De novo synthesis of trans-10, cis-12 conjugated linoleic acid in oleaginous yeast Yarrowia lipolytica

Exploiting synthetic biology platforms for enhanced biosynthesis of natural products in Yarrowia lipolytica

With the rapid development of synthetic biology, researchers can design, modify, or even synthesize microorganisms de novo, and microorganisms endowed with unnatural functions can be considered "artificial life" and facilitate the development of functional products. Based on this concept, researchers can solve critical problems related to the insufficient supply of natural products, such as low yields, long production cycles, and cumbersome procedures. Due to its superior performance and unique physiological and biochemical characteristics, Yarrowia lipolytica is a favorable chassis cell used for green biomanufacturing by numerous researchers. This paper mainly reviews the development of synthetic biology techniques for Y. lipolytica and summarizes the recent research progress on the synthesis of natural products in Y. lipolytica. This review will promote the continued innovative development of Y. lipolytica by providing theoretical guidance for research on the biosynthesis of natural products.

Enhancing Gastrodin Production in Yarrowia lipolytica by Metabolic Engineering

Gastrodin, 4-hydroxybenzyl alcohol-4-O-β-D-glucopyranoside, has been widely used in the treatment of neurogenic and cardiovascular diseases. Currently, gastrodin biosynthesis is being achieved in model microorganisms. However, the production levels are insufficient for industrial applications. In this study, we successfully engineered a Yarrowia lipolytica strain to overproduce gastrodin through metabolic engineering. Initially, the engineered strain expressing the heterologous gastrodin biosynthetic pathway, which comprises chorismate lyase, carboxylic acid reductase, phosphopantetheinyl transferase, endogenous alcohol dehydrogenases, and a UDP-glucosyltransferase, produced 1.05 g/L gastrodin from glucose in a shaking flask. Then, the production was further enhanced to 6.68 g/L with a productivity of 2.23 g/L/day by overexpressing the key node DAHP synthases of the shikimate pathway and alleviating the native tryptophan and phenylalanine biosynthetic pathways. Finally, the best strain, Gd07, produced 13.22 g/L gastrodin in a 5 L fermenter. This represents the highest reported production of gastrodin in an engineered microorganism to date, marking the first successful de novo production of gastrodin using Y. lipolytica.

Proteomics and Metabolomics Analysis Reveal the Regulation Mechanism of Linoleate Isomerase Activity and Function in Propionibacterium acnes

Conjugated linoleic acid (CLA) holds significant application prospects due to its anticancer, anti-atherosclerosis, lipid-lowering, weight-loss, and growth-promoting functions. The key to its efficient production lies in optimizing the biocatalytic performance of linoleic acid isomerase (LAI). Here, we constructed a Propionibacterium acnes mutant library and screened positive mutants with high linoleate isomerase activity. The proteomics and metabolomics were used to explore the mechanism in the regulation of linoleic acid isomerase activity. High-throughput proteomics revealed 104 differentially expressed proteins unique to positive mutant strains of linoleic acid isomerase of which 57 were upregulated and 47 were downregulated. These differentially expressed proteins were primarily involved in galactose metabolism, the phosphotransferase system, starch metabolism, and sucrose metabolism. Differential metabolic pathways were mainly enriched in amino acid biosynthesis, including glutamate metabolism, the Aminoacyl-tRNA biosynthesis pathway, and the ABC transporter pathway. The upregulated metabolites include dl-valine and Acetyl coA, while the downregulated metabolites include Glutamic acid and Phosphoenolpyruvate. Overall, the activity of linoleic acid isomerase in the mutant strain was increased by the regulation of key proteins involved in galactose metabolism, sucrose metabolism, and the phosphotransferase system. This study provides a theoretical basis for the development of high-yield CLA food.

Advances in research on microbial conjugated linoleic acid bioconversion

Conjugated linoleic acid (CLA) is a functional food ingredient with prebiotic properties that provides health benefits for various human pathologies and disorders. However, limited natural CLA sources in animals and plants have led microorganisms like Lactobacillus and Bifidobacterium to emerge as new CLA sources. Microbial conversion of linoleic acid to CLA is mediated by linoleic acid isomerase and multicomponent enzymatic systems, with CLA production efficiency dependent on microbial species and strains. Additionally, complex factors like LA concentration, growth status, culture substrates, precursor type, prebiotic additives, and co-cultured microbe identity strongly influence CLA production and isomer composition. This review summarizes advances in the past decade regarding microbial CLA production, including bacteria and fungi. We highlight CLA production and potential regulatory mechanisms and discuss using microorganisms to enhance CLA content and nutritional value of fermented products. We also identify primary microbial CLA production bottlenecks and provide strategies to address these challenges and enhance production through functional gene and enzyme mining and downstream processing. This review aims to provide a reference for microbial CLA production and broaden the understanding of the potential probiotic role of microbial CLA producers.

