Lipid Production Process Research Articles

Effect of various C/N ratio on lipid production of Mucor irregularis JR 1.1 using glucose as carbon source

Abstract The presence of limited nitrogen plays an important role in the lipid production process in oleaginous fungi, highlighting the significance of achieving an appropriate carbon-to-nitrogen (C/N) ratio to optimize biomass and lipid production. Mucor irregularis JR 1.1, an oleaginous fungi inoculated from Yogyakarta, Indonesia, shows the ability to accumulate lipids up to 43.46% of its total dry biomass. However, the optimum C/N ratio for lipid production of M. irregularis JR 1.1 has not yet been determined. This research aims to explore the effects of different C/N ratios on biomass and lipid production of M. irregularis JR 1.1, utilizing glucose as the primary carbon source. Various C/N ratio ranging from 15 to 75 was examined, alongside with incubation time of 144 hours at 29°C. The optimum C/N ratio was then utilized to construct a growth curve to evaluate the influence of varying incubation time on biomass and lipid production, as well as the lipid productivity of M. irregularis JR 1.1. Results revealed that the highest level of biomass and lipid production were achieved at C/N ratio 40. Additionally, variations in incubation time exhibited a consistent rise in both biomass and lipid production, with the highest lipid productivity achieved at 72 hours of incubation. This study suggests that variation in the C/N ratio and incubation time have discernible impact the biomass and lipid production of M. irregularis JR 1.1 while variations in incubation time did not affect the lipid productivity.

Yeast Lipids from Crude Glycerol Media and Utilization of Lipid Fermentation Wastewater as Maceration Water in Cultures of Edible and Medicinal Mushrooms

Four wild “red” yeast strains (Rhodosporidium kratochvilovae FMCC Y70, R. toruloides NRRL Y-27013, R. toruloides NRRL Y-17902 and R. toruloides NRRL Y-6985) were cultured in shake flasks on industrial glycerol at an initial substrate (Gly0) concentration ≈ 50 g/L under nitrogen limitation. Strains NRRL Y-27013, NRRL Y-17902 and NRRL Y-6985 presented appreciable dry cell weight (DCW) and lipid synthesis (DCW up to 18–19 g/L containing lipids in quantities ≈ 47%, w/w). Strains NRRL Y-27013 and NRRL Y-6985 were further tested in higher Gly0 concentrations (≈90 g/L and ≈110 g/L) with the same initial nitrogen quantity as in the first (“screening”) experiment. Both strains, despite the high Gly0 concentrations and C/N ratios (up to 120 moles/moles) imposed, presented significant DCW production (up to c. 29.0–29.5 g/L). Yeast biomass contained significant lipid (42–43%, w/w) and endopolysaccharide (up to 42%, w/w) quantities. Both lipids and endopolysaccharide quantities (in % w/w) noticeably increased as a response to the imposed nitrogen limitation. Lipids containing mainly oleic and palmitic acids constituted ideal candidates for biodiesel synthesis. Thereafter, the wastewaters derived from the lipid production process (lipid fermentation wastewaters—LFWs) were used as maceration waters in cultivations of edible and medicinal fungi, where novel (non-conventional) substrates were used in the performed cultures. CW (coffee residue + wheat straw), CB (coffee residue + beech wood shavings), OW (olive crop + wheat straw), OB (olive crop + beech wood shavings), RW (rice husk + wheat straw) and RB (rice husk + beech wood shavings) were soaked/sprayed with LFWs or tap water and utilized in the cultivation of Pleurotus, Ganoderma and Lentinula mushrooms. The impact of LFWs on the mycelial growth rate (mm/d) and biomass production was evaluated. The results show that regardless of the wetting method, the highest growth rates (6.2–6.6 mm/d) were noticed on RW and RB for Pleurotus eryngii and Ganoderma resinaceum, on OW, OB and RW for Ganoderma applanatum and on RW, OW and OB for Lentinula edodes. Nevertheless, high biomass production was obtained on substrates soaked with LFWs for Pleurotus ostreatus (RW: 443 mg/g d.w.), L. edodes (RB: 238 mg/g d.w.) and Ganoderma lucidum (RW: 450 mg/g d.w.). Overall, this study demonstrates the possibility of the industrial conversion of low-value agro-waste to mycelial mass and eventually to important food products.

