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The urgent need to address energy security risks and global warming has led to exploration of renewable energy sources. One such avenue is biodiesel specifically focusing on the potential of Rhodotorula minuta, a type of yeast known for producing lipids that can be used as a sustainable alternative for production of biodiesel. In the current study, this promising yeast was evaluated for its potential to produce lipids. The morphological characterization was carried out by scanning electron microscope (SEM), and intracellular detail was studied by transmission electron microscope (TEM). Changes in content and cellular biomass were monitored at time intervals with the highest biomass yield of 12.4 g/l and lipid content of 6.2 g/l achieved after 72 h. In the present work, magnesium oxide nanoparticles (MgO NPs) were synthesized and extensively characterized through Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), Brunauer–Emmett–Teller (BET), SEM, TEM, and X-ray diffraction (XRD). By employing response surface methodology (RSM) with Box–Behnken design (BBD), optimal process conditions for transesterification could be determined. The best result achieved was a yield of 88.6% when the conditions were optimized, using methanol to oil ratio of 18:1 and 8% (w/w) amount of catalyst maintaining a reaction temperature of 55 °C and allowing the reaction to proceed for 120 min. [ABSTRACT FROM AUTHOR]

Recently, microbial oil has become one of the promising next-generation feedstocks for producing biodiesel. While microbial oil can be extracted from different sources, there is only limited work on microbial production from fruits and vegetables. In this work, biodiesel was extracted through a two-step process: microbial conversion of vegetable waste into microbial oil using Lipomyces starkeyi, followed by transesterification of microbial oil into biodiesel. The lipid accumulation, composition of microbial oil, and the fuel properties of biodiesel were evaluated. The microbial oil consisted mainly of C16:0, C18:0 and C18:1, which were close to the properties of palm oil. The fuel properties of biodiesel comply with the EN14214:2012 standard. Thus, the vegetable waste can be a good biodiesel feedstock. Three blends (MOB10, MOB20 and MOB30 with 10, 20, and 30% of biodiesel) were tested for engine performance and emission characteristics in a 3.5 kW VCR research engine. At full load, MOB20 reduced the pollutant emissions of CO and HC by 47.8% and 33.2% with the penalty of increased NOx by 3.9%, while BTE reduced by 0.8% with the increased BSFC by 5.2%. Thus, the addition of vegetable waste biodiesel blends reduced the emissions of CO and HC significantly with slight reduction of brake thermal efficiency. [ABSTRACT FROM AUTHOR]

Abstract Background Global resource reallocation is an established critical strategy through which organisms deal with environmental stress. The regulation of intracellular lipid storage or utilization is one of the most important strategies for maintaining energy homeostasis and optimizing growth. Oleaginous microorganisms respond to nitrogen deprivation by inducing lipid hyper accumulation; however, the associations between resource allocation and lipid accumulation are poorly understood. Results Here, the time-resolved metabolomics, lipidomics, and proteomics data were generated in response to nutrient availability to examine how metabolic alternations induced by nitrogen deprivation drive the triacylglycerols (TAG) accumulation in M. alpina. The subsequent accumulation of TAG under nitrogen deprivation was a consequence of the reallocation of carbon, nitrogen sources, and lipids, rather than an up-regulation of TAG biosynthesis genes. On one hand, nitrogen deprivation induced the down-regulation of isocitrate dehydrogenase level in TCA cycle and redirected glycolytic flux of carbon from amino acid biosynthesis into fatty acids’ synthesis; on the other hand, nitrogen deprivation induced the up-regulation of cell autophagy and ubiquitin-mediated protein proteolysis which resulted in a recycling of preformed protein nitrogen and carbon. Combining with the up-regulation of glutamate decarboxylase and succinic semialdehyde dehydrogenase in GABA shunt, and the phosphoenolpyruvate carboxykinase in the central hub involving pyruvate/phosphoenolpyruvate/oxaloacetate, the products from nitrogen-containing compounds degradation were recycled to be intermediates of TCA cycle and be shunted toward de novo biosynthesis of fatty acids. We found that nitrogen deprivation increased the protein level of phospholipase C/D that contributes to degradation of phosphatidylcholine and phosphatidylethanolamine, and supplied acyl chains for TAG biosynthesis pathway. In addition, ATP from substrate phosphorylation was presumed to be a critical factor regulation of the global resource allocation and fatty acids’ synthesis rate. Conclusions The present findings offer a panoramic view of resource allocation by M. alpina in response to nutrient stress and revealed a set of intriguing associations between resource reallocation and TAG accumulation. This system-level insight provides a rich resource with which to explore in-depth functional characterization and gain information about the strategic combination of strain development and process integration to achieve optimal lipid productivity under nutrient stress.

