes. Phylogenetic analyses were conducted including 48 fungal genomes. These revealed Ustilaginomycotina and Agaricomycotina as sister groups. In the latter a well-supported sister-group relationship of two major orders, Polyporales and Russulales, was inferred. Wallemia occupies a basal position within the Agaricomycotina and X. dendrorhous represents the basal lineage of the Tremellomycetes, highlighting that the typical tremelloid parenthesomes have either convergently evolved in Wallemia and the Tremellomycetes, or were lost in the Cystofilobasidiales lineage. A detailed characterization of the CoA-related pathways was done and all genes for fatty acid, sterol and carotenoid synthesis have been assigned.

Conclusions

The current study ascertains that Wallemia with tremelloid parenthesomes is the most basal agaricomycotinous lineage and that Cystofilobasidiales without tremelloid parenthesomes are deeply rooted within Tremellomycetes, suggesting that parenthesomes at septal pores might be the core synapomorphy for the Agaricomycotina. Apart from evolutionary insights the genome sequence of X. dendrorhous will facilitate genetic pathway engineering for optimized astaxanthin or oxidative alcohol production.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1380-0) contains supplementary material, which is available to authorized users.

Development of a multi-gene expression system in Xanthophyllomyces dendrorhous

BACKGROUND

Red yeast, Xanthophyllomyces dendrorhous (Phaffia rhodozyma) is the only yeast known to produce astaxanthin, an anti-oxidant isoprenoid (carotenoid) that is widely used in the aquaculture, food, pharmaceutical and cosmetic industries. Recently, the potential of this microorganism as a platform cell factory for isoprenoid production has been recognized because of high flux through its native terpene pathway. Addition of mevalonate, the common precursor for isoprenoid biosynthesis, has been shown to be critical to enhance the astaxanthin content in X. dendrorhous. However, addition of mevalonate is unrealistic during industrial isoprenoid production because it is an unstable and costly chemical. Therefore, up-regulating the intracellular mevalonate supply by enhancing the mevalonate synthetic pathway though genetic engineering is a promising strategy to improve isoprenoid production in X. dendrorhous. However, a system to strongly express multiple genes has been poorly developed for X. dendrorhous.

RESULTS

Here, we developed a multiple gene expression system using plasmids containing three strong promoters in X. dendrorhous (actin, alcohol dehydrogenase and triose-phosphate isomerase) and their terminators. Using this system, three mevalonate synthetic pathway genes encoding acetoacetyl-CoA thiolase, HMG-CoA synthase and HMG-CoA reductase were overexpressed at the same time. This triple overexpressing strain showed an increase in astaxanthin production compared with each single overexpressing strain. Additionally, this triple overexpression of mevalonate synthetic pathway genes together with genes involved in β-carotene and astaxanthin synthesis showed a synergetic effect on increasing astaxanthin production. Finally, astaxanthin production was enhanced by 2.1-fold compared with the parental strain without a reduction of cell growth.

CONCLUSIONS

We developed a system to strongly overexpress multiple genes in X. dendrorhous. Using this system, the synthetic pathway of mevalonate, a common substrate for isoprenoid biosynthesis, was enhanced, causing an increase in astaxanthin production. Combining this multiple gene overexpression system with a platform strain that overproduces mevalonate has the potential to improve industrial production of various isoprenoids in X. dendrorhous.

Evaluation and screening of efficient promoters to improve astaxanthin production in Xanthophyllomyces dendrorhous

Astaxanthin is a valuable carotenoid that is widely used in the aquaculture, food, pharmaceutical, and cosmetic industries. Xanthophyllomyces dendrorhous is a carotenoid-synthesizing yeast strain that produces astaxanthin as its main pigment. Although metabolic engineering using gene manipulation is a valuable way to improve astaxanthin production, a gene expression system for X. dendrorhous has been poorly developed. In this study, three known promoters of X. dendrorhous, glycerol-3-phosphate dehydrogenase (gpd) promoter (Pgpd), glucose dehydrogenase (gdh) promoter (Pgdh), and actin (act) promoter (Pact), were evaluated for use in the overexpression of target proteins using green fluorescence protein (GFP) as an expression level indicator protein. The actin promoter, Pact, showed the highest expression level of GFP when compared with Pgpd and Pgdh. Additionally, to obtain new promoters for higher expression of target protein in X. dendrorhous, intracellular GFP intensity was evaluated for 13 candidate promoters. An alcohol dehydrogenase promoter, Padh4, showed more efficient expression of GFP rather than Pact. Overexpression of crtE gene encoding rate-limiting enzyme of carotenoid synthesis under the adh4 promoter yielded an increase in intracellular astaxanthin content of about 1.7-fold compared with the control strain. The promoters identified in this study must be useful for improving carotenoids production in X. dendrorhous.

