α-Ketoglutaric acid production from rapeseed oil by Yarrowia lipolytica yeast

An Eclectic Review on Dicarboxylic Acid Production Through Yeast Cell Factories and Its Industrial Prominence

Dicarboxylic acid (DCA) is a multifaceted chemical intermediate, recoursed to produce many industrially important products such as adhesives, plasticizers, lubricants, polymers, etc. To bypass the shortcomings of the chemical methods of synthesis of DCA and to reduce fossil fuel footprints, bio-based synthesis is gaining attention. In pursuit of an eco-friendly sustainable alternative method of DCA production, microbial cell factories, and renewable organic resources are gaining popularity. Among the plethora of microbial communities, yeast is being favored industrially compared to bacterial fermentation due to its hyperosmotic and low pH tolerance and flexibility for gene manipulations. By application of rapidly evolving genetic manipulation techniques, the bio-based DCA production could be made more precise and economical. To bridge the gap between supply and demand of DCA, many strategies are employed to improve the fermentation. This review briefly outlines the advancements in DCA production using yeast cell factories with the exemplification of strain improvement strategies.

Enhancement of α-Ketoglutaric Acid Production by Yarrowia lipolytica Grown on Mixed Renewable Carbon Sources through Adjustment of Culture Conditions

α-Ketoglutaric acid (KGA) is a valuable compound with a wide range of applications, e.g., in the cosmetics, pharmaceutical, chemical and food industries. The present study aimed to enhance the efficiency of KGA production by Yarrowia lipolytica CBS146773 from renewable carbon sources. In the investigation, various factors that may potentially affect KGA biosynthesis were examined in bioreactor cultures performed on a simple medium containing glycerol (20 g/L) and fed with four portions of a substrate mixture (15 + 15 g/L of glycerol and rapeseed oil). It was found that the process may be stimulated by regulation of the medium pH and aeration, application of selected neutralizing agents, supplementation with thiamine and addition of sorbitan monolaurate, whereas presence of biotin and iron ions had no positive effect on KGA biosynthesis. Adjustment of the parameters improved the process efficiency and allowed 82.4 g/L of KGA to be obtained, corresponding to productivity of 0.57 g/L h and yield of 0.59 g/g. In addition, the production of KGA was characterized by a low level (≤6.3 g/L) of by-products, i.e., citric and pyruvic acids. The results confirmed the high potential of renewable carbon sources (glycerol + rapeseed oil) for effective KGA biosynthesis by Yarrowia lipolytica.

An overview about the approaches used in the production of alpha-ketoglutaric acid with their applications

Alpha ketoglutaric acid is a biological compound found naturally in the human body. It plays an important role in the cell metabolism and has a role in various metabolic pathways including Kreb’s cycle, protein metabolism and so on. Keto glutaric acid is chemically prepared from succinic acid and oxalic acid. It is a direct precursor of glutamic acid and triazines. It can be produced by oxidative decarboxylation of isocitrate by isocitrate dehydrogenase. The yeast Yarrowia lipolytica is used as a prospective producer of alpha ketoglutaric acid from ethanol. The capability to synthesize Keto glutaric acid has so far been investigated for many microorganisms such as Pseudomonas fluoroscens , Bacillus subtilis etc. P. fluoroscens have the ability to synthesize a huge amount of alpha ketoglutaric acid in a glycerol medium supplemented with manganese (Mn). The Mangnese has a significant impact on glycerol metabolism resulting in the buildup of alpha ketoglutaric acid. The metabolism of succinate may result in the production of alpha ketoglutarate. Despite its importance in TCA cycle, alpha ketoglutaric acid buildup as an intermediate product of bacterial glucose oxidation. Along with chemical synthesis and microbial fermentation, enzymatic transformation can also be used to produce alpha ketoglutaric acid. Biodiesel waste is considered as cheap and renewable carbon source for the development of alpha ketoglutaric acid. Alpha ketoglutarate is used for kidney disease, intestinal and stomach disorders and many other conditions. It also plays an important role in the food industry as food and nutrient enhancers. The review is covering all the aspects related with the Alpha ketoglutaric acid production, utilization and product recovery.

