Converting paper mill sludge into neutral lipids by oleaginous yeast Cryptococcus vishniaccii for biodiesel production

A Novel Sustainable and Self-Sufficient Biotechnological Strategy for Directly Transforming Sewage Sludge into High-Value Liquid Biochemicals

Sewage sludge, as a carbon-rich byproduct of wastewater treatment, holds significant untapped potential as a renewable resource. Upcycling this troublesome waste stream represents great promise in addressing global escalating energy demands through its wide practice of biochemical recovery concurrently. Here, we propose a biotechnological concept to gain value-added liquid bioproducts from sewage sludge in a self-sufficient manner by directly transforming sludge into medium-chain fatty acids (MCFAs). Our findings suggest that yeast, a cheap and readily available commercial powder, would involve ethanol-type fermentation in chain elongation to achieve abundant MCFA production from sewage sludge using electron donors (i.e., ethanol) and acceptors (i.e., short-chain fatty acids) produced in situ. The enhanced abundance and transcriptional activity of genes related to key enzymes, such as butyryl-CoA dehydrogenase and alcohol dehydrogenase, affirm the robust capacity for the self-sustained production of MCFAs. This is indicative of an effective metabolic network established between yeast and anaerobic microorganisms within this innovative sludge fermentation framework. Furthermore, life cycle assessment and techno-economic analysis evidence the sustainability and economic competitiveness of this biotechnological strategy. Overall, this work provides insights into sewage sludge upgrading independent of additional carbon input, which can be applied in existing anaerobic sludge fermentation infrastructure as well as to develop new applications in a diverse range of industries.

Biorefinery of waste activated sludge: Nutrient recovery and microbial lipid production by Yarrowia lipolytica

The rising generation of waste activated sludge (WAS) demands a fundamental shift towards resource reuse and recovery. The conventional methodologies used to manage this by-product derived from wastewater treatment plants are increasingly constrained due to stringent regulatory measures aimed at mitigating its adverse impacts on the environment and public health. Therefore, this work evaluated a promising strategy for the efficient management of WAS, transforming it into a valuable renewable source to produce high-value-added compounds, such as lipids and a slow-release fertilizer (struvite). Wet oxidation (WO) was identified as a suitable technique for solubilising WAS while generating short-chain fatty acids (primarily acetic acid). It was found that conducting WO at 200 °C for 120 min resulted in a 65% reduction of the total suspended solids (TSS) content and 87% of the volatile suspended solids (VSS) content. Additionally, under these conditions, 4440 ± 105 mg/L and 593 ± 21 mg/L of acetic and propionic acid were obtained, respectively, which were assimilated by Yarrowia lipolytica to produce biolipids. Furthermore, the rupture of WAS flocs also led to the solubilisation of 980 ± 8 mg/L of ammonium. During the struvite precipitation stage, a NH4:PO4:Mg ratio of 1:1.5:1.5 was found to be the most effective for removing soluble ammonium (97.4 ± 0.8%), resulting in a high-purity struvite formation, and enhancing the carbon/nitrogen (C/N) ratio of the oxidised WAS from 3 to 105. This improvement in the C/N ratio raised the lipid content from 36 ± 1% to 49 ± 1% during the cultivation of Y. lipolytica. The application of the sequencing batch culture strategy further increased lipid content to 59 ± 1%, with 6.0 ± 0.3 g/L as the final concentration after the fifth cycle. The lipids produced, mainly monounsaturated fatty acids with 40% of oleic acid, offer potential as biodiesel feedstock. This lipid composition led to biodiesel properties, including cetane number, iodine value, kinematic viscosity and density that met international standards. Therefore, this research presents a promising alternative not only for WAS management but also for harnessing valuable resources, thereby establishing a basis for large-scale studies.

Cultivation of yeasts on liquid digestate to remove organic pollutants and nutrients and for potential application as co-culture with microalgae

In this study, the growth of yeast and yeast-like fungi in the liquid digestate from vegetable wastes was investigated in order to remove nutrients and organic pollutants, and for their application as co-culture members with green microalgae. The studied yeast strains were characterized for their assimilative and enzymatic profiles as well as temperature requirements. In the first experimental stage, the growth dynamics of each strain were determined, allowing to select the best yeasts for further studies. In the subsequent stage, the ability of selectants to remove organic pollutants was assessed. Different cultivation media containing respectively 1:3, 1:1, 3:1 vol ratio of liquid digestate and the basal minimal medium were used. Among all tested yeast strains, Rhodotorula mucilaginosa DSM 70825 showed the most promising results, demonstrating the highest potential for removing organic substrates and nutrients. Depending on the medium, this strain achieved 50-80% sCOD, 45-60% tVFAs, 21-45% TN, 33-52% PO43- reduction rates. Similar results were obtained for the strain Candida sp. OR687571. The high nutrient and organics removal efficiency by these yeasts could likely be linked to their ability to assimilate xylose (being the main source of carbon in the liquid digestate). In culture media containing liquid digestate, both yeast strains achieved good viability and proliferation potential. In the liquid digestate medium, R. mucilaginosa and Candida sp. showed vitality at the level of 51.5% and 45.0%, respectively. These strains seem to be a good starting material for developing effective digestate treatment strategies involving monocultures and/or consortia with other yeasts or green microalgae.

