Lipids by Yarrowia lipolytica Strains Cultivated on Glucose in Batch Cultures

Tracking trash to treasure: in situ monitoring of single microbial cell oil biosynthesis from waste cooking oil using Raman spectroscopy and imaging

Waste cooking oil is a major pollutant that contaminates terrestrial and aquatic bodies which is generated from household kitchens and eateries. The bioremediation of waste cooking oil (WCO) into microbial oil, also known as single microbial cell oil (SMCO), can be accomplished by oleaginous microbes. Conventional methods excel in SMCO analysis but lack efficacy for in situ or lysis-free monitoring of nascent SMCO synthesis and turnover. To bridge this knowledge gap, this study shows the applicability of Raman reverse stable isotope probing (RrSIP) in monitoring time-dependent nascent SMCO synthesis and assimilation in Yarrowia lipolytica, an oleaginous yeast grown in hydrophilic (glucose) as well as hydrophobic carbon sources (cooking oil and waste cooking oil). This study also combines the RrSIP approach with Raman imaging for temporal visualization of the distribution and turnover dynamics of the SMCO pool in a single cell. Our finding provides a unique perspective utilizing optical spectroscopy methods for lysis-free SMCO analysis and holds potential for prospective utility as an adjunct tool in bioprocess and biofuel industries.

The evaluation of Starmerella magnoliae X3 as a biodiesel feedstock based on triacylglycerol (TAG) production, lipid productivity, and fatty acid profile under nitrogen limitation and acidic pH conditions

The effects of four initial culture pH values (3, 4, 5, and 6) and nitrogen limitation on growth, TAG accumulation, lipid production, fatty acid profile, and estimated biodiesel quality of Starmerella magnoliae X3 were investigated. TAG and lipid levels were measured by Nile Red fluorescence and sulfo-phospho-vanilin (SPV) techniques, respectively. The results showed that a combination of nitrogen limitation and acidic pH significantly (p < 0.05) increased TAG accumulation, total lipid contents, and lipid productivity in Starmerella magnoliae X3 compared to the control group. Under nitrogen limitation, the highest TAG accumulation was achieved at initial pHs of 3 and 5 after 72 h of cultivation, and the highest lipid productivity (0.306 g L-1 d-1) was observed after 48 h at pH 3; the major fatty acids at the four pH values were oleic acid (63.6%-64%), palmitoleic acid (11.3%-12.5%), stearic acid (9.7%-11.4%), and palmitic acid (9.4%-10%). In addition, both stresses were associated with lower iodine value and higher cetane number of the biodiesel compared to the control. These findings suggest that cultivation in a low-nitrogen medium at an initial pH of 3 or 5 holds promise in increasing TAG production in Starmerella magnoliae X3.

Yarrowia lipolytica growth, lipids, and protease production in medium with higher alkanes and alkenes

Two strains of Yarrowia lipolytica (CBS 2075 and DSM 8218) were first studied in bioreactor batch cultures, under different controlled dissolved oxygen concentrations (DOC), to assess their ability to assimilate aliphatic hydrocarbons (HC) as a carbon source in a mixture containing 2 g·L-1 of each alkane (dodecane and hexadecane), and 2 g·L-1 hexadecene. Both strains grew in the HC mixture without a lag phase, and for both strains, 30 % DOC was sufficient to reach the maximum values of biomass and lipids. To enhance lipid-rich biomass and enzyme production, a pulse fed-batch strategy was tested, for the first time, with the addition of one or three pulses of concentrated HC medium. The addition of three pulses of the HC mixture (total of 24 g·L-1 HC) did not hinder cell proliferation, and high protease (> 3000 U·L-1) and lipids concentrations of 3.4 g·L-1 and 4.3 g·L-1 were achieved in Y. lipolytica CBS 2075 and DSM 8218 cultures, respectively. Lipids from the CBS 2075 strain are rich in C16:0 and C18:1, resembling the composition of palm oil, considered suitable for the biodiesel industry. Lipids from the DSM 8218 strain were predominantly composed of C16:0 and C16:1, the latter being a valuable monounsaturated fatty acid used in the pharmaceutical industry. Y. lipolytica cells exhibited high intrinsic surface hydrophobicity (> 69 %), which increased in the presence of HC. A reduction in surface tension was observed in both Y. lipolytica cultures, suggesting the production of extracellular biosurfactants, even at low amounts. This study marks a significant advancement in the valorization of HC for producing high-value products by exploring the hydrophobic compounds metabolism of Y. lipolytica.

