Synergistic effect of fermentable and non-fermentable carbon sources enhances TAG accumulation in oleaginous yeast Rhodosporidium kratochvilovae HIMPA1

Green extraction of carotenoids and oil produced by Rhodosporidium paludigenum using supercritical CO2 extraction: Evaluation of cell disruption methods and extraction kinetics

The constantly expanding functional food market has steered scientific research towards alternative sources of bioactive compounds. Red yeasts are valuable producers of active ingredients such as carotenoids and microbial oil. Efficient and sustainable recovery methods are required when food applications are targeted. In this study, intracellular carotenoids and oil synthesized by Rhodosporidium paludigenum in batch bioreactor cultures were recovered using supercritical CO2 (SFE-CO2) as a green alternative to conventional organic solvents. Yeast biomass was subjected to six different cell disruption methods prior to SFE-CO2. Homogenization emerged as the optimal pre-treatment method, resulting in an 80 % yield of total carotenoids and an 83 % yield of microbial oil. The use of ethanol as co-solvent was imperative for the efficient recovery of both products. β-Carotene was the main carotenoid, while the obtained microbial oil was rich in oleic acid. These results pave the way for integrating these functional compounds into innovative food products.

Efficient sugar utilization and high tolerance to inhibitors enable Rhodotorula toruloides C23 to robustly produce lipid and carotenoid from lignocellulosic feedstock

The utilization of lignocellulosic substrates for microbial oil production by oleaginous yeasts has been evidenced as an economically viable process for industrial-scale biodiesel preparation. Efficient sugar utilization and tolerance to inhibitors are critical for lipid production from lignocellulosic substrates. This study investigated the lignocellulosic sugar utilization and inhibitor tolerance characteristics of Rhodotorula toruloides C23. The results demonstrated that C23 exhibited robust glucose and xylose assimilation irrespective of their ratios, yielding over 21 g/L of lipids and 11 mg/L of carotenoids. Furthermore, C23 exhibited high resistance and efficiently degradation towards toxic inhibitors commonly found in lignocellulosic hydrolysates. The potential molecular mechanism underlying xylose metabolism in C23 was explored, with several key enzymes and signal regulation pathways identified as potentially contributing to its superior lipid synthesis performance. The study highlights R. toruloides C23 as a promising candidate for robust biofuel and carotenoid production through direct utilization of non-detoxified lignocellulosic hydrolysates.

Carotenoids production by Rhodosporidium paludigenum yeasts: Characterization of chemical composition, antioxidant and antimicrobial properties

The high market potential imposed by natural carotenoids has turned the scientific interest in search for new strains, capable of synthesizing a wide spectrum of these pigments. In this study, Rhodosporidium paludigenum NCYC 2663 and 2664 were investigated for carotenoids production and lipid accumulation utilizing different carbon sources (glucose, fructose, sucrose, mixture of glucose: galactose). Strain R. paludigenum 2663 produced the highest total carotenoids titer (2.21 mg/L) when cultivated on sucrose, together with 4 g/L lipids (30% w/w content) and 7 g/L exopolysaccharides. In the case of R. paludigenum 2664, glucose favored the production of 2.93 mg/L total carotenoids and 1.57 g/L lipids (31.8% w/w content). Analysis of the chemical profile during fermentation revealed that β-carotene was the prominent carotenoid. Strain 2663 co-produced γ-carotene, torulene and torularhodin in lower amounts, whereas 2664 synthesized almost exclusively β-carotene. The produced lipids from strain 2663 were rich in oleic acid, while the presence of linoleic acid was also detected in the lipoic fraction from strain 2664. The obtained carotenoid extracts exhibited antioxidant (IC50 0.14 mg/mL) and high antimicrobial activity, against common bacterial and fungal pathogenic strains. The results of this study are promising for the utilization of biotechnologically produced carotenoids in food applications.