Fed-batch fermentation of Mucor circinelloides reveals significant improvement in biomass and lipid accumulation through performance evaluation, chemical analysis, and expression profiling

This study aimed to improve the lipid and biomass yields of Mucor circinelloides WJ11 by implementing four different fed-batch fermentation strategies, varied in time and glucose concentration (S1-S4). The S1 fermentation strategy yielded the highest biomass, lipid, and fatty acid content (22 ± 0.7 g/L, 53 ± 1.2 %, and 28 ± 1.6 %) after 120 and 144 h, respectively. The γ-linolenic acid titer of 0.75 ± 0.0 g/L was greatest in S3 after 48 h. Quantitative reverse transcription polymerase chain reaction (RT-qPCR) was used to analyze the transcription of key genes involved in lipid accumulation. The glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, and ATP-citrate lyase genes showed increased expression levels. Fourier-transform infrared (FTIR) spectroscopy was used to analyze the biochemical profile during fermentation strategies. Optimal abiotic factors for production efficiency included pH 6.5, 25-26 °C, 15 % (v/v) inoculum, 500 rpm, 20 %-30 % dissolved oxygen, and 120 h fermentation. Glucose co-feeding offers valuable insights to develop effective fermentation strategies for lipid production.

Pulp-paper industry sludge waste biorefinery for sustainable energy and value-added products development: A systematic valorization towards waste management

The pulp-paper industry is one of the main industrial sectors that produce massive amounts of residual sludge, constituting an enormous environmental burden for the industries. Traditional sludge management practices, such as landfilling and incineration, are restricted due to mounting environmental pressures, complex regulatory frameworks, land availability, high costs, and public opinion. Valorization of pulp-paper industry sludge (PPS) to produce high-value products is a promising substitute for traditional sludge management practices, promoting their reuse and recycling. Valorization of PPIS for biorefinery beneficiation includes biomethane, biohydrogen, bioethanol, biobutanol, and biodiesel production for renewable energy generation. Additionally, the various thermo-chemical technologies can be utilized to synthesize bio-oil, hydrochar, biochar, adsorbent, and activated carbon, signifying potential for value-added generation. Moreover, PPIS can be recycled as a byproduct by incorporating it into nanocomposites, cardboard, and construction materials development. This paper aims to deliver a comprehensive overview of PPIS management approaches and thermo-chemical technologies utilized for the development of platform chemicals in industry. Substitute uses of PPIS, such as making building materials, developing supercapacitors, and making cardboard, are also discussed. In addition, this article deeply discusses recent developments in biotechnologies for valorizing PPIS to yield an array of valuable products, such as biofuels, lactic acids, cellulose, nanocellulose, and so on. This review serves as a roadmap for future research endeavors in the effective handling of PPIS.

Microbial Lipid Based Biorefinery Concepts: A Review of Status and Prospects

The use of lignocellulosic biomass as a raw material for the production of lipids has gained increasing attention, especially in recent years when the use of food in the production of biofuels has become a current technology. Thus, the competition for raw materials for both uses has brought the need to create technological alternatives to reduce this competition that could generate a reduction in the volume of food offered and a consequent commercial increase in the value of food. Furthermore, the use of microbial oils has been studied in many industrial branches, from the generation of renewable energy to the obtainment of several value-added products in the pharmaceutical and food industries. Thus, this review provides an overview of the feasibility and challenges observed in the production of microbial lipids through the use of lignocellulosic biomass in a biorefinery. Topics covered include biorefining technology, the microbial oil market, oily microorganisms, mechanisms involved in lipid-producing microbial metabolism, strain development, processes, lignocellulosic lipids, technical drawbacks, and lipid recovery.