Novel spiro[chromanone-2,4'-piperidine]-4-one derivatives as potential inhibitors of fatty acid synthesis in pathogens: Design, synthesis, and biological evaluation

Bacterial survival depends on membrane lipid homeostasis that enables to regulate lipid composition to adapt and optimize their growth in diverse environments. Therefore, the development of inhibitors that interfere with the bacterial fatty acid synthesis process is considered to be a promising tactic. In this study, 58 novel spirochromanone derivatives were prepared and their structure-activity relationship (SAR) was investigated. The bioassay results showed that all most of the compounds showed excellent biological activities, exampled by compounds B₁₄, C₁, B₁₅, and B₁₃, which had outstanding inhibitory activities toward various pathogenic bacteria with EC₅₀ values of 0.78 μg/mL ∼3.48 μg/mL. Preliminary antibacterial behavior was studied by a series of biochemical assays including, but not limited to, fluorescence imaging patterns, GC-MS analysis, TEM images, and fluorescence titration experiments. Notably, compound B₁₄ decreased the lipid content of the cell membrane, and increased cell membrane permeability, thereby destroying the integrity of the bacterial cell membrane. Further qRT-PCR results indicated that compound B₁₄ interfered with the mRNA expression levels of fatty acid synthesis process-related genes including ACC, ACP, and Fab family genes. Herein, we highlight the promising bactericidal skeleton based on the spiro[chromanone-2,4'-piperidine]-4-one as a potential inhibitor of fatty acid synthesis.

Biosynthesis of Fatty Acid Derivatives by Recombinant Yarrowia lipolytica Containing MsexD2 and MsexD3 Desaturase Genes from Manduca sexta

One of the most interesting groups of fatty acid derivates is the group of conjugated fatty acids from which the most researched include: conjugated linoleic acid (CLA) and conjugated linolenic acid (CLNA), which are associated with countless health benefits. Sex pheromone mixtures of some insect species, including tobacco horn-worm (Manduca sexta), are typical for the production of uncommon C16 long conjugated fatty acids with two and three conjugated double bonds, as opposed to C18 long CLA and CLNA. In this study, M. sexta desaturases MsexD2 and MsexD3 were expressed in multiple strains of Y. lipolytica with different genotypes. Experiments with the supplementation of fatty acid methyl esters into the medium resulted in the production of novel fatty acids. Using GCxGC-MS, 20 new fatty acids with two or three double bonds were identified. Fatty acids with conjugated or isolated double bonds, or a combination of both, were produced in trace amounts. The results of this study prove that Y. lipolytica is capable of synthesizing C16-conjugated fatty acids. Further genetic optimization of the Y. lipolytica genome and optimization of the fermentation process could lead to increased production of novel fatty acid derivatives with biotechnologically interesting properties.

Engineering Yarrowia lipolytica to produce nutritional fatty acids: Current status and future perspectives

Due to their vital physiological functions, nutritional fatty acids have great potential as nutraceutical food supplements for preventing an array of diseases such as inflammation, depression, arthritis, osteoporosis, diabetes and cancer. Microbial biosynthesis of fatty acids follows the trend of sustainable development, as it enables green, environmentally friendly and efficient production. As a natural oleaginous yeast, Yarrowia lipolytica is especially well-suited for the production of fatty acids. Moreover, it has a variety of genetic engineering tools and novel metabolic engineering strategies that make it a robust workhorse for the production of an array of value-added products. In this review, we summarize recent advances in metabolic engineering strategies for accumulating nutritional fatty acids in Y. lipolytica, including conjugated fatty acids and polyunsaturated fatty acids. In addition, the future prospects of nutritional fatty acid production using the Y. lipolytica platform are discussed in light of the current progress, challenges, and trends in this field. Finally, guidelines for future studies are also emphasized.

Engineering the β-Oxidation Pathway in Yarrowia lipolytica for the Production of trans-10, cis-12-Conjugated Linoleic Acid

trans-10, cis-12-Conjugated linoleic acid (t10, c12-CLA) is an octadecadienoic acid with various biological benefits. Previously, linoleic acid isomerase from Propionibacterium acnes (PAI) was overexpressed in Yarrowia lipolytica (Y. lipolytica) to produce t10, c12-CLA. However, the t10, c12-CLA yield was restricted by the peroxisomal β-oxidation pathway. In this study, to minimize the degradation of t10, c12-CLA, four genetically modified strains of Y. lipolytica (Δpox2-oPAI, Δpox3-oPAI, Δpox2Δpox3-oPAI, and Δpex10-oPAI) were constructed and compared in terms of production stability and yield of t10, c12-CLA using safflower seed oil as substrates. The Δpex10-oPAI strain exhibited the best results, as revealed by the reduction of the t10, c12-CLA degradation rate from 58.5 to 18.6 mg/L/h. Additionally, the YLUpex10mP recombinant strain bearing six copies of oPAI combined with PEX10 deletion enhanced t10, c12-CLA production to 7.4 g/L and exhibited a CLA degradation rate of 19.7 mg/L/h, a 78% decrease from that of the control strain. Finally, in a bioreactor containing low-cost volatile fatty acids as partial carbon sources, the t10, c12-CLA content in the YLUpex10mP strain increased to 9.7 g/L, 1.3 times higher than in flasks. To our knowledge, this is the highest t10, c12-CLA yield through microbial synthesis reported to date.