Mastering targeted genome engineering of GC-rich oleaginous yeast for tailored plant oil alternatives for the food and chemical sector

BackgroundSustainable production of triglycerides for various applications is a major focus of microbial factories. Oleaginous yeast species have been targeted for commercial production of microbial oils. Among all the oleaginous yeasts examined in a previous comparative study, Cutaneotrichosporon oleaginosus showed the highest lipid productivity. Moreover, a new lipid production process for C. oleaginosus with minimal waste generation and energy consumption resulted in the highest lipid productivity in the history of oleaginous yeasts. However, productivity and product diversity are restricted because of the genetic intractability of this yeast. To date, successful targeted genetic engineering of C. oleaginosus has not yet been reported.ResultsThe targeted gene editing was successfully carried out in C. oleaginosus using CRISPR/Cas system. A tailored enzyme system isolated to degrade the C. oleaginosus cell wall enabled the isolation of viable spheroplasts that are amenable to in-cell delivery of nucleic acids and proteins. The employment of both Cas9 protein and Cas mRNA was effective in obtaining strains with URA5 knockout that did not exhibit growth in the absence of uracil. Subsequently, we successfully created several strains with enhanced lipid yield (54% increase compared to that in wild type) or modified fatty acid profiles comparable with those of cocoa butter or sunflower oil compositions.ConclusionThis study establishes the first targeted engineering technique for C. oleaginosus using the CRISPR/Cas system. The current study creates the foundation for flexible and targeted strain optimizations towards building a robust platform for sustainable microbial lipid production. Moreover, the genetic transformation of eukaryotic microbial cells using Cas9 mRNA was successfully achieved.

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 (0g/L). This fact demonstrated the suitability of using low-phosphate concentrations to boost lipid production from SCFAs.

Carbon/nitrogen ratio as a tool to enhance the lipid production in Rhodosporidium toruloides-1588 using C5 and C6 wood hydrolysates

The interest in microbial lipids has recently increased because of their wide use to produce several value-added compounds in the biofuel, pharmaceutical and food industries. Oleaginous yeast such as Rhodosporidium toruloides could be an efficient option because of its ability to consume five-carbon sugars, high lipid accumulation, and tolerance to toxic compounds such as furans, phenolic compounds, and organic acids. The present study aims to investigate the effect of different initial sugar ratios, in combination with different carbon/nitrogen ratios, and the use of dibasic sodium phosphate (Na2HPO4) as an inducer on cell biomass production, sugar consumption, and lipid accumulation by Rhodosporidium toruloides-1588. The investigation showed a maximum lipid accumulation of 5.35 gL-1 (0.28 g of lipids/g of sugar) under the culture conditions of initial glucose: xylose ratio of 1:1, C/N ratio of 70, and Na2HPO4 concentration of 1.05 gL-1. The predominant lipids composition was palmitic, stearic, oleic, and linoleic acids which could be used as a suitable feedstock for biofuel production. Additionally, under the optimal conditions (initial glucose: xylose ratio of 1:1, 1.19 gL-1 of Na2HPO4 and C/N ratio of 70.50) an increase of 10.5% and 7.5% in lipid accumulation was observed, compared with control treatments (glucose and xylose, respectively). In addition, the study shows the ability of R. toruloides-1588 to tolerate inhibitors, a feature that could be a promising alternative to increase the feasibility of the microbial lipid production process using undetoxified wood hydrolysate as a sustainable culture media.

