Effect of crude glycerol impurities on lipid preparation by Rhodosporidium toruloides yeast 32489

Development of a multigene expression system using 2A peptides in Rhodosporidium toruloides

In eukaryotes, gene expression typically requires individual promoter and terminator for each gene, making the expression of multiple genes tedious and sometimes too difficult to handle. This is especially true for underdeveloped nonmodel organisms with few genetic engineering tools and genetic elements such as Rhodosporidium toruloides. In contrast, polycistronic expression offers advantages such as smaller size and ease of cloning. Here we report the development of a multigene expression system using 2A peptides in R. toruloides. First, twenty-two 2A peptides were evaluated for their cleavage efficiencies, which ranged from 33.65% to 93.32%. Subsequently, the 2A peptide of ERBV-1 with the highest efficiency was selected to enable simultaneous expression of four proteins. In addition, we demonstrated the optimization of the α-linolenic acid biosynthetic pathway using ERBV-1 peptide mediated polycistronic expression, which increased the α-linolenic acid production by 104.72%. These results suggest that using ERBV-1 peptide is an efficient strategy for multigene expression in R. toruloides.

Technological modes and processes to enhance the Rhodosporidium toruloides based lipid accumulation

Rhodosporidium toruloides has emerged as an excellent option for microbial lipid production due to its ability to accumulate up to 70 % of lipids per cell dry weight, consume multiple substrates such as glucose and xylose, and tolerate toxic compounds. Despite the potential of Rhodosporidium toruloides for high lipid yields, achieving these remains is a significant hurdle. A comprehensive review is essential to thoroughly evaluate the advancements in processes and technologies to enhance lipid production in R. toruloides. The review covers various strategies for enhancing lipid production like co-culture, adaptive evolution, carbon flux analysis, as well as different modes of fermentation. This review will help researchers to better understand the recent developments in technologies for sustainable and scalable lipid production from R. toruloides and simultaneously emphasize the need for developing an efficient and sustainable bioprocess.

Clostridium carboxidivorans and Rhodosporidium toruloides as a platform for the valorization of carbon dioxide to microbial oils

There is growing scientific interest in oleaginous yeasts producing microbial oils as precursors of biofuels and potential substitutes for fossil fuels. Due to the high cost of substrates commonly metabolized by yeasts, volatile fatty acids (VFAs) are gaining interest as alternative cheap and sustainable carbon sources, which can be obtained from solid, liquid and gas pollutants. In this research, Rhodosporidium toruloides was proven to be able to accumulate microbial oils from VFAs obtained from the fermentation of syngas by Clostridium carboxidivorans. Using CO2 and CO as carbon sources from the syngas mixture and H2 as energy source, this acetogen produced, via the Wood-Ljungdahl pathway, a mixture of acetic, butyric and caproic acids. It was first revealed that R. toruloides exhibited minimal inhibition at concentrations below 12 g/L when exposed to a mixture of VFAs, which included acetic, butyric and even hexanoic acids. The yeast was then grown on the culture medium derived from the acetogenic fermentation of syngas. Between the two yeast strains tested of the same species, R. toruloides DSM 4444 reached a total VFAs consumption of 69.1 g/L, supplied by successive additions of acids to the reactor, yielding a maximum lipid content of 29.7% w/w cell. The lipid profile obtained in this case, in terms of abundance followed the order C18:1 > C16:0 ≥ C18:0 > C18:2>others; in which the dominant compound (C18:1), represented approximately 50% of the total. This research opens new possibilities in the cultivation of oleaginous yeasts for the production of biofuels and bioproducts from C1 gases.

The Plasma Membrane H+-ATPase Promoter Driving the Expression of FADX Enables Highly Efficient Production of Punicic Acid in Rhodotorula toruloides Cultivated on Glucose and Crude Glycerol

Punicic acid (PuA) is a conjugated fatty acid with a wide range of nutraceutical properties naturally present in pomegranate seed oil. To meet the rising demand for pomegranate seed oil, a single-cell oil enriched in PuA provides a sustainable biomass-derived alternative. This study describes the production of a PuA-enriched single-cell oil through the engineering of the red yeast Rhodotorula toruloides grown in glucose and a low-cost substrate, crude glycerol. The gene for Punica granatum fatty acid conjugase, PgFADX, was randomly integrated into the genome of R. toruloides without disrupting the carotenoid synthesis. In shake flask studies, the effects of three promoters (PPGI1, PNAR1, and PPMA1) on PuA production were evaluated. PuA titers of 105.77 mg/L and 72.81 mg/L were obtained from engineered cells expressing PgFADX from the PPMA1 promoter cultivated for 72 h in glucose and for 168 h in crude glycerol, respectively. Furthermore, the detailed lipid analysis revealed a high enrichment PuA in the triacylglycerol lipid structures, even without substantial modifications to the metabolic pathways. This report demonstrates the high potential of R. toruloides in the upcycling of a low-cost substrate, crude glycerol, into a value-added product such as PuA. The findings support the feasibility of using engineered R. toruloides for sustainable production of PuA-enriched single-cell oil.

A systematic review on utilization of biodiesel-derived crude glycerol in sustainable polymers preparation

With the rapid development of biodiesel, biodiesel-derived glycerol has become a promising renewable bioresource. The key to utilizing this bioresource lies in the value-added conversion of crude glycerol. While purifying crude glycerol into a pure form allows for diverse applications, the intricate nature of this process renders it costly and environmentally stressful. Consequently, technology facilitating the direct utilization of unpurified crude glycerol holds significant importance. It has been reported that crude glycerol can be bio-transformed or chemically converted into high-value polymers. These technologies provide cost-effective alternatives for polymer production while contributing to a more sustainable biodiesel industry. This review article describes the global production and quality characteristics of biodiesel-derived glycerol and investigates the influencing factors and treatment of the composition of crude glycerol including water, methanol, soap, matter organic non-glycerol, and ash. Additionally, this review also focused on the advantages and challenges of various technologies for converting crude glycerol into polymers, considering factors such as the compatibility of crude glycerol and the control of unfavorable factors. Lastly, the application prospect and value of crude glycerol conversion were discussed from the aspects of economy and environmental protection. The development of new technologies for the increased use of crude glycerol as a renewable feedstock for polymer production will be facilitated by the findings of this review, while promoting mass market applications.

