Lipid Production from Hemicellulose and Holocellulose Hydrolysate of Palm Empty Fruit Bunches by Newly Isolated Oleaginous Yeasts

Cellulase mediated stress triggers the mutations of oleaginous yeast Trichosporon cutaneum with super-large spindle morphology and high lipid accumulation

Accumulation of intracellular lipid bodies in oleaginous yeast cells is highly restricted by their natural intracellular space. Here we show a cellulase mediated adaptive evolution with ultra-centrifugation fractionation of oleaginous yeast Trichosporon cutaneum to obtain the favorable cell structure for lipid accumulation. Cellulase was added to the wheat straw hydrolysate during long-term adaptive evolution for disruption of cell wall integrity of T. cutaneum cells. The cellulase, together with ultracentrifugation force, triggered multiple mutations and transcriptional expression changes of the functional genes associated with cell wall integrity and lipid synthesis metabolism. The fractionated mutant T. cutaneum YY52 demonstrated the heavily weakened cell wall and high lipid accumulation by the super-large expanded spindle cells (two orders of magnitude greater than the parental). A record-high lipid production by T. cutaneum YY52 was achieved (55.4 ± 0.5 g L-1 from wheat straw and 58.4 ± 0.1 g L-1 from corn stover). This study not only obtained an oleaginous yeast strain with industrial application potential for lipid production but also provided a new method for generation of mutant cells with high intracellular metabolite accumulation.

Ultra-centrifugation force in adaptive evolution changes the cell structure of oleaginous yeast Trichosporon cutaneum into a favorable space for lipid accumulation

Microbial lipid production from lignocellulose biomass provides an essential option for sustainable and carbon neutral supply of future aviation fuels, biodiesel, as well as various food and nutrition products. Oleaginous yeast is the major microbial cell factory but its lipid producing performance is far below the requirements of industrial application. Here we show an ultra-centrifugation fractionation in adaptive evolution (UCF) of Trichosporon cutaneum based on the minor cell density difference. The lightest cells with the maximum intracellular lipid content were isolated by ultra-centrifugation fractionation in the long-term adaptive evolution. Significant changes occurred in the cell morphology with a fragile cell wall wrapping and enlarged intracellular space (two orders of magnitude increase in cell size). Complete and coordinate assimilations of all non-glucose sugars derived from lignocellulose were triggered and fluxed into lipid synthesis. Genome mutations and significant transcriptional regulations of the genes responsible for cell structure were identified and experimentally confirmed. The obtained Trichosporon cutaneum MP11 cells achieved a high lipid production of wheat straw, approximately five-folds greater than that of the parental cells. The study provided an effective method for screening the high lipid containing oleaginous yeast cells as well as the intracellular products accumulating cells in general. This article is protected by copyright. All rights reserved.

The history, state of the art and future prospects for oleaginous yeast research

Lipid-based biofuels, such as biodiesel and hydroprocessed esters, are a central part of the global initiative to reduce the environmental impact of the transport sector. The vast majority of production is currently from first-generation feedstocks, such as rapeseed oil, and waste cooking oils. However, the increased exploitation of soybean oil and palm oil has led to vast deforestation, smog emissions and heavily impacted on biodiversity in tropical regions. One promising alternative, potentially capable of meeting future demand sustainably, are oleaginous yeasts. Despite being known about for 143 years, there has been an increasing effort in the last decade to develop a viable industrial system, with currently around 100 research papers published annually. In the academic literature, approximately 160 native yeasts have been reported to produce over 20% of their dry weight in a glyceride-rich oil. The most intensively studied oleaginous yeast have been Cutaneotrichosporon oleaginosus (20% of publications), Rhodotorula toruloides (19%) and Yarrowia lipolytica (19%). Oleaginous yeasts have been primarily grown on single saccharides (60%), hydrolysates (26%) or glycerol (19%), and mainly on the mL scale (66%). Process development and genetic modification (7%) have been applied to alter yeast performance and the lipids, towards the production of biofuels (77%), food/supplements (24%), oleochemicals (19%) or animal feed (3%). Despite over a century of research and the recent application of advanced genetic engineering techniques, the industrial production of an economically viable commodity oil substitute remains elusive. This is mainly due to the estimated high production cost, however, over the course of the twenty-first century where climate change will drastically change global food supply networks and direct governmental action will likely be levied at more destructive crops, yeast lipids offer a flexible platform for localised, sustainable lipid production. Based on data from the large majority of oleaginous yeast academic publications, this review is a guide through the history of oleaginous yeast research, an assessment of the best growth and lipid production achieved to date, the various strategies employed towards industrial production and importantly, a critical discussion about what needs to be built on this huge body of work to make producing a yeast-derived, more sustainable, glyceride oil a commercial reality.

Current Pretreatment/Cell Disruption and Extraction Methods Used to Improve Intracellular Lipid Recovery from Oleaginous Yeasts

The production of lipids from oleaginous yeasts involves several stages starting from cultivation and lipid accumulation, biomass harvesting and finally lipids extraction. However, the complex and relatively resistant cell wall of yeasts limits the full recovery of intracellular lipids and usually solvent extraction is not sufficient to effectively extract the lipid bodies. A pretreatment or cell disruption method is hence a prerequisite prior to solvent extraction. In general, there are no recovery methods that are equally efficient for different species of oleaginous yeasts. Each method adopts different mechanisms to disrupt cells and extract the lipids, thus a systematic evaluation is essential before choosing a particular method. In this review, mechanical (bead mill, ultrasonication, homogenization and microwave) and nonmechanical (enzyme, acid, base digestions and osmotic shock) methods that are currently used for the disruption or permeabilization of oleaginous yeasts are discussed based on their principle, application and feasibility, including their effects on the lipid yield. The attempts of using conventional and “green” solvents to selectively extract lipids are compared. Other emerging methods such as automated pressurized liquid extraction, supercritical fluid extraction and simultaneous in situ lipid recovery using capturing agents are also reviewed to facilitate the choice of more effective lipid recovery methods.