Heterologous Expression of CFL1 Confers Flocculating Ability to Cutaneotrichosporon oleaginosus Lipid-Rich Cells.

Lipid extraction from microbial and microalgae biomass requires the separation of oil-rich cells from the production media. This downstream procedure represents a major bottleneck in biodiesel production, increasing the cost of the final product. Flocculation is a rapid and cheap system for removing solid particles from a suspension. This natural characteristic is displayed by some microorganisms due to the presence of lectin-like proteins (called flocculins/adhesins) in the cell wall. In this work, we showed, for the first time, that the heterologous expression of the adhesin Cfl1p endows the oleaginous species Cutaneotrichosporon oleaginosus with the capacity of cell flocculation. We used Helm's test to demonstrate that the acquisition of this trait allows for reducing the time required for the separation of lipid-rich cells from liquid culture by centrifugation without altering the productivity. This improves the lipid production process remarkably by providing a more efficient downstream.

An emerging simple and effective approach to increase the productivity of thraustochytrids microbial lipids by regulating glycolysis process and triacylglycerols\u2019 decomposition

BackgroundThe oleaginous microorganism Schizochytrium sp. is widely used in scientific research and commercial lipid production processes. However, low glucose-to-lipid conversion rate (GLCR) and low lipid productivity of Schizochytrium sp. restrict the feasibility of its use.ResultsOrlistat is a lipase inhibitor, which avoids triacylglycerols (TAGs) from hydrolysis by lipase. TAGs are the main storage forms of fatty acids in Schizochytrium sp. In this study, the usage of orlistat increased the GLCR by 21.88% in the middle stage of fermentation. Whereas the productivity of lipid increased 1.34 times reaching 0.73 g/L/h, the saturated fatty acid and polyunsaturated fatty acid yield increased from 21.2 and 39.1 to 34.9 and 48.5 g/L, respectively, indicating the advantages of using a lipase inhibitor in microbial lipids fermentation. Similarly, the system was also successful in Thraustochytrid Aurantiochytrium. The metabolic regulatory mechanisms stimulated by orlistat in Schizochytrium sp. were further investigated using transcriptomics and metabolomics. The results showed that orlistat redistributed carbon allocation and enhanced the energy supply when inhibiting the TAGs’ degradation pathway. Therefore, lipase in Schizochytrium sp. prefers to hydrolyze saturated fatty acid TAGs into the β-oxidation pathway.ConclusionsThis study provides a simple and effective approach to improve lipid production, and makes us understand the mechanism of lipid accumulation and decomposition in Schizochytrium sp., offering new guidance for the exploitation of oleaginous microorganisms.

Multiobjective non linear model predictive control of transesterification and lipid oil production

Biodiesel is one of the most important alternate fuels that is clean and has no negative environmental effects. Transesterification and lipid production are the main unit operations in biodiesel production. It is important that both these processes are conducted in the most efficient manner ensuring that the best possible product is obtained. A rigorous multiobjective nonlinear model predictive control strategy for the transesterification and lipid production processes is presented. The objective is to maximize the concentration of the required products while minimizing the impurities. This is very significant for biochemical engineers as it will provide strategies to get the best possible product while minimizing the cost of purification. The simultaneous maximization of the required product and the minimization of the impurities is novel and will be instrumental in preventing equipment damage in addition to reducing the purification expenses. The optimization language pyomo is used in conjunction with the global optimization solver BARON. A comparison of the performances of the single objective optimal control and the multiobjective nonlinear model predictive control is made and it is seen that the latter is effective in maximizing the quantity of the required product while minimizing the amount of the other chemicals and thus reducing the cost of purification and demonstrates that the multiobjective approach is more beneficial than the single-objective strategy.