Increase in the astaxanthin synthase gene (crtS) dose by in vivo DNA fragment assembly in Xanthophyllomyces dendrorhous

BACKGROUND

Xanthophyllomyces dendrorhous is a basidiomycetous yeast that is relevant to biotechnology, as it can synthesize the carotenoid astaxanthin. However, the astaxanthin levels produced by wild-type strains are low. Although different approaches for promoting increased astaxanthin production have been attempted, no commercially competitive results have been obtained thus far. A promising alternative to facilitate the production of carotenoids in this yeast involves the use of genetic modification. However, a major limitation is the few available molecular tools to manipulate X. dendrorhous.

RESULTS

In this work, the DNA assembler methodology that was previously described in Saccharomyces cerevisiae was successfully applied to assemble DNA fragments in vivo and integrate these fragments into the genome of X. dendrorhous by homologous recombination in only one transformation event. Using this method, the gene encoding astaxanthin synthase (crtS) was overexpressed in X. dendrorhous and a higher level of astaxanthin was produced.

CONCLUSIONS

This methodology could be used to easily and rapidly overexpress individual genes or combinations of genes simultaneously in X. dendrorhous, eliminating numerous steps involved in conventional cloning methods.

A vaccine grade of yeast Saccharomyces cerevisiae expressing mammalian myostatin

BACKGROUND

Yeast Saccharomyces cerevisiae is a widely-used system for protein expression. We previously showed that heat-killed whole recombinant yeast vaccine expressing mammalian myostatin can modulate myostatin function in mice, resulting in increase of body weight and muscle composition in these animals. Foreign DNA introduced into yeast cells can be lost soon unless cells are continuously cultured in selection media, which usually contain antibiotics. For cost and safety concerns, it is essential to optimize conditions to produce quality food and pharmaceutical products.

RESULTS

We developed a simple but effective method to engineer a yeast strain stably expressing mammalian myostatin. This method utilized high-copy-number integration of myostatin gene into the ribosomal DNA of Saccharomyces cerevisiae. In the final step, antibiotic selection marker was removed using the Cre-LoxP system to minimize any possible side-effects for animals. The resulting yeast strain can be maintained in rich culture media and stably express mammalian myostatin for two years. Oral administration of the recombinant yeast was able to induce immune response to myostatin and modulated the body weight of mice.

CONCLUSIONS

Establishment of such yeast strain is a step further toward transformation of yeast cells into edible vaccine to improve meat production in farm animals and treat human muscle-wasting diseases in the future.

Heterologous expression of pentalenene synthase (PSS) from Streptomyces UC5319 in Xanthophyllomyces dendrorhous

For the first time, the pentalenene synthase (PSS) gene from Streptomyces UC5319 was expressed in Xanthophyllomyces dendrorhous, a native producer of astaxanthin. For the expression of the gene and the concurrent knock out of the native crtE or crtYB genes, two new vectors were engineered and used for the transformation of the wild-type strain of X. dendrorhous. The transformations resulted in white colonies, showing a complete shutdown of the carotenoid production. Furthermore, an additional vector was constructed for the insertion of the PSS gene in the rDNA of the yeast. All the mutant strains produce the sesquiterpene pentalenene and show no difference in growth when compared to the wild-type strain. In this report, we demonstrate that X. dendrorhous is a suitable host for the expression of heterologous terpene cyclases and for the production of foreign terpene compounds.

Biotechnological production of astaxanthin with Phaffia rhodozyma/Xanthophyllomyces dendrorhous

The oxygenated β-carotene derivative astaxanthin exhibits outstanding colouring, antioxidative and health-promoting properties and is mainly found in the marine environment. To satisfy the growing demand for this ketocarotenoid in the feed, food and cosmetics industries, there are strong efforts to develop economically viable bioprocesses alternative to the current chemical synthesis. However, up to now, natural astaxanthin from Haematococcus pluvialis, Phaffia rhodozyma or Paracoccus carotinifaciens has not been cost competitive with chemically synthesized astaxanthin, thus only serving niche applications. This review illuminates recent advances made in elucidating astaxanthin biosynthesis in P. rhodozyma. It intensely focuses on strategies to increase astaxanthin titers in the heterobasidiomycetous yeast by genetic engineering of the astaxanthin pathway, random mutagenesis and optimization of fermentation processes. This review emphasizes the potential of P. rhodozyma for the biotechnological production of astaxanthin in comparison to other natural sources such as the microalga H. pluvialis, other fungi and transgenic plants and to chemical synthesis.