Application of a New Engineered Strain of Yarrowia lipolytica for Effective Production of Calcium Ketoglutarate Dietary Supplements

The present study aimed to develop a technology for the production of dietary supplements based on yeast biomass and α-ketoglutaric acid (KGA), produced by a new transformant of Yarrowia lipolytica with improved KGA biosynthesis ability, as well to verify the usefulness of the obtained products for food and feed purposes. Transformants of Y. lipolytica were constructed to overexpress genes encoding glycerol kinase, methylcitrate synthase and mitochondrial organic acid transporter. The strains were compared in terms of growth ability in glycerol- and oil-based media as well as their suitability for KGA biosynthesis in mixed glycerol-oil medium. The impact of different C:N:P ratios on KGA production by selected strain was also evaluated. Application of the strain that overexpressed all three genes in the culture with a C:N:P ratio of 87:5:1 allowed us to obtain 53.1 g/L of KGA with productivity of 0.35 g/Lh and yield of 0.53 g/g. Finally, the possibility of obtaining three different products with desired nutritional and health-beneficial characteristics was demonstrated: (1) calcium α-ketoglutarate (CaKGA) with purity of 89.9% obtained by precipitation of KGA with CaCO3, (2) yeast biomass with very good nutritional properties, (3) fixed biomass-CaKGA preparation containing 87.2 μg/g of kynurenic acid, which increases the health-promoting value of the product.

Yarrowia lipolytica Strains and Their Biotechnological Applications: How Natural Biodiversity and Metabolic Engineering Could Contribute to Cell Factories Improvement

Among non-conventional yeasts of industrial interest, the dimorphic oleaginous yeast Yarrowia lipolytica appears as one of the most attractive for a large range of white biotechnology applications, from heterologous proteins secretion to cell factories process development. The past, present and potential applications of wild-type, traditionally improved or genetically modified Yarrowia lipolytica strains will be resumed, together with the wide array of molecular tools now available to genetically engineer and metabolically remodel this yeast. The present review will also provide a detailed description of Yarrowia lipolytica strains and highlight the natural biodiversity of this yeast, a subject little touched upon in most previous reviews. This work intends to fill this gap by retracing the genealogy of the main Yarrowia lipolytica strains of industrial interest, by illustrating the search for new genetic backgrounds and by providing data about the main publicly available strains in yeast collections worldwide. At last, it will focus on exemplifying how advances in engineering tools can leverage a better biotechnological exploitation of the natural biodiversity of Yarrowia lipolytica and of other yeasts from the Yarrowia clade.

Comparative analysis of the chemical and biochemical synthesis of keto acids

Keto acids are essential organic acids that are widely applied in pharmaceuticals, cosmetics, food, beverages, and feed additives as well as chemical synthesis. Currently, most keto acids on the market are prepared via chemical synthesis. The biochemical synthesis of keto acids has been discovered with the development of metabolic engineering and applied toward the production of specific keto acids from renewable carbohydrates using different metabolic engineering strategies in microbes. In this review, we provide a systematic summary of the types and applications of keto acids, and then summarize and compare the chemical and biochemical synthesis routes used for the production of typical keto acids, including pyruvic acid, oxaloacetic acid, α-oxobutanoic acid, acetoacetic acid, ketoglutaric acid, levulinic acid, 5-aminolevulinic acid, α-ketoisovaleric acid, α-keto-γ-methylthiobutyric acid, α-ketoisocaproic acid, 2-keto-L-gulonic acid, 2-keto-D-gluconic acid, 5-keto-D-gluconic acid, and phenylpyruvic acid. We also describe the current challenges for the industrial-scale production of keto acids and further strategies used to accelerate the green production of keto acids via biochemical routes.

