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

Non-sterile fermentation for enhanced lipid production by Cutaneotrichosporon oleaginosum using bifunctional benzamide as selective antibacterial agent and unique nitrogen source

The commercial success of micro-biodiesel is currently impeded by the high lipid production cost. Here, a novel non-sterile lipid fermentation strategy was successfully developed by using bifunctional benzamide as selective antibacterial agent and unique nitrogen source. DCW, lipid concentration, and lipid content reached 24.45 g/L, 15.85 g/L, and 64.80 % when Cutaneotrichosporon oleaginosum was cultured on 60 g/L glucose supplementing 1.5 g/L benzamide as sole nitrogen source under non-sterile condition in a 3-L bioreactor. Interestingly, the non-sterile fermentation containing high-loading of bacteria resulted in comparable lipid production with sterile fermentation. This non-sterile strategy could be expanded to inexpensive substrates including crude glycerol and cassava starch hydrolysate. The fatty acid compositions indicated lipids prepared by the non-sterile fermentation were suitable for biodiesel production. By avoiding the sterilization process, this strategy could effectively reduce energy consumption and simplify the production process, which was promising for improving the techno-economics of the lipid production technology.

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.

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.

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.

Cutaneotrichosporon oleaginosus: A Versatile Whole-Cell Biocatalyst for the Production of Single-Cell Oil from Agro-Industrial Wastes

Cutaneotrichosporon oleaginosus is an oleaginous yeast with several favourable qualities: It is fast growing, accumulates high amounts of lipids and has a very broad substrate spectrum. Its resistance to hydrolysis by-products makes it a promising biocatalyst for custom tailored microbial oils. C. oleaginosus can accumulate up to 60 wt.% of its biomass as lipids. This species is able to grow by using several compounds as a substrate, such as acetic acid, biodiesel-derived glycerol, N-acetylglucosamine, lignocellulosic hydrolysates, wastepaper and other agro-industrial wastes. This review is focused on state-of-the-art innovative and sustainable biorefinery schemes involving this promising yeast and second- and third-generation biomasses. Moreover, this review offers a comprehensive and updated summary of process strategies, biomass pretreatments and fermentation conditions for enhancing lipid production by C. oleaginosus as a whole-cell biocatalyst. Finally, an overview of the main industrial applications of single-cell oil is reported together with future perspectives.

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.

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.

Efficient biosynthesis of anticancer polysaccharide by a mutant Chaetomium globosum ALE20 via non-sterilized fermentation

The sterilization process, due to its immense energy consumption, high facilities investment, and loss of raw materials by caramelization, during industrial production has drawn much attention. In this study, a methanol-resistant mutant strain, Chaetomium globosum ALE20, was obtained following 20 cycles of adaptive laboratory evolution process. The titer of anticancer polysaccharide (GCP-M) from C. globosum ALE20 reached 9.2 g/L with glycerol as sole carbon source using non-sterilized and fed-batch fermentation strategy. This titer represents a 200% increase compared with the 3.3 g/L attained with batch fermentation. The GCP-M monosaccharide was comprised of galactose, glucose, mannose and glucuronic acid, in a molar ratio of 3.83:66.37:3.26:1.95, respectively, and its weight-average molecular weight and polydispersity were 3.796 × 10⁴ Da and 1.060, respectively. This work presents an ideal alternative and safer fermentation process without sterilization, and a useful approach for enhancing industrial production.

Economical lipid production from Trichosporon oleaginosus via dissolved oxygen adjustment and crude glycerol addition

The effect of dissolved oxygen concentration on lipid accumulation in Trichosporon oleaginosus has been investigated. The experiment was performed in 15 L fermenters. The dissolved oxygen concentration varied by adjusting the agitation and aeration. High dissolved oxygen level at 50%-60% enhanced cell growth. Maintaining low dissolved oxygen concentration at 20%-30% during lipogenesis phase led to high final lipid content (51%) in Trichosporon oleaginosus. The consumptions of energy and cost of the process were evaluated. The energy consumption in the dissolved oxygen level optimized process was 41% less than that with dissolved oxygen level at 50%-60%. In addition, the cost was also reduced around one time in the dissolved oxygen level optimized process compared to the one with dissolved oxygen level at 50%-60%. The study provided a feasible way of enhancing lipid accumulation in Trichosporon oleaginosus and reducing the consumption of energy and cost of lipid production from Trichosporon oleaginosus.

The pH-based fed-batch for lipid production from Trichosporon oleaginosus with crude glycerol

In this study, it was found that the optimal pH for the growth of Trichosporon oleaginosus was related to the fermentation medium. A neutral or weak acid pH condition was optimal for the growth of Trichosporon oleaginosus in the extract-peptone-dextrose and wastewater sludge medium. Significant inhibition was observed at neutral pH in the wastewater sludge + crude glycerol medium due to the high soap content of the crude glycerol. By converting the soap to free fatty acid (FFA) at pH 5, the soap inhibition could be prevented. Fed-batch fermentation was employed to produce lipid from Trichosporon oleaginosus at pH 5 controlled by feeding crude glycerol. A remarkably high biomass (65.63 g/L) and lipid (35.79 g/L) concentration were achieved from the pH-based fed-batch fermentation in this study.