Molecular mechanism of interaction between fatty acid delta 6 desaturase and acyl-CoA by computational prediction

Enzyme catalyzed desaturation of intracellular fatty acids plays an important role in various physiological and pathological processes related to lipids. Limited to the multiple transmembrane domains, it is difficult to obtain their three-dimensional structure of fatty acid desaturases. So how they interact with their substrates is unclear. Here, we predicted the complex of Micromonas pusilla delta 6 desaturase (MpFADS6) with the substrate linoleinyl-CoA (ALA-CoA) by trRosetta software and docking poses by Dock 6 software. The potential enzyme–substrate binding sites were anchored by analysis of the complex. Then, site-directed mutagenesis and activity verification clarified that W290, W224, and F352 were critical residues of the substrate tunnel and directly bonded to ALA-CoA. H94 and H69 were indispensable for transporting electrons with heme. H452, N445, and H358 significantly influenced the recognition and attraction of MpFADS6 to the substrate. These findings provide new insights and methods to determine the structure, mechanisms and directed transformation of membrane-bound desaturases.

The structure of the Δ6 fatty acid desaturase and substrate complex is modeled.

The substrate tunnel and key residues of MpFADS6 catalytic activity are determined.

The new insights to determine the mechanism of the membrane-bound desaturases.

Enhanced Soluble Expression of Linoleic Acid Isomerase by Coordinated Regulation of Promoter and Fusion Tag in Escherichia coli

PAI is a linoleic acid isomerase from Propionibacterium acnes and is the key enzyme in the synthesis of trans10, cis12-conjugated linoleic acid. However, the majority of the expressed PAI in Escherichia coli occurs in its nonfunctional form in inclusion bodies, limiting the biosynthesis of conjugated linoleic acid. In an attempt to improve the solubility of recombinant PAI in Escherichia coli, three promoters representing different transcriptional strengths (T7, CspA, and Trc), paired with three fusion tags, (His6, MBP, and Fh8), respectively, were investigated in this study. Among the nine recombinant strains, Escherichia coli BL21 (DE3) (pET24a-Mpai), containing the T7 promoter and MBP fusion tag, led to a considerable increase in PAI solubility to 86.2%. MBP-PAI was purified 41-fold using affinity column chromatography. The optimum catalytical conditions of MBP-PAI were 37 °C and pH 7.5 with the addition of 1 mmol/L Tween-20. Most of the tested metal ions inhibited MBP-PAI activity. The apparent kinetic parameters (Km and Vmax) were measured with linoleic acid concentrations ranging from 71 μM to 1428 μM. The substrate linoleic acid did not exert any inhibitory effect on MBP-PAI. The Km of MBP-PAI was 253.9 μmol/L, and the Vmax was 2253 nmol/min/mg. This study provided a new method for improving the solubility of the recombinant linoleic acid isomerase in Escherichia coli.

Consensus mutagenesis and computational simulation provide insight into the desaturation catalytic mechanism for delta 6 fatty acid desaturase

Fatty acid desaturase (FADS) generates double bond at a certain position of the corresponding polyunsaturated fatty acids (PUFAs) with high selectivity, the enzyme activity and PUFAs products of which are essential to biological systems and are associated with a variety of physiological diseases. Little is known about the structure of FADSs and their amino acid residues related to catalytic activities. Identifying key residues of Micromonas pusilla delta 6 desaturase (MpFADS6) provides a point of departure for a better understanding of desaturation. In this study, conserved amino acids were anchored through gene consensus analysis, thereby generating corresponding variants by site-directed mutagenesis. To achieve stable and high-efficiency expression of MpFADS6 and its variants in Saccharomyces cerevisiae, the key points of induced expression were optimized. The contribution of conserved residues to the function of enzyme was determined by analyzing enzyme activity of the variants. Molecular modeling indicated that these residues are essential to catalytic activities, or substrate binding. Mutants MpFADS6_[Q409R] and MpFADS6_[M242P] abolished desaturation, while MpFADS6_[F419V] and MpFADS6_[A374Q] significantly reduced catalytic activities. Given that certain residues have been identified to have a significant impact on MpFADS6 activities, it is put forward that histidine-conserved region III of FADS6 is related to electronic transfer during desaturation, while histidine-conserved regions I and II are related to desaturation. These findings provide new insights and methods to determine the structure, mechanism and directed transformation of membrane-bound desaturases.

Advances in production of high-value lipids by oleaginous yeasts

The global market for high-value fatty acids production, mainly omega-3/6, hydroxy fatty-acids, waxes and their derivatives, has seen strong development in the last decade. The reason for this growth was the increasing utilization of these lipids as significant ingredients for cosmetics, food and the oleochemical industries. The large demand for these compounds resulted in a greater scientific interest in research focused on alternative sources of oil production - among which microorganisms attracted the most attention. Microbial oil production offers the possibility to engineer the pathways and store lipids enriched with the desired fatty acids. Moreover, costly chemical steps are avoided and direct commercial use of these fatty acids is available. Among all microorganisms, the oleaginous yeasts have become the most promising hosts for lipid production - their efficient lipogenesis, ability to use various (often highly affordable) carbon sources, feasible large-scale cultivations and wide range of available genetic engineering tools turns them into powerful micro-factories. This review is an in-depth description of the recent developments in the engineering of the lipid biosynthetic pathway with oleaginous yeasts. The different classes of valuable lipid compounds with their derivatives are described and their importance for human health and industry is presented. The emphasis is also placed on the optimization of culture conditions in order to improve the yield and titer of these valuable compounds. Furthermore, the important economic aspects of the current microbial oil production are discussed.