Transcriptomic profiling of an evolved Yarrowia lipolytica strain: tackling hexanoic acid fermentation to increase lipid production from short-chain fatty acids

BACKGROUND

Short-chain fatty acids (SCFAs) are cost-effective carbon sources for an affordable production of lipids. Hexanoic acid, the acid with the longest carbon chain in the SCFAs pool, is produced in anaerobic fermentation of organic residues and its use is very challenging, even inhibiting oleaginous yeasts growth.

RESULTS

In this investigation, an adaptive laboratory evolution (ALE) was performed to improve Yarrowia lipolytica ACA DC 50109 tolerance to high hexanoic acid concentrations. Following ALE, the transcriptomic analysis revealed several genetic adaptations that improved the assimilation of this carbon source in the evolved strain compared to the wild type (WT). Indeed, the evolved strain presented a high expression of the up-regulated gene YALI0 E16016g, which codes for FAT1 and is related to lipid droplets formation and responsible for mobilizing long-chain acids within the cell. Strikingly, acetic acid and other carbohydrate transporters were over-expressed in the WT strain.

CONCLUSIONS

A more tolerant yeast strain able to attain higher lipid content under the presence of high concentrations of hexanoic acid has been obtained. Results provided novel information regarding the assimilation of hexanoic acid in yeasts.

Sustainable production of lipids from cocoa fatty acid distillate fermentation driven by adaptive evolution in Yarrowia lipolytica

Single cell oil production using oleaginous yeasts is a promising alternative to animal and plant-derived lipids. But substrate costs for microbial fermentation are a major bottleneck. Using side streams as alternative to substrates like glucose, for growing yeast, is a potential cost-effective solution. By combining a previously reported process of growing yeasts on a solid cocoa fatty acid distillate side stream with adaptive evolution techniques, the growth of oleaginous yeast Yarrowia lipolytica was improved by 2-fold. The lipid titre was also boosted by more than 3-fold. Using transcriptomics, key genes were identified that are possibly involved in tailoring of lipid composition, side stream utilisation and enhancement of lipid titres. Candidate genes were also identified that might enable efficient growth and utilization of fatty acids and triacylglycerides found in cocoa fatty acid distillate. In summary, this research has improved the understanding of side stream utilisation for lipid production in oleaginous yeast.

Dynamics of the lipid body lipidome in the oleaginous yeast Yarrowia sp

Time-dependent changes in the lipid body (LB) lipidome of two oleaginous yeasts, Yarrowia lipolytica NCIM 3589 and Yarrowia bubula NCIM 3590 differing in growth temperature was investigated. LB size and lipid content were higher in Y. lipolytica based on microscopy, Feret, and integrated density analysis with lipid accumulation and mobilization occurring at 48 h in both strains. Variations in LB lipidome were reflected in interfacial tension (59.67 and 68.59 mN m-1) and phase transition temperatures (30°C-100°C and 60°C-100°C) for Y. lipolytica and Y. bubula, respectively. Liquid Chromatography-Mass Spectroscopy (LC-MS) analysis revealed neutral lipids (NLs), phospholipids, sphingolipids, sterols, and fatty acids as the major classes present in both strains while fatty acid amides were seen only in Y. lipolytica. Amongst the lipid classes, a few species were present in abundance with a number of lipids being less dominant. Permutational multivariate analysis of variance (PERMANOVA) and Analysis of covariance (ANOCOVA) analysis suggest 22 lipids belonging to NLs, fatty acid amides, and free fatty acids were found to be statistically different between the two strains. Analysis of the ratios between different lipid components suggest changes in LB size and mobilization as a function of time. The results indicate influence of temperature and strain variation on the dynamics of LB lipidome in Yarrowia species.