Evaluating oleaginous yeasts for enhanced microbial lipid production using sweetwater as a sustainable feedstock

BACKGROUND

Yeasts exhibit promising potential for the microbial conversion of crude glycerol, owing to their versatility in delivering a wide range of value-added products, particularly lipids. Sweetwater, a methanol-free by-product of the fat splitting process, has emerged as a promising alternative feedstock for the microbial utilization of crude glycerol. To further optimize sweetwater utilization, we compared the growth and lipid production capabilities of 21 oleaginous yeast strains under different conditions with various glycerol concentrations, sweetwater types and pH.

RESULTS

We found that nutrient limitation and the unique carbon composition of sweetwater boosted significant lipid accumulation in several strains, in particular Rhodosporidium toruloides NRRL Y-6987. Subsequently, to decipher the underlying mechanism, the transcriptomic changes of R. toruloides NRRL Y-6987 were further analyzed, indicating potential sugars and oligopeptides in sweetwater supporting growth and lipid accumulation as well as exogenous fatty acid uptake leading to the enhanced lipid accumulation.

CONCLUSION

Our comparative study successfully demonstrated sweetwater as a cost-effective feedstock while identifying R. toluroides NRRL Y-6987 as a highly promising microbial oil producer. Furthermore, we also suggested potential sweetwater type and strain engineering targets that could potentially enhance microbial lipid production.

Application of adaptive laboratory evolution to improve the tolerance of Rhodotorula strain to methanol in crude glycerol and development of an effective method for cell lysis

Rhodotorula toruloides can utilize crude glycerol as the low-cost carbon source for lipid production, but its growth is subjected to inhibition by methanol in crude glycerol. Here, transcriptome profiling demonstrated that 1004 genes were significantly regulated in the strain R. toruloides TO2 under methanol stress. Methanol impaired the function of membrane transport and subsequently weakened the utilization of glycerol, activities of the primary metabolism and functions of nucleus and ribosome. Afterwards the tolerance of TO2 to methanol was improved by using two-round adaptive laboratory evolution (ALE). The final strain M2-ale had tolerance up to 3.5% of methanol. 1 H NMR-based metabolome analysis indicated that ALE not only improved the tolerance of M2-ale to methanol but also tuned the carbon flux towards the biosynthesis of glycerolipid-related metabolites. The biomass and lipid titer of M2-ale reached 14.63 ± 0.45 g L-1 and 7.06 ± 0.44 g L-1 at 96 h in the crude glycerol medium, which increased up to 17.69% and 31.39%, respectively, comparing with TO2. Afterwards, an effective method for cell lysis was developed by combining sonication and enzymatic hydrolysis (So-EnH). The lytic effect of So-EnH was validated by using confocal imaging and flow cytometry. At last, lipid recovery rate reached 95.4 ± 2.7% at the optimized condition.

Sequential bioconversion of C1-gases (CO, CO2, syngas) into lipids, through the carboxylic acid platform, with Clostridium aceticum and Rhodosporidium toruloides

Syngas (CO, CO2, H2) was effectively bioconverted into lipids in a two-stage process. In the first stage, C1-gases were bioconverted into acetic acid by the acetogenic species Clostridium aceticum through the Wood-Ljungdahl metabolic pathway in a stirred tank bioreactor, reaching a maximum acetic acid concentration of 11.5 g/L, with a production rate of 0.05 g/L·h. Throughout this experiment, samples were extracted at different periods, i.e., different concentrations, to be used in the second stage, aiming at the production of lipids from acetic acid. The yeast Rhodosporidium toruloides, inoculated in the acetogenic medium, was able to efficiently accumulate lipids from acetic acid generated in the first stage. The best results, in terms of lipid content, dry biomass, biomass yield (Y(X/S)) and lipid yield (Y(L/S)) were 39.5% g/g dry cell weight, 3 g/L, 0.35 and 0.107, respectively. In terms of abundance, the lipid profile followed the order: C18:1 > C16:0 > C18:2 > C18:0 > Others. Experiments were also performed to determine the toxicity exerted by high concentrations of acetic acid on R. toruloides, resulting in inhibition at initial acid concentrations around 18 g/L leading to a higher lag phase and being lethal to the yeast at initial acetic acid concentrations around 22 g/L and above. This research paves the way for a novel method of growing oleaginous yeasts to produce sustainable biofuels from syngas or C1-pollutant gases.

A comprehensive review on microbial lipid production from wastes: research updates and tendencies

Microbial lipids have recently attracted attention as an intriguing alternative for the biodiesel and oleochemical industries to achieve sustainable energy generation. However, large-scale lipid production remains limited due to the high processing costs. As multiple variables affect lipid synthesis, an up-to-date overview that will benefit researchers studying microbial lipids is necessary. In this review, the most studied keywords from bibliometric studies are first reviewed. Based on the results, the hot topics in the field were identified to be associated with microbiology studies that aim to enhance lipid synthesis and reduce production costs, focusing on the biological and metabolic engineering involved. The research updates and tendencies of microbial lipids were then analyzed in depth. In particular, feedstock and associated microbes, as well as feedstock and corresponding products, were analyzed in detail. Strategies for lipid biomass enhancement were also discussed, including feedstock adoption, value-added product synthesis, selection of oleaginous microbes, cultivation mode optimization, and metabolic engineering strategies. Finally, the environmental implications of microbial lipid production and possible research directions were presented.