产油微生物具有生长迅速、对环境适应能力强等诸多优点，是油脂生产领域的研究热点。与单一微生物培养相比，微生物混合培养对底物的选择性更广泛、利用效率更高，近几年越来越多地应用于工农业废弃物、城市废水和食物垃圾等的处理以及微生物油脂的生产。简要介绍了微生物油脂，综述了微生物混合培养生产油脂的现状以及发酵底物的研究情况，并提出了今后的研究方向。藻-菌、藻-藻和菌-菌混合培养是微生物混合培养生产油脂的主要研究对象，尤其是微藻与酵母混合培养利用废弃物生产油脂，对于降低生产成本和保护环境具有重要意义。今后应扩大混合培养微生物的种类，并筛选高产高附加值代谢产物的微生物作为混合培养的研究对象。Oleaginous microorganism which have many advantages, such as rapid growth and strong adaptability to the environment, has attracted intensive attention. Besides, compared with the monoculture, mixed culture exhibite wider selection for substrates as well as higher utilization efficiency. Recently, it has been increasingly used in the treatment of industrial and agricultural wastes, municipal wastewater and food wastes, as well as the microbial oil production. The microbial oil was simply introduced, the present situation of oil production by microbial mixed culture and the research status of substrates were reviewed, and the future research directions were proposed. The main object of microbial oil production by mixed culture was the combination of algae-yeast, algae-algae and yeast-yeast. Especially, oil production using wastes by mixed culture of microalgae and yeasts was of great significance in cost reduction and environment protection. Besides, it was necessary to enlarge the microorganism species as well as screening high-yield and high-value-added ones in the mixed culture in the future.

Depletion of hydrocarbons is forcing to find alternative resources to meet the energy demand of the growing population. Microbial biodiesel as a fuel can act as a cheaper and eco-friendly alternative to fossil fuel. Single-cell oil (SCO) consisting of carbon, hydrogen and oxygen grown over the lignocellulosic biomass using oleaginous microorganisms are triacylglycerols which can be converted to biodiesel, with physicochemical properties similar to conventional diesel. However, several cost-effective pretreatment methods are required to utilize lignocellulosic biomasses. The current research study investigates the SCO yield (and biodiesel characteristics) obtained from sugarcane bagasse hydrolysate through various pretreatment techniques. The pretreatment with 4% v/v H2SO4 at 25 min of ultra-sonication provided the best depolymerisation results (based on the glucose concentration). Yarrowia lipolytica was inoculated into the hydrolysates, allowed to grow at 25 °C, pH of 6.5 and rapid mixing for six days yielded biomass of 16.39 g/l. Biodiesel was extracted from the biomass via in-situ and ex-situ transesterification. In-situ transesterification carried out with the catalyst K2CO3 yields 80% biodiesel. In comparison, 63% were achieved with ex-situ transesterification, where lipid extraction was carried out as a first step and transesterified further in the presence of catalyst KOH to obtain biodiesel. The obtained fatty acid methyl esters (FAME) was subjected to FTIR analysis, and the observed physicochemical properties were within the international standards.