Integrated fermentative process for lipid and β-carotene production from acetogenic syngas fermentation using an engineered oleaginous Yarrowia lipolytica yeast

An engineered Yarrowia lipolytica strain was successfully employed to produce β-carotene and lipids from acetic acid, a product of syngas fermentation by Clostridium aceticum. The strain showed acetic acid tolerance up to concentrations of 20 g/L. Flask experiments yielded a peak lipid content of 33.7 % and β-carotene concentration of 13.6 mg/g under specific nutrient conditions. The study also investigated pH effects on production in bioreactors, revealing optimal lipid and β-carotene contents at pH 6.0, reaching 22.9 % and 44 mg/g, respectively. Lipid profiles were consistent across experiments, with C18:1 being the dominant compound at approximately 50 %. This research underscores a green revolution in bioprocessing, showing how biocatalysts can convert syngas, a potentially polluting byproduct, into valuable β-carotene and lipids with a Y. lipolytica strain.

Multi-omics view of recombinant Yarrowia lipolytica: Enhanced ketogenic amino acid catabolism increases polyketide-synthase-driven docosahexaenoic production to high selectivity at the gram scale

DHA is a marine PUFA of commercial value, given its multiple health benefits. The worldwide emerging shortage in DHA supply has increased interest in microbial cell factories that can provide the compound de novo. In this regard, the present work aimed to improve DHA production in the oleaginous yeast strain Y. lipolytica Af4, which synthetized the PUFA via a heterologous myxobacterial polyketide synthase (PKS)-like gene cluster. As starting point, we used transcriptomics, metabolomics, and 13C-based metabolic pathway profiling to study the cellular dynamics of Y. lipolytica Af4. The shift from the growth to the stationary DHA-production phase was associated with fundamental changes in carbon core metabolism, including a strong upregulation of the PUFA gene cluster, as well as an increase in citrate and fatty acid degradation. At the same time, the intracellular levels of the two DHA precursors acetyl-CoA and malonyl-CoA dropped by up to 98% into the picomolar range. Interestingly, the degradation pathways for the ketogenic amino acids l-lysine, l-leucine, and l-isoleucine were transcriptionally activated, presumably to provide extra acetyl-CoA. Supplementation with small amounts of these amino acids at the beginning of the DHA production phase beneficially increased the intracellular CoA-ester pools and boosted the DHA titer by almost 40%. Isotopic 13C-tracer studies revealed that the supplements were efficiently directed toward intracellular CoA-esters and DHA. Hereby, l-lysine was found to be most efficient, as it enabled long-term activation, due to storage within the vacuole and continuous breakdown. The novel strategy enabled DHA production in Y. lipolytica at the gram scale for the first time. DHA was produced at a high selectivity (27% of total fatty acids) and free of the structurally similar PUFA DPA, which facilitates purification for high-value medical applications that require API-grade DHA. The assembled multi-omics picture of the central metabolism of Y. lipolytica provides valuable insights into this important yeast. Beyond our work, the enhanced catabolism of ketogenic amino acids seems promising for the overproduction of other compounds in Y. lipolytica, whose synthesis is limited by the availability of CoA ester precursors.

Growth Response of Non-Conventional Yeasts on Sugar-Rich Media: Part 2: Citric Acid Production and Circular-Oriented Valorization of Glucose-Enriched Olive Mill Wastewaters Using Novel Yarrowia lipolytica Strains