Toward rapid and efficient utilization of nonconventional substrates by nonconventional yeast strains

Economic and sustainable production of biofuels and chemicals necessitates utilizing abundant and inexpensive lignocellulosic biomass. Yet, Saccharomyces cerevisiae, a workhorse strain for industrial biotechnology based on starch and sugarcane-derived sugars, is not suitable for lignocellulosic bioconversion due to a lack of pentose metabolic pathways and severe inhibition by toxic inhibitors in cellulosic hydrolysates. This review underscores the potential of nonconventional yeast strains, specifically Yarrowia lipolytica and Rhodotorula toruloides, for converting underutilized carbon sources, such as xylose and acetate, into high-value products. Multi-omics studies with nonconventional yeast have elucidated the structure and regulation of metabolic pathways for efficient and rapid utilization of xylose and acetate. The review delves into the advantages of using xylose and acetate for producing biofuels and chemicals. Collectively, value-added biotransformation of nonconventional substrates by nonconventional yeast strains is a promising strategy to improve both economics and sustainability of bioproduction.

Current advances in alteration of fatty acid profile in Rhodotorula toruloides: a mini-review

Microbial lipids are considered promising and environmentally friendly substitutes for fossil fuels and plant-derived oils. They alleviate the depletion of limited petroleum storage and the decrement of arable lands resulting from the greenhouse effect. Microbial lipids derived from oleaginous yeasts provide fatty acid profiles similar to plant-derived oils, which are considered as sustainable and alternative feedstocks for use in the biofuel, cosmetics, and food industries. Rhodotorula toruloides is an intriguing oleaginous yeast strain that can accumulate more than 70% of its dry biomass as lipid content. It can utilize a wide range of substrates, including low-cost sugars and industrial waste. It is also robust against various industrial inhibitors. However, precise control of the fatty acid profile of the lipids produced by R. toruloides is essential for broadening its biotechnological applications. This mini-review describes recent progress in identifying fatty synthesis pathways and consolidated strategies used for specific fatty acid-rich lipid production via metabolic engineering, strain domestication. In addition, this mini-review summarized the effects of culture conditions on fatty acid profiles in R. toruloides. The perspectives and constraints of harnessing R. toruloides for tailored lipid production are also discussed in this mini-review.

Enhancement production of lipid and unsaturation of fatty acids in Cryptococcus humicola via addition of calcium ion

Lipids synthesized by oleaginous yeasts are considered to be the best candidates for biodiesel production. Cryptococcus humicola as an oleaginous yeast accumulated lipid in cells. In order to optimize the conditions for lipid production, different carbon and nitrogen sources were used and metals were added into the medium. Ca²⁺ addition increased the lipid production greatly. Xylose and peptone were optimal carbon source and nitrogen source, respectively for lipid accumulation. Response surface experiment results revealed that the accumulation of lipid could be maximized when the xylose, peptone and Ca²⁺ concentration was 61 g/L, 4.31 g/L, 0.67 mmol/L. C16 and C18 fatty acid account for about 91% of the total fatty acids. The most abundant fatty acid was oleic acid (42.68%), followed by palmitic acid (29.7%) and stearic acid (13.87%). The addition of Ca²⁺ increased the content of unsaturated fatty acids (such as C16:1 and C18:1) and improved the unsaturation of fatty acids. Quantitative real time PCR analysis revealed that expression of genes related to lipid biosynthesis showed up-regulated by Ca²⁺ treatment. This study provided a strategy for increase in lipid production and content of unsaturated fatty acids.

Single-Cell Oils from Oleaginous Microorganisms as Green Bio-Lubricants: Studies on Their Tribological Performance

Biolubricants refer to eco-friendly, biodegradable, and non-toxic lubricants. Their applications are still limited compared to mineral oils; however, their sustainable credentials are making them increasingly attractive. Vegetable oils are frequently used for this purpose. However, vegetable oils have issues of low lipid productivity, dependence on climatic conditions, and need for agricultural land. Microbial oils represent a more sustainable alternative. To ensure their widespread applicability, the suitability of microbial oils from a physicochemical point of view needs to be determined first. In this study, oils obtained from various oleagenic microbes—such as microalgae, thraustochytrids, and yeasts—were characterized in terms of their fatty acid profile, viscosity, friction coefficient, wear, and thermal stability. Oleaginous microalgal strains (Auxenochlorella protothecoides and Chlorella sorokiniana), thraustochytrids strains (Aurantiochytrium limacinum SR21 and Aurantiochytrium sp. T66), and yeast strains (Rhodosporidium toruloides and Cryptococcus curvatus) synthesized 64.5%, 35.15%, 47.89%, 47.93%, 56.42%, and 52.66% of lipid content, respectively. Oils from oleaginous microalgae (A. protothecoides and C. sorokiniana) and yeasts (R. toruloides and C. curvatus) possess excellent physicochemical and tribological qualities due to high amount of monounsaturated fatty acids (oleic acid C18:1 content, 56.38%, 58.82%, 46.67%, 38.81%) than those from oleaginous thraustochytrids (A. limacinum SR21 and Aurantiochytrium sp. T66; 0.96%, 0.08%, respectively) supporting their use as renewable and biodegradable alternatives to traditional mineral oil-based lubricants. Oil obtained from microalgae showed a lower friction coefficient than oils obtained from yeasts and thraustochytrids.