Economic and environmental evaluation for a closed loop of crude glycerol bioconversion to biodiesel

Crude glycerol, a byproduct of biodiesel production, was utilized as a carbon source to produce microbial lipids by the oleaginous yeast Rhodotorula toruloides in this study. The maximum lipid production and lipid content were 10.56 g/L and 49.52%, respectively, by optimizing fermentation conditions. The obtained biodiesel met the standards of China, the United States, and the European Union. The economic value of biodiesel produced from crude glycerol increased by 48% compared with the sale of crude glycerol. In addition, biodiesel production from crude glycerol could reduce 11,928 tons of carbon dioxide emissions and 55 tons of sulfur dioxide emissions. This study provides a strategy for a closed loop of crude glycerol to biofuel and ensures sustainable and stable development of the biodiesel industries.

Development and Perspective of Rhodotorula toruloides as an Efficient Cell Factory

Rhodotorula toruloides is receiving significant attention as a novel cell factory because of its high production of lipids and carotenoids, fast growth and high cell density, as well as the ability to utilize a wide variety of substrates. These attractive traits of R. toruloides make it possible to become a low-cost producer that can be engineered for the production of various fuels and chemicals. However, the lack of understanding and genetic engineering tools impedes its metabolic engineering applications. A number of research efforts have been devoted to filling these gaps. This review focuses on recent developments in genetic engineering tools, advances in systems biology for improved understandings, and emerging engineered strains for metabolic engineering applications. Finally, future trends and barriers in developing R. toruloides as a cell factory are also discussed.

Exploring Yeast Diversity to Produce Lipid-Based Biofuels from Agro-Forestry and Industrial Organic Residues

Exploration of yeast diversity for the sustainable production of biofuels, in particular biodiesel, is gaining momentum in recent years. However, sustainable, and economically viable bioprocesses require yeast strains exhibiting: (i) high tolerance to multiple bioprocess-related stresses, including the various chemical inhibitors present in hydrolysates from lignocellulosic biomass and residues; (ii) the ability to efficiently consume all the major carbon sources present; (iii) the capacity to produce lipids with adequate composition in high yields. More than 160 non-conventional (non-Saccharomyces) yeast species are described as oleaginous, but only a smaller group are relatively well characterised, including Lipomyces starkeyi, Yarrowia lipolytica, Rhodotorula toruloides, Rhodotorula glutinis, Cutaneotrichosporonoleaginosus and Cutaneotrichosporon cutaneum. This article provides an overview of lipid production by oleaginous yeasts focusing on yeast diversity, metabolism, and other microbiological issues related to the toxicity and tolerance to multiple challenging stresses limiting bioprocess performance. This is essential knowledge to better understand and guide the rational improvement of yeast performance either by genetic manipulation or by exploring yeast physiology and optimal process conditions. Examples gathered from the literature showing the potential of different oleaginous yeasts/process conditions to produce oils for biodiesel from agro-forestry and industrial organic residues are provided.

Bioprocesses for the Biodiesel Production from Waste Oils and Valorization of Glycerol

The environmental context causes the use of renewable energy to increase, with the aim of finding alternatives to fossil-based products such as fuels. Biodiesel, an alternative to diesel, is now a well-developed solution, and its production from renewable resources makes it perfectly suitable in the environmental context. In addition, it is biodegradable, non-toxic and has low greenhouse gas emissions: reduced about 85% compared to diesel. However, the feedstock used to produce biodiesel competes with agriculture and the application of chemical reactions is not advantageous with a “green” process. Therefore, this review focuses only on bioprocesses currently taking an important place in the production of biodiesel and allow high yields, above 90%, and with very few produced impurities. In addition, the use of waste oils as feedstock, which now accounts for 10% of feedstocks used in the production of biodiesel, avoids competition with agriculture. To present a complete life-cycle of oils in this review, a second part will focus on the valorization of the biodiesel by-product, glycerol. About 10% of glycerol is generated during the production of biodiesel, so it should be recovered to high value-added products, always based on bioprocesses. This review will also present existing techniques to extract and purify glycerol. In the end, from the collection of feedstocks to the production of CO2 during the combustion of biodiesel, this review presents the steps using the “greener” possible processes.

A review on contemporary approaches in enhancing the innate lipid content of yeast cell

For the past few decades, industrialization has made a huge environmental hazard to the world with its waste. The approach of waste to wealth in the recent era has made many Eco-economical suggestions for the industries. The valuable products in biorefinery aspects of the eco-economical suggestions include; energy products, high-value drugs and novel materials. Bio-lipids are found to be the major influencing eco-economical products in the process. Production of bio-lipid from microbial sources has paved the way for future research on lipid-bioproducts. The yeast cell is a unique organism with a large unicellular structure capable of accumulating a high amount of lipids. It constitutes 90% of neutral lipids. Various strategies enhance the lipid profile of yeast cells: usage of oleaginous yeast, usage of low cost (or) alternative substrates, developing stress conditions in the growth medium, using genetically modified yeast, altering metabolic pathways of yeast and by using the symbiotic cultures of yeast with other microbes. The metabolic alterations of lipid pathways such as lipid biosynthesis, lipid elongation, lipid accumulation and lipid degradation have been a striking feature of research in lipid-based microbial work. The lipid-bioproducts have also made a strong footprint in the history of alternative energy products. It includes partial acyl glycerol, oleochemicals, phospholipids and biofuels. This report comprises the recent approaches carried out in the yeast cell for enhancing its lipid content. The limitations, challenges and future scope of individual strategies were also highlighted in this article.