Challenges in developing strategies for the valorization of lignin-a major pollutant of the paper mill industry

Apart from protecting the environment from undesired waste impacts, wastewater treatment is a crucial platform for recovery. The exploitation of suitable technology to transform the wastes from pulp and paper industries (PPI) to value-added products is vital from an environmental and socio-economic point of view that will impact everyday life. As the volume and complexity of wastewater increase in a rapidly urbanizing world, the challenge of maintaining efficient wastewater treatment in a cost-effective and environmentally friendly manner must be met. In addition to producing treated water, the wastewater treatment plant (WWTP) has a large amount of paper mill sludge (PMS) daily. Sludge management and disposal are significant problems associated with wastewater treatment plants. Applying the biorefinery concept is necessary for PPI from an environmental point of view and because of the piles of valuables contained therein in the form of waste. This will provide a renewable source for producing valuables and bio-energy and aid in making the overall process more economical and environmentally sustainable. Therefore, it is compulsory to continue inquiry on different applications of wastes, with proper justification of the environmental and economic factors. This review discusses current trends and challenges in wastewater management and the bio-valorization of paper mills. Lignin has been highlighted as a critical component for generating valuables, and its recovery prospects from solid and liquid PPI waste have been suggested.

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.

Removal of phosphorus from wastewater by Diutina rugosa BL3: Efficiency and pathway

A novel phosphorus removal yeast BL3 was isolated from an alternating anaerobic/aerobic biofilter and identified as Diutina rugosa by 26S rDNA gene sequence analysis. Yeast BL3 could effectively remove phosphorus from synthetic wastewater containing 2-20 mg/L phosphorus under optimal environmental conditions. The highest phosphorus removal efficiency was above 70% under the conditions of DO 6.86 mg/L, C/P ratios of 60, N/P ratios of 3.3, pH 6.0-9.0, and at 25.0-35.0 °C. The phosphorus distribution in the aqueous solution and different components of yeast BL3 analysis indicated that around 55%-70% and 20%-40% of removed phosphorus were transferred into extracellular polymeric substances (EPS) and yeast cells, respectively. The plausible phosphorus transfer pathway was proposed based on the phosphorus distribution and species analysis, suggesting the important role of EPS as a phosphorus reservoir. These results indicate that yeast BL3 can efficiently remove phosphorus under aerobic conditions without alternating anaerobic/aerobic cycling, and thus has significant potential for practical application in wastewater phosphorus removal.

Wood-feeding termite gut symbionts as an obscure yet promising source of novel manganese peroxidase-producing oleaginous yeasts intended for azo dye decolorization and biodiesel production

BACKGROUND

The ability of oxidative enzyme-producing micro-organisms to efficiently valorize organic pollutants is critical in this context. Yeasts are promising enzyme producers with potential applications in waste management, while lipid accumulation offers significant bioenergy production opportunities. The aim of this study was to explore manganese peroxidase-producing oleaginous yeasts inhabiting the guts of wood-feeding termites for azo dye decolorization, tolerating lignocellulose degradation inhibitors, and biodiesel production.

RESULTS

Out of 38 yeast isolates screened from wood-feeding termite gut symbionts, nine isolates exhibited high levels of extracellular manganese peroxidase (MnP) activity ranged between 23 and 27 U/mL after 5 days of incubation in an optimal substrate. Of these MnP-producing yeasts, four strains had lipid accumulation greater than 20% (oleaginous nature), with Meyerozyma caribbica SSA1654 having the highest lipid content (47.25%, w/w). In terms of tolerance to lignocellulose degradation inhibitors, the four MnP-producing oleaginous yeast strains could grow in the presence of furfural, 5-hydroxymethyl furfural, acetic acid, vanillin, and formic acid in the tested range. M. caribbica SSA1654 showed the highest tolerance to furfural (1.0 g/L), 5-hydroxymethyl furfural (2.5 g/L) and vanillin (2.0 g/L). Furthermore, M. caribbica SSA1654 could grow in the presence of 2.5 g/L acetic acid but grew moderately. Furfural and formic acid had a significant inhibitory effect on lipid accumulation by M. caribbica SSA1654, compared to the other lignocellulose degradation inhibitors tested. On the other hand, a new MnP-producing oleaginous yeast consortium designated as NYC-1 was constructed. This consortium demonstrated effective decolorization of all individual azo dyes tested within 24 h, up to a dye concentration of 250 mg/L. The NYC-1 consortium's decolorization performance against Acid Orange 7 (AO7) was investigated under the influence of several parameters, such as temperature, pH, salt concentration, and co-substrates (e.g., carbon, nitrogen, or agricultural wastes). The main physicochemical properties of biodiesel produced by AO7-degraded NYC-1 consortium were estimated and the results were compared to those obtained from international standards.

CONCLUSION

The findings of this study open up a new avenue for using peroxidase-producing oleaginous yeasts inhabiting wood-feeding termite gut symbionts, which hold great promise for the remediation of recalcitrant azo dye wastewater and lignocellulosic biomass for biofuel production.

