Search

Using oleaginous microbial lipid-based biorefinery from lignocellulosic biomass (LCB) to produce fermentative bioenergy (i.e., biodiesel) represents an innovative second-generation fuel production technology. These lipids are predominantly intracellular triglycerides that accumulate through the metabolism of sugars in fermentation following pretreatment and enzymatic hydrolysis of LCB. This review investigates the recent advances in the microbial lipid production from LCB, focusing on the factors influencing the lead microbial lipid producers, different pretreatment methods (i.e., physical, chemical, biological, and combined pretreatment), enzymatic hydrolysis approaches, novel bioprocessing strategies (i.e., microbes-specific and fermentation model specific), and engineering techniques of the oleaginous microbes (i.e., genetic and metabolic alterations). The study demonstrates that oleaginous yeasts can synthesize significantly higher quantities of lipids when incorporated into the system, known as separated hydrolysis and lipid production, following various combined pretreatment methods. Interestingly, CRISPR is found to be the most suitable way of engineering microbes genetically and metabolically for increased lipid synthesis. The study also explores economically viable strategies for fermentative lipid production, addressing associated challenges, and outlines future directions, including comprehensive techno-economic and life cycle assessments. This review offers invaluable insights into microbial lipid production from LCB, highlighting the potential for significant technological and environmental enhancements through ongoing research and development efforts.

Using oleaginous microbial lipid-based biorefinery from lignocellulosic biomass (LCB) to produce fermentative bioenergy (i.e., biodiesel) represents an innovative second-generation fuel production technology. These lipids are predominantly intracellular triglycerides that accumulate through the metabolism of sugars in fermentation following pretreatment and enzymatic hydrolysis of LCB. This review investigates the recent advances in the microbial lipid production from LCB, focusing on the factors influencing the lead microbial lipid producers, different pretreatment methods (i.e., physical, chemical, biological, and combined pretreatment), enzymatic hydrolysis approaches, novel bioprocessing strategies (i.e., microbes-specific and fermentation model specific), and engineering techniques of the oleaginous microbes (i.e., genetic and metabolic alterations). The study demonstrates that oleaginous yeasts can synthesize significantly higher quantities of lipids when incorporated into the system, known as separated hydrolysis and lipid production, following various combined pretreatment methods. Interestingly, CRISPR is found to be the most suitable way of engineering microbes genetically and metabolically for increased lipid synthesis. The study also explores economically viable strategies for fermentative lipid production, addressing associated challenges, and outlines future directions, including comprehensive techno-economic and life cycle assessments. This review offers invaluable insights into microbial lipid production from LCB, highlighting the potential for significant technological and environmental enhancements through ongoing research and development efforts. [ABSTRACT FROM AUTHOR]

Bio-valorization approach of frying oil waste (FOW) to exploit it in different ways to produce added-value compounds is attractive from an economic and ecological standpoint. The aim of the current study was to investigate the incorporation of FOW in the fungal culture medium in order to develop feasible products such as single cell oils (SCOs), lipase, and citric acid (CA). According to response surface methodology (RSM), three independent variables have a significant effect on lipase and lipid accumulation by Lichtheimia corymbifera, namely, FOW amount (15 mL/L), ammonium sulfate concentration (5 g/L), and pH (6.0). The contour plots and 3D surface responses show the significant interaction of FOW amount and pH with ammonium sulfate concentration during lipase production. At these conditions, SCOs, lipase, and CA were produced with percentages 1.55 g/L, 54.3 U/mL, and 4.93 g/L, respectively. Fatty acid profile of the produced SCOs includes unsaturated fatty acids (USFAs) higher than saturated fatty acids (SFAs), which were 56.27 and 43.17% respectively. Furthermore, the dominant SFA is palmitic acid (29.22%), while the dominant USFA is oleic acid (30.78%). In conclusion, this study succeeded in valorization of FOW for SCOs, lipase, and CA in a one batch. [ABSTRACT FROM AUTHOR]

To combat the shortage of single agro-residue and overcome the problem of seasonal availability, it is beneficial to use mixture of lignocellulosic biomasses. In the present study, efforts were made to use mixed lignocellulosic biomass for production of bioethanol, along with microbial lipids and lactic acid. Upon enzymatic hydrolysis of mixed biomass at varied proportions it was observed that mixture of paddy straw and jute in the ratio 3:1 resulted in best sugar yield (41.50 g/L) at 10% substrate loading. Ethanolic fermentation of mixed substrate hydrolysate by thermotolerant yeast, Saccharomyces cerevisiae JRC6 resulted in 8.39 g/L of ethanol. To maintain sustainability and economic impact, oleaginous yeast (Trichosporon mycotoxinivorans S2) and lactic acid bacteria (Lactobacillus plantarum LP-9) were used for lipid production (14.5 g/L) and lactic acid production (11.08 g/L), respectively. Therefore, this study explored the potential of mixed lignocellulosic biomass to be exploited for production of various value-added products. [ABSTRACT FROM AUTHOR]

