Lipid production from a mixture of sugarcane top hydrolysate and biodiesel-derived crude glycerol by the oleaginous red yeast, Rhodosporidiobolus fluvialis

Impact of glucose and propionic acid on even and odd chain fatty acid profiles of oleaginous yeasts

BACKGROUND

Odd chain fatty acids (OCFAs) are gaining attention for their valuable medical and nutritional applications. Microbial fermentation offers a sustainable and environmentally friendly alternative for OCFA production compared to traditional extraction or chemical synthesis methods. To achieve an economically feasible OCFA production process, it is essential to identify and develop microbial cell factories capable of producing OCFAs with high titers and yields.

RESULTS

We selected 19 yeast species, including both oleaginous yeasts and representatives from the Ascomycota and Basidiomycota phyla, based on their known or potential ability to produce OCFAs. These species were screened under various growth conditions to evaluate their OCFA production potential. In glucose-based, nitrogen-limited media, the strains produced fatty acids to varying extents, with OCFAs comprising 0.5-5% of the total fatty acids. When using the OCFAs precursor propionic acid as the sole carbon source, only eight strains exhibited growth, with tolerance to propionic acid concentrations between 5 and 29 g/L. The strains also displayed varying efficiencies in converting propionic acid into fatty acids, yielding between 0.16 and 1.22 g/L of fatty acids, with OCFAs constituting 37-89% of total fatty acids. Among the top performing strains, Cutaneotrichosporon oleaginosus produced the highest OCFA titers and yields (0.94 g/L, 0.07 g/g), Yarrowia lipolytica demonstrated superior growth rates even at elevated propionic acid concentrations, and Rhodotorula toruloides achieved the highest proportion of OCFAs relative to total fatty acids (89%).

CONCLUSIONS

Our findings highlight the diverse capacities of the selected yeast species for OCFA production, identifying several promising strains for further optimization as microbial cell factories in sustainable OCFA production processes.

Biotechnological potential of red yeast isolated from birch forests in Poland

OBJECTIVES

This study aimed to isolate red yeast from sap, bark and slime exudates collected from Polish birch forests and then assessment of their biotechnological potential.

RESULTS

24 strains of red yeast were isolated from the bark, sap and spring slime fluxes of birch (Betula pendula). Strains belonging to Rhodotorula mucilaginosa (6), Rhodosporidiobolus colostri (4), Cystrofilobasidium capitaum (3), Phaffia rhodozyma (3) and Cystobasidium psychroaquaticum (3) were dominant. The highest efficiency of carotenoid biosynthesis (5.04 mg L-1) was obtained by R. mucilaginosa CMIFS 004, while lipids were most efficiently produced by two strains of P. rhodozyma (5.40 and 5.33 g L-1). The highest amount of exopolysaccharides (3.75 g L-1) was produced by the R. glutinis CMIFS 103. Eleven strains showed lipolytic activity, nine amylolytic activity, and only two proteolytic activity. The presence of biosurfactants was not found. The growth of most species of pathogenic moulds was best inhibited by Rhodotorula yeasts.

CONCLUSION

Silver birch is a good natural source for the isolation of new strains of red yeast with wide biotechnological potential.

Application of microbial resources in biorefineries: Current trend and future prospects

The recent growing interest in sustainable and alternative sources of energy and bio-based products has driven the paradigm shift to an integrated model termed "biorefinery." Biorefinery framework implements the concepts of novel eco-technologies and eco-efficient processes for the sustainable production of energy and value-added biomolecules. The utilization of microbial resources for the production of various value-added products has been documented in the literatures. However, the appointment of these microbial resources in integrated resource management requires a better understanding of their status. The main of aim of this review is to provide an overview on the defined positioning and overall contribution of the microbial resources, i.e., algae, fungi and bacteria, for various bioprocesses and generation of multiple products from a single biorefinery. By utilizing waste material as a feedstock, biofuels can be generated by microalgae while sequestering environmental carbon and producing value added compounds as by-products. In parallel, fungal biorefineries are prolific producers of lignocellulose degrading enzymes along with pharmaceutically important novel products. Conversely, bacterial biorefineries emerge as a preferred platform for the transformation of standard cells into proficient bio-factories, developing chassis and turbo cells for enhanced target compound production. This comprehensive review is poised to offer an intricate exploration of the current trends, obstacles, and prospective pathways of microbial biorefineries, for the development of future biorefineries.