Optimization of medium composition and fermentation conditions for α-ketoglutaric acid production from biodiesel waste by Yarrowia lipolytica

This work demonstrates the ability of the yeast Yarrowia lipolytica cultivated on biodiesel waste to synthesize α-ketoglutaric acid with a minimal content of pyruvic acid as the main byproduct. The key factor promoting the microbial production of α-ketoglutaric acid from the waste is a strong deficiency of thiamine in the cultivation medium. The production of α-ketoglutaric acid by the yeast can be regulated by changing the concentration of nitrogen, iron, zinc, copper, and manganese in the medium, as well as by pH medium and the aeration rate. The optimization of these parameters in flask experiments allowed us to increase the concentration of α-ketoglutaric acid in the medium by 2.6 times and to shift the α-ketoglutaric acid/pyruvic acid ratio from 5:1 to 30:1. During cultivation in a fermentor under optimized conditions, Y. lipolytica produced 80.4 g/L α-ketoglutaric acid with a process selectivity of 96.7% and the product yield (Y_KGA) equal to 1.01 g/g. KEY POINTS: • α-Ketoglutaric acid is commercially important biotechnological product. • Biosynthesis of α-ketoglutaric acid from biodiesel waste. • Optimization of cultivation medium and nutrition medium.

Alpha-Ketoglutaric Acid Production from a Mixture of Glycerol and Rapeseed Oil by Yarrowia lipolytica Using Different Substrate Feeding Strategies

The microbiological biosynthesis of α-ketoglutaric acid (KGA) has recently captured the attention of many scientists as an alternative to its common chemical synthesis. The present study aimed to evaluate the effect of the feeding strategy of substrates, i.e., glycerol (G = 20 g·dm−3) and rapeseed oil (O = 20 g·dm−3), on yeast growth and the parameters of KGA biosynthesis by a wild strain Yarrowia lipolytica A-8 in fed-batch and repeated-batch cultures. The effectiveness of KGA biosynthesis was demonstrated to depend on thiamine concentration and the substrate feeding method. In the fed-batch culture incubated with 3 µg·dm−3 of thiamine and a substrate feeding variant 2G(_OGO), KGA was produced in the amount of 62.1 g·dm−3 at the volumetric production rate of 0.37 g·dm−3·h−1. These values of KGA production parameters were higher than these obtained in the control culture (with rapeseed oil only). During 10 cycles of the 1788-h repeated-batch culture carried out acc. to the feeding strategy 2G(_OGO), in the last 5 cycles the yeast produced from 55.6 to 58.2 g·dm−3 of KGA and maximally 2.9 g·dm−3 of the pyruvic acid as a by-product.

Analysis of Yarrowia lipolytica growth, catabolism, and terpenoid biosynthesis during utilization of lipid-derived feedstock

This study employs biomass growth analyses and ¹³C-isotope tracing to investigate lipid feedstock utilization by Yarrowia lipolytica. Compared to glucose, oil-feedstock in the minimal medium increases the yeast's biomass yields and cell sizes, but decreases its protein content (<20% of total biomass) and enzyme abundances for product synthesis. Labeling results indicate a segregated metabolic network (the glycolysis vs. the TCA cycle) during co-catabolism of sugars (glucose or glycerol) with fatty acid substrates, which facilitates resource allocations for biosynthesis without catabolite repressions. This study has also examined the performance of a β-carotene producing strain in different growth mediums. Canola oil-containing yeast-peptone (YP) has resulted in the best β-carotene titer (121 ± 13 mg/L), two-fold higher than the glucose based YP medium. These results highlight the potential of Y. lipolytica for the valorization of waste-derived lipid feedstock.

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¹³C tracing was used to track Y. lipolytica metabolism of lipid-based feedstock.

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Y. lipolytica has a segregated flux network for lipid and sugar co-utilizations.

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Lipid feedstock and nitrogen sources affect cell morphology and optical density.

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Lipid feedstock benefits both Y. lipolytica growth and carotenoid biosynthesis.

Sugar Alcohols and Organic Acids Synthesis in Yarrowia lipolytica: Where Are We?