Mucoromycota are diverse in microbial oils, but oil-related studies have long been confined to a few particular genera and species. This study used the Sherlock Microbial Identification System to determine fatty acid compositions and consequently discover potential resources from 669 strains representing 133 species in 28 genera in 11 families from the core mucoromycotan orders Mortierellales, Mucorales, and Umbelopsidales. Results showed that 34% of strains, 50% of species, and 46% of genera were oleaginous. Eleven genera were proposed as oleaginous taxa for the first time. Among them, Backusella was highlighted in accumulating as high as 59.08 ± 2.24% of oils. Twenty-five and 50 strains were screened as potential high-yield fungi for oils and high-value fatty acids respectively. Pilaira produced the most C18:2, while Rhizopus and Thamnostylum produced the most C18:3. Only strains of Mortierella produced C20:4; Mo. amoeboidea CGMCC 3.15949 yielded 58.00% ± 1.15% of C20:4, which suggests it is an excellent source of C20:4. This study suggests for the first time that the bulk of Mucoromycota is rich in lipids. More genera and species were discovered herein as oil-producing resources. These findings serve as a foundation for further research on microbial oil production. [ABSTRACT FROM AUTHOR]

Abstract Background Over the last years oleaginous yeasts have been studied for several energetic, oleochemical, medical and pharmaceutical purposes. However, only a small number of yeasts are known and have been deeply exploited. The search for new isolates with high oleaginous capacity becomes imperative, as well as the use of alternative and ecological carbon sources for yeast growth. Results In the present study a high-throughput screening comprising 366 distinct yeast isolates was performed by applying an optimised protocol based on two approaches: (I) yeast cultivation on solid medium using acetic acid as carbon source, (II) neutral lipid estimation by fluorimetry using the lipophilic dye Nile red. Conclusions Results showed that, with the proposed methodology, the oleaginous potential of yeasts with broad taxonomic diversity and variety of growth characteristics was discriminated. Furthermore, this work clearly demonstrated the association of the oleaginous yeast character to the strain level, contrarily to the species-level linkage, as usually stated.

• Rhodotorula glutinis T13, characterized as an oleaginous yeast, shows good growth parameters, and produces and stores lipids. • The oil from R. glutinis T13 shows an adequate lipid composition for the production of biodiesel. • The biodiesel obtained from R. glutinis T13 complies with international fuel standards. • R. glutinis T13 is a promising source of oils suitable for the biofuel, pharmaceutical and/or food industry. Single cell oils (SCO) are a promising source of oils that could be exploited in different industrial areas. SCO for biodiesel production circumvents the controversy food vs. fuel, does not require large land areas for culture, and is independent of climate and seasonal variations, among other advantages in comparison to vegetable oils. In this study, a red yeast isolated from a mountain water source, identified as Rhodotorula glutinis T13, showed high potential for lipid production (40% w/w) with suitable growth parameters, yields, and fatty acids profile. Yeast lipids showed a high content of unsaturated fatty acids (56.44%; C18:1, C18:2), and the fuel properties (cetane number, iodine value, density, kinematic viscosity, etc.) of yeast oil analysed were in good agreement with international biodiesel standards. The results show that R. glutinis T13 can be used in the future as a promising microorganism for the commercial production of biodiesel. [ABSTRACT FROM AUTHOR]

Corncob is a kind of abundant lignocellulosic biomass. One of the bottlenecks in utilization of corncob in fermentation industry is many microorganisms cannot ferment xylose, which is the main component of corncob hydrolysate. Here we identified a novel oily yeast strain AM2352 of Rhodotorula taiwanensis , which could effectively convert corncob hydrolysate into microbial lipid. Notably, the fatty acid synthase alpha-subunit of R. taiwanensis has two acyl carrier protein (ACP) domains, which may be involved in high-level oil contents in its cells. Based on a 5-L fermentation analysis, the coefficient of lipid production was 55.8 g oil per kilogram of corncob. Long-chain fatty acids (C16–C18) were the main components of the intracellular lipid accumulated by the yeast strain AM2352. Over 81.5% of the extracted oil could be converted into biodiesel. This work not only provides an inspiring information into the utilization of corncob hydrolysate by the yeast strain AM2352 for microbial lipid production, but also probably promotes biofuel production. Image 1 • The lipid yield from corncob by R. taiwanensis AM2353 was 55.8 g oil per kilogram of corncob. • Fatty acid synthase (Fas2) of R. taiwanensis contains two ACP domains. • Over 81.5% of the microbial lipid could be converted into biodiesel. [ABSTRACT FROM AUTHOR]

Watermelon peel waste (WPW) is being used for first time in single cell oils (SCOs) production via a promising oleaginous fungus Lichtheimia corymbifera which was isolated from Egyptian ecosystem. Pretreatments of WPW were carried out by mechanical, physical and chemical methods; the most potent pretreatment was selected according to total reducing sugar and total lipid production. Accordingly, the mechanical ptetreatment of WPW was distinctly the best pretreatment method for SCOs production from L. corymbifera. Taguchi design clarified that the most optimal culture conditions were 35 °C and pH 7.0 for 4 days by which the highest potential of SCOs and lipid content was yielded (2.93 gl−1 and 39.56% respectively). Mechanical treatment revealed that the dominant fatty acid was palmitic and oleic acids with 41.98 and 34.65% respectively with appearance of γ linolenic acid (GLA) at low concentration 1.43%. Finally, this study showed that WPW was used as a natural, effective, economic, ecofriendly and integrated substrate without adding any outsource nutrients to produce sustainable SCOs with low cost production. [ABSTRACT FROM AUTHOR]