Combination of alkaline biodiesel-derived crude glycerol pretreated corn stover with dilute acid pretreated water hyacinth for highly-efficient single cell oil production by oleaginous yeast Cutaneotrichosporon oleaginosum

Single cell oil (SCO) prepared from biodiesel-derived crude glycerol (BCG) and lignocellulosic biomass (LCB) via oleaginous yeasts is an intriguing alternative precursor of biodiesel. Here, a novel strategy combining alkaline BCG pretreated corn stover and dilute acid pretreated water hyacinth for SCO overproduction was developed. The mixed pretreatment liquors (MPLs) were naturally neutralized and adjusted to a proper carbon-to-nitrogen ratio beneficial for SCO overproduction by Cutaneotrichosporon oleaginosum. The toxicity of inhibitors was relieved by dilution detoxification. The enzymatic hydrolysate of solid fractions was suitable for SCO production either separately or simultaneously with MPLs. Fed-batch fermentation of the MPLs resulted in high cell mass, SCO content, and SCO titer of 80.7 g/L, 75.7 %, and 61.1 g/L, respectively. The fatty acid profiles of SCOs implied high-quality biodiesel characteristics. This study offers a novel BCG&LCB-to-SCO route integrating BCG-based pretreatment and BCG/LCB hydrolysates co-utilization, which provides a cost-effective technical route for micro-biodiesel production.

Challenges and prospects of yeast-based microbial oil production within a biorefinery concept

Biodiesel, unlike to its fossil-based homologue (diesel), is renewable. Its use contributes to greater sustainability in the energy sector, mainly by reducing greenhouse gas emissions. Current biodiesel production relies on plant- and animal-related feedstocks, resulting in high final costs to the prices of those raw materials. In addition, the production of those materials competes for arable land and has provoked a heated debate involving their use food vs. fuel. As an alternative, single-cell oils (SCOs) obtained from oleaginous microorganisms are attractive sources as a biofuel precursor due to their high lipid content, and composition similar to vegetable oils and animal fats. To make SCOs competitive from an economic point of view, the use of readily available low-cost substrates becomes essential. This work reviews the most recent advances in microbial oil production from non-synthetic sugar-rich media, particularly sugars from lignocellulosic wastes, highlighting the main challenges and prospects for deploying this technology fully in the framework of a Biorefinery concept.

OctoShaker: A versatile robotic biomechanical agitator for cellular and organoid research

Mechanical forces have increasingly been recognized as a key regulator in the fate of cellular development and functionality. Different mechanical transduction methods, such as substrate stiffness and magnetic bead vibration, have been experimented with to understand the interaction between the biophysical cues and cellular outcome. In the exploration and utilization of the intrinsic cellular mechanism, bio-shakers, traditionally invented for stirring liquid, have garnered more interest as a tool to provide precise mechanical stimuli to aid in this study. Nonetheless, despite the usefulness of current bio-shaking technology, each type of shaker often offers a single mode of motion, insufficient for generating complex force dynamics needed to resemble the actual physical condition that occurs inside living organisms. In this study, we present OctoShaker, a robotic instrument capable of creating a multitude of motions that could be sequenced or programmed to mimic sophisticated hemodynamics in vivo. We demonstrated the programmed motion of circular convection and investigated its influence on micro-particle distribution in 96-well culture microplates. Biological samples, including HeLa cells and organoids, were tested, and unique resultant patterns were observed. We anticipate the open-source dissemination of OctoShaker in diverse biological applications, encompassing biomechanical studies for cellular and organoid research, as well as other disciplines that demand dynamic mechanical force generation.