Sugar alcohols and organic acids that derive from the metabolism of certain microorganisms have a panoply of applications in agro-food, chemical and pharmaceutical industries. The main challenge in their production is to reach a productivity threshold that allow the process to be profitable. This relies on the construction of efficient cell factories by metabolic engineering and on the development of low-cost production processes by using industrial wastes or cheap and widely available raw materials as feedstock. The non-conventional yeast Yarrowia lipolytica has emerged recently as a potential producer of such metabolites owing its low nutritive requirements, its ability to grow at high cell densities in a bioreactor and ease of genome edition. This review will focus on current knowledge on the synthesis of the most important sugar alcohols and organic acids in Y. lipolytica.

Yarrowia lipolytica as an emerging biotechnological chassis for functional sugars biosynthesis

Functional sugars have unique structural and physiological characteristics with applied perspectives for modern biomedical and biotechnological sectors, such as biomedicine, pharmaceutical, cosmeceuticals, green chemistry, and agro-food. They can also be used as starting matrices to produce biologically active metabolites of interests. Though numerous chemical synthesis routes have been proposed and deployed for the synthesis of rare sugars, however, many of them are limited and economically incompetent because of expensive raw starting feedstocks. Whereas, the biosynthesis by enzymatic means are often associated with high catalyst costs and low space-time yields. Microbial production of rare sugars via green routes using bio-renewable resources offers noteworthy solutions to overcome the aforementioned limitations of synthetic and enzymatic synthesis routes. From the microbial-based synthesis perspective, the lipogenic yeast Yarrowia lipolytica is rapidly evolving as the most prevalent and unique "non-model organism" in the bio-production arena. Due to high flux tendency through the tri-carboxylic acid cycle intermediates and precursors such as acetyl-CoA and malonyl-CoA, this yeast has been widely investigated to meet the increasing demand of industrially relevant fine chemicals, including functional sugars. Incredible interest in Y. lipolytica originates from its robust tolerance to unstable pH, salt levels, and organic compounds, which subsequently enable easy bioprocess optimization. Meaningfully, GRAS (generally recognized as safe) status creates Y. lipolytica as an attractive and environmentally friendly microbial host for the manufacturing of nutraceuticals, fermented food, and dietary supplements. In this review, we highlight the recent and state-of-the-art research progress on Y. lipolytica as a host to synthesize bio-based compounds of interest beyond the realm of well-known fatty acid production. The unique physicochemical properties, biotechnological applications, and biosynthesis of an array of value-added functional sugars including erythritol, threitol, fructooligosaccharides, galactooligosaccharides, isomalto-oligosaccharides, isomaltulose, trehalose, erythrulose, xylitol, and mannitol using sustainable carbon sources are thoroughly vetted. Finally, we conclude with perspectives that would be helpful to engineer Y. lipolytica in greening the twenty-first century biomedical and biotechnological sectors of the modern world.

Engineering of L-glutamate oxidase as the whole-cell biocatalyst for the improvement of α-ketoglutarate production

L-glutamate oxidase (LGOX) catalyzes the oxidative deamination of l-glutamate to α-ketoglutarate (α-KG) with the formation of ammonia and hydrogen peroxide. Consequently, identifying a novel LGOX with high enzymatic activity is a prime target for industrial biotechnology. In this study, error-prone PCR mutagenesis of Streptomyces mobaraensis LGOX followed by high-throughput screening was performed to yield four single point mutants with improved enzymatic activity, termed F94L, S280T, I282M and H533R. Moreover, site-saturation mutagenesis at these four residues was employed, yielding two additionally improved mutants, termed I282L and H533L. Subsequently, we employed combinatorial mutagenesis of two, three and four point mutants, and the best mutant S280TH533L showed 90 % higher enzymatic activity than the wild-type control. The data also showed that the presence of these point mutations greatly enhanced enzymatic activity, but did not alter its optimum temperature and pH. Furthermore, the S280TH533L mutant had the maximal velocity (V_max) of 231.3 μmol/mg/min and the Michaelis-Menten constant (K_M) of 2.7 mM, which were the highest V_max and lowest K_M values of LGOX reported so far. Finally, we developed a whole-cell biocatalyst for α-KG production by co-expression of both S280TH533L mutant and KatE catalase. Randomized ribosome binding site (RBS) sequences were introduced to generate vectors with varying expression levels of S280TH533L and KatE, and two optimized co-expression strains were obtained after screening. The α-KG production reached a maximum titer of 181.9 g/L after 12 h conversation using the optimized whole-cell biocatalyst, with a molar conversion rate of substrate higher than 86.3 % in the absence of exogenous catalase, while the molar conversion rate of substrate using the wild-type biocatalyst was less than 30 %. Taken together, these data suggest that the engineering of LGOX has great potentials to enhance the industrial production of α-KG.