Xanthophyllomyces dendrorhous for the industrial production of astaxanthin

Astaxanthin is a red xanthophyll (oxygenated carotenoid) with large importance in the aquaculture, pharmaceutical, and food industries. The green alga Haematococcus pluvialis and the heterobasidiomycetous yeast Xanthophyllomyces dendrorhous are currently known as the main microorganisms useful for astaxanthin production at the industrial scale. The improvement of astaxanthin titer by microbial fermentation is a requirement to be competitive with the synthetic manufacture by chemical procedures, which at present is the major source in the market. In this review, we show how the isolation of new strains of X. dendrorhous from the environment, the selection of mutants by the classical methods of random mutation and screening, and the rational metabolic engineering, have provided improved strains with higher astaxanthin productivity. To reduce production costs and enhance competitiveness from an industrial point of view, low-cost raw materials from industrial and agricultural origin have been adopted to get the maximal astaxanthin productivity. Finally, fermentation parameters have been studied in depth, both at flask and fermenter scales, to get maximal astaxanthin titers of 4.7 mg/g dry cell matter (420 mg/l) when X. dendrorhous was fermented under continuous white light. The industrial scale-up of this biotechnological process will provide a cost-effective method, alternative to synthetic astaxanthin, for the commercial exploitation of the expensive astaxanthin (about $2,500 per kilogram of pure astaxanthin).

Towards industrial pentose-fermenting yeast strains

Production of bioethanol from forest and agricultural products requires a fermenting organism that converts all types of sugars in the raw material to ethanol in high yield and with a high rate. This review summarizes recent research aiming at developing industrial strains of Saccharomyces cerevisiae with the ability to ferment all lignocellulose-derived sugars. The properties required from the industrial yeast strains are discussed in relation to four benchmarks: (1) process water economy, (2) inhibitor tolerance, (3) ethanol yield, and (4) specific ethanol productivity. Of particular importance is the tolerance of the fermenting organism to fermentation inhibitors formed during fractionation/pretreatment and hydrolysis of the raw material, which necessitates the use of robust industrial strain background. While numerous metabolic engineering strategies have been developed in laboratory yeast strains, only a few approaches have been realized in industrial strains. The fermentation performance of the existing industrial pentose-fermenting S. cerevisiae strains in lignocellulose hydrolysate is reviewed. Ethanol yields of more than 0.4 g ethanol/g sugar have been achieved with several xylose-fermenting industrial strains such as TMB 3400, TMB 3006, and 424A(LNF-ST), carrying the heterologous xylose utilization pathway consisting of xylose reductase and xylitol dehydrogenase, which demonstrates the potential of pentose fermentation in improving lignocellulosic ethanol production.

Non-viral ex vivo transduction of human hepatocyte cells to express factor VIII using a human ribosomal DNA-targeting vector

BACKGROUND

In gene therapy, one of the most important issues is the choice of the vectors. pHrneo is a human-derived vector previously constructed by our group, which can target a foreign gene into a human ribosomal DNA (hrDNA) locus.

METHODS AND RESULTS

In this study, we inserted an expression cassette of reconstructive hFVIII (hFVIII-BDDAK39) to pHrneo to construct a targeting vector: pHrneo-BDDAK39. Through electroporation of pHrneo-BDDAK39 into HL7702 cells (human hepatocyte), we identified the homologous recombinants using polymerase chain reaction, and tested the expression of hFVIII-BDDAK39 located at the hrDNA locus. The hFVIII-BDDAK39 was successfully targeted into the hrDNA locus of HL7702 by pHrneo-BDDAK39, and the efficiency of site-specific integration was 1.1 x 10(-5). The hFVIII-BDDAK39 at the hrDNA locus of HL7702 was found to be able to express efficiently (4.3 +/- 0.9 ng 10(-6) cells 24 h(-1)).

CONCLUSION

It has been indicated that the targeting vector pHrneo-BDDAK39 can be used in gene therapy for hemophilia A.