The global market for citric acid (CA) is one of the biggest and fastest expanding markets in the food industry. The CA production employing microbial bioprocessing with efficient GRAS strains and renewable waste streams is in line with the European Union binding targets for resource efficiency, sustainable consumption-production, and low-carbon technologies. In this work, the potential of three novel wild-type Yarrowia lipolytica strains (namely LMBF Y-46, LMBF Y-47 and ACA-YC 5033) regarding the production of CA and other valuable metabolites was tested on glucose-based media, and the most promising amongst the screened strains (viz. the strain ACA-YC 5033) was cultured on glucose-based media, in which part of the fermentation water had been replaced by olive-mill wastewaters (OMWs) in a novel approach of simultaneous OMW valorization and bioremediation. In the first part of this study, the mentioned strains were cultured under nitrogen-limited conditions with commercial (low-cost) glucose employed as a sole carbon source in shake-flask cultures at an initial concentration (S0) ≈ of 50 g/L. Variable quantities of secreted citric acid (CA) and intra-cellular compounds (viz. polysaccharides and lipids) were produced. All strains did not accumulate significantly high lipid quantities (i.e., maximum lipid in dry cell weight [DCW] values ≈30% w/w were noted) but produced variable CA quantities. The most promising strain, namely ACA-YC 5033, produced CA up to c. 24 g/L, with a yield of CA produced on glucose consumed (YCA/S) ≈ 0.45 g/g. This strain in stirred tank bioreactor experiments, at remarkably higher S0 concentrations (≈110 g/L) and the same initial nitrogen quantity added into the medium, produced notably higher CA quantities, up to 57 g/L (YCA/S ≈ 0.52 g/g). The potential of the same strain (ACA-YC 5033) to bioremediate OMWs and to produce value-added compounds, i.e., yeast cells, CA, and intra-cellular metabolites, was also assessed; under nitrogen-limited conditions in which OMWs had partially replaced tap water and significant glucose concentrations had been added (S0 ≈ 100 g/L, simultaneous molar ratio C/N ≈ 285 g/g, initial phenolic compounds [Phen0] adjusted to ≈1.0 g/L; these media were similar to the OMWs generated from the traditional press extraction systems) the notable CA quantity of 60.2 g/L with simultaneous YCA/S = 0.66 g/g, was obtained in shake flasks, together with satisfactory phenolic compounds removal (up to 19.5% w/w) and waste decolorization (up to 47.0%). Carbon-limited conditions with Phen0 ≈ 1.0 g/L favored the production of yeast DCW (up to 25.3 g/L), with equally simultaneous interesting phenolic compounds and color removal. The fatty acid profile showed that cellular lipids were highly unsaturated with oleic, linoleic and palmitoleic acids, accounting for more than 80% w/w. This study proposed an interesting approach that could efficiently address the biotreatment of toxic effluents and further convert them into circular-oriented bioproducts.

Development and Perspective of Rhodotorula toruloides as an Efficient Cell Factory

Rhodotorula toruloides is receiving significant attention as a novel cell factory because of its high production of lipids and carotenoids, fast growth and high cell density, as well as the ability to utilize a wide variety of substrates. These attractive traits of R. toruloides make it possible to become a low-cost producer that can be engineered for the production of various fuels and chemicals. However, the lack of understanding and genetic engineering tools impedes its metabolic engineering applications. A number of research efforts have been devoted to filling these gaps. This review focuses on recent developments in genetic engineering tools, advances in systems biology for improved understandings, and emerging engineered strains for metabolic engineering applications. Finally, future trends and barriers in developing R. toruloides as a cell factory are also discussed.

Insights into the Genomic and Phenotypic Landscape of the Oleaginous Yeast Yarrowia lipolytica

Although Yarrowia lipolytica is a model yeast for the study of lipid metabolism, its diversity is poorly known, as studies generally consider only a few standard laboratory strains. To extend our knowledge of this biotechnological workhorse, we investigated the genomic and phenotypic diversity of 56 natural isolates. Y. lipolytica is classified into five clades with no correlation between clade membership and geographic or ecological origin. A low genetic diversity (π = 0.0017) and a pan-genome (6528 genes) barely different from the core genome (6315 genes) suggest Y. lipolytica is a recently evolving species. Large segmental duplications were detected, totaling 892 genes. With three new LTR-retrotransposons of the Gypsy family (Tyl4, Tyl9, and Tyl10), the transposable element content of genomes appeared diversified but still low (from 0.36% to 3.62%). We quantified 34 traits with substantial phenotypic diversity, but genome-wide association studies failed to evidence any associations. Instead, we investigated known genes and found four mutational events leading to XPR2 protease inactivation. Regarding lipid metabolism, most high-impact mutations were found in family-belonging genes, such as ALK or LIP, and therefore had a low phenotypic impact, suggesting that the huge diversity of lipid synthesis and accumulation is multifactorial or due to complex regulations.