Heterologous overexpression of bacterial hemoglobin VHb improves erythritol biosynthesis by yeast Yarrowia lipolytica

Background

Yarrowia lipolytica is an unconventional yeast with a huge industrial potential. Despite many advantages for biotechnological applications, it possesses enormous demand for oxygen, which is a bottleneck in large scale production. In this study a codon optimized bacterial hemoglobin from Vitreoscilla stercoraria (VHb) was overexpressed in Y. lipolytica for efficient growth and erythritol synthesis from glycerol in low-oxygen conditions. Erythritol is a natural sweetener produced by Y. lipolytica under high osmotic pressure and at low pH, and this process requires high oxygen demand.

Results

Under these conditions the VHb overexpressing strain showed mostly yeast-type cells resulting in 83% higher erythritol titer in shake-flask experiments. During a bioreactor study the engineered strain showed higher erythritol productivity (Q_ERY = 0.38 g/l h) and yield (Y_ERY = 0.37 g/g) in comparison to the control strain (Q_ERY = 0.30 g/l h, Y_ERY = 0.29 g/g). Moreover, low stirring during the fermentation process resulted in modest foam formation.

Conclusions

This study showed that overexpression of VHb in Y. lipolytica allows for dynamic growth and efficient production of a value-added product from a low-value substrate.

Organic Wastes as Feedstocks for Non-Conventional Yeast-Based Bioprocesses

Non-conventional yeasts are efficient cell factories for the synthesis of value-added compounds such as recombinant proteins, intracellular metabolites, and/or metabolic by-products. Most bioprocess, however, are still designed to use pure, ideal sugars, especially glucose. In the quest for the development of more sustainable processes amid concerns over the future availability of resources for the ever-growing global population, the utilization of organic wastes or industrial by-products as feedstocks to support cell growth is a crucial approach. Indeed, vast amounts of industrial and commercial waste simultaneously represent an environmental burden and an important reservoir for recyclable or reusable material. These alternative feedstocks can provide microbial cell factories with the required metabolic building blocks and energy to synthesize value-added compounds, further representing a potential means of reduction of process costs as well. This review highlights recent strategies in this regard, encompassing knowledge on catabolic pathways and metabolic engineering solutions developed to endow cells with the required metabolic capabilities, and the connection of these to the synthesis of value-added compounds. This review focuses primarily, but not exclusively, on Yarrowia lipolytica as a yeast cell factory, owing to its broad range of naturally metabolizable carbon sources, together with its popularity as a non-conventional yeast.

Morphological response of Yarrowia lipolytica under stress of heavy metals

The marine dimorphic yeast Yarrowia lipolytica has been proposed as a suitable model for the dimorphism study. In this study, the morphological behaviour of two marine strains of Y. lipolytica (NCIM 3589 and NCIM 3590) was studied under stress of different heavy metals. Scanning electron microscopy was used to investigate the morphological features of yeast cells. This study revealed that the normal ellipsoidal shape of yeast cells was changed into oval, rounded, or elongated in response to different heavy-metal stress. Light microscopy was also used to investigate individual properties of yeast cells. The average cell length and radius of both marine strains was increased with increasing concentrations of heavy-metal ions. In addition, the elongation factor was calculated and was increased in the presence of heavy metals like Pb(II), Co(II), Cr(III), Cr(VI), and Zn(II) under the static conditions.