Microbial contamination control mechanism in lipid production using distillery wastewater and oleaginous yeast – Antimicrobial compounds in wastewater as a double-edged sword

Microbial contamination and the high expense of sterilization are the key factors limiting the application of resource recovery in processes such as producing lipids (can be converted to biodiesel via transesterification) from wastewater. This study was conducted to study the succession of contaminating and indigenous microorganisms, analyze the mechanism and propose a control strategy for undesirable microorganisms in the non-sterile lipid production process using distillery wastewater and oleaginous yeast. In the early stage, indigenous microorganisms (Pichia, Saccharomyces, Acetobacter and Gluconobacter) were the main competitors. Based on antimicrobial experiment and analyses of liquid chromatography-tandem mass spectrometry (LC-MS/MS) and gas chromatography mass spectrometry (GC-MS), the antimicrobial compounds (such as lactic acid 10,011–17,498 mg/L, succinic acid 210–325 mg/L and furfural 0.63–1.23 mg/L) combined with the low pH (3.2–3.8) in distillery wastewater played the primary role in the prevention of contaminating bacteria in this stage rather than the potential antimicrobial compounds from oleaginous yeast. Cinnamic acid (56–143 mg/L) was the main inhibitor against oleaginous yeast among the major antimicrobial compounds in wastewater. Its inhibition decreased when pH increased from 3.2 to 5.5. In the later stage, as the pH increased to over 7 during the culture, heterotrophic bacteria (Chryseobacterium and Sphingobacterium) with a relatively low tolerance for acidic conditions became the dominant undesirable microorganisms. Utilizing the antimicrobial activity of distillery wastewater combined with a high inoculum size and proper pH control could be effective for achieving dominant oleaginous yeast growth and improving lipid production in non-sterile conditions.

Co‐production of microbial lipids with valuable chemicals

AbstractMicrobial lipids are promising substitutes for petroleum and plant oil. However, the industrialization of microbial lipids is still limited and cannot compete with petrochemical petroleum due to its high production cost. Microorganisms capable of accumulating lipids and additional valuable chemicals are attractive for improving the economics of the microbial lipid production process. Compared with the increase in production of complex metabolic engineering to improve the overall economy, the multi‐chemical co‐production system is more advantageous in balancing the metabolic flux and optimal cell physiological recovery. In this review, various chemicals co‐produced with microbial lipids are classified according to their cell location. Efficient strategies, including the fermentation process and genetic engineering for regulating and enhancing such co‐production systems, are comprehensively discussed. The prospective and challenges during the scale‐up of lipids and valuable chemicals co‐production process are also highlighted. © 2021 Society of Chemical Industry and John Wiley & Sons, Ltd

Continuous Production of Lipids with Microchloropsis salina in Open Thin-Layer Cascade Photobioreactors on a Pilot Scale

Studies on microalgal lipid production as a sustainable feedstock for biofuels and chemicals are scarce, particularly those on applying open thin-layer cascade (TLC) photobioreactors under dynamic diurnal conditions. Continuous lipid production with Microchloropsis salina was studied in scalable TLC photobioreactors at 50 m2 pilot scale, applying a physically simulated Mediterranean summer climate. A cascade of two serially connected TLC reactors was applied, promoting biomass growth under nutrient-replete conditions in the first reactor, while inducing the accumulation of lipids via nitrogen limitation in the second reactor. Up to 4.1 g L−1 of lipids were continuously produced at productivities of up to 0.27 g L−1 d−1 (1.8 g m2 d−1) at a mean hydraulic residence time of 2.5 d in the first reactor and 20 d in the second reactor. Coupling mass balances with the kinetics of microalgal growth and lipid formation enabled the simulation of phototrophic process performances of M. salina in TLC reactors in batch and continuous operation at the climate conditions studied. This study demonstrates the scalability of continuous microalgal lipid production in TLC reactors with M. salina and provides a TLC reactor model for the realistic simulation of microalgae lipid production processes after re-identification of the model parameters if other microalgae and/or varying climate conditions are applied.