Phosphate limitation as crucial factor to enhance yeast lipid production from short-chain fatty acids

Microbial lipids for chemical synthesis are commonly obtained from sugar-based substrates which in most cases is not economically viable. As a low-cost carbon source, short-chain fatty acids (SCFAs) that can be obtained from food wastes offer an interesting alternative for achieving an affordable lipid production process. In this study, SCFAs were employed to accumulate lipids using Yarrowia lipolytica ACA DC 50109. For this purpose, different amounts of SCFAs, sulfate, phosphate and carbon: phosphate ratios were used in both synthetic and real SCFAs-rich media. Although sulfate limitation did not increase lipid accumulation, phosphate limitation was proved to be an optimal strategy for increasing lipid content and lipid yields in both synthetic and real media, reaching a lipid productivity up to 8.95 g/L h. Remarkably, the highest lipid yield (0.30 g/g) was achieved under phosphate absence condition (0 g/L). This fact demonstrated the suitability of using low-phosphate concentrations to boost lipid production from SCFAs.

Key role of fluorescence quantum yield in Nile Red staining method for determining intracellular lipids in yeast strains

Background

Microbial lipids are found to be an interesting green alternative to expand available oil sources for the chemical industry. Yeasts are considered a promising platform for sustainable lipid production. Remarkably, some oleaginous yeasts have even shown the ability to grow and accumulate lipids using unusual carbon sources derived from organic wastes, such as volatile fatty acids. Recent research efforts have been focused on developing rapid and accurate fluorometric methods for the quantification of intracellular yeast lipids. Nevertheless, the current methods are often tedious and/or exhibit low reproducibility.

Results

This work evaluated the reliability of different fluorescence measurements (fluorescence intensity, total area and fluorescence quantum yield) using Nile Red as lipid dye in two yeast strains (Yarrowia lipolytica ACA-DC 50109 and Cutaneotrichosporon curvatum NRRL-Y-1511). Different standard curves were obtained for each yeast specie. Fermentation tests were carried with 6-month difference to evaluate the effect of the fluorometer lamp lifetime on lipid quantification.

Conclusions

Fluorescence quantum yield presented the most consistent measurements along time and the closer estimations when compared with lipids obtained by conventional methods (extraction and gravimetrical determination). The need of using fluorescence quantum yield to estimate intracellular lipids, which is not the common trend in studies focused on microbial lipid production, was stressed. The information here provided will surely enable more accurate results comparison.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13068-022-02135-9.

Tailoring and optimizing fatty acid production by oleaginous yeasts through the systematic exploration of their physiological fitness

Background

The use of palm oil for our current needs is unsustainable. Replacing palm oil with oils produced by microbes through the conversion of sustainable feedstocks is a promising alternative. However, there are major technical challenges that must be overcome to enable this transition. Foremost among these challenges is the stark increase in lipid accumulation and production of higher content of specific fatty acids. Therefore, there is a need for more in-depth knowledge and systematic exploration of the oil productivity of the oleaginous yeasts. In this study, we cultivated Cutaneotrichosporon oleaginosus and Yarrowia lipolytica at various C/N ratios and temperatures in a defined medium with glycerol as carbon source and urea as nitrogen source. We ascertained the synergistic effect between various C/N ratios of a defined medium at different temperatures with Response Surface Methodology (RSM) and explored the variation in fatty acid composition through Principal Component Analysis.