Separation and purification of α-ketoglutarate and pyruvate from the fermentation broth of Yarrowia lipolytica

A strategy to achieve the efficient co-production of α-ketoglutarate (KGA) and pyruvate (PYR) via Yarrowia lipolytica fermentation was established in our previous work. The next big challenge is to achieve an efficient separation of the two keto acids. A strategy for simultaneously separating and purifying KGA and PYR based on their different boiling points was established, leading to the efficient separation and purification of the two keto acids from the fermentation broth of Y. lipolytica. The purity and yield of KGA/PYR reached 99.3/99.5 and 79.8/80.6%, respectively. Application of the separation method on industrial scale could further decrease the cost of the production of the two keto acids by biotechnological routes.

Application of organic acids for plant protection against phytopathogens

The basic tendency in the field of plant protection concerns with reducing the use of pesticides and their replacement by environmentally acceptable biological preparations. The most promising approach to plant protection is application of microbial metabolites. In the last years, bactericidal, fungicidal, and nematodocidal activities were revealed for citric, succinic, α-ketoglutaric, palmitoleic, and other organic acids. It was shown that application of carboxylic acids resulted in acceleration of plant development and the yield increase. Of special interest is the use of arachidonic acid in very low concentrations as an inductor (elicitor) of protective functions in plants. The bottleneck in practical applications of these simple, nontoxic, and moderately priced preparations is the absence of industrial production of the mentioned organic acids of required quality since even small contaminations of synthetic preparations decrease their quality and make them dangerous for ecology and toxic for plants, animals, and human. This review gives a general conception on the use of organic acids for plant protection against the most dangerous pathogens and pests, as well as focuses on microbiological processes for production of these microbial metabolites of high quality from available, inexpensive, and renewable substrates.

Biotechnological production of alpha-keto acids: Current status and perspectives

Alpha-keto (α-keto) acids are used widely in feeds, food additives, pharmaceuticals, and in chemical synthesis processes. Although most α-keto acids are currently produced by chemical synthesis, their biotechnological production from renewable carbohydrates is a promising new approach. In this mini-review, we first present the different types of α-keto acids as well as their applications; next, we summarize the recent progresses in the biotechnological production of some important α-keto acids; namely, pyruvate, α-ketoglutarate, α-ketoisovalerate, α-ketoisocaproate, phenylpyruvate, α-keto-γ-methylthiobutyrate, and 2,5-diketo-d-gluconate. Finally, we discuss the future prospects as well as favorable directions for the biotechnological production of keto acids that ultimately would be more environment-friendly and simpler compared with the production by chemical synthesis.

Citric acid production from hydrolysate of pretreated straw cellulose by Yarrowia lipolytica SWJ-1b using batch and fed-batch cultivation

In this study, crude cellulase produced by Trichoderma reesei Rut-30 was used to hydrolyze pretreated straw. After the compositions of the hydrolysate of pretreated straw were optimized, the study showed that natural components of pretreated straw without addition of any other components such as (NH4)2SO4, KH2PO4, or Mg(2+) were suitable for citric acid production by Yarrowia lipolytica SWJ-1b, and the optimal ventilatory capacity was 10.0 L/min/L medium. Batch and fed-batch production of citric acid from the hydrolysate of pretreated straw by Yarrowia lipolytica SWJ-1b has been investigated. In the batch cultivation, 25.4 g/L and 26.7 g/L citric acid were yields from glucose and hydrolysate of straw cellulose, respectively, while the cultivation time was 120 hr. In the three-cycle fed-batch cultivation, citric acid (CA) production was increased to 42.4 g/L and the cultivation time was extended to 240 hr. However, iso-citric acid (ICA) yield in fed-batch cultivation (4.0 g/L) was similar to that during the batch cultivation (3.9 g/L), and only 1.6 g/L of reducing sugar was left in the medium at the end of fed-batch cultivation, suggesting that most of the added carbon was used in the cultivation.