Sync between leucine, biotin and citric acid to improve lipid production by Yarrowia lipolytica on crude glycerol-based media

The use of biodiesel-derived glycerol as a carbon source for single cell oil (SCO) production is a biorefinery engineering strategy that aims to valorize the by-product waste and make the microbial lipid production process more cost-effective. This work aimed to improve the capacity of Yarrowia lipolytica to produce large amounts of lipids and replace genetic engineering by a metabolic approach based on the stimulation of the rate-limiting enzymes and reducing the activation energy thereby increasing the rate of lipids synthesis. The effects of biotin and leucine addition on the lipid content of Y. lipolytica have been investigated. The lipid content of Y. lipolytica was strongly influenced by the addition of biotin. In fact, an increase in biotin concentration from 25 μg/L to 200 μg/L practically increased the lipid concentration up to 15 g/L. Besides, to channel metabolic flux into lipid biosynthesis, the addition of citric acid as lipid precursor led to an increase in total catabolism activation and lipid accumulation to reach around 63% (w/w). The biochemical approach can be a useful target for improving the efficiency of lipid-producing yeast strain rather than genetic engineering.

Parkin on serine: a Parkinson disease gene suppresses serine synthesis in cancer.

Phosphoglycerate dehydrogenase (PHGDH) catalyzes the first step in the synthesis of the amino acid serine, important for protein synthesis, one-carbon metabolism, lipid production, redox homeostasis, and other key processes of normal and cancer metabolism. While PHGDH is often overexpressed in cancer cells, how it is regulated has been unclear. In this issue of the JCI, Liu and colleagues describe a new aspect of PHGDH regulation, demonstrating that the Parkinson disease gene and tumor suppressor Parkin bound and ubiquitinated PHGDH. Parkin promoted PHGDH degradation, suppressed serine synthesis, and inhibited tumor growth in human cancer cell line xenografts. Conversely, inactivation of Parkin not only accelerated tumor growth, but also sensitized tumors to small molecule inhibitors of PHGDH. These results offer a new link between Parkin and the serine synthesis pathway, and they bear translational potential that warrants further study in Parkin-deficient human cancers.

Production of linoleic acid‐rich lipids in molasses‐based medium by oleaginous fungus Galactomyces geotrichum TS61

This study was performed to produce linoleic acid-rich lipids in molasses-based medium using locally isolated fungus Galactomyces geotrichum TS61 (GenBank accession: MN749818). The most favorable culture conditions for lipid production were determined as 200 ml/L molasses, 1.5 g/L ammonium sulfate, 1.5 g/L KH2PO4, pH 6, and 8 days incubation time. Maximum values of cell concentration, lipid concentration, and lipid content were 17.1 g/L, 11.9 g/L, and 69.6%, respectively. Polyunsaturated fatty acids (PUFAs) (42.49%) accounted for the majority of fatty acids in this fungus. Linoleic acid (23.67%) was the most abundant fatty acid followed by oleic acid (22.14%). Minor fatty acids were palmitoleic acid, stearic acid, palmitic acid, pentadecanoic acid, and myristic acid. Fatty acid analyses show that lipids of this fungus may be used as food supplement and/or medicinal therapeutics. The lipid production by G. geotrichum in molasses-based medium was investigated for the first time in this study. Practical applications Galactomyces geotrichum strains are not pathogenic and can be used as starter culture in the preparation of fermented foods. This study demonstrated that the local isolate G. geotrichum TS61 could accumulate high amounts of polyunsaturated fatty acids (PUFAs), especially linoleic acid, when was cultivated in molasses-based simple medium. Due to fatty acid composition, lipids of this fungus may be used as food supplement and/or medicinal therapeutics. Moreover, the high lipid productivity, simple nutrient requirement, and nonhuman pathogenicity can make this fungus an ideal platform for lipid production processes. On the contrary, this fungus can be employed as a tool in bioremediation of molasses since it can tolerate high concentrations of molasses.