Microbial lipids have similar fatty acid composition to plant oils, and therefore, are considered as an alternative feedstock for biodiesel production. Oleaginous yeasts accumulate considerable amounts of lipids intracellularly during growth on low-cost renewable feedstocks such as lignocellulosic biomass. In this study, we cultivated yeast Trichosporon oleaginosus on hydrolysate of alkaline pretreated corn cobs. Different process configurations were evaluated and compared, including separate hydrolysis and fermentation (SHF) with cellulase recycle and simultaneous saccharification and fermentation (SSF) in batch and fed-batch mode. At low enzyme loading, the highest lipid concentration of 26.74 g L-1 was reached in fed-batch SSF fed with 2.5% (g g-1) substrate. Batch SHF was conducted for four rounds with recycling the cellulase adsorbed on unhydrolyzed lignocellulosic biomass. Thirty percent of cellulase saving was achieved for rounds 2–4 without compromising productivity and lipid yield. The addition of Tween 80 to lignocellulosic slurry improved the hydrolysis rate of structural carbohydrates in pretreated lignocellulosic biomass. Furthermore, supplementing the growth medium with Tween 80 improved lipid yield and productivity without affecting yeast growth. Oleaginous yeast T. oleaginosus is a promising strain for the sustainable and efficient production of lipids from renewable lignocellulosic feedstock. [ABSTRACT FROM AUTHOR]

[Display omitted] • M. isabellina efficiently converts lignocellulosic sugars into lipids. • Vegetative mycelium exhibits higher tolerance to HMF and furfural than spores. • Phenolic compounds inhibit growth and lipid accumulation at low concentrations. • Biodiesel produced from fungal lipids meets the ASTM standard. High production costs of microbial lipids can be reduced by using available and cheap lignocellulosic biomass. The present study optimizes the cultivation conditions of oleaginous fungus Mortierella isabellina and lipid production in corn cobs hydrolysate regarding initial carbon to nitrogen ratio (C:N) in the growth medium, a pretreatment method and, inoculum type. Additionally, we studied the effect of the most abundant lignocellulose-derived inhibitors on lipid synthesis and fungus growth. Low C:N ratios from 5 to 25 mol mol−1 stimulated the fungus growth, while C:N ratios above 50 mol mol−1 gave rise to lipid accumulation. Corn cobs were subjected to dilute acid and alkali pretreatment, using 0.369 g of sulphuric acid and 0.16 g of sodium hydroxide per gram of lignocellulosic biomass, respectively. Growth media based on hydrolysate of alkaline pretreated corn cobs has proved suitable for growth and lipid production. Lipid yield and lipid concentration was 0.13 g g−1 and 8.40 g L−1, respectively. The most toxic inhibitors generated during pretreatment were phenolics, followed by furan aldehydes and aliphatic acids. Using vegetative mycelium instead of spores as inoculum helped cells to overcome the inhibition effect by 5-hydroxymethylfurfural and furan. [ABSTRACT FROM AUTHOR]

Background: Global resource reallocation is an established critical strategy through which organisms deal with environmental stress. The regulation of intracellular lipid storage or utilization is one of the most important strategies for maintaining energy homeostasis and optimizing growth. Oleaginous microorganisms respond to nitrogen deprivation by inducing lipid hyper accumulation; however, the associations between resource allocation and lipid accumulation are poorly understood. Results: Here, the time-resolved metabolomics, lipidomics, and proteomics data were generated in response to nutrient availability to examine how metabolic alternations induced by nitrogen deprivation drive the triacylglycerols (TAG) accumulation in M. alpina. The subsequent accumulation of TAG under nitrogen deprivation was a consequence of the reallocation of carbon, nitrogen sources, and lipids, rather than an up-regulation of TAG biosynthesis genes. On one hand, nitrogen deprivation induced the down-regulation of isocitrate dehydrogenase level in TCA cycle and redirected glycolytic flux of carbon from amino acid biosynthesis into fatty acids' synthesis; on the other hand, nitrogen deprivation induced the up-regulation of cell autophagy and ubiquitin-mediated protein proteolysis which resulted in a recycling of preformed protein nitrogen and carbon. Combining with the up-regulation of glutamate decarboxylase and succinic semialdehyde dehydrogenase in GABA shunt, and the phosphoenolpyruvate carboxykinase in the central hub involving pyruvate/phosphoenolpyruvate/oxaloacetate, the products from nitrogen-containing compounds degradation were recycled to be intermediates of TCA cycle and be shunted toward de novo biosynthesis of fatty acids. We found that nitrogen deprivation increased the protein level of phospholipase C/D that contributes to degradation of phosphatidylcholine and phosphatidylethanolamine, and supplied acyl chains for TAG biosynthesis pathway. In addition, ATP from substrate phosphorylation was presumed to be a critical factor regulation of the global resource allocation and fatty acids' synthesis rate. Conclusions: The present findings offer a panoramic view of resource allocation by M. alpina in response to nutrient stress and revealed a set of intriguing associations between resource reallocation and TAG accumulation. This system-level insight provides a rich resource with which to explore in-depth functional characterization and gain information about the strategic combination of strain development and process integration to achieve optimal lipid productivity under nutrient stress. [ABSTRACT FROM AUTHOR]