Lipomyces starkeyi has been regarded as one of the model oleaginous yeasts. However, in this study, Lipomyces kononenkoae BF1S57 strain was found to be able to yield 60.06% (w/v) lipids (11.3 g/L lipids) from 90.0 g/L glucose, its cell mass was 18.8 ± 0.3 g/L within 96 h of a 10-L fermentation. Furthermore, the genome of L. kononenkoae has two copies of the genes encoding the β-subunit and α-subunit of fatty acid synthase, respectively. This may be related to high lipid contents in its cells. Over 94% of the fatty acids of the extracted lipids produced by L. kononenkoae BF1S57 strain was C 16:0 , C 16:1 , C 18:0 , C 18:1 and C 18:2 fatty acids. The properties of the prepared biodiesels in this study totally met the requirements of US biodiesel ASTM D6751 and EU biodiesel EN 14214. All these results demonstrated that the produced cellular lipids could be used as raw materials for biofuel production. • L. kononenkoae BF1S57 strain yielded 60.06% (w/v) lipids within 96 h of the 10-L fermentation. • Over 94% of the fatty acids of the extracted lipids was C 16:0 , C 16:1 , C 18:0 , C 18:1 and C 18:2 fatty acids. • The prepared fatty acid methyl esters could be used as biodiesels. [ABSTRACT FROM AUTHOR]

Objective: Oleaginous yeasts are a renewable and alternative source of oil for third-generation biodiesel. This work aimed to evaluate the effects of glucose concentration (30–100 g L−1) on growth, lipid synthesis, and fatty acids (FA) profile of three Rhodotorula spp. (R. glacialis R15, R. glutinis R4, and R. glutinis R48) isolated from Antarctica, and estimate the key quality parameters of the biodiesel produced by yeasts to confirm their potential as feedstocks for third-generation biodiesel synthesis. Results: Yeasts accumulated 50–69.5% of lipids (w/w) under nitrogen-limitation and glucose-excess (C/N = 40–133). Glucose concentration increase influenced positively lipid accumulation (69.5% w/w) and FA profile of R. glacialis R15. Lipid accumulation (53% on average) of R. glutinis strains was not significantly affected by glucose concentration; content of saturated (~ 30%) and polyunsaturated FA (~ 29–30%) was slightly influenced. FA profiles of lipids synthesized by R15, R4, and R48 are similar to vegetable oils used in biodiesel industry with C16 and C18 FA (95–99%) as the major components, and contain mainly oleic (C18:1), palmitic (C16:0), and linoleic (C18:2) acids, which are suitable for biodiesel synthesis. Estimated fuel properties for biodiesel produced by R15, R4, and R48 satisfied all the criteria established by ASTM D6751 and EN 14214 with good cetane number, iodine value, and oxidation stability. An improvement in biodiesel quality of R15 was observed with the glucose increase. The best global properties of biodiesel from R4 were obtained with 30 g L−1 of glucose. Conclusions: Rhodotorula spp. from Antarctica are promising candidates for third-generation biodiesel synthesis. [ABSTRACT FROM AUTHOR]

Background: Over the last years oleaginous yeasts have been studied for several energetic, oleochemical, medical and pharmaceutical purposes. However, only a small number of yeasts are known and have been deeply exploited. The search for new isolates with high oleaginous capacity becomes imperative, as well as the use of alternative and ecological carbon sources for yeast growth. Results: In the present study a high-throughput screening comprising 366 distinct yeast isolates was performed by applying an optimised protocol based on two approaches: (I) yeast cultivation on solid medium using acetic acid as carbon source, (II) neutral lipid estimation by fluorimetry using the lipophilic dye Nile red. Conclusions: Results showed that, with the proposed methodology, the oleaginous potential of yeasts with broad taxonomic diversity and variety of growth characteristics was discriminated. Furthermore, this work clearly demonstrated the association of the oleaginous yeast character to the strain level, contrarily to the species-level linkage, as usually stated. [ABSTRACT FROM AUTHOR]

• Lipid production and growth by R. glutinis R4 and other oleaginous yeasts were compared. • R. glutinis R4 showed remarkable capacity for lipid production and fast growth. • Microbial oils produced by R. glutinis R4 are similar to vegetable oils. • Fatty Acyl Methyl Esters (FAME) produced from R. glutinis R4 lipids are adequate for biodiesel synthesis. • Biodiesel derived from R. glutinis R4 complies with international fuel standards. Some Rhodotorula spp. have been characterized as oleaginous yeasts. Under certain culture conditions they can accumulate neutral lipids, which are mainly triglycerides (TAG). Microbial TAG that can be used as raw material for biodiesel synthesis are attractive for the biofuel industry. In this study, the ability to synthesize lipids of Rhodotorula glutinis R4, isolated in Antarctica, was compared with eight strains belonging to the genera Rhodotorula and Yarrowia with the aim of proposing a novel source of oils for biodiesel synthesis. All strains were cultured under nitrogen (N) limiting conditions and an excess of carbon (C) in the culture medium. We found that yeasts accumulated between 9–48.9 % (w/w) of lipids. Among them, R. glutinis R4 showed the highest growth (14 g L−1, μmax 0,092 h−1) and lipid production (7 g L−1; 47 % w/w). Microbial oils produced by R. glutinis R4 are similar to vegetable oils, with 61 % of oleic acid, indicating that it is adequate for biodiesel synthesis. Our results demonstrate that biodiesel derived from R. glutinis R4 complies with international fuel standards ASTM D6751 and EN 14214. Therefore, this work demonstrates that Rhodotorula glutinis R4 is a novel and valuable source of microbial oils for biodiesel synthesis. [ABSTRACT FROM AUTHOR]