Bioprospecting lipid-producing microorganisms: From metagenomic-assisted isolation techniques to industrial application and innovations

Traditionally, lipid-producing microorganisms have been obtained via conventional bioprospecting based on isolation and screening techniques, demanding time and effort. Thus, high-throughput sequencing combined with conventional microbiological approaches has emerged as an advanced and rapid strategy for recovering novel oleaginous microorganisms from target environments. This review highlights recent developments in lipid-producing microorganism bioprospecting, following (i) from traditional cultivation techniques to state-of-the-art metagenomics approaches; (ii) related topics on workflow, next-generation sequencing platforms, and knowledge bioinformatics; and (iii) biotechnological potential of the production of docosahexaenoic acid (DHA) by Aurantiochytrium limacinum, arachidonic acid (ARA) by Mortierella alpina and biodiesel by Rhodosporidium toruloides. These three species have been shown to be highly promising and studied in research articles, patents and commercialized products. Trends, innovations and future perspectives of these microorganisms are also addressed. Thus, these microbial lipids allow the development of food, feed and biofuels as alternative solutions to animal and vegetable oils.

Waste cooking oil used as carbon source for microbial lipid production: Promoter or inhibitor

In this study, waste cooking oil (WCO) co-fermentation with food waste by variable pH strategy was developed for microbial lipid production. Results showed that when WCO substitution rate within the range of 1.56-4.68% (corresponding to the WCO content in food waste), lipid production from Rhodosporidium toruloides 2.1389 could be increased by 7.2 g/kg food waste because of the better synergistic effect. Mechanism analysis revealed that the fatty acid salt produced from WCO under alkaline condition, as a surface active agent, could improve lipid production, but excessive WCO (29.2 g/L) would inhibit the lipid production due to its hindrance to the oxygen. The lipid composition analysis found that the produced lipid could be used as raw material for biodiesel production. It was estimated that 15.0 million tonnes of biodiesel could be produced from global food waste yearly by adopting the proposed WCO co-fermentation with variable pH strategy, together with reduction of about 0.31 million tonnes of CO₂ equivalents and 1435 tonnes of SO₂. It is expected that this study may lead to the paradigm shift in future biodiesel production from food waste.

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.

Microbial lipid production from banana straw hydrolysate and ethanol stillage

In this study, the feasibility of banana straw (BS) hydrolysate as carbon source and reutilizing the pretreated liquor (PL) of BS in the Rhodosporidium toruloides fermentation was explored for the first time. When BS hydrolysate was used as the carbon source, total biomass concentration, lipid concentration, and lipid content under optimal conditions reached 15.52 g/L, 5.83 g/L, and 37.56% (w/w), respectively, which was similar to the results of pure sugar control. After detoxification, 50% PL can be returned to enzymatic hydrolysis and fermentation, and total biomass concentration, lipid concentration, and lipid content can reach 15.14 g/L, 5.59 g/L, and 36.91% (w/w). Then, ethanol stillage (ES) was used as the nitrogen source. The NaCl and glycerol of ES could promote lipid accumulation, reaching 7.52 g/L under optimized conditions. Finally, microbial lipid production from BS hydrolysate and ES without any additional nutrients was investigated, and the maximum total biomass concentration, lipid concentration, and lipid content were 13.55 g/L, 4.88 g/L, and 36.01% (w/w), respectively. Besides, the main compositions of microbial lipid produced were C16 and C18, and the biodiesel production from the microbial lipid could meet Chinese and US standard through theoretical numerical calculation.

Microbial lipid production from crude glycerol and hemicellulosic hydrolysate with oleaginous yeasts

BACKGROUND

Crude glycerol (CG) and hemicellulose hydrolysate (HH) are low-value side-products of biodiesel transesterification and pulp-and paper industry or lignocellulosic ethanol production, respectively, which can be converted to microbial lipids by oleaginous yeasts. This study aimed to test the ability of oleaginous yeasts to utilise CG and HH and mixtures of them as carbon source.

RESULTS

Eleven out of 27 tested strains of oleaginous yeast species were able to grow in plate tests on CG as sole carbon source. Among them, only one ascomycetous strain, belonging to Lipomyces starkeyi, was identified, the other 10 strains were Rhodotorula spec. When yeasts were cultivated in mixed CG/ HH medium, we observed an activation of glycerol conversion in the Rhodotorula strains, but not in L. starkeyi. Two strains-Rhodotorula toruloides CBS 14 and Rhodotorula glutinis CBS 3044 were further tested in controlled fermentations in bioreactors in different mixtures of CG and HH. The highest measured average biomass and lipid concentration were achieved with R. toruloides in 10% HH medium mixed with 55 g/L CG-19.4 g/L and 10.6 g/L, respectively, with a lipid yield of 0.25 g lipids per consumed g of carbon source. Fatty acid composition was similar to other R. toruloides strains and comparable to that of vegetable oils.

CONCLUSIONS

There were big strain differences in the ability to convert CG to lipids, as only few of the tested strains were able to grow. Lipid production rates and yields showed that mixing GC and HH have a stimulating effect on lipid accumulation in R. toruloides and R. glutinis resulting in shortened fermentation time to reach maximum lipid concentration, which provides a new perspective on converting these low-value compounds to microbial lipids.

Microbial lipids from organic wastes: Outlook and challenges

Microbial lipids have recently drawn a lot of attention as renewable sources for biochemicals production. Strong research efforts have been addressed to efficiently use organic wastes as carbon source for microbial lipids, which would definitively increase the profitability of the production process and boost a bio-based economy. This review compiles interesting traits of oleaginous microorganisms and highlights current trends on microbial- and process-oriented approaches to maximize microbial oil production from inexpensive substrates like lignocellulosic sugars, volatile fatty acids and glycerol. Furthermore, downstream processes such as cell harvesting or lipid extraction, that are decisive for the cost-effectiveness of the process, are discussed. To underpin microbial oils within the so demanded circular economy, associated challenges, recent advances and possible industrial applications that are also identified in this review.