Lipid production by oleaginous yeasts

Microbial lipid production has been studied extensively for years; however, lipid metabolic engineering in many of the extraordinarily high lipid-accumulating yeasts was impeded by inadequate understanding of the metabolic pathways including regulatory mechanisms defining their oleaginicity and the limited genetic tools available. The aim of this review is to highlight the prominent oleaginous yeast genera, emphasizing their oleaginous characteristics, in conjunction with diverse other features such as cheap carbon source utilization, withstanding the effect of inhibitory compounds, commercially favorable fatty acid composition-all supporting their future development as economically viable lipid feedstock. The unique aspects of metabolism attributing to their oleaginicity are accentuated in the pretext of outlining the various strategies successfully implemented to improve the production of lipid and lipid-derived metabolites. A large number of in silico data generated on the lipid accumulation in certain oleaginous yeasts have been carefully curated, as suggestive evidences in line with the exceptional oleaginicity of these organisms. The different genetic elements developed in these yeasts to execute such strategies have been scrupulously inspected, underlining the major types of newly-found and synthetically constructed promoters, transcription terminators, and selection markers. Additionally, there is a plethora of advanced genetic toolboxes and techniques described, which have been successfully used in oleaginous yeasts in the recent years, promoting homologous recombination, genome editing, DNA assembly, and transformation at remarkable efficiencies. They can accelerate and effectively guide the rational designing of system-wide metabolic engineering approaches pinpointing the key targets for developing industrially suitable yeast strains.

Recent advances in lipid metabolic engineering of oleaginous yeasts

With the increasing demand to develop a renewable and sustainable biolipid feedstock, several species of non-conventional oleaginous yeasts are being explored. Apart from the platform oleaginous yeast Yarrowia lipolytica, the understanding of metabolic pathway and, therefore, exploiting the engineering prospects of most of the oleaginous species are still in infancy. However, in the past few years, enormous efforts have been invested in Rhodotorula, Rhodosporidium, Lipomyces, Trichosporon, and Candida genera of yeasts among others, with the rapid advancement of engineering strategies, significant improvement in genetic tools and techniques, generation of extensive bioinformatics and omics data. In this review, we have collated these recent progresses to make a detailed and insightful summary of the major developments in metabolic engineering of the prominent oleaginous yeast species. Such a comprehensive overview would be a useful resource for future strain improvement and metabolic engineering studies for enhanced production of lipid and lipid-derived chemicals in oleaginous yeasts.

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

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

Metabolic Engineering for Unusual Lipid Production in Yarrowia lipolytica

Using microorganisms as lipid-production factories holds promise as an alternative method for generating petroleum-based chemicals. The non-conventional yeast Yarrowia lipolytica is an excellent microbial chassis; for example, it can accumulate high levels of lipids and use a broad range of substrates. Furthermore, it is a species for which an array of efficient genetic engineering tools is available. To date, extensive work has been done to metabolically engineer Y. lipolytica to produce usual and unusual lipids. Unusual lipids are scarce in nature but have several useful applications. As a result, they are increasingly becoming the targets of metabolic engineering. Unusual lipids have distinct structures; they can be generated by engineering endogenous lipid synthesis or by introducing heterologous enzymes to alter the functional groups of fatty acids. In this review, we describe current metabolic engineering strategies for improving lipid production and highlight recent researches on unusual lipid production in Y. lipolytica.

Kinetics and function of two mutants of CLA hydrase from Lactobacillus plantarum p-8

In this work, the gene of conjugated linoleic acid hydrase (CLA-HY) was cloned from L. plantarum p-8, and the protein of CLA-HY was expressed in Escherichia coli BL21. Gas chromatography-mass spectrometry was employed to verify that the purified CLA-HY can convert linoleic acid (LA) into 10-hydroxy-cis-12-octadecenoic acid (10-HOE) in the presence of flavin adenine dinucleotide (FAD). The optimal pH and temperature for maximizing CLA-HY catalytic activity were found to be 6.0 and 35°C, respectively. In addition, the catalytic ability of CLA-HY can be inhibited by a number of cations such as Mg2+, Mn2+, Zn2+, Cu2+, Fe2+, Fe3+, Ni2+ and Ca2+. Finally, the Km,Vmax, Kcat and Kcat/Km of CLA-HY were determined as 7.62 mM, 2.59 mM h-1, 8.33 × 103 h-1 and 1.09 × 103 mM-1 h-1, respectively. Moreover, it was demonstrated that both M76 and G74 residues played significant roles in catalysing the conversion of LA into 10-HOE using site-directed mutation technology and molecular simulations.