[Display omitted] • Concentration-dependent dual roles of PAs on oxidative stress were verified. • Appropriate PAs addition significantly enhanced lipid and DHA production. • Low concentration of PAs reduced ROS and enhanced key enzyme activities and NADPH. • High concentration of PAs inhibited cell growth and lipid accumulation. • High concentration of PAs exerted pro-oxidant effect rather than antioxidant effect. Antioxidant addition is an effective strategy to achieve docosahexaenoic acid (DHA) overproduction in oleaginous microorganisms. Nevertheless, antioxidants like phenolic compounds sometimes exert pro-oxidant activity. In this work, effects of proanthocyanidins (PAs) on fermentation performance and oxidative stress in Schizochytrium sp. were investigated. Low PAs addition (5 mg/L) reduced reactive oxygen species and enhanced lipogenic enzymes activities and NADPH, resulting in significant increase in lipid (20.3 g/L) by 33.6 % and DHA yield (9.8 g/L) by 53.4 %. In contrast, high PAs addition (500 mg/L) exerted pro-oxidant effects, aggravated oxidative damage and lipid peroxidation, leading to sharp decrease in biomass (21.3 g/L) by 35.1 %, lipid (8.2 g/L) by 46.0 %, and DHA (2.9 g/L) by 54.8 %. Therefore, the antioxidant concentration is especially crucial in DHA production. This study is the first to report concentration-dependant dual roles of PAs in oxidative stress and DHA production in Schizochytrium sp., providing new insights into microbial DHA production. [ABSTRACT FROM AUTHOR]

Two strains of yeast-like achlorophyllous alga belonging to the genus Prototheca were isolated from the water and soil, respectively, from a mangrove forest in Thailand. Cultures of both strains were achlorophyllous when grown under light and dark conditions, and they reproduced by release of sporangiospores. Phylogenetic analyses, based on the D1/D2 region of the large subunit ribosomal RNA gene and the small subunit ribosomal RNA gene nucleotide sequences, revealed these two strains were closely related to Prototheca cutis. The strains grew well at 25 °C, weakly or slowly at 30 °C, but not at 35 °C and higher, and were found to be susceptible to 50 μg/disk clotrimazole, as determined by the disk diffusion test. They assimilated a limited number of carbon/nitrogen compounds; glucose, galactose, trehalose, ethanol, glycerol, propylene glycol, lactic acid, fructose and mannose as sole sources of carbon, and ammonium, lysine and cadaverine as sole sources of nitrogen. The two strains are clearly distinguished from P. cutis by the abilities to assimilate polypropylene glycol and the inability to grow at 35 °C and higher. In this study, the ninth member of the genus Prototheca, Prototheca paracutis sp. nov. (ex-type strain YMTW3-1T = JCM 32112T = TBRC8745T), is proposed. The MycoBank number is MB 821626. In addition, P. paracutis sp. nov. was observed to accumulate lipid at up to 21% of the cell dry weight, characterizing it as an oleaginous microorganism. • Two strains of Prototheca, achlorophyllous microalga, were isolated from mangrove. • Prototheca paracutis sp. nov. is proposed to accommodate the two strains. • Prototheca paracutis produced a substantial amount of intracellular lipids. [ABSTRACT FROM AUTHOR]