Biodiesel Production From Lignocellulosic Biomass Using Oleaginous Microbes: Prospects for Integrated Biofuel Production

Biodiesel is an eco-friendly, renewable, and potential liquid biofuel mitigating greenhouse gas emissions. Biodiesel has been produced initially from vegetable oils, non-edible oils, and waste oils. However, these feedstocks have several disadvantages such as requirement of land and labor and remain expensive. Similarly, in reference to waste oils, the feedstock content is succinct in supply and unable to meet the demand. Recent studies demonstrated utilization of lignocellulosic substrates for biodiesel production using oleaginous microorganisms. These microbes accumulate higher lipid content under stress conditions, whose lipid composition is similar to vegetable oils. In this paper, feedstocks used for biodiesel production such as vegetable oils, non-edible oils, oleaginous microalgae, fungi, yeast, and bacteria have been illustrated. Thereafter, steps enumerated in biodiesel production from lignocellulosic substrates through pretreatment, saccharification and oleaginous microbe-mediated fermentation, lipid extraction, transesterification, and purification of biodiesel are discussed. Besides, the importance of metabolic engineering in ensuring biofuels and biorefinery and a brief note on integration of liquid biofuels have been included that have significant importance in terms of circular economy aspects.

Rhodosporidium sp. DR37: a novel strain for production of squalene in optimized cultivation conditions

BACKGROUND

Rhodosporidium strain, a well-known oleaginous yeast, has been widely used as a platform for lipid and carotenoid production. However, the production of squalene for application in lipid-based biofuels is not reported in this strain. Here, a new strain of Rhodosporidium sp. was isolated and identified, and its potential was investigated for production of squalene under various cultivation conditions.

RESULTS

In the present study, Rhodosporidium sp. DR37 was isolated from mangrove ecosystem and its potential for squalene production was assessed. When Rhodosporidium sp. DR37 was cultivated on modified YEPD medium (20 g/L glucose, 5 g/L peptone, 5 g/L YE, seawater (50% v/v), pH 7, 30 °C), 64 mg/L of squalene was produced. Also, squalene content was obtained as 13.9% of total lipid. Significantly, use of optimized medium (20 g/L sucrose, 5 g/L peptone, seawater (20% v/v), pH 7, 25 °C) allowed highest squalene accumulation (619 mg/L) and content (21.6% of total lipid) in Rhodosporidium sp. DR37. Moreover, kinetic parameters including maximum specific cell growth rate (μ_max, h^-1), specific lipid accumulation rate (q_p, h^-1), specific squalene accumulation rate (q_sq, h^-1) and specific sucrose consumption rate (q_s, h^-1) were determined in optimized medium as 0.092, 0.226, 0.036 and 0.010, respectively.

CONCLUSIONS

This study is the first report to employ marine oleaginous Rhodosporidium sp. DR37 for accumulation of squalene in optimized medium. These findings provide the potential of Rhodosporidium sp. DR37 for production of squalene as well as lipid and carotenoids for biofuel applications in large scale.

Nile Red Incubation Time Before Reading Fluorescence Greatly Influences the Yeast Neutral Lipids Quantification

High-throughput screening methodologies to estimate lipid content in oleaginous yeasts use Nile red fluorescence in a given solvent and optimized excitation/emission wavelengths. However, Nile red fluorescence stabilization has been poorly analyzed, and high variability occurs when relative fluorescence is measured immediately or a few minutes after dye addition. The aim of this work was to analyze the fluorescence of Nile red at different incubation times using a variety of solvents and oleaginous/non-oleaginous yeast strains. We showed that fluorescence stabilization occurs between 20 and 30 min, depending on the strain and solvent. Therefore, we suggest that fluorescence measurements should be followed until stabilization, where Relative Fluorescence Units should be considered after stabilization for lipid content estimation.