Results

By applying RSM, we determined a temperature of 30 °C and a C/N ratio of 175 g/g to enable maximal oil production by C. oleaginosus and a temperature of 21 °C and a C/N ratio of 140 g/g for Y. lipolytica. We increased production by 71% and 66% respectively for each yeast compared to the average lipid accumulation in all tested conditions. Modulating temperature enabled us to steer the fatty acid compositions. Accordingly, switching from higher temperature to lower cultivation temperature shifted the production of oils from more saturated to unsaturated by 14% in C. oleaginosus and 31% in Y. lipolytica. Higher cultivation temperatures resulted in production of even longer saturated fatty acids, 3% in C. oleaginosus and 1.5% in Y. lipolytica.

Conclusions

In this study, we provided the optimum C/N ratio and temperature for C. oleaginosus and Y. lipolytica by RSM. Additionally, we demonstrated that lipid accumulation of both oleaginous yeasts was significantly affected by the C/N ratio and temperature. Furthermore, we systematically analyzed the variation in fatty acids composition and proved that changing the C/N ratio and temperature steer the composition. We have further established these oleaginous yeasts as platforms for production of tailored fatty acids.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-022-01956-5.

Oleaginous yeasts: Time to rethink the definition?

Oleaginous yeasts are typically defined as those able to accumulate more than 20% of their cell dry weight as lipids or triacylglycerides. Research on these yeasts has increased lately fuelled by an interest to use biotechnology to produce lipids and oleochemicals that can substitute those coming from fossil fuels or offer sustainable alternatives to traditional extractions (e.g., palm oil). Some oleaginous yeasts are attracting attention both in research and industry, with Yarrowia lipolytica one of the best-known and studied ones. Oleaginous yeasts can be found across several clades and different metabolic adaptations have been found, affecting not only fatty acid and neutral lipid synthesis, but also lipid particle stability and degradation. Recently, many novel oleaginous yeasts are being discovered, including oleaginous strains of the traditionally considered non-oleaginous Saccharomyces cerevisiae. In the face of this boom, a closer analysis of the definition of "oleaginous yeast" reveals that this term has instrumental value for biotechnology, while it does not give information about distinct types of yeasts. Having this perspective in mind, we propose to expand the term "oleaginous yeast" to those able to produce either intracellular or extracellular lipids, not limited to triacylglycerides, in at least one growth condition (including ex novo lipid synthesis). Finally, a critical look at Y. lipolytica as a model for oleaginous yeasts shows that the term "oleaginous" should be reserved only for strains and not species and that in the case of Y. lipolytica, it is necessary to distinguish clearly between the lipophilic and oleaginous phenotype.

Valorization of Low-Cost Substrates for the Production of Odd Chain Fatty Acids by the Oleaginous Yeast Yarrowia lipolytica

Odd-chain fatty acids (OCFAs) have recently gained interest as target compounds in microbial production due to their diverse applications in the medical, pharmaceutical and chemical industries for the production of biofuels. Yarrowia lipolytica is a promising oleaginous yeast that has the ability to accumulate high quantities of fatty acids. However, the use of Y. lipolytica oils is still under research, in order to decrease the production costs related to the fermentation process and improve economic feasibility. In this work, sugar beet molasses (10–50 g/L) and crude glycerol (30 g/L) were used as the main carbon sources to reduce the processing costs of oil production from a genetically engineered Y. lipolytica strain. The effects of medium composition were studied on biomass production, lipid content, and OCFAs profile. Lipid production by yeast growing on molasses (20 g/L sucrose) and crude glycerol reached 4.63 ± 0.95 g/L of culture medium. OCFAs content represented 58% of the total fatty acids in lipids, which corresponds to ≈2.69 ± 0.03 g/L of culture medium. The fermentation was upscaled to 5 L bioreactors and fed-batch co-feeding increased OCFA accumulation in Y. lipolytica by 56% compared to batch cultures.