Lipid Production from Native Oleaginous Yeasts Isolated from Southern Chilean Soil Cultivated in Industrial Vinasse Residues

In this research, six strains of oleaginous yeasts native to southern Chile were analyzed for their biotechnological potential in lipid accumulation. For this purpose, the six strains, named PP1, PP4, PR4, PR10, PR27 and PR29, were cultivated in a nitrogen-deficient synthetic mineral medium (SMM). Then, two strains were selected and cultivated in an industrial residual "vinasse", under different conditions of temperature (°C), pH and carbon/nitrogen (C/N) ratio. Finally, under optimized conditions, the growth kinetics and determination of the lipid profile were evaluated. The results of growth in the SMM indicate that yeasts PP1 and PR27 presented biomass concentrations and lipid accumulation percentages of 2.73 and 4.3 g/L of biomass and 36.6% and 45.3% lipids, respectively. Subsequently, for both strains, when cultured in the residual vinasse under optimized environmental conditions, biomass concentrations of 14.8 ± 1.51 g/L (C/N 80) and 15.83 ± 0.57 g/L (C/N 50) and lipid accumulations of 28% and 30% were obtained for PP1 and PR27, respectively. The composition of the triglycerides (TGs), obtained in the culture of the yeasts in a 2 L reactor, presented 64.25% of saturated fatty acids for strain PR27 and 47.18% for strain PP1. The saturated fatty acid compositions in both strains are mainly constituted of fatty acids, myristic C 14:0, heptadecanoic C 17:0, palmitic C 16:0 and stearic C 18:0, and the monounsaturated fatty acids constituted of oleic acid C 18:1 (cis 9) (28-46%), and in smaller amounts, palmitoleic acid and heptadecenoic acid. This work demonstrates that the native yeast strains PP1 and PR27 are promising strains for the production of microbial oils similar to conventional vegetable oils. The potential applications in the energy or food industries, such as aquaculture, are conceivable.

An Approach for Incorporating Glycerol as a Co-Substrate into Unconcentrated Sugarcane Bagasse Hydrolysate for Improved Lipid Production in Rhodotorula glutinis

Sugarcane bagasse is a potential raw material for microbial lipid production by oleaginous yeasts. Due to the limited sugar concentrations in bagasse hydrolysate, increasing carbon the concentration is necessary in order to improve lipid production. We aimed to increase carbon concentration by incorporating glycerol as a co-substrate into unconcentrated bagasse hydrolysate in the cultivation of Rhodotorula glutinis TISTR 5159. Cultivation in hydrolysate without nitrogen supplementation (C/N = 42) resulted in 60.31% lipid accumulation with 11.45 ± 0.75 g/L biomass. Nitrogen source supplementation increased biomass to 26.29 ± 2.05 g/L without losing lipid accumulation at a C/N of 25. Yeast extract improved lipid production in the hydrolysate due to high growth without altering the lipid content of the cells. Mixing glycerol up to 10% v/v into the unconcentrated hydrolysate improved biomass and lipid production. A further increase in glycerol concentrations drastically decreased growth and lipid accumulation by the yeast. By maintaining C/N at 27 using yeast extract as the sole nitrogen source, hydrolysate mixed with 10% v/v glycerol resulted in the highest lipid yield, at 19.57 ± 0.53 g/L with 50.55% lipid content, which was a 2.8-fold increase compared to using the hydrolysate alone. In addition, yeast extracts were superior for promoting growth and lipid production compared to inorganic nitrogen sources.

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.

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.

A novel oleaginous yeast Saccharomyces cerevisiae CU-TPD4 for lipid and biodiesel production

This study reports on the novel Saccharomyces cerevisiae CU-TPD4 that was isolated from coconut waste residues obtained from a coconut factory in Thailand. The CU-TPD4 isolate was confirmed to be a S. cerevisiae by molecular analysis and to be an oleaginous yeast with more than 20% (w/w) of the cell dry weight (CDW) present in the form of lipids. The lipid content and lipid yield of CU-TPD4 (52.96 ± 1.15% of CDW and 1.78 ± 0.06 g/L, respectively) under optimized growth conditions were much higher than those under normal growth conditions (22.65 ± 1.32% of CDW and 1.24 ± 0.12 g/L, respectively). The major fatty acids produced by CU-TPD4 were oleic (C18:1), palmitoleic (C16:1), stearic (C18:0), and palmitic (C16:0) acids. Mathematical estimation of the physical properties of the biodiesel obtained by transesterification of the extracted lipid suggested it was suitable as biodiesel with respect to the ASTM D6751 and EN 14214 international standards. Consequently, S. cerevisiae CU-TPD4 is expected to emerge as a promising alternative for biodiesel production.