Valorization of volatile fatty acids derived from low-cost organic waste for lipogenesis in oleaginous microorganisms-A review

To meet environmental sustainability goals, microbial oils have been suggested as an alternative to petroleum-based products. At present, microbial fermentation for oil production relies on pure sugar-based feedstocks. However, these feedstocks are expensive and are in limited supply. Volatile fatty acids, which are generated as intermediates during anaerobic digestion of organic waste have emerged as a renewable feedstock that has the potential to replace conventional sugar sources for microbial oil production. They comprise short-chain (C2 to C6) organic acids and are employed as building blocks in the chemical industry. The present review discusses the use of oleaginous microorganisms for the production of biofuels and added-value products starting from volatile fatty acids as feedstocks. The review describes the metabolic pathways enabling lipogenesis from volatile fatty acids, and focuses on strategies to enhance lipid accumulation in oleaginous microorganisms by tuning the ratios of volatile fatty acids generated via anaerobic fermentation.

Lignocellulosic Biomass as a Substrate for Oleaginous Microorganisms: A Review

Microorganisms capable of accumulating lipids in high percentages, known as oleaginous microorganisms, have been widely studied as an alternative for producing oleochemicals and biofuels. Microbial lipid, so-called Single Cell Oil (SCO), production depends on several growth parameters, including the nature of the carbon substrate, which must be efficiently taken up and converted into storage lipid. On the other hand, substrates considered for large scale applications must be abundant and of low acquisition cost. Among others, lignocellulosic biomass is a promising renewable substrate containing high percentages of assimilable sugars (hexoses and pentoses). However, it is also highly recalcitrant, and therefore it requires specific pretreatments in order to release its assimilable components. The main drawback of lignocellulose pretreatment is the generation of several by-products that can inhibit the microbial metabolism. In this review, we discuss the main aspects related to the cultivation of oleaginous microorganisms using lignocellulosic biomass as substrate, hoping to contribute to the development of a sustainable process for SCO production in the near future.

Modeling and optimization of microbial lipid fermentation from cellulosic ethanol wastewater by Rhodotorula glutinis based on the support vector machine

To establish the models of microbial lipid production from cellulosic ethanol wastewater by R. glutinis, the biomass, lipid yield, and COD removal rate were investigated under different conditions. Subsequently, the genetic algorithm based on SVM was adopted to optimize parameters for obtaining the maximum biomass. The results demonstrated that the initial COD and glucose content had a significant effect on lipids synthesis. Most of the organic matter in the wastewater was consumed with the production of lipid. Compared with BP-ANN, SVM had better fitting and generalization ability for small amount of experimental data. By genetic algorithm optimization based on SVM, the maximum biomass and lipid yield could reach 11.87 g/L and 2.18 g/L, respectively. The results suggest that the SVM model could be used as an effective tool to optimize fermentation conditions.

An Overview of Potential Oleaginous Microorganisms and Their Role in Biodiesel and Omega-3 Fatty Acid-Based Industries

Microorganisms are known to be natural oil producers in their cellular compartments. Microorganisms that accumulate more than 20% w/w of lipids on a cell dry weight basis are considered as oleaginous microorganisms. These are capable of synthesizing vast majority of fatty acids from short hydrocarbonated chain (C6) to long hydrocarbonated chain (C36), which may be saturated (SFA), monounsaturated (MUFA), or polyunsaturated fatty acids (PUFA), depending on the presence and number of double bonds in hydrocarbonated chains. Depending on the fatty acid profile, the oils obtained from oleaginous microorganisms are utilized as feedstock for either biodiesel production or as nutraceuticals. Mainly microalgae, bacteria, and yeasts are involved in the production of biodiesel, whereas thraustochytrids, fungi, and some of the microalgae are well known to be producers of very long-chain PUFA (omega-3 fatty acids). In this review article, the type of oleaginous microorganisms and their expertise in the field of biodiesel or omega-3 fatty acids, advances in metabolic engineering tools for enhanced lipid accumulation, upstream and downstream processing of lipids, including purification of biodiesel and concentration of omega-3 fatty acids are reviewed.