[Display omitted] • Combination of alkali-BCG pretreated CS and dilute acid pretreated WH was proposed. • The mixed pretreatment liquors (MPLs) were excellent for SCO overproduction. • The toxicity of inhibitors was alleviated via dilution detoxification. • Fed-batch culture of MPLs realized high cell-density and SCO production. • Micro-biodiesel from the combined utilization showed high-quality fuel property. Single cell oil (SCO) prepared from biodiesel-derived crude glycerol (BCG) and lignocellulosic biomass (LCB) via oleaginous yeasts is an intriguing alternative precursor of biodiesel. Here, a novel strategy combining alkaline BCG pretreated corn stover and dilute acid pretreated water hyacinth for SCO overproduction was developed. The mixed pretreatment liquors (MPLs) were naturally neutralized and adjusted to a proper carbon-to-nitrogen ratio beneficial for SCO overproduction by Cutaneotrichosporon oleaginosum. The toxicity of inhibitors was relieved by dilution detoxification. The enzymatic hydrolysate of solid fractions was suitable for SCO production either separately or simultaneously with MPLs. Fed-batch fermentation of the MPLs resulted in high cell mass, SCO content, and SCO titer of 80.7 g/L, 75.7 %, and 61.1 g/L, respectively. The fatty acid profiles of SCOs implied high-quality biodiesel characteristics. This study offers a novel BCG&LCB-to-SCO route integrating BCG-based pretreatment and BCG/LCB hydrolysates co-utilization, which provides a cost-effective technical route for micro-biodiesel production. [ABSTRACT FROM AUTHOR]

Polyunsaturated fatty acids (PUFAs), especially docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA) and arachidonic acid (ARA), are beneficial for reducing blood cholesterol and enhancing memory. Traditional PUFA production relies on extraction from plants and animals, which is unsustainable. Thus, using microorganisms as lipid-producing factories holds promise as an alternative way for PUFA production. Several oleaginous microorganisms have been successfully industrialized to date. These can be divided into universal and specialized hosts according to the products range of biosynthesis. The Yarrowia lipolytica is universal oleaginous host that has been engineered to produce a variety of fatty acids, such as γ-linolenic acid (GLA), EPA, ARA and so on. By contrast, the specialized host are used to produce only certain fatty acids, such as ARA in Mortierella alpina , EPA in Nannochloropsis , and DHA in Thraustochytrids. The metabolic engineering and fermentation strategies for improving PUFA production in universal and specialized hosts are different, which is the subject of this review. In addition, the widely applicable strategies for microbial lipid production that are not specific to individual hosts were also reviewed. [ABSTRACT FROM AUTHOR]

Recent developments in molecular biology and metabolic engineering have resulted in a large increase in the number of strains that need to be tested, positioning high-throughput screening of microorganisms as an important step in bioprocess development. Scalability is crucial for performing reliable screening of microorganisms. Most of the scalability studies from microplate screening systems to controlled stirred-tank bioreactors have been performed so far with unicellular microorganisms. We have compared cultivation of industrially relevant oleaginous filamentous fungi and microalga in a Duetz-microtiter plate system to benchtop and pre-pilot bioreactors. Maximal glucose consumption rate, biomass concentration, lipid content of the biomass, biomass, and lipid yield values showed good scalability for Mucor circinelloides (less than 20% differences) and Mortierella alpina (less than 30% differences) filamentous fungi. Maximal glucose consumption and biomass production rates were identical for Crypthecodinium cohnii in microtiter plate and benchtop bioreactor. Most likely due to shear stress sensitivity of this microalga in stirred bioreactor, biomass concentration and lipid content of biomass were significantly higher in the microtiter plate system than in the benchtop bioreactor. Still, fermentation results obtained in the Duetz-microtiter plate system for Crypthecodinium cohnii are encouraging compared to what has been reported in literature. Good reproducibility (coefficient of variation less than 15% for biomass growth, glucose consumption, lipid content, and pH) were achieved in the Duetz-microtiter plate system for Mucor circinelloides and Crypthecodinium cohnii. Mortierella alpina cultivation reproducibility might be improved with inoculation optimization. In conclusion, we have presented suitability of the Duetz-microtiter plate system for the reproducible, scalable, and cost-efficient high-throughput screening of oleaginous microorganisms. [ABSTRACT FROM AUTHOR]