Lipid bioproduction from delignified native grass (Cyperus distans) hydrolysate by Yarrowia lipolytica

In the present study, native grass (Cyperus distans) was utilized for the production of lipid using Yarrowia lipolytica MTCC 9519. Initially, pretreatment methods using hydrothermal and alkaline delignification were performed to obtain cellulose rich liquid fractions. Delignified native grass biomass was enzymatically hydrolyzed to convert non fermentable sugars in to fermentable sugars. The growth of Y. lipolytica MTCC 9519 by utilizing pretreated native grass hydrolysate was evaluated. The yield and concentration of total reducing sugars after enzyme hydrolysis were found to be 378 ± 35 mg/g of pretreated biomass and 28.64 g/L ± 1.25 g/L, respectively. When pretreated, delignified native grass hydrolysate was used with (NH₄)₂SO₄ (30C/N ratio) and sodium n-octanoate (0.4% w/w), the dry cell weight and lipid accumulation of Y. lipolytica MTCC 9519 reached about 19.88 ± 1.54 g/L and 53.62% (w/w) respectively after 96 h. Thus, native grass could become a promising substrate for biolipid production.

Microbial biodiesel production from industrial organic wastes by oleaginous microorganisms: Current status and prospects

This review aims to encourage the technical development of microbial biodiesel production from industrial-organic-wastes-derived volatile fatty acids (VFAs). To this end, this article summarizes the current status of several key technical steps during microbial biodiesel production, including (1) acidogenic fermentation of bio-wastes for VFA collection, (2) lipid accumulation in oleaginous microorganisms, (3) microbial lipid extraction, (4) transesterification of microbial lipids into crude biodiesel, and (5) crude biodiesel purification. The emerging membrane-based bioprocesses such as electrodialysis, forward osmosis and membrane distillation, are promising approaches as they could help tackle technical challenges related to the separation and recovery of VFAs from the fermentation broth. The genetic engineering and metabolic engineering approaches could be applied to design microbial species with higher lipid productivity and rapid growth rate for enhanced fatty acids synthesis. The enhanced in situ transesterification technologies aided by microwave, ultrasound and supercritical solvents are also recommended for future research. Technical limitations and cost-effectiveness of microbial biodiesel production from bio-wastes are also discussed, in regard to its potential industrial development. Based on the overview on microbial biodiesel technologies, an integrated biodiesel production line incorporating all the critical technical steps is proposed for unified management and continuous optimization for highly efficient biodiesel production.

Consolidated bioprocesses for efficient bioconversion of palm biomass wastes into biodiesel feedstocks by oleaginous fungi and yeasts

Consolidated bioprocesses for bioconversion of lignocellulosic biomass into biodiesel feedstocks were developed. Palm empty fruit bunch (EFB) was biologically pretreated coupling with fungal lipid production (121.4 ± 2.7 mg/g-EFB) by lignocellulolytic oleaginous fungi prior to lipid production by oleaginous yeasts. In subsequent separate hydrolysis and fermentation (SHF) of fungal pretreated EFB (FPEFB), the oleaginous yeast with the maximum lipid yield of 37.0 ± 0.1 mg/g-FPEFB was screened. While a higher lipid yield of 47.9 ± 1.5 mg/g-FPEFB was achieved in simultaneous saccharification and fermentation (SSF) with less enzyme requirement. Fed-batch SSF of non-sterile FPEFB was proven as a practical and efficient strategy to increase lipid yield up to 53.4 ± 0.5 mg/g-FPEFB. Total lipid yield by both fungi and yeast was 165.0 ± 4.4 mg/g-EFB. Interestingly, the consolidated bioprocesses of enzyme and lipid production also achieved comparable total lipid yield of 149.3 ± 6.6 mg/g-EFB. These strategies may contribute greatly to cost-effective and sustainable bioconversion of lignocellulosic biomass into biodiesel feedstocks.