Identifying economical route for crude glycerol valorization: Biodiesel versus polyhydroxy-butyrate (PHB)

Crude glycerol, a by-product of biodiesel industry, has been used for production of biodiesel and polyhydroxy-alkanoates. But question is: which product is economically favorable using crude glycerol as substrate? In this study, energy balance and economic assessment has been carried out for crude glycerol valorization for B10 biodiesel and polyhydroxy-butyrate (PHB) production. For same quantity of crude glycerol utilized, energy ratio for B10 production was higher than PHB production while unit production cost for B10 was lower than that of PHB. For 50 million L plant capacity of biodiesel, unit production cost was 0.77 $/L B10 while for 2 million kg plant capacity of PHB, unit production cost was 4.88 $/kg PHB. Thus, in present scenario production of biodiesel seems economically better than production of PHA with crude glycerol as raw material. This study is useful for researchers, environmental scientists and industries in identifying effective route for crude glycerol valorization.

Crude glycerol impurities improve Rhizomucor miehei lipase production by Pichia pastoris

Crude glycerol, a by-product of biodiesel production, was employed as the carbon source to produce lipase using Pichia pastoris. Under identical fermentation conditions, cell growth and lipase activity were improved using crude glycerol instead of pure glycerol. The impacts of crude glycerol impurities (methyl ester, grease, glycerol, methanol, and metal ions Na⁺, Ca²⁺, and Fe³⁺) on lipase production were investigated. Impurities accelerated P. pastoris entering the stationary phase. Na⁺, Ca²⁺, and grease in waste crude glycerol were the main factors influencing higher lipase activity. Through response surface optimization of Ca²⁺, Na⁺, and grease concentrations, lipase activity reached 1437 U/mL (15,977 U/mg), which was 2.5 times that of the control. This study highlights the economical and highly efficient valorization of crude glycerol, demonstrating its possible utilization as a carbon source to produce lipase by P. pastoris without pretreatment.

Sustainable and stepwise waste-based utilisation strategy for the production of biomass and biofuels by engineered microalgae

Waste streams have emerged as potential feedstocks for biofuel production via microbial bioconversion. Metabolic engineering of the microalga Phaeodactylum tricornutum in its lipid biosynthetic pathways has been conducted with an aim to improve lipid production. However, there has been only limited achievement in satisfying biofuel demands by utilising extracellular organic carbons from low-cost waste streams. Herein, we present a successive staged cultivation mode, based on a previously engineered strain that co-overexpresses two key triacylglycerol biosynthesis genes. We first optimised microalgal biomass and lipid production by using food waste hydrolysate and crude glycerol as the cultivation media. Food waste hydrolysate (5% v/v) is a low-cost organic carbon source for enhanced microalgal biomass production, and the resulting lipid concentration was 1.08-fold higher with food-waste hydrolysate than that of the defined medium. Additionally, the resultant lipid concentration after using crude glycerol (100 mM) was 1.24-fold higher than that using the defined medium. Two carbon feeding modes (hybrid and sequential) were also performed to investigate the potential of engineered P. tricornutum with preliminary mechanistic analyses. The biodiesel properties of lipids produced in the hybrid mode were evaluated for potential application prospects. Collectively, this study demonstrates a waste stream utilisation strategy for efficient and sustainable microalgal biofuel production.

Exogenous l-proline improved Rhodosporidium toruloides lipid production on crude glycerol

BACKGROUND

Crude glycerol as a promising feedstock for microbial lipid production contains several impurities that make it toxic stress inducer at high amount. Under stress conditions, microorganisms can accumulate l-proline as a safeguard. Herein, l-proline was assessed as an anti-stress agent in crude glycerol media.

RESULTS

Crude glycerol was converted to microbial lipids by the oleaginous yeast Rhodosporidium toruloides CGMCC 2.1389 in a two-staged culture mode. The media was supplied with exogenous l-proline to improve lipid production efficiency in high crude glycerol stress. An optimal amount of 0.5 g/L l-proline increased lipid titer and lipid yield by 34% and 28%, respectively. The lipid titer of 12.2 g/L and lipid content of 64.5% with a highest lipid yield of 0.26 g/g were achieved with l-proline addition, which were far higher than those of the control, i.e., lipid titer of 9.1 g/L, lipid content of 58% and lipid yield of 0.21 g/g. Similarly, l-proline also improved cell growth and glycerol consumption. Moreover, fatty acid compositional profiles of the lipid products was found suitable as a potential feedstock for biodiesel production.

CONCLUSION

Our study suggested that exogenous l-proline improved cell growth and lipid production on crude glycerol by R. toruloides. The fact that higher lipid yield as well as glycerol consumption indicated that l-proline might act as a potential anti-stress agent for the oleaginous yeast strain.

Valorisation of crude glycerol to value-added products: Perspectives of process technology, economics and environmental issues

The enormous production of glycerol, a waste stream from biodiesel industries, as a low-value product has been causing a threat to both the environment and the economy. Therefore, it needs to be transformed effectively and efficiently into valued products for contributing positively towards the biodiesel economy. It can either be converted directly into competent chemicals or can be used as a feedstock/precursor for deriving valuable derivatives. In this review article, a technical evaluation has been stirred up, various factors and technologies used for producing value-added products from crude glycerol, Environmental and economic aspects of different conversion routes, cost factors and challenges of integration of the different routes for biorefinery have been reviewed and elaborated. There are tremendous environmental benefits in the conversion of crude glycerol via the biochemical route, the product and residue become eco-friendly. However, chemical conversions are faster processes, and economically viable if environmental aspects are partially ignored.