Marine macroalgae (seaweed) has many advantages over terrestrial crops as a source of renewable biomass but is severely underutilised at present, especially within Europe. In particular, macroalgae has elevated poly- and monosaccharide content, making it an ideal feedstock as a heterotrophic fermentation sugar source for the production of higher value chemicals. Recent reports have detailed the suitability of seaweeds as a feedstock for the production of single-cell oils (SCOs) which have application in food, oleochemicals and fuels. It is proposed that a biorefinery system based on the production of SCOs alongside other secondary metabolites, has the potential to provide a sustainable replacement to terrestrial oils such as palm oil. This work therefore evaluates, for the first time, the environmental and economic sustainability of a production process for SCOs from seaweed Saccharina latissima using the oleaginous yeast Metschnikowia pulcherrima. Two alternative fermentation systems were considered, and uncertainties associated with the seasonal variation in seaweed carbohydrate yield and fermentation performance were integrated into the analysis. From an environmental perspective, the work indicates that seaweed derived SCO lipids and fats can be comparable to a terrestrial oil mix, with a potential climate change impact ranging between 2.5 and 9.9 kg CO 2 eq. kg−1 refined SCO. Interestingly and of particular significance, environmental impacts are mainly dominated by energy demand within fermentation and upstream processing steps. From an economic perspective, a break-even selling price for the oil was determined as between €5,300-€31,000 tonne−1 refined SCO, which was highly dependent on cost of the seaweed feedstock. Overall, we demonstrate that key uncertainties relating to seaweed cultivation costs and hydrolysate fermentation at scale result in a large range in values for environmental impact and economic return on investment. Yet even within the constraints and limitations of current knowhow, seaweed already offers a viable proposition for the competitive production of exotic oils similar to cocoa or shea butter in price and nature. • LCA and economic analysis of SCOs derived from seaweed Saccharina latissima performed for the first time. • Climate change impact for process determined to be between 2.5 and 9.9 kg CO 2 eq. kg−1 refined SCO. • Break-even selling price for the oil calculated as between €5,300-€31,000 tonne−1 refined SCO. • Climate change impacts within the range of what has previously been quoted for microalgae and terrestrial oil mixes. • Lower-end break-even pricing is closer to that of exotic oils and fats than terrestrial oils like palm oil. [ABSTRACT FROM AUTHOR]

This study determines the ability of an isolated Trichosporon domesticum yeast strain to accumulate intracellular lipids in media with deproteinated potato wastewater (DPW) containing various carbon sources. The yeast strain was isolated from kefir and identified by internal transcribed spacer (ITS) region sequence analysis. The sequence was deposited in GenBank under accession number MH094668, and the strain was deposited in Polish Collection of Microorganisms as T. domesticum PCM 2960. DPW is an inexpensive and valuable source of nitrogen, potassium, phosphorus, and other elements in yeast cultures. DPW supplemented with glucose medium was most effective at stimulating lipid biosynthesis by T. domesticum PCM 2960 and bioreactor incubation resulted in a final lipid yield of 4.8 g L−1. The lipids of the T. domesticum PCM 2960 biomass were characterized by high contents of linoleic acid (Δ9,12C18:2), oleic acid (Δ9C18:1), palmitic acid (C16:0), and α-linolenic acid (Δ9,12,15C18:3). Theoretical calculations for biodiesel properties showed that the methylated esters of lipids from T. domesticum PCM 2960 biomass cannot be used as a biodiesel in diesel engines. Additionally, the ability to produce biofilm as one criterion for pathogenicity was tested. The ability for biofilm formation by the isolated strain was low. This study provides a promising solution for the more economical production of microbial lipids with DPW. [ABSTRACT FROM AUTHOR]

Oleaginous yeasts are of interest for production of single cell oils from sugars. Eighteen members of the Lipomyces and Myxozyma clade were screened for lipid production when cultured on 10%w/v glucose. The highest ranking yeasts included L. tetrasporus (21 g/L), L. spencer-martinsiae (19.6 g/L), and L. lipofer (16.7 g/L). By contrast, Rhodosporidium toruloides, which was included as a positive control, produced 16.7 g/L. The L. tetrasporus and L. lipofer were further characterized for growth and lipid production on sugars present in biomass hydrolysates. These included L-arabinose, xylose, and an equal glucose and xylose mixture. L. tetrasporus had lipid titers of 16.3–20.8 g/L and L. lipofer 12.5–17.0 g/L. When both strains were grown on an equal mixture of glucose and xylose, xylose was consumed immediately following glucose. Lipid contents for the yeasts consisted primarily of C18:1 and C16:0, which makes them a promising source of lipids for fuel applications.

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.