Manothermonication is a recognized and efficient method used for sterilization in food preservation. The synergistic effect of sonication combined with pressure and temperature allows enhancing the cavitation activity. Never employed for extraction, this study is about the transposition of this process as a tool of extraction. In this study, Rhodosporidium toruloides yeast was submitted to extraction by four modes of sonication, with a temperature ranged from 20 to 55 °C and a pressure between 1 to 2 bars. The lipids extraction yields were compared to the conventional maceration. Microbial oils obtained from both processes were analyzed and quantified by HPTLC (High Performance Thin-Layer Chromatography) and GC-FID (Gas Chromatography with flame ionization detector) after transesterification of lipids. Manothermosonication (30 min, 2 bars, 55 °C) permits to enhance of approximately 20% the extraction yield of lipids to compared to conventional maceration. The fatty acid profiles of each pretreatment and extraction by US, MS, TS and MTS do not affect the fatty acid profiles of yeast (majority of oleic acid (C18:1n9), linoleic acid (C18:2n6) and palmitic acid (C16:0)). Manothermosonication technique shows a great potential for lipid extraction from oleaginous microorganisms. [ABSTRACT FROM AUTHOR]

Population expansion, global warming, and food scarcity have all increased the demand for alternative lipid sources to ensure food and energy security. Furthermore, over the last few decades, industrialization has posed a significant environmental risk to the world through its waste. Utilization of agri-food waste and byproducts as a substrate by oleaginous microorganisms for production of microbial lipids could be a phenomenal approach. Oleaginous microorganisms have numerous advantages, including a shorter life span, rapid growth rate, ease of cultivation, ability to use a variety of substrates, and adaptability to metabolic/genetic changes. Exploiting oleaginous microorganisms for the production of microbial lipids can be viewed as an alternative sustainable food source as well as a versatile raw material for the production of food additives, surfactants, and tailored triacylglycerol's. Microbial oil production processes that mimic plant, animal, and marine lipids are non-toxic, sustainable, and adaptable, as well as energy efficient. Recent research on oleaginous microorganisms, as well as recent interventions in waste management, have resulted in microbial oils being the next and most viable product for a variety of end-user applications and an efficient way of waste management. • Agro-waste as potential substrate for growth of oleaginous microorganisms. • Synergistic conjunction for techno-economic feasibility and quality lipid production. • Oleaginous microorganisms can accumulate >25% lipids. • Improved lipid profile achieved by exogenous and endogenous strategies. • Microbial oil production provides consistent and high-quality PUFA production. [ABSTRACT FROM AUTHOR]

The relationship between morphology of Schizochytrium sp. BCC 25505 and 25509 and production of docosahexaenoic (DHA) were studied in batch and pulsed-batch processes in optimized medium. In batch cultivation, the highest production by Schizochytrium sp. BCC 25505 (60-100% vegetative cells for 72 h) of biomass, DHA, and total fatty acid were 38.7 ± 0.14 g/L at 72 h, 5.9 ± 1.56 g/L at 63 h, and 13.03 ± 0.09 g/L at 54 h, respectively, whereas that of Schizochytrium sp. BCC 25509 (70-100% vegetative cells for 72 h) were 41.35 ± 0.46 g/L at 72 h, 12.09 ± 0.81 g/L at 69 h, and 26.32 ± 2.28 g/ L at 66 h. In pulsed-batch cultivation, the highest production by Schizochytrium sp. BCC 25505 (57-86% vegetative cells) of biomass, DHA, and total fatty acid were 97.05 ± 1.63 g/ L at 166 h, 20.73 ± 1.21 at 166 h, and 35.24 ± 3.27 g/L at 166 h, respectively, whereas that of Schizochytrium sp. BCC 25509 (25-94% vegetative cells) were 101.75 ± 2.19 g/L at 166 h, 20.0 ± 1.31 g/L at 143 h, and 36.48 ± 3.97 g/L at 118 h, respectively. Synchronous vegetative growth in high nitrogen content medium and in controlled high glucose supply for lipid accumulation enhanced efficiency of DHA production. [ABSTRACT FROM AUTHOR]