Effect of utilization of crude glycerol as substrate on fatty acid composition of an oleaginous yeast Rhodotorula mucilagenosa IIPL32: Assessment of nutritional indices

This work studied the use of crude glycerol obtained from biodiesel industry as substrate to generate yeast lipid from Rhodotorula mucilagenosa IIPL32 MTCC 25056. Crude glycerol is a low value by product obtained from biodiesel industry. Rhodotorula mucilagenosa IIPL32 MTCC 25056 was evaluated for its potential to produce lipid using crude glycerol as sole source of carbon. Under nitrogen limiting condition a lipid and biomass content of 5.6 g/L and19.7 g/L were obtained from crude glycerol. The fatty acid profile was found to be interestingly rich in oleic acid (61.88%), linoleic acid (16.17%) and linolenic acid (1.03%) comprising ~80% of MUFA and PUFA of total lipid. Further, evaluations were attempted to compare MUFA rich yeast lipid against different plant-borne edible oils commonly used in India. In this study, nutritional indices were calculated to check feasibility of using yeast oil as a plausible blend to edible oil.

Valorization of Biodiesel Byproduct Crude Glycerol for the Production of Bioenergy and Biochemicals

The rapid growth of global biodiesel production requires simultaneous effective utilization of glycerol obtained as a by-product of the transesterification process. Accumulation of the byproduct glycerol from biodiesel industries can lead to considerable environment issues. Hence, there is extensive research focus on the transformation of crude glycerol into value-added products. This paper makes an overview of the nature of crude glycerol and ongoing research on its conversion to value-added products. Both chemical and biological routes of glycerol valorization will be presented. Details of crude glycerol conversion into microbial lipid and subsequent products will also be highlighted.

Feeding Strategies of Two-Stage Fed-Batch Cultivation Processes for Microbial Lipid Production from Sugarcane Top Hydrolysate and Crude Glycerol by the Oleaginous Red Yeast Rhodosporidiobolus fluvialis

Microbial lipids are able to produce from various raw materials including lignocellulosic biomass by the effective oleaginous microorganisms using different cultivation processes. This study aimed to enhance microbial lipid production from the low-cost substrates namely sugarcane top hydrolysate and crude glycerol by Rhodosporidiobolus fluvialis DMKU-SP314, using two-stage fed-batch cultivation with different feeding strategies in a 3 L stirred-tank fermenter. The effect of two feeding strategies of 147.5 g/L crude glycerol solution was evaluated including pulse feeding at different starting time points (48, 24, and 72 h after initiation of batch operation) and constant feeding at different dilution rates (0.012, 0.020, and 0.033 h-1). The maximum lipid concentration of 23.6 g/L and cell mass of 38.5 g/L were achieved when constant feeding was performed at the dilution rate of 0.012 h-1 after 48 h of batch operation, which represented 1.24-fold and 1.27-fold improvements in the lipid and cell mass concentration, respectively. Whereas, batch cultivation provided 19.1 g/L of lipids and 30.3 g/L of cell mass. The overall lipid productivity increased to 98.4 mg/L/d in the two-stage fed-batch cultivation. This demonstrated that the two-stage fed-batch cultivation with constant feeding strategy has the possibility to apply for large-scale production of lipids by yeast.

Enhanced polyunsaturated fatty acid production using food wastes and biofuels byproducts by an evolved strain of Phaeodactylum tricornutum

This study investigates the prospective of utilizing kitchen wastewater and food wastes, biofuels industry byproducts as alternative water and carbon sources. Kitchen wastewater did not impede cellular growth rate of the evolved Phaeodactylum strain E70, which indicates its potential as an alternative to freshwater resources. Among the organic wastes assessed, food waste hydrolysate significantly increased cell growth. Supplement of crude glycerol in cultivation medium enhances the total fatty acid content. Mixed food waste hydrolysate and crude glycerol remarkably increased both the cell density and total fatty acid content. Also, the supplement of butylated hydroxytoluene alleviated the oxidative stress induced by impurities in organic wastes and concomitantly increased microalgal total fatty acids and polyunsaturated fatty acids content. The experimental results reported in this study show that a waste-based biorefinery could lead to utilization of organic waste resources for the efficient production of value-added products.

Application of de-lignified cellulose to enhance intracellular and extracellular lipid production from oleaginous yeast using acetic acid

Two de-lignified cellulose of loofah sponge and sawdust were applied in two ways to enhance the lipid production from oleaginous yeast using acetic acid. When 30 g/L of acetic acid was used as a carbon source, direct addition of de-lignified loofah sponge or sawdust increased the extracellular lipid content to 33.94% and 53.25%, respectively. The latter reduced the energy input of lipid extraction process from 0.86 to 0.57 GJ per ton of biodiesel production. To relieve the inhibition caused by 40 g/L acetic acid, immobilization of oleaginous yeast on de-lignified sawdust increased the lipid concentration and yield from 3.83 g/L, 0.18 g/g C to 7.15 g/L, 0.20 g/g C, respectively. These improvements occurred due to the cell-immobilized sawdust which play an important role in the loading of cells and adsorption of acetic acid. Immobilized cultivation also increased the fatty acid proportion of C18:1, thereby improving biodiesel performance.

A review on variation in crude glycerol composition, bio-valorization of crude and purified glycerol as carbon source for lipid production

Crude glycerol (CG) is a by-product formed during the trans-esterification reaction for biodiesel production. Although crude glycerol is considered a waste stream of the biodiesel industry, it can replace expensive carbon substrates required for lipid production by oleaginous micro-organisms. However, crude glycerol has several impurities, such as methanol, soap, triglycerides, fatty acids, salts and metals, which are created during the trans-esterification process and may affect the cellular metabolism involved in lipid synthesis. This review aims to critically present a variation in crude glycerol composition depending on trans-esterification process and impact of impurities present in the crude glycerol on the cell growth and lipid accumulation by oleaginous microbes. This study also draws comparison between purified and crude glycerol for lipid production. Several techniques for crude glycerol purification (chemical treatment, thermal treatment, membrane technology, ion-exchange chromatography and adsorption) have been presented and discussed with reference to cost and environmental effects.