Disruption of polyunsaturated fatty acids (PUFA) metabolism leads to many diseases. In this study, producers of γ-linolenic acid (GLA), arachidonic acid (ARA) and eicosapentaenoic acid (EPA) were selected: Cephalosporium humicola IE (on glucose, dry biomass – 14 g/l, total lipids – 18-20%, GLA in lipids – 12.0%), Mucor globosus 11 (respectively – 15 g/l, 18% and 5%) and Pythium irregulare LX (on glucose, dry biomass – 14.5 g/l, total lipids – 18-20%, 9.2 and 7.8% of ARA and EPA, respectively). On crude oil as the only source of carbon, the amount of biomass of the specified fungi decreases by 3-4 times, whereas the quantity of lipids and highly unsaturated fatty acids increases in four and 1.2 - 3.4 times, respectively. The maximum γ-linolenic acid in M. globosus and C. humicola was detected at neutral рН. Optimum volume of inoculate was 2.0-4.0%, nitrogen source NH4NO3, a carbon-nitrogen ratio 34:1. For biosynthesis of ARA and EPA by P. irregulare, the optimum nitrogen source was NH4Cl, рН 7.0- 8.0 and С/N - 50:1 at 28°C. The process of adaptation to stressful situation under crude oil motivated the increase of the rate of membrane phospholipids with high quantity of unsaturated fatty acids.

Single cell oils (SCO) can be a source of nutritionally valuable fatty acids and raw material in biodiesel production. Among the oleaginous yeasts, those which additionally generate carotenoid pigments are beneficially distinguished. Rhodotorula and Sporobolomyces strains were screened for the ability to grow and produce intracellular lipids in medium containing pure glycerol. In this paper, we verified that glycerol is unfavorable carbon source for a strain of S. salmonicolor and a good source of carbon for the growth and increases lipids content in the biomass of examined Rhodotorula yeast compared to glucose. The best volumetric efficiency of lipids biosynthesis (4.73 g L) in the medium with glycerol showed R. glutinis var. rubescens LOCKR13. In all investigated strains, oleic acid had the highest proportion of the total fatty acids. Nutritionally beneficial features were demonstrated by R. mucilaginosa, strain ATCC 66034 containing docosapentaenoic acid and reaching a high lipids biosynthesis efficiency (3.24 g L). Compared to glucose after incubation of R. aurantiaca, R. glutinis, R. gracilis and R. mucilaginosa strains with glycerol, the higher PUFA content per unit volume of medium was observed. [ABSTRACT FROM AUTHOR]

Oleaginous yeasts are of interest for production of single cell oils from sugars. Eighteen members of the Lipomyces and Myxozyma clade were screened for lipid production when cultured on 10%w/v glucose. The highest ranking yeasts included L. tetrasporus (21 g/L), L. spencer-martinsiae (19.6 g/L), and L. lipofer (16.7 g/L). By contrast, Rhodosporidium toruloides, which was included as a positive control, produced 16.7 g/L. The L. tetrasporus and L. lipofer were further characterized for growth and lipid production on sugars present in biomass hydrolysates. These included L-arabinose, xylose, and an equal glucose and xylose mixture. L. tetrasporus had lipid titers of 16.3-20.8 g/L and L. lipofer 12.5-17.0 g/L. When both strains were grown on an equal mixture of glucose and xylose, xylose was consumed immediately following glucose. Lipid contents for the yeasts consisted primarily of C18:1 and C16:0, which makes them a promising source of lipids for fuel applications. [ABSTRACT FROM AUTHOR]

Oleaginous yeasts utilize renewable resources to produce lipids, which benefits sustainable development, and it is of great interest to screen robust lipid producers. Curvibasidium sp. belongs to nonconventional yeast that are very limitedly studied. Here, two cold-adaptive strains of Curvibasidium sp., namely, Y230 and Y231, isolated from the medicinal lichen Usnea diffracta were investigated for their potential in lipid production. Genome mining of Curvibasidium sp. Y231 was performed, and the special features related to fatty acid biosynthesis were revealed. Glucose, xylose, and glycerol were tested as sole carbon sources for yeast cell growth and lipid production. The total lipid contents of Curvibasidium sp. Y230 and Y231 range from 38.43% to 54.62% of the cell dry cell weight at 20°C, and glucose is the optimal carbon source. These results indicate that the Curvibasidium sp. strains are promising for sustainable lipid production. Our study provides basis for exploration of lichen-derived strains for biotechnological applications, and also benefits utilization of other nonconventional yeasts for sustainable production based on genome-based studies., (© The Author(s) 2023. Published by Oxford University Press on behalf of FEMS.)

Disruption of polyunsaturated fatty acids (PUFA) metabolism leads to many diseases. In this study, producers of γ-linolenic acid (GLA), arachidonic acid (ARA) and eicosapentaenoic acid (EPA) were selected: Cephalosporium humicola IE (on glucose, dry biomass - 14 g/l, total lipids - 18-20%, GLA in lipids - 12.0%), Mucor globosus 11 (respectively - 15 g/l, 18% and 5%) and Pythium irregulare LX (on glucose, dry biomass - 14.5 g/l, total lipids - 18-20%, 9.2 and 7.8% of ARA and EPA, respectively). On crude oil as the only source of carbon, the amount of biomass of the specified fungi decreases by 3-4 times, whereas the quantity of lipids and highly unsaturated fatty acids increases in four and 1.2 - 3.4 times, respectively. The maximum γ-linolenic acid in M. globosus and C. humicola was detected at neutral pH. Optimum volume of inoculate was 2.0-4.0%, nitrogen source NH4NO3, a carbon-nitrogen ratio 34:1. For biosynthesis of ARA and EPA by P. irregulare, the optimum nitrogen source was NH4Cl, pH 7.0- 8.0 and C/N - 50:1 at 28°C. The process of adaptation to stressful situation under crude oil motivated the increase of the rate of membrane phospholipids with high quantity of unsaturated fatty acids. [ABSTRACT FROM AUTHOR]

A brief overview is provided of the microbial oils (single cell oils - SCOs) that have been, or are still being, produced commercially. Oils rich in gamma-linolenic acid (18:3 n-6), arachidonic acid (20:4 n-6), eicosapentaenoic acid (20:5 n-3) and docosahexaenoic acid (22:6 n-3) are covered. The prospects of using other SCOs for biofuels are discussed with the conclusion that it is highly unlikely that algae will provide oils that are competitive with alternative sources of fatty acids.