Integration of heterologous genes in several yeast species using vectors containing a Hansenula polymorpha-derived rDNA-targeting element

A method that has been successfully used to generate recombinant Hansenula polymorpha strains by transformation with rDNA-targeting vectors was applied in the present study to a range of alternative yeast hosts, using vectors with an H. polymorpha-derived integration sequence. The dimorphic yeast Arxula adeninivorans, which is currently being assessed for heterologous gene expression, was the main focus of the study. As in H. polymorpha, it was possible to co-integrate more than a single plasmid carrying an expressible gene. Additionally, the vectors were examined in two further species, Pichia stipitis and Saccharomyces cerevisiae. Based on these results the design of a 'universal' fungal vector appears to be feasible.

Genetic aspects of targeted insertion mutagenesis in yeasts

Targeted insertion mutagenesis is a main molecular tool of yeast science initially applied in Saccharomyces cerevisiae. The method was extended to fission yeast Schizosaccharomyces pombe and to "non-conventional" yeast species, which show specific properties of special interest to both basic and applied research. Consequently, the behaviour of such non-Saccharomyces yeasts is reviewed against the background of the knowledge of targeted insertion mutagenesis in S. cerevisiae. Data of homologous integration efficiencies obtained with circular, ends-in or ends-out vectors in several yeasts are compared. We follow details of targeted insertion mutagenesis in order to recognize possible rate-limiting steps. The route of the vector to the target and possible mechanisms of its integration into chromosomal genes are considered. Specific features of some yeast species are discussed. In addition, similar approaches based on homologous recombination that have been established for the mitochondrial genome of S. cerevisiae are described.

Metabolic engineering of the carotenoid biosynthetic pathway in the yeast Xanthophyllomyces dendrorhous (Phaffia rhodozyma)

The crtYB locus was used as an integrative platform for the construction of specific carotenoid biosynthetic mutants in the astaxanthin-producing yeast Xanthophyllomyces dendrorhous. The crtYB gene of X. dendrorhous, encoding a chimeric carotenoid biosynthetic enzyme, could be inactivated by both single and double crossover events, resulting in non-carotenoid-producing transformants. In addition, the crtYB gene, linked to either its homologous or a glyceraldehyde-3-phosphate dehydrogenase promoter, was overexpressed in the wild type and a beta-carotene-accumulating mutant of X. dendrorhous. In several transformants containing multiple copies of the crtYB gene, the total carotenoid content was higher than in the control strain. This increase was mainly due to an increase of the beta-carotene and echinone content, whereas the total content of astaxanthin was unaffected or even lower. Overexpression of the phytoene synthase-encoding gene (crtI) had a large impact on the ratio between mono- and bicyclic carotenoids. Furthermore, we showed that in metabolic engineered X. dendrorhous strains, the competition between the enzymes phytoene desaturase and lycopene cyclase for lycopene governs the metabolic flux either via beta-carotene to astaxanthin or via 3,4-didehydrolycopene to 3-hydroxy-3'-4'-didehydro-beta-psi-caroten-4-one (HDCO). The monocylic carotenoid torulene and HDCO, normally produced as minority carotenoids, were the main carotenoids produced in these strains.

Transformation systems of non-Saccharomyces yeasts

This review describes the transformation systems including vectors, replicons, genetic markers, transformation methods, vector stability, and copy numbers of 13 genera and 31 species of non-Saccharomyces yeasts. Schizosaccharomyces pombe was the first non-Saccharomyces yeast studied for transformation and genetics. The replicons of non-Saccharomyces yeast vectors are from native plasmids, chromosomal DNA, and mitochondrial DNA of Saccharomyces cerevisiae, non-Saccharomyces yeasts, protozoan, plant, and animal. Vectors such as YAC, YCp, YEp, YIp, and YRp were developed for non-Saccharomyces yeasts. Forty-two types of genes from bacteria, yeasts, fungi, and plant were used as genetic markers that could be classified into biosynthetic, dominant, and colored groups to construct non-Saccharomyces yeasts vectors. The LEU2 gene and G418 resistance gene are the two most popular markers used in the yeast transformation. All known transformation methods such as spheroplast-mediating method, alkaline ion treatment method, electroporation, trans-kingdom conjugation, and biolistics have been developed successfully for non-Saccharomyces yeasts, among which the first three are most widely used. The highest copy number detected from non-Saccharomyces yeasts is 60 copies in Kluyveromyces lactis. No general rule is known to illustrate the transformation efficiency, vector stability, and copy number, although factors such as vector composition, host strain, transformation method, and selective pressure might influence them.

