Single cell oils (SCOs) accumulated by oleaginous yeasts have emerged as potential alternative feedstocks for biodiesel production. As lipid accumulation is species and substrate specific, selection of an appropriate strain is critical. Five strains of Y. lipolytica, a known model oleaginous yeast, were investigated to explore their potential for biodiesel production when grown on glucose and inexpensive wastes. All the strains were found to accumulate > 20% (w/w) of their dry cell mass as lipids with neutral lipid as the major fraction when grown on glucose and on wastes such as waste cooking oil (WCO), waste motor oil (WMO). However, amongst them, Y. lipolytica NCIM 3589, a tropical marine yeast, exhibited a maximal lipid/biomass coefficient, YL/X on 30 g L-1 glucose (0.29 g g-1) and on 100 g L-1 WCO (0.43 g g-1) with a high content of saturated and monounsaturated fatty acids similar to conventional vegetable oils used for biodiesel production. The experimentally determined and predicted biodiesel properties of strain 3589 when grown on glucose and WCO, such as density (0.81 and 1.04 g cm-3), viscosity (4.44 and 3.6 mm2 s-1), SN (190.81 and 256), IV (65.7 and 37.8) and CN (56.6 and 50.8) are reported for the first time for Y. lipolytica and correlate well with specified standards. Thus, the SCO of oleaginous tropical marine yeast Y. lipolytica NCIM 3589 could be used as a potential feedstock for biodiesel production.

Background: Single cell oils (SCOs) accumulated by oleaginous fungi have emerged as a potential alternative feedstock for biodiesel production. Though fungi from mangrove ecosystem have been reported for production of several lignocellulolytic enzymes, they remain unexplored for their SCO producing ability. Thus, these oleaginous fungi from the mangrove ecosystem could be suitable candidates for production of SCOs from lignocellulosic biomass. The accumulation of lipids being species specific, strain selection is critical and therefore, it is of importance to evaluate the fungal diversity of mangrove wetlands. The whole cells of these fungi were investigated with respect to oleaginicity, cell mass, lipid content, fatty acid methyl ester profiles and physicochemical properties of transesterified SCOs in order to explore their potential for biodiesel production. Results: In the present study, 14 yeasts and filamentous fungi were isolated from the detritus based mangrove wetlands along the Indian west coast. Nile red staining revealed that lipid bodies were present in 5 of the 14 fungal isolates. Lipid extraction showed that these fungi were able to accumulate > 20% (w/w) of their dry cell mass (4.14 -6.44 g L -1 ) as lipids with neutral lipid as the major fraction. The profile of transesterified SCOs revealed a high content of saturated and monounsaturated fatty acids i.e., palmitic (C16:0), stearic (C18:0) and oleic (C18:1) acids similar to conventional vegetable oils used for biodiesel production. The experimentally determined and predicted biodiesel properties for 3 fungal isolates correlated well with the specified standards. Isolate IBB M1, with the highest SCO yield and containing high amounts of saturated and monounsaturated fatty acid was identified as Aspergillus terreus using morphotaxonomic study and 18 S rRNA gene sequencing. Batch flask cultures with varying initial glucose concentration revealed that maximal cell biomass and lipid content were obtained at 30gL -1 . The strain was able to utilize cheap renewable substrates viz., sugarcane bagasse, grape stalk, groundnut shells and cheese whey for SCO production. Conclusion: Our study suggests that SCOs of oleaginous fungi from the mangrove wetlands of the Indian west coast could be used as a potential feedstock for biodiesel production with Aspergillus terreus IBB M1 as a promising candidate.

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Recent research has focused on use of waste agroresidues for growth of oleaginous microbial biomass as renewable feedstock for biodiesel. However, pretreatment of lignocellulosic biomass into fermentable sugar is necessary for microbial growth, increasing production costs. An oleaginous fungal isolate from the tropical mangrove wetlands, IBB G4, identified as Aspergillus candidus was assessed for its growth on waste agroresidues viz., banana peel, copra meal, corn cob, grape stalks and sugarcane bagasse,which had not been given any thermochemical or enzymatic pre-treatment. The resulting fungal biomass was subjected to in situ (direct) acid transesterification for fatty acid methyl esters (FAME) extraction. Maximal FAME production was obtained on raw untreated banana peel (420 mg/L) and sugarcane bagasse (400 mg/L) with the yields significantly higher (52-68 mg/g of fermented biomass) than those for glucose (32 mg/g). The FAMEs showed major presence of monounsaturated methyl esters (41.7 %; C18:1, C15:1, C17:1, C14:1) and methyl linoleate (C18:2, 36.8 %) and 20 % as saturated fraction when sugarcane bagasse was the substrate for fungal strain. For banana peel, the saturated fatty acid methyl esters (48.6 %; C16:0, C18:0) were abundant, methyl oleate (C18:1, 25 %) was the major monounsaturated fatty ester while methyl linoleate (C18:2, 19 %) and methyl arachidonate (C20:4, 3.8 %) were prevalent as polyunsaturated methyl esters. Biodiesel fuel properties (density, kinematic viscosity, iodine value, cetane number, free and total glycerol) were in accordance with international(ASTM D6751, EN 14214) and national (IS 15607) biodiesel standards, suggesting their suitability as biodiesel fuel.The results in our study indicate the potential suitability of A. candidus IBBG4 biomass grown on raw untreated banana peel and sugarcane bagasse waste and its conversion to FAME by direct in situ acid transesterification. This would help improve process economics for a green and sustainable production of biodiesel.