Considering the demand from many industrial sectors, the production of microbial lipids constitutes an attractive topic for research. Oleaginous microorganisms can produce over 60% of their dry matter in single cell oils (SCOs), especially in the form of triglycerides (TAGs). Approximately forty microbial genera, especially yeasts and moulds, are known to be high lipid producers. Many abiotic factors, such as the culture conditions or nutriment availability, influence the production of microbial lipids that are of interest. Among the factors that can influence SCO production, the carbon source, limiting nutriments (especially nitrogen), pH and temperature are cited most often in the literature. Improvement in SCO production through the optimisation of abiotic factors encounters several limitations. Thus, research is currently increasingly oriented toward genetic modifications to optimise the synthesis of lipids by oleaginous microorganisms. [ABSTRACT FROM AUTHOR]

Effects of media compositions on biomass and lipid accumulation of the isolate Chlorella sp. TISTR 8990 were investigated under a Plackett-Burman experimental design with mixotrophic cultivation conditions. Under this experimental design there were 15 different runs with ten factors-yeast extract, KH2PO4, MgSO4, FeSO4, MnCl2, CuSO4, Na2MoO4, H3BO3, ZnSO4 and pH. Cultures were grown mixotrophically under 16 h light and 8 h dark regime at 30 ºC for a period of 7 days. During the light regime, the light intensity at the surface of the vessels and agitation speed were set to 67.5 µmol photons m-2s-1 and 150 rpm, respectively. Initial cell concentration was set to an absorbance (A540) of 0.5. For high biomass production (2.2 g/L, run no. 6), the most effective and significant factors were yeast extract, KH2PO4, FeSO4 and ZnSO4 at concentrations 0.3 g/L, 0.3 g/L, 3 mg/L and 0.3 mg/L, respectively. Whereas for high lipid accumulation (19.59 %DCW, run no. 2), these were KH2PO4, pH and yeast extract, at a level of 1.7 g/L, 6.0 and 0.1 g/L, respectively. No significant factors were obtained for higher lipid content. The best treatment for biomass and lipid content was run no. 6, whose medium formula consisted of 0.3 g/L yeast extract, 1.7 g/L KH2PO4, 1.7 g/L MgSO4, 1 mg/L FeSO4, 0.9 mg/L MnCl2, and pH 7.0, together with fixed concentrations of glucose, NaHCO3 and KNO3 at 5 g/L, 0.05 g/L and 0.5 g/L, respectively.

Diverse health benefits are associated with dietary consumption of omega-3 long-chain polyunsaturated fatty acids (ω-3 LC-PUFA), particularly docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). Traditionally, these fatty acids have been obtained from fish oil, but limited supply, variably quality, and an inability to sustainably increase production for a rapidly growing market, are driving the quest for alternative sources. DHA derived from certain marine protists (heterotrophic thraustochytrids) already has an established history of commercial production for high-value dietary use, but is too expensive for use in aquaculture feeds, a much larger potential market for ω-3 LC-PUFA. Sustainable expansion of aquaculture is prevented by its current dependence on wild-caught fish oil as the source of ω-3 LC-PUFA nutrients required in the diet of aquacultured animals. Although several thraustochytrids have been shown to produce DHA and EPA, there is a particular interest in Schizochytrium spp. (now Aurantiochytrium spp.), as some of the better producers. The need for larger scale production has resulted in development of many strategies for improving productivity and production economics of ω-3 PUFA in Schizochytrium spp. Developments in fermentation technology and metabolic engineering for enhancing LC-PUFA production in Schizochytrium spp. are reviewed. [ABSTRACT FROM AUTHOR]

Omega-3 fatty acids, namely docosahexaenoic acid and eicosapentaenoic acid, have been linked to several beneficial health effects (i.e. mitigation effects of hypertension, stroke, diabetes, osteoporosis, depression, schizophrenia, asthma, macular degeneration, rheumatoid arthritis, etc.). The main source of omega-3 fatty acids is fish oil; lately however, fish oil market prices have increased significantly. This has prompted a significant amount of research on the use of single-cell oils as a source of omega-3 fatty acids. Some of the microbes reported to produce edible oil that contains omega-3 fatty acids are from the genus Schizochytrium, Thraustochytrium and Ulkenia. An advantage of a single cell oil is that it usually contains a significant amount of natural antioxidants (i.e. carotenoids and tocopherols), which can protect omega-3 fatty acids from oxidation, hence making this oil less prone to oxidation than oils derived from plants and marine animals. Production yields of single cell oils and of omega-3 fatty acids vary with the microbe used, with the fermentative growing conditions, and extractive procedures employed to recover the oil. This paper presents an overview of recent advances, reported within the last 10 years, in the production of single cell oils rich in omega-3 fatty acids. [ABSTRACT FROM AUTHOR]