Aspergillus caespitosus ASEF14, an oleaginous fungus as a potential candidate for biodiesel production using sago processing wastewater (SWW)

Background

Oleaginous microorganisms are sustainable alternatives for the production of biodiesel. Among them, oleaginous fungi are known for their rapid growth, short life cycles, no light requirement, easy scalability, and the ability to grow in cheap organic resources. Among all the sources used for biodiesel production, industrial wastewater streams have been least explored. We used oleaginous fungi to decontaminate sago processing wastewater and produce biodiesel.

Results

Among the 15 isolates screened for lipid production and starch utilization using the Nile red staining assay and amylase plate screening, three isolates accumulated > 20% (w/w) of their dry cell mass as lipids. The isolate ASEF14 exhibited the highest lipid accumulation (> 40%) and was identified as Aspergillus caespitosus based on the 28S rRNA gene sequencing. The maximum lipid content of 54.4% in synthetic medium (SM) and 37.2% in sago processing wastewater (SWW) was produced by the strain. The Fourier-transform infrared (FTIR) spectroscopy of the fungal oil revealed the presence of functional peaks corresponding to major lipids. Principal component analysis (PCA) of the FTIR data revealed major changes in the fatty acid composition during the transition from the growth phase (Days 1–3) to the lipid accumulation phase (Days 4–7). The fatty acid methyl esters (FAME) analysis of fungal oil from SWW contained 43.82% and 9.62% of saturated and monounsaturated fatty acids, respectively. The composition and percentage of individual FAME derived from SWW were different from SM, indicating the effect of nutrient and fermentation time. The fuel attributes of the SM- and SWW-grown fungal biodiesel (kinematic viscosity, iodine value, cetane number, cloud and pour point, linolenic acid content, FA > 4 double bonds) met international (ASTM D6751, EN 14214) and national (IS 15607) biodiesel standards. In addition to biodiesel production, the strain removed various contaminants such as total solids (TS), total suspended solids (TSS), total dissolved solids (TDS), dissolved oxygen (DO), chemical oxygen demand (COD), biological oxygen demand (BOD), total nitrogen (TN), total phosphorus (TP), and cyanide up to 58.6%, 53.0%, 35.2%, 94.5%, 89.3%, 91.3%, 74.0%, 47.0%, and 53.84%, respectively, from SWW.

Conclusion

These findings suggested that A. caespitosus ASEF14 is a potential candidate with high lipid accumulating ability (37.27%), capable of using SWW as the primary growth medium. The medium and incubation time alter the FAME profile of this fungus. The physical properties of fungal oil were in accordance with the biodiesel standards. Moreover, it decontaminated SWW by reducing several polluting nutrients and toxicants. The fungal biodiesel produced by this cost-effective method could serve as an alternate path to meet global energy demand.

Biodiesel Production From Lignocellulosic Biomass Using Oleaginous Microbes: Prospects for Integrated Biofuel Production

Biodiesel is an eco-friendly, renewable, and potential liquid biofuel mitigating greenhouse gas emissions. Biodiesel has been produced initially from vegetable oils, non-edible oils, and waste oils. However, these feedstocks have several disadvantages such as requirement of land and labor and remain expensive. Similarly, in reference to waste oils, the feedstock content is succinct in supply and unable to meet the demand. Recent studies demonstrated utilization of lignocellulosic substrates for biodiesel production using oleaginous microorganisms. These microbes accumulate higher lipid content under stress conditions, whose lipid composition is similar to vegetable oils. In this paper, feedstocks used for biodiesel production such as vegetable oils, non-edible oils, oleaginous microalgae, fungi, yeast, and bacteria have been illustrated. Thereafter, steps enumerated in biodiesel production from lignocellulosic substrates through pretreatment, saccharification and oleaginous microbe-mediated fermentation, lipid extraction, transesterification, and purification of biodiesel are discussed. Besides, the importance of metabolic engineering in ensuring biofuels and biorefinery and a brief note on integration of liquid biofuels have been included that have significant importance in terms of circular economy aspects.

Recent advances in lipid metabolic engineering of oleaginous yeasts

With the increasing demand to develop a renewable and sustainable biolipid feedstock, several species of non-conventional oleaginous yeasts are being explored. Apart from the platform oleaginous yeast Yarrowia lipolytica, the understanding of metabolic pathway and, therefore, exploiting the engineering prospects of most of the oleaginous species are still in infancy. However, in the past few years, enormous efforts have been invested in Rhodotorula, Rhodosporidium, Lipomyces, Trichosporon, and Candida genera of yeasts among others, with the rapid advancement of engineering strategies, significant improvement in genetic tools and techniques, generation of extensive bioinformatics and omics data. In this review, we have collated these recent progresses to make a detailed and insightful summary of the major developments in metabolic engineering of the prominent oleaginous yeast species. Such a comprehensive overview would be a useful resource for future strain improvement and metabolic engineering studies for enhanced production of lipid and lipid-derived chemicals in oleaginous yeasts.