Microbial lipid production from food waste saccharified liquid under two-stage process

This study aimed to clarify the composition changes of food waste after being placed for few days and propose a two-stage fermentation method to effectively convert food waste saccharified liquid (FWSL) into lipids by Rhodosporidium toruloides. Food waste generally needs 3-5 days to be transported and stored before treatment. The lactic acid concentration of FWSL produced from 5-days-placed-at-room-temperature food waste reached to 15 g/L. Lactic acid promoted yeast proliferation, and its main mechanism was the conversion of lactic acid into pyruvic acid, which could provide energy for yeast growth through TCA cycle. The optimal lipid concentration in the two-stage fermentation reached to 9.19 g/L, and lipid yield amounted to 0.204 g lipid/g total sugar; the values increased by 44.27% and 60.63%, respectively, when compared with those in traditional fermentation. This study could provide a strategy for food waste treatment closer to industrial production.

High-affinity transport, cyanide-resistant respiration, and ethanol production under aerobiosis underlying efficient high glycerol consumption by Wickerhamomyces anomalus

Wickerhamomyces anomalus strain LBCM1105 was originally isolated from the wort of cachaça (the Brazilian fermented sugarcane juice-derived Brazilian spirit) and has been shown to grow exceptionally well at high amounts of glycerol. This paramount residue from the biodiesel industry is a promising cheap carbon source for yeast biotechnology. The assessment of the physiological traits underlying the W. anomalus glycerol consumption ability in opposition to Saccharomyces cerevisiae is presented. A new WaStl1 concentrative glycerol-H⁺ symporter with twice the affinity of S. cerevisiae was identified. As in this yeast, WaSTL1 is repressed by glucose and derepressed/induced by glycerol but much more highly expressed. Moreover, LBCM1105 aerobically growing on glycerol was found to produce ethanol, providing a redox escape to compensate the redox imbalance at the level of cyanide-resistant respiration (CRR) and glycerol 3P shuttle. This work is critical for understanding the utilization of glycerol by non-Saccharomyces yeasts being indispensable to consider their industrial application feeding on biodiesel residue.

Biodiesels from microbial oils: Opportunity and challenges

Although biodiesel has been extensively explored as an important renewable energy source, the raw materials-associated cost poses a serious challenge on its large-scale commercial production. The first and second generations of biodiesel are mainly produced from usable raw materials, e.g. edible oils, crops etc. Such a situation inevitably imposes higher demands on land and water usage, which in turn compromise future food and water supply. Obviously, there is an urgent need to explore alternative feedstock, e.g. microbial oils which can be produced by many types of microorganisms including microalgae, fungi and bacteria with the advantages of small footprint, high lipid content and efficient uptake of carbon dioxide. Therefore, this review offers a comprehensive picture of microbial oil-based technology for biodiesel production. The perspectives and directions forward are also outlined for future biodiesel production and commercialization.

Utilization of methanol in crude glycerol to assist lipid production in non-sterilized fermentation from Trichosporon oleaginosus

In this work, methanol in crude glycerol solution was used to assist the lipid production with oleaginous yeast Trichosporon oleaginosus cultivated under non-sterilized conditions. The investigated methanol concentration was 0%, 1.4%, 2.2%, 3.3% and 4.4% (w/v). The results showed that methanol played a significant role in the non-sterilized fermentation for lipid production. The optimal methanol concentration was around 1.4% (w/v) in which the growth of T. oleaginosus was promoted and overcame that of the contaminants. The non-sterilized fed-batch fermentation with initial methanol concentration of 1.4% (w/v) was then performed and high biomass production (43.39 g/L) and lipid production (20.42 g/L) were achieved.

Malic acid production by chemically induced Aspergillus niger MTCC 281 mutant from crude glycerol

In the present investigation, crude glycerol derived from transesterification process was utilized to produce the commercially-valuable malic acid. A combined resistant on methanol and malic acid strain of Aspergillus niger MTCC 281 mutant was generated in solid medium containing methanol (1-5%) and malic acid (40-80 g/L) by the adaptation process for 22 weeks. The ability of induced Aspergillus niger MTCC 281 mutant to utilize crude glycerol and pure glycerol to produce malic acid was studied. The yield of malic acid was increased with 4.45 folds compared with that of parent strain from crude glycerol. The highest concentration of malic acid from crude glycerol by using beneficial mutant was found to be 77.38 ± 0.51 g/L after 192 h at 25 °C. This present study specified that crude glycerol by-product from biodiesel production could be used for producing high amount of malic acid without any pretreatment.

Metabolomic elucidation of the effects of media and carbon sources on fatty acid production by Yarrowia lipolytica

Lipid production by oleaginous Yarrowia lipolytica depends highly on culture environments, such as carbon sources, carbon/nitrogen (C/N) ratios, types of media, and cellular growth phases. In this study, the effects of media and carbon sources on lipid and metabolite production were investigated by profiling fatty acids and intracellular metabolites of Y. lipolytica grown in various media. The highest total fatty acid yield 114.04 ± 6.23 mg/g dry cell weight was achieved by Y. lipolytica grown in minimal medium with glycerol (SCG) in the exponential phase. The high lipid production by Y. lipolytica in SCG was presumed to be due to the higher C/N ratio in SCG than in the complex media. Moreover, glycerol promoted lipid production better than glucose in both complex and minimal media because glycerol can easily incorporate into the core of triglycerides. Metabolite profiling revealed that levels of long-chain fatty acids, such as stearic acid, palmitic acid, and arachidic acid, increased in SCG medium. Meanwhile, in complex media supplemented with either glucose or glycerol, levels of amino acids, such as cysteine, methionine, and glycine, highly increased. This metabolomic approach could be applied to modulate the global metabolic network of Y. lipolytica for producing lipids and other valuable products.