Mutagenesis of conserved active site residues of dihydrolipoamide succinyltransferase enhances the accumulation of α-ketoglutarate in Yarrowia lipolytica

α-Ketoglutarate (α-KG) is an important intermediate in the tricarboxylic acid cycle and has broad applications. The mitochondrial ketoglutarate dehydrogenase (KGDH) complex catalyzes the oxidation of α-KG to succinyl-CoA. Disruption of KGDH, which may enhance the accumulation of α-KG theoretically, was found to be lethal to obligate aerobic cells. In this study, individual overexpression of dihydrolipoamide succinyltransferase (DLST), which serves as the inner core of KGDH, decreased overall activity of the enzyme complex. Furthermore, two conserved active site residues of DLST, His419, and Asp423 were identified. In order to determine whether these residues are engaged in enzyme reaction or not, these two conserved residues were individually mutated. Analysis of the kinetic parameters of the enzyme variants provided evidence that the catalytic reaction of DLST depended on residues His419 and Asp423. Overexpression of mutated DLST not only impaired balanced assembly of KGDH, but also disrupted the catalytic integrity of the enzyme complex. Replacement of the Asp423 residue by glutamate increased extracellular α-KG by 40 % to 50 g L(-1) in mutant strain. These observations uncovered catalytic roles of two conserved active site residues of DLST and provided clues for effective metabolic strategies for rational carbon flux control for the enhanced production of α-KG and related bioproducts.

Simultaneous saccharification and fermentation of cellulose in ionic liquid for efficient production of α-ketoglutaric acid by Yarrowia lipolytica

Ionic liquids (ILs) are benign solvents that are highly effective for biomass pretreatment. However, their applications for scale-up biorefinery are limited due to multiple expensive IL recovery and separation steps that are required. To overcome this limitation, it is very critical to develop a compatible enzymatic and microbial biocatalyst system to carry the simultaneous saccharification and fermentation in IL environments (SSF-IL). While enzymatic biocatalysts have been demonstrated to be compatible with various IL environments, it is challenging to develop microbial biocatalysts that can thrive and perform efficient biotransformation under the same conditions (pH and temperature). In this study, we harnessed the robust metabolism of Yarrowia lipolytica as a microbial platform highly compatible with the IL environments such as 1-ethyl-3-methylimidazolium acetate ([EMIM][OAc]). We optimized the enzymatic and microbial biocatalyst system using commercial cellulases and demonstrated the capability of Y. lipolytica to convert cellulose into high-value organics such as α-ketoglutaric acid (KGA) in the SSF-IL process at relatively low temperature 28 °C and high pH 6.3. We showed that SSF-IL not only enhanced the enzymatic saccharification but also produced KGA up to 92% of the maximum theoretical yield.

The production of succinic acid by yeast Yarrowia lipolytica through a two-step process

The production of α-ketoglutaric acid by yeast Yarrowia lipolytica VKMY-2412 from ethanol and its subsequent chemical conversion to succinic acid (SA) were investigated. A highly effective and environmentally friendly process of α-ketoglutaric acid production was developed using a special pH-controlling strategy, in which the titration of the culture broth with KOH in the acid-formation phase was minimal, that allowed accumulation of only low amounts of inorganic wastes in the course of SA recovery. The culture broth filtrate containing α-ketoglutaric acid (88.7 g l(-1)) was directly employed for SA production; the amount of SA produced comprised 71.7 g l(-1) with the yield of 70% from ethanol consumed. SA was isolated from the culture broth filtrate in a crystalline form with the purity of 100%. The yield of isolated SA was as high as 72% of its amount in the culture broth filtrate. The antimicrobial and nematocidic effects of SA of microbial origin on pathogenic organisms that cause human and plant diseases were revealed for the first time.