Modulating Heterologous Pathways and Optimizing Culture Conditions for Biosynthesis of trans-10, cis-12 Conjugated Linoleic Acid in Yarrowia lipolytica

A novel recombinant strain has been constructed for converting glycerol into a specific conjugated linoleic acid isomer (trans-10, cis-12 CLA) using Yarrowia lipolytica as host. The lipid accumulation pathway was modified for increasing lipid content. Overexpression of the diacylglycerol transferase (DGA1) gene improved the intracellular lipid yield by approximately 45% as compared to the original strain. The corresponding intracellular lipid yield of recombinant strain WXYL037 reached 52.2% of the cell dry weight. In combination with integration of Δ12 desaturase from Mortierella alpina (MA12D) and DGA1, the linoleic acid (LA) production content reached 0.88 g/L, which was 2-fold that of the original strain. Furthermore, with overexpressed DGA1, MA12D and Propionibacterium acnes isomerase (PAI), the titer of trans-10, cis-12 CLA in WXYL037 reached 110.6 mg/L after 72 h of shake flask culture, representing a 201.8% improvement when compared with that attained in the WXYL030 strain, which manifested overexpressed PAI. With optimal medium, the maximum CLA content and lipid yield of Y. lipolytica Po1g were 132.6 mg/L and 2.58 g/L, respectively. This is the first report of the production of trans-10, cis-12 CLA by the oleaginous yeast Y. lipolytica using glycerol as the sole carbon source through expression of DGA1 combined with MA12D and PAI.

Combining 26s rDNA and the Cre-loxP System for Iterative Gene Integration and Efficient Marker Curation in Yarrowia lipolytica

Conventional plasmid-based gene expression tends to introduce genetic instability and gene copy number variations that lead to degenerated production. The limited number of auxotrophic markers in Yarrowia lipolytica also restricts our ability to perform iterative genetic modifications and manipulate long gene clusters. To overcome these limitations, we combined the high recombination efficiency of the Cre-loxP system and the high integration rate of 26s rDNA, and developed a versatile framework to iteratively integrate multicopy metabolic pathways in Y. lipolytica. We demonstrated the efficient genome integration of a plant-derived flavonoid pathway at random sites with multiple copies. Transient expression of Cre recombinase enabled efficient marker removal and allowed for the next round of genome integration. Investigating the recombination events demonstrated that the iterative integration is happening at sufficiently high rates (more than 80%) without disrupting the previous integration. Both the flavonoid precursor pathway and the plant-derived cytochrome c P450 enzymes were functionally integrated to improve flavonoid and hydroxylated flavonoid production. The engineered strains produced 71.2 mg/L naringenin, 54.2 mg/L eriodyctiol, and 48.1 mg/L taxifolin. The reported work provides a versatile platform to iteratively integrate functional gene clusters at high copy numbers. This work may streamline and expand our capability to build efficient microbial cell factories for high-value natural products and commodity chemical production in Y. lipolytica.

Synthetic biology tools for engineering Yarrowia lipolytica

The non-conventional oleaginous yeast Yarrowia lipolytica shows great industrial promise. It naturally produces certain compounds of interest but can also artificially generate non-native metabolites, thanks to an engineering process made possible by the significant expansion of a dedicated genetic toolbox. In this review, we present recently developed synthetic biology tools that facilitate the manipulation of Y. lipolytica, including 1) DNA assembly techniques, 2) DNA parts for constructing expression cassettes, 3) genome-editing techniques, and 4) computational tools.

Simple glycolipids of microbes: Chemistry, biological activity and metabolic engineering

Glycosylated lipids (GLs) are added-value lipid derivatives of great potential. Besides their interesting surface activities that qualify many of them to act as excellent ecological detergents, they have diverse biological activities with promising biomedical and cosmeceutical applications. Glycolipids, especially those of microbial origin, have interesting antimicrobial, anticancer, antiparasitic as well as immunomodulatory activities. Nonetheless, GLs are hardly accessing the market because of their high cost of production. We believe that experience of metabolic engineering (ME) of microbial lipids for biofuel production can now be harnessed towards a successful synthesis of microbial GLs for biomedical and other applications. This review presents chemical groups of bacterial and fungal GLs, their biological activities, their general biosynthetic pathways and an insight on ME strategies for their production.

Conjugated linoleic acid: A potent fatty acid linked to animal and human health

Conjugated linoleic acid (CLA) is a mixture of isomers of linoleic acid (C18:2 n-6), which is mostly found in the ruminant meat and dairy products. The CLA is known to have many potential health benefits, and considered a potent powerful fatty acid, which is linked to animal and human health. The present work aims to discuss the source and production, mechanism of action, and effects of CLA on humans, poultry, and ruminants by reviewing the recent studies carried out on CLA. Despite most of the recent studies indicating beneficial effects of CLA on improving body weight control parameters, its effects on reducing risk factors of cardiovascular diseases (CVD), inflammation, blood glucose, and insulin are still controversial, and need to be further studied in different hosts.