Lignocellulosic Biomass as a Substrate for Oleaginous Microorganisms: A Review

Microorganisms capable of accumulating lipids in high percentages, known as oleaginous microorganisms, have been widely studied as an alternative for producing oleochemicals and biofuels. Microbial lipid, so-called Single Cell Oil (SCO), production depends on several growth parameters, including the nature of the carbon substrate, which must be efficiently taken up and converted into storage lipid. On the other hand, substrates considered for large scale applications must be abundant and of low acquisition cost. Among others, lignocellulosic biomass is a promising renewable substrate containing high percentages of assimilable sugars (hexoses and pentoses). However, it is also highly recalcitrant, and therefore it requires specific pretreatments in order to release its assimilable components. The main drawback of lignocellulose pretreatment is the generation of several by-products that can inhibit the microbial metabolism. In this review, we discuss the main aspects related to the cultivation of oleaginous microorganisms using lignocellulosic biomass as substrate, hoping to contribute to the development of a sustainable process for SCO production in the near future.

Scale-up of two-step acid-catalysed glycerol pretreatment for production of oleaginous yeast biomass from sugarcane bagasse by Rhodosporidium toruloides

Two-step dilute acid and acid-catalysed glycerol pretreatment was developed to maximise sugar yield from sugarcane bagasse. At the laboratory scale, dilute acid pretreatment at 130 °C followed by acid-catalysed glycerol pretreatment at 170 °C led to a total sugar (C5 + C6) yield of 82%, 31% higher than that from one-step acid-catalysed glycerol pretreatment. At the pilot scale, the two-step dilute acid and acid-catalysed glycerol pretreatment led to a maximum sugar yield of 74%, 13% higher than that from one-step pretreatment with 52% reduction in glycerol usage. The enzymatic hydrolysate containing glucose and residual glycerol were used to produce microbial oils by a Rhodosporidium toruloides strain. A fed-batch cultivation strategy led to the production of 44.8 g/L cell mass, including 26.6 g/L oil, 8.6 g/L protein and 12.7 mg/L carotenoid. The cell mass and oil yields were 19% higher than those from batch cultivation as feedstock inhibition and catabolite repression were alleviated.

Lipid Production from Sugarcane Top Hydrolysate and Crude Glycerol with Rhodosporidiobolus fluvialis using a Two-Stage Batch-Cultivation Strategy with Separate Optimization of Each Stage

Lipids from oleaginous microorganisms, including oleaginous yeasts, are recognized as feedstock for biodiesel production. A production process development of these organisms is necessary to bring lipid feedstock production up to the industrial scale. This study aimed to enhance lipid production of low-cost substrates, namely sugarcane top and biodiesel-derived crude glycerol, by using a two-stage cultivation process with Rhodosporidiobolus fluvialis DMKU-SP314. In the first stage, sugarcane top hydrolysate was used for cell propagation, and in the second stage, cells were suspended in a crude glycerol solution for lipid production. Optimization for high cell mass production in the first stage, and for high lipid production in the second stage, were performed separately using a one-factor-at-a-time methodology together with response surface methodology. Under optimum conditions in the first stage (sugarcane top hydrolysate broth containing; 43.18 g/L total reducing sugars, 2.58 g/L soy bean powder, 0.94 g/L (NH₄)₂SO₄, 0.39 g/L KH₂PO₄ and 2.5 g/L MgSO₄ 7H₂O, pH 6, 200 rpm, 28 °C and 48 h) and second stage (81.54 g/L crude glycerol, pH 5, 180 rpm, 27 °C and 196 h), a high lipid concentration of 15.85 g/L, a high cell mass of 21.07 g/L and a high lipid content of 73.04% dry cell mass were obtained.

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.