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

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

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.

Characterization of two sugar transporters responsible for efficient xylose uptake in an oleaginous yeast Candida tropicalis SY005

Microbial conversion of lignocellulosic feedstock to the target bioproduct requires efficient assimilation of its constituent sugars, a large part of which comprises of glucose and xylose. This study aims to identify and characterize sugar transporters capable of xylose uptake in an oleaginous strain of the industrially relevant yeast Candida tropicalis. In silico database mining resulted in two sugar transporter proteins- CtStp1 and CtStp2, containing conserved amino acid residues and motifs that have been previously reported to be involved in xylose transport in other organisms. Several softwares predicted the likelihood of 10-12 transmembrane (TM) helices to be present in both the Stps, while molecular modelling showed 12 TM helices that were organized into a typical structure found in the major facilitator superfamily of transporters. Docking with different sugars also predicted favorable interactions. Heterologous expression in a Saccharomyces cerevisiae strain harboring functional xylose metabolic genes validated the broad substrate specificity of the two Stps. Each transporter supported prominent growth of recombinant S. cerevisiae strains on six sugars including xylose at various concentrations. Expression of CtSTP1 and CtSTP2 along with the xylose metabolic genes in yeast transformants grown in presence of xylose was confirmed by transcript detection. Growth curve and sugar consumption profiles revealed uptake of both glucose and xylose simultaneously by the recombinant yeast strains, though CtStp1 showed relatively less effect of glucose repression in mixed sugars and was a better transporter of xylose than CtStp2. Such glucose-xylose utilizing efficient transporters can be effective tools for developing co-fermenting yeasts through genetic engineering in future, with noteworthy applications in renewable biomass utilization.

Harnessing pongamia shell hydrolysate for triacylglycerol agglomeration by novel oleaginous yeast Rhodotorula pacifica INDKK

BACKGROUND

To meet the present transportation demands and solve food versus fuel issue, microbial lipid-derived biofuels are gaining attention worldwide. This study is focussed on high-throughput screening of oleaginous yeast by microwave-aided Nile red spectrofluorimetry and exploring pongamia shell hydrolysate (PSH) as a feedstock for lipid production using novel oleaginous yeast Rhodotorula pacifica INDKK.

RESULTS

A new oleaginous yeast R. pacifica INDKK was identified and selected for microbial lipid production. R. pacifica INDKK produced maximum 12.8 ± 0.66 g/L of dry cell weight and 6.78 ± 0.4 g/L of lipid titre after 120 h of growth, showed high tolerance to pre-treatment-derived inhibitors such as 5-hydroxymethyl furfural (5-HMF), (2 g/L), furfural (0.5 g/L) and acetic acid (0.5 g/L), and ability to assimilate C3, C5 and C6 sugars. Interestingly, R. pacifica INDKK showed higher lipid accumulation when grown in alkali-treated saccharified PSH (AS-PSH) (0.058 ± 0.006 g/L/h) as compared to acid-treated detoxified PSH (AD-PSH) (0.037 ± 0.006 g/L/h) and YNB medium (0.055 ± 0.003 g/L/h). The major fatty acid constituents are oleic, palmitic, linoleic and linolenic acids with an estimated cetane number (CN) of about 56.7, indicating the good quality of fuel.

CONCLUSION

These results suggested that PSH and R. pacifica INDKK could be considered as potential feedstock for sustainable biodiesel production.

Isolation of a new Papiliotrema laurentii strain that displays capacity to achieve high lipid content from xylose