Effects of media compositions on biomass and lipid accumulation of the isolate Chlorella sp. TISTR 8990 were investigated under a Plackett-Burman experimental design with mixotrophic cultivation conditions. Under this experimental design there were 15 different runs with ten factors-yeast extract, KH2PO4, MgSO4, FeSO4, MnCl2, CuSO4, Na2MoO4, H3BO3, ZnSO4 and pH. Cultures were grown mixotrophically under 16 h light and 8 h dark regime at 30 °C for a period of 7 days. During the light regime, the light intensity at the surface of the vessels and agitation speed were set to 67.5 µ.mol photons m-2s-1 and 150 rpm, respectively. Initial cell concentration was set to an absorbance (A540) of 0.5. For high biomass production (2.2 g/L, run no. 6), the most effective and significant factors were yeast extract, KH2PO4, FeSO4 and ZnSO4 at concentrations 0.3 g/L, 0.3 g/L, 3 mg/L and 0.3 mg/L, respectively. Whereas for high lipid accumulation (19.59 %DCW, run no. 2), these were KH2PO4, pH and yeast extract, at a level of 1.7 g/L, 6.0 and 0.1 g/L, respectively. No significant factors were obtained for higher lipid content. The best treatment for biomass and lipid content was run no. 6, whose medium formula consisted of 0.3 g/L yeast extract, 1.7 g/L KH2PO4, 1.7 g/L MgSO4, 1 mg/L FeSO4, 0.9 mg/L MnCl2, and pH 7.0, together with fixed concentrations of glucose, NaHCO3 and KNO3 at 5 g/L, 0.05 g/L and 0.5 g/L, respectively. [ABSTRACT FROM AUTHOR]

Abstract: The continued increase in human population has resulted in the rise in the demand as well as the price of edible oils, leading to the search for alternative unconventional sources of oils, particularly in the developing countries. There are hundreds of un- or underexplored plant seeds rich in oil suitable for edible or industrial purposes. Many of them are rich in polyunsaturated essential fatty acids, which establish their utility as “healthy oils.” Some agrowaste products such as rice bran have gained importance as a potential source of edible oil. Genetic modification has paved the way for increasing the oil yields and improving the fatty acid profiles of traditional as well as unconventional oilseeds. Single cell oils are also novel sources of edible oil. Some of these unconventional oils may have excellent potential for medicinal and therapeutic uses, even if their low oil contents do not promote commercial production as edible oils. [Copyright &y& Elsevier]

The feasibility of the conversion of acetic acid, a metabolite commonly obtained during anaerobic fermentation processes, into oils using the yeast Cryptococcus curvatus was reported. This microorganism exhibited very slow growth rates on acetate as carbon source, which led to design a two-stage cultivation process. The first consisted of cell growth on glucose as carbon source until its complete exhaustion. The second step involved the use of acetate as carbon source under nitrogen limitation in order to induce lipid accumulation. A typical experiment performed in a bioreactor involved a preliminary yeast growth with a glucose initial concentration of 15 g/L glucose. Further additions of acetate and nitrogen source allowed a final lipid accumulation up to 50% ( w/ w). These promising results demonstrated the suitability of the technique proposed. [ABSTRACT FROM AUTHOR]

Abstract: The total amount of lipids produced in Rhodotorula glutinis is a subject which has attracted increasing attention due to the potential biodiesel conversion from these microbial oils. The effects of the dissolved oxygen (DO) level in lipid accumulation were examined in this study. Variations of different medium volumes (30, 40 and 50ml) and shaking speed (60, 150 and 210rpm) in the flask trials were adopted to explore the DO effects on lipid production. All of the results revealed that a low DO could retard cell growth, while enhancing lipid accumulation. The 5l-fermentor results also confirm that a low DO (25±10%) batch could have higher lipid content than that of high DO batch (60±10%). Nevertheless, the DO level would not obviously affect the lipid composition profile. Oleic acid (C18:1) was the primary fatty acid in both batches. Due to the slow biomass growth rate resulting from the low DO, a two-stage DO controlled strategy (consisting of a high DO stage and following a low DO stage) was performed to improve the cell growth and lipid accumulation simultaneously. However, the strategy was not successful on the enhancement of total lipid production as compared to other batches. Conclusively, even a low DO could retard cell growth; the total production of lipids in the batch with low DO was higher that of the high DO batch due to the enhancement of lipid accumulation. Therefore, the batch operation of R. glutinis at the low DO was suggested for the purpose of lipid production. [Copyright &y& Elsevier]

Thraustochytrids, in particular Schizochytrium spp., are used for the production of the valuable polyunsaturated fatty acid, docosahexaenoic acid (DHA; 22:6 n-3). Growth of Schizochytrium sp. G13/2S in a defined medium was initially made in shake-flask cultures to determine the optimum concentrations of glucose (100–200 g l−1) and ammonia (∼300 mg l−1) that could be used by this microorganism. In subsequent fermenter cultures, a pH-auxostat method was used to maintain NH3 from 200–300 mg l−1. During the first 49 h of fermentation, 150 g glucose l−1 produced 63 g cell dry wt l−1. Although growth was not limited by the supply of nitrogen, total fatty acids were at 25% cell dry wt which is more than half the final lipid content of commercially-grown Schizochytrium biomass which uses N-limited medium in the final stages for maximum lipid accumulation. This strategy is therefore useful for the cultivation of Schizochytrium to a high cell density up to the point when lipid accumulation can be triggered by N exhaustion. [ABSTRACT FROM AUTHOR]