Biological lipids derived from oleaginous microorganisms are promising precursors for renewable biofuel productions. Direct lipid extraction from wet cell-biomass is favored because it eliminates the need for costly dehydration. However, the development of a practical and scalable process for extracting lipids from wet cell-biomass is far from ready to be commercialized, instead, requiring intensive research and development to understand the lipid accessibility, mechanisms in mass transfer and establish robust lipid extraction approaches that are practical for industrial applications. This paper aims to present a critical review on lipid recovery in the context of biofuel productions with special attention to cell disruption and lipid mass transfer to support extraction from wet biomass. [ABSTRACT FROM AUTHOR]

Biodiesel is a promising alternative energy source as it is renewable, biodegradable, and environmental friendly. This study deals with oils production from wastewater sludge. Primary, secondary, and mixed municipal sludge and pulp and paper secondary sludge collected in Québec City, Canada has 5–11% oil content (based on weight) in initial sludge. The oil content is in the order of pulp and paper secondary sludge > municipal primary sludge > municipal mixed sludge > municipal secondary sludge. Different types of sludge were also used for lipid production by Pichia amethionina sp ., Galactomyces sp ., and Trichosporon oleaginosus . The results showed that maximum lipid content was obtained in municipal secondary sludge among all types. Further, the effect of initial sludge suspended solids concentration (10–30 g/L) on lipid accumulation was investigated. The maximum lipid content of 30.17% and 32.42% w/w dry weight, was reached by P . amethionina sp. and Galactomyces sp., respectively, at 25 g/L suspended solids concentration, and that of 37.69% w/w dry weight by T . oleaginosus at 30 g/L suspended solids concentration all with municipal secondary sludge. The results showed that carbon to nitrogen ratio had more obvious effect on lower suspended solids concentration (10 g/L) than on the higher one (30 g/L) in lipid accumulation of the three strains. [ABSTRACT FROM AUTHOR]

Highlights: [•] Ultrasonication was used in lipid extraction from oleaginous microorganisms. [•] Green solvent was used for lipid extraction. [•] Ultrasonication reduced lipid extraction time. [•] Ultrasonication had no effect on fatty acid profiles. [ABSTRACT FROM AUTHOR]

Lipids are a biorefinery platform to prepare fuel, food and health products. They are traditionally obtained from plants, but those of microbial origin allow for a better use of land and C resources, among other benefits. Several (thermo)chemical and biochemical strategies are used for the conversion of C contained in lignocellulosic biomass into lipids. In particular, pyrolysis can process virtually any biomass and is easy to scale up. Products offer cost-effective, renewable C in the form of readily fermentable molecules and other upgradable intermediates. Although the production of microbial lipids has been studied for 30 years, their incorporation into biorefineries was only described a few years ago. As pyrolysis becomes a profitable technology to depolymerize lignocellulosic biomass into assimilable C, the number of investigations on it raises significantly. This article describes the challenges and opportunities resulting from the combination of lignocellulosic biomass pyrolysis and lipid biosynthesis with oleaginous microorganisms. First, this work presents the basics of the individual processes, and then it shows state-of-the-art processes for the preparation of microbial lipids from biomass pyrolysis products. Advanced knowledge on separation techniques, structure analysis, and fermentability is detailed for each biomass pyrolysis fraction. Finally, the microbial fatty acid platform comprising biofuel, human food and animal feed products, and others, is presented. Literature shows that the microbial lipid production from anhydrosugars, like levoglucosan, and short-chain organic acids, like acetic acid, is straightforward. Indeed, processes achieving nearly theoretical yields form the latter have been described. Some authors have shown that lipid biosynthesis from different lignin sources is biochemically feasible. However, it still imposes major challenges regarding strain performance. No report on the fermentation of pyrolytic lignin is yet available. Research on the microbial uptake of pyrolytic humins remains vacant. Microorganisms that make use of methane show promising results at the proof-of-concept level. Overall, despite some issues need to be tackled, it is now possible to conceive new versatile biorefinery models by combining lignocellulosic biomass pyrolysis products and robust oleaginous microbial cell factories. [ABSTRACT FROM AUTHOR]