Manipulation of Culture Conditions: Tool for Correlating/Improving Lipid and Carotenoid Production by Rhodotorula glutinis

The coproduction of lipid and carotenoid by red yeasts in one cycle is more convenient and economical for the industrial sectors, while the kinetics correlation between both products under different culture conditions has been scarcely studied. This study is aiming to correlate the impact of different carbon sources, carbon to phosphorus ratio (C/P), temperature, aeration, pH, and metals on dry cell weight, lipid (GC and fluorescence microscope), and carotenoid (HPLC) production by Rhodotorula glutinis, and applying a novel feeding approach using a 5 L bioreactor to enhance carotenoid and unsaturated fatty acid production by R. glutinis. Whatever the culture condition is, the reversible correlation between lipid and carotenoid production was detected. Remarkably, when adding 0.1 mM BaCl2, cellular lipid was significantly increased 14% more than the control, with 79.3% unsaturated fatty acid (46% C18:2 and C18:3) and 50% γ-carotene, while adding 1 mM NiSO4, cellular carotenoid was enhanced around 53% than the control (torulene 88%) with 81% unsaturated fatty acid (61% oleic acid). Excitingly, 68.8 g/l biomass with 41% cellular lipid (79% unsaturated fatty acid) and 426 µgpigment/gdcw cellular carotenoid (29.3 mg/L) (71% torulene) were obtained, when the pH-temperature dual controlled process combined with metallo-sulfo-phospho-glucose feeding approach in the 5 L bioreactor during the accumulation phase was conducted. This is the first study on the kinetic correlation between lipid and carotenoid under different C/P ratio and the dual effect of different metals like NiSO4 on lipid and carotenoid production by red oleaginous yeasts, which in turn significant for enhancing the coproduction of lipid and carotenoid by R. glutinis.

Transcriptome analysis of the dimorphic transition induced by pH change and lipid biosynthesis in Trichosporon cutaneum

Trichosporon cutaneum, a dimorphic oleaginous yeast, has immense biotechnological potential, which can use lignocellulose hydrolysates to accumulate lipids. Our preliminary studies on its dimorphic transition suggested that pH can significantly induce its morphogenesis. However, researches on dimorphic transition correlating with lipid biosynthesis in oleaginous yeasts are still limited. In this study, the unicellular yeast cells induced under pH 6.0-7.0 shake flask cultures resulted in 54.32% lipid content and 21.75 g/L dry cell weight (DCW), so lipid production was over threefold than that in hypha cells induced by acidic condition (pH 3.0-4.0). Furthermore, in bioreactor batch cultivation, the DCW and lipid content in unicellular yeast cells can reach 21.94 g/L and 58.72%, respectively, both of which were also more than twofold than that in hypha cells. Moreover, the activities of isocitrate dehydrogenase (IDH), malic enzyme (MAE), isocitrate lyase (ICL) and ATP citrate lyase (ACL) in unicellular cells were all higher than in the hyphal cells. In the meanwhile, the transcriptome data showed that the genes related to fatty acid biosynthesis, carbon metabolism and encoded Rim101 and cAMP-PKA signaling transduction pathways were significantly up-regulated in unicellular cells, which may play an important role in enhancing the lipid accumulation. In conclusion, our results provided insightful information focused on the molecular mechanism of dimorphic transition and process optimization for enhancing lipid accumulation in T. cutaneum.

Comparative evaluation of different carbon sources supply on simultaneous production of lipid and carotene of Rhodotorula glutinis with irradiation and the assessment of key gene transcription

To investigate the feasibility of simultaneously enhancing lipid and carotene production by irradiation with different carbon sources, a strategy by controlling the carbon sources supply were selected to culture Rhodotorula glutinis under the irradiation condition. The results demonstrated that the irradiation indeed enhanced cell growth, lipid and carotene production with different carbon sources supply. Besides, the fatty acids profiling as revealed by more unsaturated fatty acids (mainly C16:1, C18:2 and C18:3) and less saturated fatty acids (C18:0, C22:0 and C24:0) were found during the process of irradiation. Compared with the control, the increase of the transcription levels in genes connected with substrates assimilation, lipid production and carotene accumulation were observed under the irradiation condition. The results suggest the possibility of using irradiation as an effective strategy to increase the production of both lipid and carotene with the controlled carbon sources supply.