Development of the sexual reproductive cycle of Xanthophyllomyces dendrorhous

Conditions inducing the development of holobasidia with terminal basidiospores in wild-type and astaxanthin mutant strains of Xanthophyllomyces dendrorhous were reexamined. Important factors for the development of holobasidia were the incubation temperature and the medium composition. A temperature of 9 degrees C was demonstrated to enhance holobasidia formation. Minimal growth medium with glucose as sole carbon source at concentrations between 80 and 120 mM, and ammonium nitrate with concentrations of 28 mM gave optimal results. A period of 20 or more days was needed for the formation of holobasidia with basidiospores. Additionally, mutant strains of X. dendrorhous were observed to have different abilities to produce holobasidia and strains obtained after protoplast fusion, which have been called fusant in this study, to have an increased capacity to form holobasidia.

Vectors for gene expression and amplification in the yeast Yarrowia lipolytica

New vector systems were developed for gene expression in Y. lipolytica. These plasmids contain: (a) as integration target sequences, either a rDNA region or the long terminal repeat zeta of the Y. lipolytica retrotransposon Ylt1; (b) the YlURA3 gene as selection marker for Y. lipolytica, either as the non-defective ura3d1 allele for single integration or the promotor truncated ura3d4 allele for multiple integration; (c) the inducible ICL1 or XPR2 promoters for gene expression; and (d) unique restriction sites for gene insertion. Multiple plasmid integration occurred as inserted tandem-repeats, which are present at 3-39 copies per cell. A correlation between gene copy number and the expressed enzyme activity was demonstrated with Escherichia coli lacZ as reporter gene under the control of the regulated ICL1 promoter. Increases in copy numbers from 5 to 13 for the lacZ expression cassettes resulted in an up to 10-11-fold linear increase of the beta-galactosidase activity in multicopy transformants during their growth on ethanol or glucose, compared with the low-copy replicative plasmid transformants (1.6 plasmid copies). These new tools will enhance the interest in Y. lipolytica as an alternative host for heterologous protein production.

Cloning and nucleotide sequence of a linear DNA plasmid from Xanthophyllomyces dendrorhous (Phaffia rhodozyma)

Extrachromosomal elements were found in a strain of X. dendrorhous, and were characterized as linear DNA forming two well defined groups, pPh1 with 3 high-copy-number molecules, pPh11 (6.9 kb), pPh12 (5.7), pPh13 (4.7), and pPh2 with 2 low-copy-number molecules, pPh21 (3.6 kb), pPh22 (3.0). A 4077 bp fragment from pPh13 was cloned in pUC18 (pDK1) and sequenced (accession no. AJ 278,424). Seven putative ORF and some possible regulator sequences were defined.

Autocloning and amplification of LIP2 in Yarrowia lipolytica

We synthesized a Yarrowia lipolytica strain overproducing lipase for industrial applications by using long terminal repeat (zeta) of the Y. lipolytica retrotransposon Ylt1 and an allele of URA3 with a promoter deletion to construct JMP3. JMP3 is a derivative of plasmid pHSS6 carrying a NotI-NotI cassette which contains a defective URA3 allele, a polylinker sequence, and the zeta region for targeting to multiple sites in the genome of the recipient. We inserted the LIP2 gene (encoding extracellular lipase) under the control of the strong POX2 promoter into JMP3 to generate JMP6. The pHSS6 region was removed by NotI digestion prior to transformation. Two Y. lipolytica strains transformed with the JMP6 LIP2 cassette had a mean of 10 integrated copies devoid of the Escherichia coli region, corresponding to an autocloning event. The copy number in the transformants was stable even after 120 generations in nonselective and lipase-inducing conditions. The resulting strains could produce 0.5 g of active lipase per liter in the supernatant, 40 times more than the single-copy strain with the LIP2 promoter. This work provides a new expression system in Y. lipolytica that results in strains devoid of bacterial DNA and in strains producing a high level of lipase for industrial uses, waste treatment, and pancreatic insufficiency therapy.