Green Synthesis of Conjugated Linoleic Acids from Plant Oils Using a Novel Synergistic Catalytic System

A novel and efficient method has been developed for converting plant oil into a specific conjugated linoleic acid (CLA) using a synergistic biocatalytic system based on immobilized Propionibacterium acnes isomerase (PAI) and Rhizopus oryzae lipase (ROL). PAI exhibited the greatest catalytic activity when immobilized on D301R anion-exchange resin under optimal conditions (PAI dosage of 12 410 U of PAI/g of D301R, glutaraldehyde concentration of 0.4%, and reaction conditions of pH 7.0, 25 °C, and 60 min). Up to 109 g/L trans-10,cis-12-CLA was obtained after incubation of 200 g/L sunflower oil with PAI (1659 U/g of oil) and ROL (625 mU/g of oil) at pH 7.0 and 35 °C for 36 h; the corresponding conversion ratio of linoleic acid (LA) to CLA was 90.5%. This method exhibited the highest proportion of trans-10,cis-12-CLA yet reported and is a promising method for large-scale production.

A metabolic engineering strategy for producing conjugated linoleic acids using the oleaginous yeast Yarrowia lipolytica

Conjugated linoleic acids (CLAs) have been found to have beneficial effects on human health when used as dietary supplements. However, their availability is limited because pure, chemistry-based production is expensive, and biology-based fermentation methods can only create small quantities. In an effort to enhance microbial production of CLAs, four genetically modified strains of the oleaginous yeast Yarrowia lipolytica were generated. These mutants presented various genetic modifications, including the elimination of β-oxidation (pox1-6∆), the inability to store lipids as triglycerides (dga1∆ dga2∆ are1∆ lro1∆), and the overexpression of the Y. lipolytica ∆12-desaturase gene (YlFAD2) under the control of the constitutive pTEF promoter. All strains received two copies of the pTEF-oPAI or pPOX-oPAI expression cassettes; PAI encodes linoleic acid isomerase in Propionibacterium acnes. The strains were cultured in neosynthesis or bioconversion medium in flasks or a bioreactor. The strain combining the three modifications mentioned above showed the best results: when it was grown in neosynthesis medium in a flask, CLAs represented 6.5% of total fatty acids and in bioconversion medium in a bioreactor, and CLA content reached 302 mg/L. In a previous study, a CLA degradation rate of 117 mg/L/h was observed in bioconversion medium. Here, by eliminating β-oxidation, we achieved a much lower rate of 1.8 mg/L/h.

Lipid biosynthesis in yeasts: A comparison of the lipid biosynthetic pathway between the model nonoleaginous yeast Saccharomyces cerevisiae and the model oleaginous yeast Yarrowia lipolytica

Lipid biosynthesis and its regulation have been studied mostly in the nonoleaginous yeast Saccharomyces cerevisiae that serves as a model for eukaryotic cells. On the other hand, the yeast Yarrowia lipolytica has been put forward as a model for oleaginous microorganisms because its genetics is known and tools for its genetic manipulation are becoming increasingly available. A comparison of the lipid biosynthetic pathways that function in these two microorganisms shows many similarities in key biosynthetic and regulatory steps. An example is the enzyme phosphatidic acid phosphatase that controls the synthesis of triacylglycerol (TAG) in both yeasts. Controlling the TAG synthesis is crucial for metabolic engineering efforts that aim to increase the production of microbial lipids (i.e. single cell oils) because TAG comprises the final product of these processes. At the same time the comparison reveals fundamental differences (e.g. in the generation of acetyl-CoA for lipid biosynthesis) stemming from the oleaginous nature of Y. lipolytica. These differences warranty more studies in Y. lipolytica where the biochemistry and molecular biology of oleaginicity can be further explored.

Enhanced lipid accumulation in the yeast Yarrowia lipolytica by over-expression of ATP:citrate lyase from Mus musculus

Yarrowia lipolytica can accumulate large amounts of storage lipids and has considerable potential for the production of polyunsaturated fatty acids and other lipids for biofuels. When the nitrogen source is exhausted in the medium, the key intermediate, citrate, is converted to acetyl-CoA by ATP:citrate lyase (ACL) for lipid accumulation. However, in this yeast most of the citrate is also secreted into the culture medium. To increase the endogenous substrate (acetyl-CoA) level for lipid biosynthesis, the acl gene from Mus musculus was over-expressed in Y. lipolytica with mono-copy integration vector pINA1312sp and multi-copy integration vector pINA1292sp. This increased the lipid content from 7.3% to between 11% and 23% (w/w) of the cell dry weight. Cell growth was only slightly affected. Multi-copy integration transformants had higher lipid contents than mono-copy integration transformants; the lipid content of the transformants was consistent with the copy number of acl gene integrated. Over-expression of ACL had no significant effect on fatty acid profile of the yeast. These results suggested that ACL is an important acetyl-CoA producer and plays a vital role in lipid accumulation in oleaginous yeast Y. lipolytica.