Development of a Circular Oriented Bioprocess for Microbial Oil Production Using Diversified Mixed Confectionery Side-Streams

Diversified mixed confectionery waste streams were utilized in a two-stage bioprocess to formulate a nutrient-rich fermentation media for microbial oil production. Solid-state fermentation was conducted for the production of crude enzyme consortia to be subsequently applied in hydrolytic reactions to break down starch, disaccharides, and proteins into monosaccharides, amino acids, and peptides. Crude hydrolysates were evaluated in bioconversion processes using the red yeast Rhodosporidium toruloides DSM 4444 both in batch and fed-batch mode. Under nitrogen-limiting conditions, during fed-batch cultures, the concentration of microbial lipids reached 16.6-17 g·L-1 with the intracellular content being more than 40% (w/w) in both hydrolysates applied. R. toruloides was able to metabolize mixed carbon sources without catabolite repression. The fatty acid profile of the produced lipids was altered based on the substrate employed in the bioconversion process. Microbial lipids were rich in polyunsaturated fatty acids, with oleic acid being the major fatty acid (61.7%, w/w). This study showed that mixed food side-streams could be valorized for the production of microbial oil with high unsaturation degree, pointing towards the potential to produce tailor-made lipids for specific food applications. Likewise, the proposed process conforms unequivocally to the principles of the circular economy, as the entire quantity of confectionery by-products are implemented to generate added-value compounds that will find applications in the same original industry, thus closing the loop.

Utilization of Clarified Butter Sediment Waste as a Feedstock for Cost-Effective Production of Biodiesel

The rising demand and cost of fossil fuels (diesel and gasoline), together with the need for sustainable, alternative, and renewable energy sources have increased the interest for biomass-based fuels such as biodiesel. Among renewable sources of biofuels, biodiesel is particularly attractive as it can be used in conventional diesel engines without any modification. Oleaginous yeasts are excellent oil producers that can grow easily on various types of hydrophilic and hydrophobic waste streams that are used as feedstock for single cell oils and subsequently biodiesel production. In this study, cultivation of Rhodosporidium kratochvilovae on a hydrophobic waste (clarified butter sediment waste medium (CBM)) resulted in considerably high lipid accumulation (70.74% w/w). Maximum cell dry weight and total lipid production were 15.52 g/L and 10.98 g/L, respectively, following cultivation in CBM for 144 h. Neutral lipids were found to accumulate in the lipid bodies of cells, as visualized by BODIPY staining and fluorescence microscopy. Cells grown in CBM showed large and dispersed lipid droplets in the intracellular compartment. The fatty acid profile of biodiesel obtained after transesterification was analyzed by gas chromatography-mass spectrometry (GC–MS), while its quality was determined to comply with ASTM 6751 and EN 14214 international standards. Hence, clarified sediment waste can be exploited as a cost-effective renewable feedstock for biodiesel production.

A comparative study on de novo and ex novo lipid fermentation by oleaginous yeast using glucose and sonicated waste cooking oil

There are only a few reports available about the assimilation of hydrophobic substrates by microorganisms, however, it is well known that oleaginous microorganisms are capable of utilizing both hydrophilic and hydrophobic substrates and accumulate lipids via two different pathways namely de novo and ex novo lipid synthesis, respectively. In the present study, an oleaginous yeast, Cryptococcus curvatus, was investigated for its potentials to utilize a waste substrate of hydrophobic nature (waste cooking oil - WCO) and compared with its ability to utilize a hydrophilic carbon source (glucose). To facilitate the utilization of WCO by C. curvatus, the broth was sonicated to form a stable oil-in-water emulsion without adding any emulsifier, which was then compared with WCO samples without any ultrasound treatment (unsonicated) for the yeast cultivation. Ultrasonication reduces the size of hydrophobic substrates and improves their miscibility in an aqueous broth making them easily assimilated by oleaginous yeast. Under de novo lipid fermentation, the yeast synthesized 9.93 ± 0.84 g/L of cell dry weight and 5.23 ± 0.49 g/L lipids (lipid content of 52.66 ± 0.93% w/w) when cultivated on 40 g/L of glucose (C/N ratio of 40). The amount of cell dry weight, lipid concentration, and lipid content were considerably higher during the ex novo lipid synthesis. More specifically, the highest lipid content achieved was 70.13 ± 1.65% w/w with a corresponding dry cell weight and lipid concentration of 18.62 ± 0.76 g/L and 13.06 ± 0.92 g/L respectively, when grown on 20 g/L sonicated WCO. The highest lipid concentration, however, was observed when the yeast was cultivated on 40 g/L sonicated WCO. Under these conditions, 20.34 g/L lipids were produced with a lipid content of 57.05% w/w. On the other hand, lipid production with unsonicated WCO was significant lower, reaching 11.16 ± 1.02 g/L (69.14 ± 1.34% w/w of lipid content) and 12.21 ± 1.34 g/L (47.39 ± 1.67% w/w of lipid content) for 20 g/L and 40 g/L of WCO, respectively. This underpins the significance of the sonication treatment, especially at elevated WCO concentrations, to improve the accessibility of the yeast to the WCO. Sonication treatment that was used in this study assisted the utilization of WCO without the need to add emulsifiers, thus reducing the need for chemicals and in turn has a positive impact on the production costs. The microbial lipids produced presented a different fatty acid composition compared to the WCO, making them more suitable for biodiesel production as suggested by the theoretical estimation of the biodiesel properties.