Abstract: Replacing fish oil with that from a docosahexaenoic acid (22:6ω3, DHA) rich single cell micro-organism, thraustochytrid Schizochytrium sp. L, in diets for Atlantic salmon (Salmo salar) was investigated. Four experimental diets containing 100% thraustochytrid oil (TO), 100% palm oil (PO) and a 4:1 palm and thraustochytrid oil mixture (MX) were compared to a fish oil (FO) diet over 9 weeks. A saltwater transfer challenge occurred at the end of the trial for 14 days to test the diet treatments on the ability of salmon to smolt. There were no significant differences in the feed consumption of the diets or the digestibility of the ω3 or ω6 PUFA, indicating no differences in the digestibility of fatty acids between diets. No significant differences were noted between the growth of fish on the four diet treatments. Significant differences were noted in the fatty acid profiles of the fish muscle tissues between all diets. Fish on the TO diet had a significantly greater percentage of DHA in muscle tissue compared with fish on all other diets. Blood osmolarity, which is inversely related to the ability of salmon to smolt, from the TO and FO fed fish was significantly lower than that of fish on the PO diet. This study showed that thraustochytrid oil can be used to replace fish oil in Atlantic salmon diets without detriment to the growth of parr. Including thraustochytrid oil in fish diets significantly increases the amount of DHA in Atlantic salmon muscle and therefore is a candidate for use in oil blends for salmon diets. Thraustochytrid oil provides a renewable source of essential fatty acids, in particular DHA, for aquafeeds. [Copyright &y& Elsevier]

• SCOs are interesting bioproducts to be applied in different industrial sectors. • To use of alternative carbon sources is crucial for the profitability of the SCOs. • Lignocellulosic sugars, VFAs and glycerol are alternative substrates for SCOs. • Lipid yields from low-cost carbon sources are increased by synthetic biology tools. • Downstream processes are decisive for the effectiveness of the SCO production. Microbial lipids have recently drawn a lot of attention as renewable sources for biochemicals production. Strong research efforts have been addressed to efficiently use organic wastes as carbon source for microbial lipids, which would definitively increase the profitability of the production process and boost a bio-based economy. This review compiles interesting traits of oleaginous microorganisms and highlights current trends on microbial- and process-oriented approaches to maximize microbial oil production from inexpensive substrates like lignocellulosic sugars, volatile fatty acids and glycerol. Furthermore, downstream processes such as cell harvesting or lipid extraction, that are decisive for the cost-effectiveness of the process, are discussed. To underpin microbial oils within the so demanded circular economy, associated challenges, recent advances and possible industrial applications that are also identified in this review. [ABSTRACT FROM AUTHOR]

Abstract: A yeast, Rhodotorula glutinis, is regarded as a potential microbial oil producer, due to its high lipid content. The flask results of this study indicated that irradiation could increase the growth of R. glutinis compared to that of a batch without irradiation. Further 5-l fermenter results confirmed that irradiation could greatly enhance the cells’ growth rate and total lipid productivity. The maximum lipid productivity obtained in the fed-batch operation with 3 LED (light emitting diode) lamps was 0.39g/lh as compared to 0.34g/lh in the batch with 3 LED lamps and 0.19g/lh in the batch without irradiation. Conclusively, the irradiation could significantly increase the cells’ growth rate, which, in turn, could be applied to the commercialized production of biodiesel from single cell oils. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]

Using residual material instead of sugars as substrate for oleaginous microorganisms is a promising approach that may reduce the production costs of microbial lipid. In this study, five oleaginous yeasts were screened for their ability to grow and produce lipid utilizing volatile fatty acids (VFAs), generated from anaerobic fermentation of microalgal biomass, as the only carbon and energy source. Yeasts growth and lipid accumulation capacity at three VFAs concentrations (i.e. 5, 10 and 15 g L−1) were evaluated. Regardless of VFAs concentration four of the five strains were able to grow in digestates reaching biomass yields from VFAs between 0.22 and 0.37 g g−1. The highest lipid content in dry biomass was observed in Cutaneotrichosporon curvatum and Cyberlindnera saturnus (36.9 and 33.9% on dry biomass, respectively) corresponding to lipid yields from VFAs of 0.11 and 0.13 g g−1, respectively. Oleic, palmitic and linoleic acids were the major fatty acids, accounting for more than 70% of the fatty acids contained in total yeast lipids, profile similar to that of common vegetable oils. The above findings suggest that microalgal biomass derived VFAs could be converted into yeast lipid suitable as feedstock in the chemical (including biofuel) industry. • Yeasts use volatile fatty acids from anaerobic fermentation as carbon source. • Five oleaginous yeasts showed differences in growth and lipid accumulation. • The highest lipid content was provided by C. curvatu s and W. saturnus. • Obtained lipid yields were comparable to the achieved with sugar-based substrates. • Organic wastes bioconversion to microbial oils is a feasible technology. [ABSTRACT FROM AUTHOR]