Production of human milk fat substitute by engineered strains of Yarrowia lipolytica

Human milk fat has a distinctive stereoisomeric structure where palmitic acid is esterified to the middle (sn-2) position on the glycerol backbone of the triacylglycerol and unsaturated fatty acids to the outer (sn-1/3) positions. This configuration allows for more efficient nutrient absorption in the infant gut. However, the fat used in most infant formulas originates from plants, which exclude palmitic acid from the sn-2 position. Oleaginous yeasts provide an alternative source of lipids for human nutrition. However, these yeasts also exclude palmitic acid from the sn-2 position of their triacylglycerol. Here we show that Yarrowia lipolytica can be engineered to produce triacylglycerol with more than 60% of the palmitic acid in the sn-2 position, by expression of lysophosphatidic acid acyltransferases with palmitoyl-Coenzyme A specificity. The engineered Y. lipolytica strains can be cultured on glycerol, glucose, palm oil or a mixture of substrates, under nitrogen limited condition, to produce triacylglycerol with a fatty acid composition that resembles human milk fat, in terms of the major molecular species (palmitic, oleic and linoleic acids). Culture on palm oil or a mixture of glucose and palm oil produced the highest lipid titre and a triacylglycerol composition that is most similar with human milk fat. Our data show that an oleaginous yeast can be engineered to produce a human milk fat substitute (β-palmitate), that could be used as an ingredient in infant formulas.

Evaluation of the Potential of Lipid-Extracted Chlorella vulgaris Residue for Yarrowia lipolytica Growth at Different pH Levels

Projections show that the cultivation of microalgae will extend to the production of bio-based compounds, such as biofuels, cosmetics, and medicines. This will generate co-products or residues that will need to be valorized to reduce the environmental impact and the cost of the process. This study explored the ability of lipid-extracted Chlorella vulgaris residue as a sole carbon and nitrogen source for growing oleaginous yeasts without any pretreatment. Both wild-type Yarrowia lipolytica W29 and mutant JMY3501 (which was designed to accumulate more lipids without their remobilization or degradation) showed a similar growth rate of 0.28 h⁻¹ at different pH levels (3.5, 5.5, and 7.5). However, the W29 cell growth had the best cell number on microalgal residue at a pH of 7.5, while three times fewer cells were produced at all pH levels when JMY3501 was grown on microalgal residue. The JMY3501 growth curves were similar at pH 3.5, 5.5, and 7.5, while the fatty-acid composition differed significantly, with an accumulation of α-linolenic acid on microalgal residue at a pH of 7.5. Our results demonstrate the potential valorization of Chlorella vulgaris residue for Yarrowia lipolytica growth and the positive effect of a pH of 7.5 on the fatty acid profile.

Production of single cell oil by Yarrowia lipolytica JCM 2320 using detoxified desiccated coconut residue hydrolysate

Nowadays, the replacement of petro-diesel with biodiesel has raised the concern among the community for the utilization of improper feedstocks and the cost involved. However, these issues can be solved by producing single cell oil (SCO) from lignocellulosic biomass hydrolysates by oleaginous microorganisms. This study introduced Yarrowia lipolytica JCM 2320 with a desiccated coconut residue (DCR) hydrolysate (obtained from the 2% dilute sulphuric acid pretreatment) as a carbon source in generating SCO. However, common inhibitors formed during acid pretreatment of biomass such as five-hydroxymethylfurfural (HMF), furfural, acetic acid and levulinic acid resulting from the sugar degradations may have detrimental effects towards the fermentation process. To visualize the effect of inhibitors on Y. lipolytica, an inhibitory study was conducted by adding 0.5-5.0 g/L of potential inhibitors to the YPD (yeast, peptone and D-glucose) medium. It was found that the presence of furfural at 0.5 g/L would increase the lag phase, which beyond that was detrimental to Y. lipolytica. Furthermore, increasing the five-hydroxymethylfurfural (HMF) concentration would increase the lag phase of Y. lipolytica, whereas, for acetic acid and levulinic acid, it showed a negligible effect. Detoxification was hence conducted to remove the potential inhibitors from the DCR hydrolysate prior its utilization in the fermentation. To examine the possibility of using adsorption resins for the detoxification of DCR hydrolysate, five different resins were tested (Amberlite® XAD-4, Amberlite® XAD-7, Amberlite® IR 120, Amberlite® IRA 96 and Amberlite® IRA 402) with five different concentrations of 1%, 3%, 5%, 10% and 15% (w/v), respectively. At resin concentration of 10%, Amberlite® XAD-4 recorded the highest SCO yield, 2.90 ± 0.02 g/L, whereas the control and the conventional overliming detoxification method, recorded only 1.29 ± 0.01 g/L and 1.27 ± 0.02 g/L SCO accumulation, respectively. Moreover, the fatty acid profile of the oil produced was rich in oleic acid (33.60%), linoleic acid (9.90%), and palmitic acid (14.90%), which indicates the potential as a good biodiesel raw material.