A novel rapid ultrasonication-microwave treatment for total lipid extraction from wet oleaginous yeast biomass for sustainable biodiesel production

Oleaginous yeasts have emerged as a sustainable source of renewable oils for liquid biofuels. However, biodiesel production from them has a few constraints with respect to their cell disruption and lipid extraction techniques. The lipid extraction from oleaginous yeasts commonly includes dewatering and drying of cell biomass, which requires energy and time. The aim of this work was to establish a process for the lipid extraction from wet biomass applying acid catalyzed hot water, as well as microwave, and rapid ultrasonication-microwave treatment together with the conventional Bligh and Dyer method. In the wake of testing all procedures, it was revealed that rapid ultrasonication-microwave treatment has great potential to give high lipid content (70.86% w/w) on the cell dry weight basis. The lipid profile after treatment showed the presence of appropriate quantities of saturated (10.39 ± 0.15%), monounsaturated (76.55 ± 0.19%) and polyunsaturated fatty acids (11.49 ± 0.23%) which further improves biodiesel quality compared to the other methods. To the best of our knowledge, this is the first report of using rapid ultrasonication-microwave treatment for the lipid extraction from wet oleaginous yeast biomass in the literature.

Production of Oleaginous Organisms or Lipids Using Sewage Water and Industrial Wastewater

Worldwide, wastewater produced from sewage and industry poses a serious risk to the surrounding environment. As a way to address this problem, an integrated approach for cultivation of oleaginous microorganisms on wastewater leading to effective removal of hazardous components and sustainable production of biodiesel is proposed. Oleaginous yeasts have the unique ability to utilize wastewater as feedstock and accumulate large amounts of triacylglycerols within their cellular compartments at stationary phase (144 h). The lipids stored in an oleaginous microbe can be visualized by fluorescence microscopy and converted into biodiesel through transesterification after extraction. Here, we describe the batch cultivation of oleaginous yeast on sewage and industrial wastewater at 25 °C. High lipid accumulation with efficient removal of toxic chemicals can be achieved by utilizing this integrated method.

Triauxic growth of an oleaginous red yeast Rhodosporidium toruloides on waste 'extract' for enhanced and concomitant lipid and β-carotene production

BACKGROUND

Vegetable 'mandi' (road-side vegetable market) waste was converted to a suitable fermentation medium for cultivation of oleaginous yeast Rhodosporidium toruloides by steaming under pressure. This cultivation medium derived from waste was found to be a comparatively better source of nutrients than standard culture media because it provided more than one type of usable carbon source(s) to yeast.

RESULTS

HPLC results showed that the extract contained glucose, xylose and glycerol along with other carbon sources, allowing triauxic growth pattern with preferably usage of glucose, xylose and glycerol resulting in enhanced growth, lipid and carotenoid production. Presence of saturated and unsaturated fatty acid methyl esters (FAMEs) (C_14-20) in the lipid profile showed that the lipid may be transesterified for biodiesel production.

CONCLUSION

Upscaling these experiments to fermenter scale for the production of lipids and biodiesel and other industrially useful products would lead to waste management along with the production of value added commodities. The technique is thus environment friendly and gives good return upon investment.