Exploring medium-chain-length polyhydroxyalkanoates production in the engineered yeast Yarrowia lipolytica

Medium-chain-length polyhydroxyalkanoates (mcl-PHAs) are a large class of biopolymers that have attracted extensive attention as renewable and biodegradable bio-plastics. They are naturally synthesized via fatty acid de novo biosynthesis pathway or β-oxidation pathway from Pseudomonads. The unconventional yeast Yarrowia lipolytica has excellent lipid/fatty acid catabolism and anabolism capacity depending of the mode of culture. Nevertheless, it cannot naturally synthesize PHA, as it does not express an intrinsic PHA synthase. Here, we constructed a genetically modified strain of Y. lipolytica by heterologously expressing PhaC1 gene from P. aeruginosa PAO1 with a PTS1 peroxisomal signal. When in single copy, the codon optimized PhaC1 allowed the synthesis of 0.205 % DCW of PHA after 72 h cultivation in YNBD medium containing 0.1 % oleic acid. By using a multi-copy integration strategy, PHA content increased to 2.84 % DCW when the concentration of oleic acid in YNBD was 1.0 %. Furthermore, when the recombinant yeast was grown in the medium containing triolein, PHA accumulated up to 5.0 % DCW with as high as 21.9 g/L DCW, which represented 1.11 g/L in the culture. Our results demonstrated the potential use of Y. lipolytica as a promising microbial cell factory for PHA production using food waste, which contains lipids and other essential nutrients.

Production of conjugated linoleic acid by heterologous expression of linoleic acid isomerase in oleaginous fungus Mortierella alpina

OBJECTIVE

To increase the commercial value of oleaginous fungus Mortierella alpina by incorporation of trans-10,cis-12 conjugated linoleic acid (CLA) into the polyunsaturated fatty acids (PUFAs) of M. alpina via Propionibacterium acnes isomerase (PAI) conversion.

RESULTS

The PAI gene and the codon optimization version were heterologously expressed in M. alpina via Agrobacterium tumefaciens-mediated transformation (ATMT). Coding usage modification significantly improved the translation of PAI transcripts and trans-10,cis-12 CLA was produced up to 1.2 mg l(-1), which corresponds to approx. 0.05% of the total fatty acid (TFA). Since PAI prefers free linoleic acid as a substrate rather than any other forms, 5 μM long-chain acyl CoA synthetase inhibitor was added and the trans-10,cis-12 CLA content increased approx. 24-fold to 29 mg l(-1), reaching up to 1.2% (w/w) of the TFA in M. alpina.

CONCLUSION

Heterologous expression of PAI in M. alpina by ATMT methods is a practicable way in biosynthesis of CLA and this system may be a feasible platform for industrial production of CLA.

Food-related applications of Yarrowia lipolytica

Yarrowia lipolytica is a non-pathogenic generally regarded as safe yeast. It displays unique physiological as well as biochemical properties that are relevant in food-related applications. Strains naturally associated with meat and dairy products contribute towards specific textures and flavours. On some occasions they cause food spoilage. They produce food-additives such as aroma compounds, organic acids, polyalcohols, emulsifiers and surfactants. The yeast biomass has been projected as single cell oil and single cell protein. Y. lipolytica degrades or upgrades different types of food wastes and in some cases, value-added products have also been obtained. The yeast is thus involved in the manufacture of food stuffs, making of food ingredients, generation of biomass that can be used as food or feed and in the effective treatment of food wastes. On account of all these features, this versatile yeast is of considerable significance in food-related applications.

A novel multigene expression construct for modification of glycerol metabolism in Yarrowia lipolytica

BACKGROUND

High supply of raw, residual glycerol from biodiesel production plants promote the search for novel biotechnological methods of its utilization. In this study we attempted modification of glycerol catabolism in a nonconventional yeast species Yarrowia lipolytica through genetic engineering approach.

RESULTS

To address this, we developed a novel genetic construct which allows transferring three heterologous genes, encoding glycerol dehydratase, its reactivator and a wide-spectrum alcohol oxidoreductase under the control of glycerol-induced promoter. The three genes, tandemly arrayed in an expression cassette with a marker gene ura3, regulatory and targeting sequences (G3P dh promoter and XPR-like terminator, 28S rDNA as a target locus), were transferred into Yarrowia lipolytica cells. The obtained recombinant strain NCYC3825 was characterized at the molecular level and with respect to its biotechnological potential. Our experiments indicated that the novel recombinant strain stably borne one copy of the expression cassette and efficiently expressed heterologous alcohol oxidoreductase, while glycerol dehydratase and its reactivator were expressed at lower level. Comparative shake flask cultivations in glucose- and glycerol-based media demonstrated higher biomass production by the recombinant strain when glycerol was the main carbon source. During bioreactor (5 L) fed-batch cultivation in glycerol-based medium, the recombinant strain was characterized by relatively high biomass and lipids accumulation (up to 42 gDCW L(-1), and a peak value of 38%LIPIDS of DCW, respectively), and production of high titers of citric acid (59 g L(-1)) and 2-phenylethanol (up to 1 g L(-1) in shake flask cultivation), which are industrially attractive bioproducts.