Recent advances in biotechnological production of polyunsaturated fatty acids by Yarrowia lipolytica

Owing to the important physiological functions, polyunsaturated fatty acids (PUFAs) play a vital role in protecting human health, such as preventing cancer, cardiovascular disease, and diabetes. Specifically, Yarrowia lipolytica has been identified as the most popular non-conventional oleaginous yeast, which can accumulate the abundant intracellular lipids, indicating that has great potential as an industrial host for production of PUFAs. Notably, some novel engineering strategies have been applied to endow and improve the abilities of Y. lipolytica to synthesize PUFAs, including construction and optimization of PUFAs biosynthetic pathways, improvement of preucrsors acetyl-coA and NADPH supply, inhibition of competing pathways, knockout of β-oxidation pathways, regulation of oxidative stress defense pathways, and regulation of genes involved in upstream lipid metabolism. Besides, some bypass approaches, such as strain mating, evolutionary engineering, and computational model based on omics, also have been proposed to improve the performance of engineering strains. Generally, in this review, we summarized the recent advances in engineering strategies and bypass approaches for improving PUFAs production by Y. lipolytica. In addition, we further summarized the latest efforts of CRISPR/Cas genome editing technology in Y. lipolytica, which is aimed to provide its potential applications in PUFAs production.

Oleaginous Yeasts as Cell Factories for the Sustainable Production of Microbial Lipids by the Valorization of Agri-Food Wastes

The agri-food industry annually produces huge amounts of crops residues and wastes, the suitable management of these products is important to increase the sustainability of agro-industrial production by optimizing the entire value chain. This is also in line with the driving principles of the circular economy, according to which residues can become feedstocks for novel processes. Oleaginous yeasts represent a versatile tool to produce biobased chemicals and intermediates. They are flexible microbial factories able to grow on different side-stream carbon sources such as those deriving from agri-food wastes, and this characteristic makes them excellent candidates for integrated biorefinery processes through the production of microbial lipids, known as single cell oils (SCOs), for different applications. This review aims to present an extensive overview of research progress on the production and use of oleaginous yeasts and present discussions on the current bottlenecks and perspectives of their exploitation in different sectors, such as foods, biofuels and fine chemicals.

Single Cell Oil Production by Oleaginous Yeasts Grown in Synthetic and Waste-Derived Volatile Fatty Acids

Four yeast isolates from the species—Apiotrichum brassicae, Candida tropicalis, Metschnikowia pulcherrima, and Pichia kudriavzevii—previously selected by their oleaginous character and growth flexibility in different carbon sources, were tested for their capacity to convert volatile fatty acids into lipids, in the form of single cell oils. Growth, lipid yields, volatile fatty acids consumption, and long-chain fatty acid profiles were evaluated in media supplemented with seven different volatile fatty acids (acetic, butyric, propionic, isobutyric, valeric, isovaleric, and caproic), and also in a dark fermentation effluent filtrate. Yeasts A. brassicae and P. kudriavzevii attained lipid productivities of more than 40% (w/w), mainly composed of oleic (>40%), palmitic (20%), and stearic (20%) acids, both in synthetic media and in the waste-derived effluent filtrate. These isolates may be potential candidates for single cell oil production in larger scale applications by using alternative carbon sources, combining economic and environmental benefits.