Biodegradation of phenol via meta cleavage pathway triggers de novo TAG biosynthesis pathway in oleaginous yeast

Phenol is reported to be one of the most toxic environmental pollutants present in the discharge of various industrial effluents causing a serious threat to the existing biome. Biodegradation of phenol by oleaginous yeast Rhodosporidium kratochvilovae HIMPA1 was found to degrade 1000mg/l phenol. The pathways for phenol degradation by both ortho and meta-cleavage were proposed by the identification of metabolites and enzymatic assays of ring cleavage enzymes in the cell extracts. Results suggest that this oleaginous yeast degrade phenol via meta-cleavage pathway and accumulates a high quantity of lipid content (64.92%; wt/wt) as compared to control glucose synthetic medium (GSM). Meta-cleavage pathway of phenol degradation leads to formation of pyruvate and acetaldehyde. Both these end products feed as precursors for de novo triacylglycerols (TAG) biosynthesis pathway which causes accumulation of TAG in the lipid droplets (LD) of 6.12±0.78μm grown on phenol while 2.38±0.52μm observed on GSM. This was confirmed by fluorescence microscopic images of BODIPY_505-515nm stained live yeast cells. GC-MS analysis of extracted total lipid showed enhanced amount of monounsaturated fatty acid (MUFA) which was as 51.87%, 58.33% and 62.98% in presence of 0.5, 0.75 and 1g/l of phenol.

Isolation, identification and characterization of Cystobasidium oligophagum JRC1: A cellulase and lipase producing oleaginous yeast

Oleaginous yeast closely related to Cystobasidium oligophagum was isolated from soil rich in cellulosic waste. The yeast was isolated based on its ability to accumulate intracellular lipid, grow on carboxymethylcellulose (CMC) and produce lipase. It could accumulate up to 39.44% lipid in a glucose medium (12.45±0.97g/l biomass production). It was able to grow and accumulate lipids (36.46%) in the medium containing CMC as the sole carbon source. The specific enzyme activities obtained for endoglucanase, exoglucanase, and β-glucosidase were 2.27, 1.26, and 0.98IU/mg respectively. The specific enzyme activities obtained for intracellular and extracellular lipase were 2.16 and 2.88IU/mg respectively. It could grow and accumulate lipids in substrates including glycerol (42.04%), starch (41.54%), xylose (36.24%), maltose (26.31%), fructose (24.29%), lactose (21.91%) and sucrose (21.72%). The lipid profile of the organism was suitable for obtaining biodiesel with desirable fuel properties.

Co-utilization of corn stover hydrolysates and biodiesel-derived glycerol by Cryptococcus curvatus for lipid production

In the present study, synergistic effects were observed when glycerol was co-fermented with glucose and xylose for lipid production by the oleaginous yeast Cryptococcus curvatus. Glycerol was assimilated simultaneously with sugars at the beginning of the culture without adaption time. Furthermore, better lipid production results, i.e., lipid yield and lipid productivity of 18.0g/100g and 0.13g/L/h, respectively, were achieved when cells were cultured in blends of corn stover hydrolysates and biodiesel-derived glycerol than those in the hydrolysates alone. The lipid samples had fatty acid compositional profiles similar to those of vegetable oils, suggesting their potential for biodiesel production. This co-utilization strategy provides an extremely simple solution to advance lipid production from both lignocelluloses and biodiesel-derived glycerol in one step.

Biodiesel production from non-edible lignocellulosic biomass of Cassia fistula L. fruit pulp using oleaginous yeast Rhodosporidium kratochvilovae HIMPA1

This study explored biodiesel production from a low cost, abundant, non-edible lignocellulosic biomass from aqueous extract of Cassia fistula L. (CAE) fruit pulp. The CAE was utilized as substrate for cultivating novel oleaginous yeast Rhodosporidium kratochvilovae HIMPA1. This oleaginous yeast accumulates high amount of triacylglycerides as large intracellular lipid droplets (4.35±0.54μm) using CAE as sole nutritional source. Total lipids (4.86±0.54g/l) with lipid content of 53.18% (w/w) were produced by R. kratochvilovae HIMPA1 on CAE. The FAME profile obtained revealed palmitic acid (C16:0) 43.06%, stearic acid (C18:0) 28.74%, and oleic acid (C18:1) 17.34% as major fatty acids. High saturated fatty acids content (72.58%) can be blended with high PUFA feedstocks to make it an industrially viable renewable energy product.