The molecular biology of Schwanniomyces occidentalis klocker

This review describes the molecular studies of Schwanniomyces occidentalis (Debaryomyces occidentalis) concerning transformation, genome, gene cloning, gene structure, gene expression and its characteristics to application. Schw. occidentalis appears to have at least five or seven chromosomes and no native plasmid from the yeast has been reported. Four transformation systems based on complement of Schw. occidentalis auxotrophic mutants were established. Vectors with the replicon of 2-micron plasmid and autonomous replication sequences (ARS) of Saccharomyces cerevisiae and Schw. occidentalis ARS replicated extrachromosomally in Schw. occidentalis transformants, without modification of the transformed vector DNA. So far, at least 21 Schw. occidentalis genes encoding 14 different proteins have been cloned. Most of the Schw. occidentalis genes have shown homologies (45 to 91%) with the corresponding genes of other organisms, especially of S. cerevisiae. However, some Schw. occidentalis genes possess other unique structures for their operators, promoters, transcription initiation sites, and terminators. Some foreign genes were expressed in Schw. occidentalis, while Schw. occidentalis genes functioned in other yeasts and bacteria, Escherichia coli, and Streptomyces lividans. Due to a strong ability of secretion and low level of glycosylation, Schw. occidentalis might be a promising host to produce heterologous proteins.

Cloning and characterization of the astaxanthin biosynthetic gene encoding phytoene desaturase of Xanthophyllomyces dendrorhous

The first carotenoid biosynthetic gene from the basidiomycetous yeast Xanthophyllomyces dendrorhous was isolated by heterologous complementation in Escherichia coli. The isolated gene, denominated as crtI, was found to encode for phytoene desaturase. The coding region is interrupted by 11 introns. The deduced amino acid sequence showed significant homology with its bacterial and eukaryotic counterparts, especially those of fungal origin. A plasmid containing the geranylgeranyl diphosphate synthase and phytoene synthase encoding genes from Erwinia uredovora was introduced in E. coli together with the phytoene desaturase encoding cDNA from X. dendrorhous. As a result, lycopene accumulation was observed in these transformants. We conclude that in X. dendrorhous the four desaturase steps, by which phytoene is converted into lycopene, are carried out by a single gene product.

Cloning of the ribosomal protein L41 gene of Phaffia rhodozyma and its use a drug resistance marker for transformation

The ribosomal protein L41 gene of Phaffia rhodozyma was cloned and used as a dominant selectable marker for cycloheximide resistance in the transformation of P. rhodozyma. Electrotransformation with a plasmid containing a ribosomal DNA fragment as a targeting signal typically yielded 800 to 1,200 transformants/microgram of DNA with an integrated copy number of about seven per haploid genome.

Production of the carotenoids lycopene, beta-carotene, and astaxanthin in the food yeast Candida utilis

The food-grade yeast Candida utilis has been engineered to confer a novel biosynthetic pathway for the production of carotenoids such as lycopene, beta-carotene, and astaxanthin. The exogenous carotenoid biosynthesis genes were derived from the epiphytic bacterium Erwinia uredovora and the marine bacterium Agrobacterium aurantiacum. The carotenoid biosynthesis genes were individually modified based on the codon usage of the C. utilis glyceraldehyde 3-phosphate dehydrogenase gene and expressed in C. utilis under the control of the constitutive promotes and terminators derived from C. utilis. The resultant yeast strains accumulated lycopene, beta-carotene, and astaxanthin in the cells at 1.1, 0.4, and 0.4 mg per g (dry weight) of cells, respectively. This was considered to be a result of the carbon flow into ergosterol biosynthesis being partially redirected to the nonendogenous pathway for carotenoid production.

Molecular characterization of the glyceraldehyde-3-phosphate dehydrogenase gene of Phaffia rhodozyma

The glyceraldehyde-3-phosphate dehydrogenase (GPD; EC1.2.1.12)-encoding gene (gpd) was isolated from a genomic library of Phaffia rhodozyma CBS 6938. Unlike some other eukaryotic organisms the gpd gene is represented by a single copy in P. rhodozyma. The complete nucleotide sequence of the coding, as well as the flanking non-coding regions was determined. The nucleotide sequence of gpd predicted six introns and a polypeptide chain of 339 amino acids. The codon usage in the gpd gene of P. rhodozyma was highly biased and was significantly different from the codon usage in other yeasts. Phylogenetic analysis of different yeasts and filamentous asco- and basidiomycetes gpd sequences indicated that the gpd gene of P. rhodozyma forms a cluster with the corresponding genes of filamentous basidiomycetes.