The oleaginous fungus Mortierella alpina has distinct advantages in long-chain PUFAs production, and it is the only source for dietary arachidonic acid (ARA) certificated by FDA and European Commission. This review provides an overall introduction to M. alpina , including its major research methods, key factors governing lipid biosynthesis, metabolic engineering and omics studies. Currently, the research interests in M. alpina focus on improving lipid yield and fatty acid desaturation degree by enhancing fatty acid precursors and the reducing power NADPH, and genetic manipulation on PUFAs synthetic pathways is carried to optimise fatty acid composition. Besides, multi-omics studies have been applied to elucidate the global regulatory mechanism of lipogenesis in M. alpina. However, research challenges towards achieving a lipid cell factory lie in strain breeding and cost control due to the coenocytic mycelium, long fermentation period and insufficient conversion rate from carbon to lipid. We also proposed future research goals based on a multilevel regulating strategy: obtaining ideal chassis by directional evolution and high-throughput screening; rewiring central carbon metabolism and inhibiting competitive pathways by multi-gene manipulation system to enhance carbon to lipid conversion rate; optimisation of protein function based on post-translational modification; application of dynamic fermentation strategies suitable for different fermentation phases. By reviewing the comprehensive research progress of this oleaginous fungus, we aim to further comprehend the fungal lipid metabolism and provide reference information and guidelines for the exploration of microbial oils from the perspectives of fundamental research to industrial application. [ABSTRACT FROM AUTHOR]

• Lignocellulolytic oleaginous fungi could pretreat biomass wastes and produce lipid. • Simultaneous saccharification and fermentation (SSF) was efficient process. • Non-sterile fed-batch SSF is practical and effective for yeast lipid production. • Combination use of both oleaginous fungi and yeast increased overall lipid yield. • Consolidated bioprocess of enzyme and lipid production was feasible. Consolidated bioprocesses for bioconversion of lignocellulosic biomass into biodiesel feedstocks were developed. Palm empty fruit bunch (EFB) was biologically pretreated coupling with fungal lipid production (121.4 ± 2.7 mg/g-EFB) by lignocellulolytic oleaginous fungi prior to lipid production by oleaginous yeasts. In subsequent separate hydrolysis and fermentation (SHF) of fungal pretreated EFB (FPEFB), the oleaginous yeast with the maximum lipid yield of 37.0 ± 0.1 mg/g-FPEFB was screened. While a higher lipid yield of 47.9 ± 1.5 mg/g-FPEFB was achieved in simultaneous saccharification and fermentation (SSF) with less enzyme requirement. Fed-batch SSF of non-sterile FPEFB was proven as a practical and efficient strategy to increase lipid yield up to 53.4 ± 0.5 mg/g-FPEFB. Total lipid yield by both fungi and yeast was 165.0 ± 4.4 mg/g-EFB. Interestingly, the consolidated bioprocesses of enzyme and lipid production also achieved comparable total lipid yield of 149.3 ± 6.6 mg/g-EFB. These strategies may contribute greatly to cost-effective and sustainable bioconversion of lignocellulosic biomass into biodiesel feedstocks. [ABSTRACT FROM AUTHOR]