Scale-up strategy for yeast single cell oil production for Rhodotorula mucilagenosa IIPL32 from corn cob derived pentosan

This work was aimed to strategically scale-up the yeast lipid production process using Reynolds number as a standard rheological parameter from 50 mL to 50 L scale. Oleaginous yeast Rhodotorula mucilaginosa IIPL32 was cultivated in xylose rich corncob hydrolysate. The fermentation process for growth and maturation was operated in fed-batch with two different C/N ratios of 40 and 60. The hydrodynamic parameters were used to standardize and represent the effect of rheology on the fermentation process. The growth pattern of the yeast was found similar in both shake flask and fermenter with the maximum growth observed at 48 h. The lipid yield increased from 0.4 g/L and 0.5 g/L to 1.3 g/L and 1.83 g/L for 50 mL to 50 L for C/N ratio 40 and 60 respectively. The increase in productivity during the growth phase and lipid accumulation during the maturation phase showed that the scale-up strategy was successful.

Utilization of Amino Acid-Rich Wastes for Microbial Lipid Production.

To produce microbial lipids for biofuel production, carbohydrates and related compounds from biomass have been routinely utilized, yet amino acids (AA) from protein-rich wastes have been overlooked so far. We use the oleaginous yeast Cryptococcus curvatus ATCC 20509 as a lipid producer and evaluate the capacity for lipid production on proteinogenic AA individually or in designated blends under two-staged culture conditions. It was found that cellular lipid contents reached 48.8%, 44.5% and 29.0% when yeast cells were cultivated in media-contained AA blends with compositional profiles similar to those of sheep viscera, meat industry by-products and fish muscle, respectively, and that lipid coefficients were more than 0.10gg-1. Furthermore, cellular lipid contents were higher than 20% when most AA were used individually. High lipid coefficients of over 0.23gg-1 were observed when Pro, Trp or Leu were used as a substrate. Results also indicated that higher initial media pH or reduced phosphate concentration was beneficial for lipid production on AA. This work demonstrated the potential to use AA and related wastes as substrates for microbial lipid production by the yeast C. curvatus, which fit well with the protein-based biorefinery concept. Further efforts should be devoted to recognizing the metabolic features, identifying more robust lipid producer and optimizing lipid production processes.

Rheology analysis of sago processing wastewater with variable starch content

Rheology properties are considered to be essential for designing a bioreactor to understand the flow behavior of materials inside the reactor. In this regard, rheological measurements of sago processing wastewater with different starch concentrations ranged 10, 20, 30, 40, 50, 60, 70, and 80 g L-1 were evaluated. The sago wastewater with a starch concentration of 10 and 20 g L-1 indicated a non- Newtonian behavior, showing yield stress and shear thinning. Based on the results, it is concded that sago wastewater with starch concentrations up to 20 g L-1 could be well suited for airlift bioreactors used for the microbial lipid production process.

Lipids production from Scenedesmus obliquus through carbon/nitrogen ratio optimization

Microalgae are one of the most promising sources of raw material for biofuel production and derivatives since its high yield of biomass and metabolites possess a low environmental impact. However, its implementation on large scale facilites still faces challenges such as the optimisation of lipid production (due to strain capacity and environmental factors) and downstream processes (extraction and separation of the lipidic fraction). The objective of the present investigation was to determine the potential of the carbon/nitrogen ratio as a technical tool for the improvement of total lipids on Scenedesmus obliquus. The carbon/nitrogen ratio was evaluated using a non-factorial design coupled with surface response methodology with sodium bicarbonate and sodium nitrate as carbon and nitrogen source. Results showed that the optimal conditions that enhanced the lipid deposition (up to 66% w/w) were 1.5 g L−1 sodium bicarbonate and 0,125 g L−1 of sodium nitrate. Finally, the results of the fatty acid profile shown the presence of stearic acid (C18: 0) with 22.63% and elaidic acid (C18:1) with 77.38%, with the absence of fatty acids of two or more double bonds. In conclusion, the adjustment in the carbon/nitrogen ratio favours the final deposition of lipids in Scenedesmus obliquus which is emerging as a possible candidate for the production of lipids of interest for the generation of biodiesel.