In this work, we isolated and selected oleaginous yeasts from rock field soils from two National Parks in Brazil (Caparaó and Serra dos Órgãos) with the potential to accumulate oil from xylose, the main pentose sugar found in lignocellulosic biomass. From the 126 isolates, two were selected based on their lipid contents. They were taxonomically identified as Papiliotrema laurentii (UFV-1 and UFV-2). Of the two, P. laurentii UFV-1 was selected as the best lipid producer. Under unoptimized conditions, lipid production by P. laurentii UFV-1 was higher in glucose than in xylose. To improve its lipid production from xylose, we applied response surface methodology (RSM) with a face-centered central composite design (CCF). We evaluated the effects of agitation rate, initial cell biomass (OD₆₀₀), carbon/nitrogen ratio (C/N ratio) and pH on lipid production. P. laurentii UFV-1 recorded the highest lipid content, 63.5% (w/w) of the cell dry mass, under the following conditions: C/N ratio = 100:1, pH value = 7.0, initial OD₆₀₀ = 0.8 and agitation = 300 rpm. Under these optimized conditions, biomass, lipid titer and volumetric lipid productivity were 9.31 g/L, 5.90 g/L and 0.082 g/L.h, respectively. Additionally, we determined the fatty acid composition of P. laurentii UFV-1 as follows: C14:0 (0.5%), C16:0 (28.4-29.4%), C16:1 (0.2%), C18:0 (9.5-11%), C18:1 (58.6-60.5%), and C20:0 (0.7-0.8%). Based on this composition, the predicted properties of biodiesel showed that P. laurentii UFV-1 oil is suitable for use as feedstock in biodiesel production.

Biochemical profiling, prediction of total lipid content and fatty acid profile in oleaginous yeasts by FTIR spectroscopy

BACKGROUND

Oleaginous yeasts are considered as a potential lipid source for food, feed and biofuel production. In order to make the yeast-based lipid production environmentally and economically sustainable, there is a need for screening studies in order to find the best yeast lipid producers on different substrates, and to optimize cultivation conditions. Since the target parameter of such screening studies are lipid amounts and profiles, an analytical technique that is able to perform lipid analyses rapidly, reproducible and with high precision is highly desirable. The main objective of this study was to establish the non-invasive high-throughput Fourier transform infrared (FTIR) spectroscopy analysis for the prediction of lipid content and profile in oleaginous yeasts.

RESULTS

High-throughput FTIR spectroscopy allowed characterizing the total biochemical profile of oleaginous yeasts and enabled us to identify strains and substrate(s) providing the highest total lipid content. Some of the yeast strains grown under nitrogen-limiting conditions with glucose/xylose/mixture of glucose and xylose as carbon sources were accumulating lipids with a high proportion of free fatty acids. FTIR spectra were used to predict gravimetric and gas chromatography data by establishing multivariate calibration models. Coefficients of determination (R ²) for calibration models were obtained in a range between 0.62 and 0.92 for predicting lipid content. When using an independent test set, R ² values between 0.53 and 0.79 were achieved for predicting fatty acid profile. The best spectral region(s) for the prediction of total lipid content was 3100-2800 cm^-1 combined with 1800-700 cm^-1, and for prediction of summed saturated (SAT), monounsaturated (MUFA) and polyunsaturated (PUFA) fatty acids: 3100-2800 cm^-1, 3100-2800 cm^-1 combined with 1700-1715 cm^-1 and 3100-2800 cm^-1 combined with 1800-1715 cm^-1, respectively. The highest lipid accumulation was observed for strains Rhodotorula babjevae DBVPG 8058 on glucose and mixture of glucose and xylose and Lipomyces starkeyi CBS 2512 on xylose.

CONCLUSIONS

Applying FTIR spectroscopy combined with multivariate data analysis allows performing rapid, non-invasive, reproducible and precise quantitative predictions of total lipid content and lipid profile. It allows also detecting different lipid fractions as triacylglycerols (TAGs) and free fatty acids and evaluating the total biochemical profile of cells. Several yeast strains with high lipid accumulation were identified.

Turbo thin film continuous flow production of biodiesel from fungal biomass

Direct biodiesel production from wet fungal biomass may significantly reduce production costs, but there is a lack of fast and cost-effective processing technology. A novel thin film continuous flow process has been applied to study the effects of its operational parameters on fatty acid (FA) extraction and FA to fatty acid methyl ester (FAME) conversion efficiencies. Single factor experiments evaluated the effects of catalyst concentration and water content of biomass, while factorial experimental designs determined the interactions between catalyst concentration and biomass to methanol ratio, flow rate, and rotational speed. Direct transesterification (DT) of wet Mucor plumbeus biomass at ambient temperature and pressure achieved a FA to FAME conversion efficiency of >90% using 3 wt/v % NaOH concentration, if the water content was ≤50% (w/w). In comparison to existing DT methods, this continuous flow processing technology has an estimated 90-94% reduction in energy consumption, showing promise for up-scaling.