Chemical and biological conversion of crude glycerol derived from waste cooking oil to biodiesel

In this study, crude, purified, and pure glycerol were used to cultivate Trichosporon oleaginosus for lipid production which was then used as feedstock of biodiesel production. The purified glycerol was obtained from crude glycerol by removing soap with addition of H₃PO₄ which converted soap to free fatty acids and then separated from the solution. The results showed that purified glycerol provided similar performance as pure glycerol in lipid accumulation; however, crude glycerol as carbon source had negatively impacted the lipid production of T. oleaginosus. Purified glycerol was later used to determine the optimal glycerol concentration for lipid production. The highest lipid yield 0.19g/g glycerol was obtained at 50g/L purified glycerol in which the biomass concentration and lipid content were 10.75g/L and 47% w/w, respectively. An energy gain of 4150.51MJ could be obtained with 1tonne of the crude glycerol employed for biodiesel production through the process proposed in this study. The biodiesel production cost estimated was 6.32US$/gal. Fatty acid profiles revealed that C16:0 and C18:1 were the major compounds of the biodiesel from the lipid produced by T. oleaginosus cultivated with crude and purified glycerol. The study found that purified glycerol was promising carbon source for biodiesel production.

The Engineering Potential of Rhodosporidium toruloides as a Workhorse for Biotechnological Applications

Moving our society towards a bioeconomy requires efficient and sustainable microbial production of chemicals and fuels. Rhodotorula (Rhodosporidium) toruloides is a yeast that naturally synthesizes substantial amounts of specialty chemicals and has been recently engineered to (i) enhance its natural production of lipids and carotenoids, and (ii) produce novel industrially relevant compounds. The use of R. toruloides by companies and research groups has exponentially increased in recent years as a result of recent improvements in genetic engineering techniques and the availability of multiomics information on its genome and metabolism. This review focuses on recent engineering approaches in R. toruloides for bioproduction and explores its potential as a biotechnological chassis.

Non-sterile fermentations for the economical biochemical conversion of renewable feedstocks

Heavy reliance on petroleum-based products drives continuous exploitation of fossil fuels, and results in serious environmental and climate problems. To address such an issue, there is a shift from petroleum sources to renewable ones. Biochemical conversion via fermentation is a primary platform for converting renewable sources to biofuels and bulk chemicals. In order to provide cost-competitive alternatives, it is imperative to develop efficient, cost-saving, and robust fermentation processes. Non-sterile fermentation offers several benefits compared to sterile fermentation, including elimination of sterility, reduced maintenance requirements, relatively simple bioreactor design, and simplified operation. Thus, cost effectiveness of non-sterile fermentation makes it a practical platform for low cost, large volume production of biofuels and bulk chemicals. Many approaches have been developed to conduct non-sterile fermentation without sacrificing the yields and productivities of fermentation products. This review focuses on the strategies for conducting non-sterile fermentation. The challenges facing non-sterile fermentation are also discussed.

Utilization of microbial oil obtained from crude glycerol for the production of polyol and its subsequent conversion to polyurethane foams

We have demonstrated possible use of microbial oil in biopolymer industries. Microbial oil was produced from biodiesel based crude glycerol and subsequently converted into polyol. Fermentation of crude glycerol in a batch bioreactor using Rhodosporidium toruloides ATCC 10788 produced 18.69g/L of lipid at the end of 7days. The microbial oil was then chemically converted to polyol and characterized using FT-IR and ¹H NMR. For comparison, canola oil and palm oil were also converted into their respective polyols. The hydroxyl numbers of polyols from canola, palm and microbial oil were found to be 266.86, 222.32 and 230.30 (mgKOH/g of sample) respectively. All the polyols were further converted into rigid and semi-rigid polyurethanes (maintaining the molar -NCO/-OH ratio of 1.1) to examine their suitability in polymer applications. Conversion of microbial lipid to polyurethane foam also provides a new route for the production of polymers using biodiesel based crude glycerol.

Effects of Salts Contained in Lignocellulose-Derived Sugar Streams on Microbial Lipid Production

This study aimed at developing low-cost, robust non-sterile fermentation processes for microbial lipid production from lignocellulose-derived sugars. Three representative oleaginous yeasts, Lipomyces tetrasporus (NRRL Y-11562), Rhodotorula toruloides (NRRL Y-1091), and Yarrowia lipolytica (NRRL YB-437), were tested for lipid production via non-sterile fermentation. Under optimal non-sterile conditions, all the tested strains had good performance on salt tolerance and lipid production. L. tetrasporus (NRRL Y-11562) gave the highest lipid titer of 12.79 g/L along with the depletion of both glucose and xylose, while Y. lipolytica (NRRL YB-437) showed the lowest lipid production and limited capability of xylose utilization. The key factors, including inoculation size, initial pH, and salt, all contributed to successful non-sterile fermentation. This study demonstrated that it is feasible to perform both sterile and non-sterile fermentation for lipid production using salt-containing lignocellulose-derived sugar streams.

Compositional Shift in Fatty Acid Profiles of Lipids Obtained from Oleaginous Yeasts upon the Addition of Essential Oil from Citrus sinensis L

Tailoring lipids from oleaginous yeasts to contain specific types of fatty acid is of considerable interest to food, fuel, and pharmaceutical industries. In this study, the essential oil obtained from Citrus sinesus L. has been used to alter the fatty acid composition of two common oleaginous yeasts, Rhodosporidium toruloides and Cryptococcus curvatus. With increasing levels of essential oil in the medium, the metabolic flux of the fatty acid biosynthesis pathway shifted towards saturated fatty acid production. Essential oil reduced the activities of elongase and ∆9 desaturase. This made the lipid obtained from both these yeasts rich in saturated fatty acids. At certain specific concentrations of the essential oil in the medium, the lipid obtained from R. toruloides and C. curvatus cultures was similar to mahuwa butter and palm oil, respectively. Limonene is the major constituents of orange essential oil. Its effect on one of the oleaginous yeasts, R. toruloides, was also studied separately. Effects similar to orange essential oil were obtained with limonene. Thus, we can conclude that limonene in orange essential oil brings about compositional change of microbial lipid produced in this organism.