Efficient approaches to convert Coniochaeta hoffmannii lipids into biodiesel by in-situ transesterification

Coniochaeta hoffmannii was isolated from soils contaminated with biscuit factory wastes showed the maximum lipid accumulation capacity in the study. Lipid production was optimized in terms of pH, carrot pomace loading, nitrogen type and amount, incubation time. Solvent, alcohol type and catalyst concentration, dried/wet biomass concentration, reaction approaches and time were optimized for lipid extraction and transesterification. The highest lipid accumulation was found as 52.0% at pH 4 in the presence of 10% carrot pomace, 0.5 g/L cheese whey at the end of the 48 h incubation. The maximum total C16 and C18 FAME rates were detected at the 25 °C, in the presence of 4 g/L dried C. hoffmannii biomass, methanol and 3% NaOH by using the in-situ transesterification process at the end of the 0.5 h as 96.3%. This is the first report about the usage of C. hoffmannii lipids obtained from carrot pomace for sustainable biodiesel production.

Co-utilization of acidified glycerol pretreated-sugarcane bagasse for microbial oil production by a novel Rhodosporidium strain

Acidified glycerol pretreatment is very effective to deconstruct lignocellulosics for producing glucose. Co-utilization of pretreated biomass and residual glycerol to bioproducts could reduce the costs associated with biomass wash and solvent recovery. In this study, a novel strain Rhodosporidium toruloides RP 15, isolated from sugarcane bagasse, was selected and tested for coconversion of pretreated biomass and residual glycerol to microbial oils. In the screening trails, Rh. toruloides RP 15 demonstrated the highest oil production capacity on glucose, xylose, and glycerol among the 10 strains. At the optimal C:N molar ratio of 140:1, this strain accumulated 56.7, 38.3, and 54.7% microbial oils based on dry cell biomass with 30 g/L glucose, xylose, and glycerol, respectively. Furthermore, sugarcane bagasse medium containing 32.6 g/L glucose from glycerol-pretreated bagasse and 23.4 g/L glycerol from pretreatment hydrolysate were used to produce microbial oils by Rh. toruloides RP 15. Under the preliminary conditions without pH control, this strain produced 7.7 g/L oil with an oil content of 59.8%, which was comparable or better than those achieved with a synthetic medium. In addition, this strain also produced 3.5 mg/L carotenoid as a by-product. It is expected that microbial oil production can be significantly improved through process optimization.

Microbial oil production from acidified glycerol pretreated sugarcane bagasse by Mortierella isabellina

An integrated microbial oil production process consisting of acidified glycerol pretreatment of sugarcane bagasse, enzymatic hydrolysis, microbial oil production by Mortierella isabellina NRRL 1757 and oil recovery by hydrothermal liquefaction (HTL) of fungal biomass in fermentation broth was assessed in this study. Following pretreatment, the effect of residual pretreatment hydrolysate (containing glycerol) on enzymatic hydrolysis was firstly studied. The residual pretreatment hydrolysate (corresponding to 2.0–7.5% glycerol) improved glucan enzymatic digestibilities by 10–11% compared to the enzymatic hydrolysis in water (no buffer). Although residual pretreatment hydrolysate at 2.0–5.0% glycerol slightly inhibited the consumption of glucose in enzymatic hydrolysate by M. isabellina NRRL 1757, it did not affect microbial oil production due to the consumption of similar amounts of total carbon sources including glycerol. When the cultivation was scaled-up to a 1 L bioreactor, glucose was consumed more rapidly but glycerol assimilation was inhibited. Finally, HTL of fungal biomass in fermentation broth without any catalyst at 340 °C for 60 min efficiently recovered microbial oils from fungal biomass and achieved a bio-oil yield of 78.7% with fatty acids being the dominant oil components (∼89%). HTL also led to the hydrogenation of less saturated fatty acids (C18:2 and C18:3) to more saturated forms (C18:0 and C18:1).

A microbial oil production process consisting of acidified glycerol pretreatment of sugarcane bagasse, enzymatic hydrolysis, microbial oil production by M. isabellina NRRL 1757 and oil recovery by hydrothermal liquefaction of fungal biomass in fermentation broth was assessed.