Rhodococcus and Yarrowia-Based Lipid Production Using Lignin-Containing Industrial Residues

Improvement in biorefining technologies coupled with development of novel fermentation strategies and analysis will be paramount in establishing supplementary and sustainable biofuel pathways. Oleaginous microorganisms that are capable of accumulating triacylglycerides (TAGs) and fatty acid methyl esters (FAMEs), such as Rhodococcus and Yarrowia species, can be used to produce second-generation biofuels from non-food competing carbon sources. These "microbiorefineries" provide a pathway to upgrade agricultural and industrial waste streams to fungible fuels or precursors to chemicals and materials. Here we provide a general overview on cultivating Rhodococcus and Yarrowia on agro-waste/industrial biomass pretreatment waste streams to produce single-cell oils/lipids and preparing samples for FAME detection.

Production of Oleaginous Organisms or Lipids Using Sewage Water and Industrial Wastewater

Worldwide, wastewater produced from sewage and industry poses a serious risk to the surrounding environment. As a way to address this problem, an integrated approach for cultivation of oleaginous microorganisms on wastewater leading to effective removal of hazardous components and sustainable production of biodiesel is proposed. Oleaginous yeasts have the unique ability to utilize wastewater as feedstock and accumulate large amounts of triacylglycerols within their cellular compartments at stationary phase (144 h). The lipids stored in an oleaginous microbe can be visualized by fluorescence microscopy and converted into biodiesel through transesterification after extraction. Here, we describe the batch cultivation of oleaginous yeast on sewage and industrial wastewater at 25 °C. High lipid accumulation with efficient removal of toxic chemicals can be achieved by utilizing this integrated method.

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.

Aromatic hydrocarbon biodegradation activates neutral lipid biosynthesis in oleaginous yeast

In this study, the biodegradation ability of oleaginous yeast Cryptococcus psychrotolerans IITRFD for aromatic hydrocarbons (AHs) was investigated. It was found to completely degrade range of AHs such as 1 g/L phenol, 0.75 g/L naphthalene, 0.50 g/L anthracene and 0.50 g/L pyrene with lipid productivity (g/L/h) of 0.0444, 0.0441, 0.0394 and 0.0383, respectively. This work demonstrated the ring cleavage pathways of AHs by this yeast which follow ortho route for phenol and naphthalene while meta route for anthracene and pyrene degradation. The end products generated during biodegradation of AHs are feed as precursors for de novo triacylglycerols (TAG) biosynthesis pathway of oleaginous yeast. A high quantity of lipid content (46.54%) was observed on phenol as compared to lipid content on naphthalene (46.38%), anthracene (44.97%) and pyrene (44.16%). The lipid profile revealed by GC-MS analysis shows elevated monounsaturated fatty acid (MUFA) content with improved biodiesel quality.

Enhanced single cell oil production by mixed culture of Chlorella pyrenoidosa and Rhodotorula glutinis using cassava bagasse hydrolysate as carbon source

The single cell oil (SCO) production by the mono and mixed culture of microalgae Chlorella pyrenoidosa and red yeast Rhodotorula glutinis was investigated using non-detoxified cassava bagasse hydrolysate (CBH) as carbon source. The results suggested that the two strains were able to tolerate and even degrade some byproducts presented in the CBH, and the mixed culture approach enhanced the degradation of certain byproducts. Biomass (20.37 ± 0.38 g/L) and lipid yield (10.42 ± 1.21 g/L) of the mixed culture achieved in the batch culture were significantly higher than that of the mono-cultures (p < 0.05). The fed-batch culture further raised the biomass and lipid yield to 31.45 ± 4.93 g/L and 18.47 ± 3.25 g/L, respectively. The lipids mainly composed of oleic acid and palmitic acid, suggesting the potential applications such as biofuel feedstock, cosmetics, food additives and lubricant. This study provided new insights for the integration of the economical SCO production with agro-industrial waste disposal.

Amaranth seeds (Amaranthus palmeri L.) as novel feedstock for biodiesel production by oleaginous yeast

The potential of lipid accumulation by oleaginous yeast Cryptococcus vishniaccii grown on amaranth seed aqueous extract (AAE) media was assessed. Maximum cell biomass productivity of 104 mg/L/h, lipid productivity of 54 mg/L/h, and lipid content of 52.31% were recorded on AAE when carbon to nitrogen (C:N) ratio increased from 134 to 147 after removal of ammonia nitrogen. The lipid droplet (LD) size (2.32 ± 0.38 μm) was visualized by fluorescence microscopy using Nile red stain indicating maximum accumulated triacylglycerol (TAG) at C:N 147. Fatty acid methyl ester (FAME) profile obtained after transesterification of extracted lipid revealed the presence of palmitic acid (16:0), palmitoleic acid (16:1), stearic acid (18:0), oleic acid (18:1), and linoleic acid (18:2). Data showed the presence of high monounsaturated fatty acid (MUFA) content (68.17%) depicting improved winter operating conditions of biodiesel. Various quality parameters of biodiesel were evaluated and compared to the American and European biodiesel standards specifications. Based on the lipid productivity, distribution of fatty acids, and evaluated properties obtained; the lipid accumulation by C. vishniaccii utilizing amaranth seeds as substrate could serve as a feasible feedstock for biodiesel production.