Metagenomic insights into bioaugmentation and biovalorization of oily industrial wastes by lipolytic oleaginous yeast Yarrowia lipolytica during successive batch fermentation

The lipolytic oleaginous yeast Yarrowia lipolytica was used in the bioaugmentation and biovalorization of oily industrial wastes during successive-batch fermentation. Five cycles of nonsterile successive batch fermentation with 70% medium replacement achieved the highest oil removal of 68.1 ± 5.60% and produced biomass and lipid yields of 0.213 ± 0.07 g/g-COD and 146.2 ± 46.5 mg/g-COD, respectively. The cell-bound lipase activity observed in the system was 170.74 ± 32 U/L. The auto-flocculation efficiency of the biomass was >90% within 60 Min. The microbial community changes between Y. lipolytica and indigenous microorganisms were monitored by metagenomic next-generation sequencing of internal transcribed spacer rDNA regions for yeasts and 16S rRNA gene for bacteria. Ylipolytica lipolytica was retained in the consortium together with other indigenous strains until the fifth cycle. Other minor oleaginous yeasts such as Kodamaea ohmeri and Candida tropicalis as well as polyhydroxyalkanoate-accumulating bacteria were found and are likely to have participated in lipid production. This study has shown the robustness of Y. lipolytica in nonsterile successive batch fermentation and its use could contribute greatly to the practical valorization of industrial wastes for lipids and lipases.

Utilization of Wheat Bran Acid Hydrolysate by Rhodotorula mucilaginosa Y-MG1 for Microbial Lipid Production as Feedstock for Biodiesel Synthesis

The lignocellulosic hydrolysate was used as the fermentation feedstock of Rhodotorula mucilaginosa Y-MG1 for the production of microbial lipids as the potential raw material for biodiesel synthesis. On synthetic media and under nitrogen-limiting condition, the Y-MG1 strain produces 2.13 g/L of lipids corresponding to 32.7% of lipid content. This strain was able to assimilate a wide range of substrates, especially C5 and C6 sugars as well as glycerol and sucrose. Fatty acid composition shows a divergence depending on the nature of used carbon source with a predominance of oleic acid or linoleic acid. An effective hydrolysis process, based on diluted acid treatment, was established for providing the maximum of fermentable sugars from different characterized lignocellulosic wastes. The highest yield of reducing sugars (56.6 g/L) could be achieved when wheat bran was used as the raw material. Hydrolysate detoxification step was not required in this study since the Y-MG1 strain was shown to grow and produce lipids in the presence of inhibitors and without the addition of external elements. Operating by controlled fed-batch fermentation yielded a dry biomass and oil yield of up to 11 g/L and 38.7% (w/w), respectively. The relative fatty acid composition showed the presence of increased levels of monounsaturated (66.8%) and saturated (23.4%) fatty acids in lipids of Y-MG1 grown on wheat bran. The predictive determination of biodiesel properties suggests that this oil may effectively be used for biodiesel production.

Fostering triacylglycerol accumulation in novel oleaginous yeast Cryptococcus psychrotolerans IITRFD utilizing groundnut shell for improved biodiesel production

The investigation was carried out to examine the potential of triacylglycerol (TAG) accumulation by novel oleaginous yeast isolate Cryptococcus psychrotolerans IITRFD on utilizing groundnut shell acid hydrolysate (GSH) as cost-effective medium. The maximum biomass productivity and lipid productivity of 0.095±0.008g/L/h and 0.044±0.005g/L/h, respectively with lipid content 46% was recorded on GSH. Fatty acid methyl ester (FAME) profile obtained by GC-MS analysis revealed oleic acid (37.8%), palmitic (29.4%) and linoleic (32.8%) as major fatty acids representing balance between oxidative stability (OS) and cold flow filter properties (CFFP) for improved biodiesel quality. The biodiesel property calculated were correlated well with the fuel standards limits of ASTM D6751, EN 14214 and IS 15607. The present findings raise the possibility of using agricultural waste groundnut shell as a substrate for production of biodiesel by novel oleaginous yeast isolate C. psychrotolerans IITRFD.

Single Cell Oil Production from Hydrolysates of Inulin by a Newly Isolated Yeast Papiliotrema laurentii AM113 for Biodiesel Making

Microbial oils are among the most attractive alternative feedstocks for biodiesel production. In this study, a newly isolated yeast strain, AM113 of Papiliotrema laurentii, was identified as a potential lipid producer, which could accumulate a large amount of intracellular lipids from hydrolysates of inulin. P. laurentii AM113 was able to produce 54.6% (w/w) of intracellular oil in its cells and 18.2 g/l of dry cell mass in a fed-batch fermentation. The yields of lipid and biomass were 0.14 and 0.25 g per gram of consumed sugar, respectively. The lipid productivity was 0.092 g of oil per hour. Compositions of the fatty acids produced were C_14:0 (0.9%), C_16:0 (10.8%), C_16:1 (9.7%), C_18:0 (6.5%), C_18:1 (60.3%), and C_18:2 (11.8%). Biodiesel obtained from the extracted lipids could be burnt well. This study not only provides a promising candidate for single cell oil production, but will also probably facilitate more efficient biodiesel production.