Lipids of oleaginous yeasts. Part II: Technology and potential applications

Potential utilization of waste sweetpotato vines hydrolysate as a new source for single cell oils production by Trichosporon fermentans

The enzymatic hydrolysate of sweetpotato vines (SVH) characterized as an effective nutrients supplier with low nitrogen availability was firstly used as a substrate by Trichosporon fermentans for single cell oils (SCOs) production. Batch-fermentation experiments on various SVH based media suggested that co-fermentation of SVH and some high-sugar content substrates would be much more efficient and less-cost for SCOs production. A lipid yield of 9.6 g l(-1) with a lipid content of 35.6% was achieved on the SVH without any addition, while 27.6 and 17.7 g l(-1) lipid were respectively obtained on the fructose supplemented SVH media and the SVH mixed with acid treated wheat straw hydrolysate (WSH). The positive effect of SVH on the lipid production of T. fermentans was further demonstrated with a kinetic investigation revealing that SVH had a remarkable promoting effect on the biomass formation and the substrate uptake.

Sweetpotato vines hydrolysate induces glycerol to be an effective substrate for lipid production of Trichosporon fermentans

By co-fermented with sweetpotato vines hydrolysate (SVH), glycerol can be used as an effective substrate for Trichosporon fermentans to produce lipids. Submerged fermentation results showed that T. fermentans exhibited a maximum lipid yield of 7.45 g l(-1) with a biomass of 17.95 g l(-1) on 10% SVH added glycerol mineral medium (Glycerol MM-10% SVH), which was 4.34-fold higher than that on glycerol mineral medium. Lipids produced on glycerol based media exhibited a significantly different fatty acid composition profile from that produced on sugar based media accompanying by a sharp increase in polyunsaturated fatty acids content. Biochemical behaviors characterization further demonstrated that SVH has a remarkable promoting effect on the biomass formation and glycerol uptake. The extremely high lipid yield on Glycerol MM-10% SVH was mainly attributed to the enhancement of SVH on biomass, although SVH is an excellent nutrient supplier for lipid accumulation due to its low nitrogen availability.

Yarrowia lipolytica: safety assessment of an oleaginous yeast with a great industrial potential

Yarrowia lipolytica has been developed as a production host for a large variety of biotechnological applications. Efficacy and safety studies have demonstrated the safe use of Yarrowia-derived products containing significant proportions of Yarrowia biomass (as for DuPont's eicosapentaenoic acid-rich oil) or with the yeast itself as the final product (as for British Petroleum's single-cell protein product). The natural occurrence of the species in food, particularly cheese, other dairy products and meat, is a further argument supporting its safety. The species causes rare opportunistic infections in severely immunocompromised or otherwise seriously ill people with other underlying diseases or conditions. The infections can be treated effectively by the use of regular antifungal drugs, and in some cases even disappeared spontaneously. Based on our assessment, we conclude that Y. lipolytica is a "safe-to-use" organism.

A multi-omic map of the lipid-producing yeast Rhodosporidium toruloides

Triacylglycerols are among the most attractive alternative raw materials for biofuel development. Current oil plant-based technologies are limited in terms of triacylglycerol production capacity and rate. These limitations may be circumvented by biotransformation of carbohydrates into lipids; however, our understanding of microbial oleaginicity remains limited. Here we present the results of a multi-omic analysis of Rhodosporidium toruloides, a robust triacylglycerol-producing fungus. The assembly of genome and transcriptome sequencing data reveals a genome of 20.2 Mb containing 8,171 protein-coding genes, the majority of which have multiple introns. Genes including a novel fatty acid synthase are predicted to participate in metabolic pathways absent in non-oleaginous yeasts. Transcriptomic and proteomic data suggest that lipid accumulation under nitrogen-limited conditions correlates with the induction of lipogenesis, nitrogenous compound recycling, macromolecule metabolism and autophagy. The multi-omic map of R. toruloides therefore provides a valuable resource for efforts to rationally engineer lipid-production pathways.

Effects of selected ionic liquids on lipid production by the oleaginous yeast Rhodosporidium toruloides

Lignocellulosic biomass pretreatment with ionic liquids (ILs) has been emerged as a new technology, but the effects of residual ILs on the downstream biotransformation remain largely unknown. Here, three typical ILs were tested for their effects on lipid production by the oleaginous yeast Rhodosporidium toruloides AS 2.1389. When cultures were maintained at pH 6.0 in the presence of 30mM ILs, [Emim]Cl, [Emim][DEP], or [Emim][OAc], minor inhibition effects were observed. When cultures were performed in the presence of 60mM ILs or without pH control, inhibition was largely dependent on ILs. Detailed analysis indicated that the anion of [Emim][OAc] was assimilated, leading to a rapid alkaline-pH shift and enhanced inhibition on cell growth and lipid production. Our results demonstrated that R. toruloides is a robust lipid producer tolerating ILs at low concentrations, and that care should be taken in bioprocess control and data analysis when ILs are involved.

Lipid production by Rhodosporidium toruloides Y2 in bioethanol wastewater and evaluation of biomass energetic yield

The oleaginous yeast Rhodosporidium toruloides Y2 was employed to remove waste nutrients from bioethanol wastewater while simultaneously producing biomass enriched in microbial lipids. Under optimal conditions, the COD degradation ratio, biomass and lipid content reached 72.3%, 3.8 g/l and 34.9%, respectively. For accelerating biomass and lipid accumulation, different feeding strategies of substrate were conducted. The biomass and lipid production increased by 39.5% and 53.8%, respectively, when glucose at 1.2g/(ld) was added during the last three days of the cultivation. An equation was established to estimate biomass energetic yield. Under optimal conditions, the biomass energetic yield was 50.9% and an increase of 26.0% was obtained by feeding glucose at 1.2g/(ld) during the last three days. The fatty acid composition of the lipids was similar to that from plant oils and other microbial lipids, and could thus be used as raw material for feed additives and biodiesel production.