This study analyzes the single cell oil (SCO), fatty acid profile, and biodiesel fuel properties of the yeast Rhodotorula mucilaginosa IIPL32 grown on the pentose fraction of acid pre-treated sugarcane bagasse as a carbon source. The yeast biomass from nitrogen limiting culture conditions (15.3 g L ) was able to give the SCO yield of 0.17 g g of xylose consumed. Acid digestion, cryo-pulverization, direct in situ transesterification, and microwave assisted techniques were evaluated in comparison to the Soxhlet extraction for the total intracellular yeast lipid recovery. The significant differences were observed among the SCO yield of different methods and the in situ transesterification stood out most for effective yeast lipid recovery generating 97.23 mg lipid as FAME per gram dry biomass. The method was fast and consumed lesser solvent with greater FAME yield while accessing most cellular fatty acids present. The yeast lipids showed the major presence of monounsaturated fatty esters (35-55%; 18:1, 16:1) suitable for better ignition quality, oxidative stability, and cold-flow properties of the biodiesel. Analyzed fuel properties (density, kinematic viscosity, cetane number) of the yeast oil were in good agreement with international biodiesel standards. The sugarcane bagasse-derived xylose and the consolidated comparative assessment of lab scale SCO recovery methods highlight the necessity for careful substrate choice and validation of analytical method in yeast oil research. The use of less toxic co-solvents together with solvent recovery and recycling would help improve process economics for sustainable production of biodiesel from the hemicellulosic fraction of cheap renewable sources.

Yeast lipid as single cell oil (SCO) is evaluated as an alternative renewable source of vegetable oils for a biolubricant formulation. The Rhodotorula mucilaginosa IIPL32 yeast strain is cultivated on lignocellulosic pentosans derived from sugarcane bagasse to produce the SCO. The chemical composition and distribution of variable fatty acids in the yeast SCO are characterized by NMR, FTIR, and GC × GC analyses. The high viscosity index and a low pour point of yeast SCO owing to the favorable composition of saturated and unsaturated fatty acids promise its potential as a renewable and environmentally friendly lube base oil. The yeast SCO as lube base oil significantly reduced the coefficient of friction (72%) and wear (24%) compared to those of conventional mineral lube base oil (SN 150). The fatty acids in the yeast SCO formed a good quality tribo-chemical thin film on the engineering surfaces, which not only reduced the friction but also protected the contact interfaces against wear. This study demonstrates that yeast SCO being renewable, biodegradable, and nontoxic, provides favorable physicochemical and tribophysical properties for good quality lubricant formulation and it can be a good alternative to the conventional mineral lube oil-based lubricants.

Strains of the yeast genus Blastobotrys (subphylum Saccharomycotina) represent a valuable biotechnological resource for basic biochemistry research, single-cell protein, and heterologous protein production processes. Species of this genus are dimorphic, non-pathogenic, thermotolerant, and can assimilate a variety of hydrophilic and hydrophobic substrates. These can constitute a single-cell oil platform in an emerging bio-based economy as oleaginous traits have been discovered recently. However, the regulatory network of lipogenesis in these yeasts is poorly understood. To keep pace with the growing market demands for lipidderived products, it is critical to understand the lipid biosynthesis in these unconventional yeasts to pinpoint what governs the preferential channelling of carbon flux into lipids instead of the competing pathways. This review summarizes information relevant to the regulation of lipid metabolic pathways and prospects of metabolic engineering in Blastobotrys yeasts for their application in food, feed, and beyond, particularly for fatty acid-based fuels and oleochemicals. Key points• The production of biolipids by heterotrophic yeasts is reviewed. • Summary of information concerning lipid metabolism regulation is highlighted.• Special focus on the importance of diacylglycerol acyltransferases encoding genes in improving lipid production is made.