The peculiarities of succinic acid production from rapeseed oil by Yarrowia lipolytica yeast

The process of succinic acid (SA) production represents the combination of microbial synthesis of α-ketoglutaric acid from rapeseed oil by yeast Yarrowia lipolytica VKM Y-2412 and subsequent decarboxylation of α-ketoglutaric acid by hydrogen peroxide to SA that leads to the production of 69.0 g l(-1) of SA and 1.36 g l(-1) of acetic acid. SA was isolated from the culture broth filtrate in a crystalline form. The SA recovery from the culture filtrate has certain difficulties due to the presence of residual triglycerides of rapeseed oil. The effect of different methods of the culture filtrate treatment and various sorption materials on the coagulation of triglycerides was studied, and as a result, the precipitation of residual triglycerides by acetone was chosen. The subsequent isolation procedures involved the decomposition of H2O2 in the filtrate followed by filtrate bleaching and acidification with a mineral acid, evaporation of filtrate, and SA extraction with ethanol from the residue. The purity of crystalline SA isolated from the culture broth filtrate achieved 97.6-100 %. The product yield varied from 62.6 to 71.6 % depending on the acidity of the supernatant.

Morphological and metabolic shifts of Yarrowia lipolytica induced by alteration of the dissolved oxygen concentration in the growth environment

Yarrowia lipolytica, an ascomycete with biotechnological potential, is able to form either yeast cells or hyphae and pseudohyphae in response to environmental conditions. This study shows that the morphology of Y. lipolytica, cultivated in batch cultures on hydrophilic (glucose and glycerol) and hydrophobic (olive oil) media, was not affected by the nature of the carbon source, nor by the nature or the concentration of the nitrogen source. By contrast, dissolved oxygen concentration (DOC) should be considered as the major factor affecting yeast morphology. Specifically, when growth occurred at low or zero DOC the mycelial and/or pseudomycelial forms predominated over the yeast form independently of the carbon and nitrogen sources used. Experimental data obtained from a continuous culture of Y. lipolytica on glycerol, being used as carbon and energy source, demonstrated that the mycelium-to-yeast form transition occurs when DOC increases from 0.1 to 1.5 mg l(-1). DOC also affected the yeast physiology, as the activity of enzymes implicated in lipid biosynthesis (i.e. ATP-citrate lyase, malic enzyme) was upregulated at high DOC whereas the activity of enzymes implicated in glycerol assimilation (such as glycerol dehydrogenase and kinase) remained fundamentally unaffected in the cell-free extract.

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.

Engineering the α-ketoglutarate overproduction from raw glycerol by overexpression of the genes encoding NADP+-dependent isocitrate dehydrogenase and pyruvate carboxylase in Yarrowia lipolytica

To establish and develop a biotechnological process of α-ketoglutaric acid (KGA) production by Yarrowia lipolytica, it is necessary to increase the KGA productivity and to reduce the amounts of by-products, e.g. pyruvic acid (PA) as major by-product and fumarate, malate and succinate as minor by-products. The aim of this study was the improvement of KGA overproduction with Y. lipolytica by a gene dose-dependent overexpression of genes encoding NADP(+)-dependent isocitrate dehydrogenase (IDP1) and pyruvate carboxylase (PYC1) under KGA production conditions from the renewable carbon source raw glycerol. Recombinant Y. lipolytica strains were constructed, which harbour multiple copies of the respective IDP1, PYC1 or IDP1 and PYC1 genes together. We demonstrated that a selective increase in IDP activity in IDP1 multicopy transformants changes the produced amount of KGA. Overexpression of the gene IDP1 in combination with PYC1 had the strongest effect on increasing the amount of secreted KGA. About 19% more KGA compared to strain H355 was produced in bioreactor experiments with raw glycerol as carbon source. The applied cultivation conditions with this strain significantly reduced the main by-product PA and increased the KGA selectivity to more than 95% producing up to 186 g l(-1) KGA. This proved the high potential of this multicopy transformant for developing a biotechnological KGA production process.