CONCLUSIONS

Due to heterogeneous nature of the observed alterations, we postulate that the main driving force of the modified phenotype was faster growth in glycerol-based media, triggered by modifications in the red-ox balance brought by the wide spectrum oxidoreductase. Our results demonstrate the potential multidirectional use of a novel Yarrowia lipolytica strain as a microbial cell factory.

Optimized invertase expression and secretion cassette for improving Yarrowia lipolytica growth on sucrose for industrial applications

Yarrowia lipolytica requires the expression of a heterologous invertase to grow on a sucrose-based substrate. This work reports the construction of an optimized invertase expression cassette composed of Saccharomyces cerevisiae Suc2p secretion signal sequence followed by the SUC2 sequence and under the control of the strong Y. lipolytica pTEF promoter. This new construction allows a fast and optimal cleavage of sucrose into glucose and fructose and allows cells to reach the maximum growth rate. Contrary to pre-existing constructions, the expression of SUC2 is not sensitive to medium composition in this context. The strain JMY2593, expressing this new cassette with an optimized secretion signal sequence and a strong promoter, produces 4,519 U/l of extracellular invertase in bioreactor experiments compared to 597 U/l in a strain expressing the former invertase construction. The expression of this cassette strongly improved production of invertase and is suitable for simultaneously high production level of citric acid from sucrose-based media.

Regulatory properties of malic enzyme in the oleaginous yeast, Yarrowia lipolytica, and its non-involvement in lipid accumulation

Malic enzyme (EC 1.1.1.40) converts L-malate to pyruvate and CO2 providing NADPH for metabolism especially for lipid biosynthesis in oleaginous microorganisms. However, its role in the oleaginous yeast, Yarrowia lipolytica, is unclear. We have cloned the malic enzyme gene (YALI0E18634g) from Y. lipolytica into pET28a, expressed it in Escherichia coli and purified the recombinant protein (YlME). YlME used NAD(+) as the primary cofactor. Km values for NAD(+) and NADP(+) were 0.63 and 3.9 mM, respectively. Citrate, isocitrate and α-ketoglutaric acid (>5 mM) were inhibitory while succinate (5-15 mM) increased NADP(+)- but not NAD(+)-dependent activity. To determine if fatty acid biosynthesis could be increased in Y. lipolytica by providing additional NADPH from an NADP(+)-dependent malic enzyme, the malic enzyme gene (mce2) from an oleaginous fungus, Mortierella alpina, was expressed in Y. lipolytica. No significant changes occurred in lipid content or fatty acid profiles suggesting that malic enzyme is not the main source of NADPH for lipid accumulation in Y. lipolytica.

Genetic engineering of Yarrowia lipolytica for enhanced production of trans-10, cis-12 conjugated linoleic acid

Background

Conjugated linoleic acid (CLA) has been extensively studied for decades because of its health benefits including cancer prevention, anti-atherogenic and anti-obesity effects, and modulation of the immune system. We previously described the production of trans-10, cis-12 CLA in Yarrowia lipolytica by expressing the gene coding for linoleic acid isomerase from Propionibacterium acnes (pai). However the stable strain produced CLA at about 0.08% of dry cell weight (DCW), a level of production which was not high enough for practical applications. The goal of the present study was to enhance production of CLA by genetic engineering of Y. lipolytica strains.

Results

We have now co-expressed the delta 12-desaturase gene (FADS12, d12) from Mortierella alpina together with the codon-optimized linoleic acid isomerase (opai) gene in Y. lipolytica, expressed under the control of promoter hp16d modified by fusing 12 copies of UAS1B to the original promoter hp4d. A multi-copy integration plasmid was used to further enhance the expression of both genes. Using glucose as the sole carbon source, the genetically-modified Y. lipolytica produced trans-10, cis-12-CLA at a level of up to 10% of total fatty acids and 0.4% of DCW. Furthermore, when the recombinant yeast was grown with soybean oil, trans-10, cis-12-CLA now accumulated at a level of up to 44% of total fatty acids, which represented 30% of DCW after 38.5 h of cultivation. In addition, trans-10, cis-12-CLA was also detected in the growth medium up to 0.9 g/l.

Conclusions

We have successfully produced trans-10, cis-12-CLA with a titre of 4 g/l of culture (3.1 g/l in cells and 0.9 g/l in culture medium). Our results demonstrate the potential use of Y. lipolytica as a promising microbial cell factory for trans-10, cis-12-CLA production.

Yarrowia lipolytica: safety assessment of an oleaginous yeast with a great industrial potential

Yarrowia lipolytica has been developed as a production host for a large variety of biotechnological applications. Efficacy and safety studies have demonstrated the safe use of Yarrowia-derived products containing significant proportions of Yarrowia biomass (as for DuPont's eicosapentaenoic acid-rich oil) or with the yeast itself as the final product (as for British Petroleum's single-cell protein product). The natural occurrence of the species in food, particularly cheese, other dairy products and meat, is a further argument supporting its safety. The species causes rare opportunistic infections in severely immunocompromised or otherwise seriously ill people with other underlying diseases or conditions. The infections can be treated effectively by the use of regular antifungal drugs, and in some cases even disappeared spontaneously. Based on our assessment, we conclude that Y. lipolytica is a "safe-to-use" organism.