Optimization of lipid production by the oleaginous yeast Lipomyces starkeyi by random mutagenesis coupled to cerulenin screening

In this work we performed assays for the genetic improvement of the oleaginous yeast Lipomyces starkeyi DSM 70296 focusing on its utilization for lipid biosynthesis from renewable sources. The genetic optimization was carried out by random mutagenesis by ultraviolet irradiation and mutant selection by cerulenin, a compound displaying inhibitory effects on lipid biosynthesis. Mutants demonstrating normal growth in presence of cerulenin were considered as good candidates for further studies. Using this strategy, we selected 6 mutants for further studies, in which their productivities were evaluated by fermentation in shaken flasks and bioreactor. The evaluation of the fermentative performance of mutants was carried out using xylose as sole carbon source; the fermentation of wild-type strain was used as reference. Using this strategy it was possible to identify one mutant (termed A1) presenting a significant increase in the productivity rates of both biomass and lipid in comparison to wild-type strain. A1 mutant was further studied in bioreactor using the same fermentation parameters optimized for L. starkeyi lipid production from a mixed carbon source (xylose:glucose), as previously determined by other studies in our laboratory. A1 presented a productivity increase of 15.1% in biomass and 30.7% in lipid productivity when compared to the wild-type strain with a similar fatty acid composition, despite a slight increase (approx. 7%) on the unsaturated fraction. Our work demonstrates the feasibility of the random mutagenesis strategy coupled with mutant selection based on cerulenin screening for the genetic improvement of the oleaginous yeast L. starkeyi.

High level lipid production by a novel inulinase-producing yeast Pichia guilliermondii Pcla22

In this study, an inulinase-producing yeast strain Pcla22 of Pichia guilliermondii was identified. It was found that the yeast strain Pcla22 could produce higher amount of oil and more lipid bodies in its cells than any other yeast strains tested in this study. Under the optimal conditions, 60.6%(w/w) of lipid based on cell dry weight, 20.4 g/l of the dry cell mass, SCO produced per g of consumed sugar of 0.19 g/g and biomass produced per g of consumed sugar of 0.32 g/g were obtained in the culture of the yeast strain Pcla22 after 96 h of the fed-batch fermentation. Over 79.8% of the fatty acids from the yeast strain Pcla22 grown in the oil production medium containing inulin was C(16:0) and C(18:1), especially C(18:1) (57.9%). The biodiesel obtained from the produced lipid could be burnt well.

Oil production on wastewaters after butanol fermentation by oleaginous yeast Trichosporon coremiiforme

From the distillation process after butanol fermentation, wastewaters mainly consisted of organic acids and residual sugars and with high COD (usually >20,000 mg/L) are generated. Without any pretreatment and adding other nutrients (nitrogen sources and trace elements), these wastewaters were used as substrate for microbial oil production by oleaginous yeast Trichosporon coremiiforme. After 5 days' lipid fermentation, all the sugars and organic acids measured were totally utilized by T. coremiiforme and a 68% of COD degradation could be obtained. The highest biomass and lipid content of T. coremiiforme on the wastewaters were 5.8 g/L and 19.1%, respectively. This work shows that T. coremiiforme is a promising strain for microbial oil production on the wastewaters after butanol fermentation.

Yeast fermentation of carboxylic acids obtained from pyrolytic aqueous phases for lipid production

The presence of very reactive C1-C4 molecules adversely affects the quality bio-oils produced from the pyrolysis of lignocellulosic materials. In this paper a scheme to produce lipids with Cryptococcus curvatus from the carboxylic acids in the pyrolytic aqueous phase collected in fractional condensers is proposed. The capacities of three oleaginous yeasts C. curvatus, Rhodotorula glutinis, Lipomyces starkeyi to ferment acetate, formate, hydroxylacat-aldehyde, phenol and acetol were investigated. While acetate could be a good carbon source for lipid production, formate provides additional energy and contributes to yeast growth and lipid production as auxiliary energy resource. Acetol could slightly support yeast growth, but it inhibits lipid accumulation. Hydroxyacetaldehyde and phenols showed high yeast growth and lipid accumulation inhibition. A pyrolytic aqueous phase with 20 g/L acetate was fermented with C. curvatus, after neutralization and detoxification to produce 6.9 g/L dry biomass and 2.2 g/L lipid.

Evaluation of single cell oil (SCO) from a tropical marine yeast Yarrowia lipolytica NCIM 3589 as a potential feedstock for biodiesel

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.

Oil production by the yeast Trichosporon dermatis cultured in enzymatic hydrolysates of corncobs

Corncob was hydrolyzed with Trichoderma reesei cellulase and used as substrate for growth by the oleaginous yeast Trichosporon dermatis without detoxification or addition of a nitrogen source or trace elements. A total biomass of 24.4g/L with a lipid content of 40.1% (corresponding to a lipid yield of 9.8g/L), and a high lipid coefficient (lipid yield per mass of sugar, %g/g) of 16.7 could be achieved after cultivation for 7days. Therefore, T. dermatis is a promising strain for microbial oil production from lignocellulosic biomass.