Proteome analysis of xylose metabolism in Rhodotorula toruloides during lipid production

BackgroundRhodotorula toruloides is a promising platform organism for production of lipids from lignocellulosic substrates. Little is known about the metabolic aspects of lipid production from the lignocellolosic sugar xylose by oleaginous yeasts in general and R. toruloides in particular. This study presents the first proteome analysis of the metabolism of R. toruloides during conversion of xylose to lipids.ResultsRhodotorula toruloides cultivated on either glucose or xylose was subjected to comparative analysis of its growth dynamics, lipid composition, fatty acid profiles and proteome. The maximum growth and sugar uptake rate of glucose-grown R. toruloides cells were almost twice that of xylose-grown cells. Cultivation on xylose medium resulted in a lower final biomass yield although final cellular lipid content was similar between glucose- and xylose-grown cells. Analysis of lipid classes revealed the presence of monoacylglycerol in the early exponential growth phase as well as a high proportion of free fatty acids. Carbon source-specific changes in lipid profiles were only observed at early exponential growth phase, where C18 fatty acids were more saturated in xylose-grown cells. Proteins involved in sugar transport, initial steps of xylose assimilation and NADPH regeneration were among the proteins whose levels increased the most in xylose-grown cells across all time points. The levels of enzymes involved in the mevalonate pathway, phospholipid biosynthesis and amino acids biosynthesis differed in response to carbon source. In addition, xylose-grown cells contained higher levels of enzymes involved in peroxisomal beta-oxidation and oxidative stress response compared to cells cultivated on glucose.ConclusionsThe results obtained in the present study suggest that sugar import is the limiting step during xylose conversion by R. toruloides into lipids. NADPH appeared to be regenerated primarily through pentose phosphate pathway although it may also involve malic enzyme as well as alcohol and aldehyde dehydrogenases. Increases in enzyme levels of both fatty acid biosynthesis and beta-oxidation in xylose-grown cells was predicted to result in a futile cycle. The results presented here are valuable for the development of lipid production processes employing R. toruloides on xylose-containing substrates.

Microbial lipid production from food waste saccharified liquid and the effects of compositions

The residues of food waste after removing waste cooking oils could be converted to microbial lipid by oleaginous yeasts and microbial lipid could be used as a raw material of biodiesel with waste cooking oils. This process would have positive environmental and economic benefits. However, the composition of food waste is extremely complex. Many types of organic acids, such as lactic acid and acetic acid, could be accumulated during the collection, transportation and storage processes. The effects of these substances on microbial lipid production remained unknown. In this study, food waste saccharified liquid (FWSL) without any additional nutrients was fed to Rhodosporidium toruloides 2.1389 for microbial lipid production. Total biomass concentration, lipid concentration and lipid yield increased by 87.4%, 69.4% and 69.3%, respectively, compared with the YPD medium. Remarkably, increasing the concentration of lactic acid in the medium promoted the total biomass concentration of yeast. Furthermore, lipid concentration decreased slightly when single lactic acid or single acetic acid concentration was below 5 g/L or 1 g/L in the culture media. Metal elements that were present in the medium had considerable synergistic effects on lipid production. When four metal elements (i.e. Mg, Ca, Na and K) were present in the medium, total biomass concentration, lipid concentration, lipid content and lipid yield increased by 22.01%, 33.51%, 9.43% and 33.33%, respectively, compared with those in the control group. The interaction among the FWSL compositions that led to the promotion of microbial lipid production was beyond the inhibition effect. The engineering implication analysis evidently suggested that the process of microbial lipid production from FWSL was economically feasible and had potential industrial application prospects.