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.

From low-cost substrates to Single Cell Oils synthesized by oleaginous yeasts

As new feedstock for biofuels, microbial oils have received worldwide attentions due to their environmentally-friendly characters. Microbial oil production based on low-cost raw materials is significantly attractive to the current biodiesel refinery industry. In terms of SCOs production, oleaginous yeast has numerous advantages over bacteria, molds and microalgae based on their high growth rate and lipid yield. Numerous efforts have been made on the competitive lipid production combining the use of cheap raw materials as substrates by yeasts. In this paper, we provided an overview of lipid metabolism in yeast cells. New advances using oleaginous yeast as a cell factory for high-value lipid production from various low-cost substrates are also reviewed, and the enhanced strategies based on synergistic effects of oleaginous yeast and microalgae in co-culture are discussed in details.

Characterization and robust nature of newly isolated oleaginous marine yeast Rhodosporidium spp. from coastal water of Northern China

A total of ten marine yeast strains isolated from Bohai Sea, Northern China were identified to be members of three genera Rhodosporidium, Rhodotorula, and Cryptococcus. Two representative strains Rhodosporidium TJUWZ4 and Cryptococcus TJUWZA11 with high lipid content based on Nile red staining method were further characterized. A wide range of culture conditions (C and N sources, pH, temperature, salinity and C/N ratio) were tested to characterize the biomass and lipid production (yield and productivity) of these strains. Results indicated that Rhodosporidium TJUWZ4 was capable of achieving lipid yield up to 44% and 0.09 g/l-h productivity on glucose and peptone medium at pH 4, 20 °C, 30% salinity, and C/N 80. Three fatty acids, namely oleic acid (18:1), palmitic acid (C16:0) and linoleic acid (18:2) were the major intracellular fatty acids, which accounted for 90% of total lipids. With promising features for intracellular lipid accumulation, Rhodosporidium TJUWZ4 is a robust strain with great potentials for application in biodiesel production from renewable feedstocks.

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

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

Potential of oleaginous yeast Trichosporon sp., for conversion of sugarcane bagasse hydrolysate into biodiesel

This study reports production of microbial oil from a yeast strain Trichosporon sp., (RW) isolated from decayed wood. Preliminary analysis based on fluorescence microscopy and spectroscopy of Nile red stained yeast cells showed accumulation of lipid globules. The potential of the yeast to produce lipids was evaluated on glucose, glycerol and acid hydrolysate of sugarcane bagasse, where Trichosporon sp. (RW) was found to accumulate 21.45 (59.6%), 18.41 (56%) and 10.25g/l (40.5%) of the lipids after 120h of fermentation at 30°C. FAME analysis of lipids by GC-FID and NMR revealed oleic acid (18:1) as the major constituent, corresponding to 50.05, 46.48 and 54.66% of the accumulated lipids in glucose, glycerol and hydrolysate grown cultures, respectively. Other accumulated lipids included palmitic (16:0), linoleic (18:2) and stearic acids (18:0) in that order. The cetane number of the lipids ranged from 52.39 to 59.57 indicating suitability for biodiesel production.

Microbial oil - A plausible alternate resource for food and fuel application

Microbes have recourse to low-priced substrates like agricultural wastes and industrial efflux. A pragmatic approach towards an emerging field- the exploitation of microbial oils for biodiesel production, pharmaceutical and cosmetic applications, food additives, biopolymer production will be of immense remunerative significance in the near future. Due to high free fatty acid, nutritive content and simpler solvent extraction processes of microbial oils with plant oil, microbial oils can back plant oils in food applications. The purpose of this review is to evaluate the opulence of lipid production in native and standard micro-organisms and also to emphasize the vast array of applications including food and fuel by obtaining maximum yield.

Recent advances and industrial viewpoint for biological treatment of wastewaters by oleaginous microorganisms

Recently, technology of using oleaginous microorganisms for biological treatment of wastewaters has become one hot topic in biochemical and environmental engineering for its advantages such as easy for operation in basic bioreactor, having potential to produce valuable bio-products, efficient wastewaters treatment in short period, etc. To promote its industrialization, this article provides some comprehensive analysis of this technology such as its advances, issues, and outlook especially from industrial viewpoint. In detail, the types of wastewaters can be treated and the kinds of oleaginous microorganisms used for biological treatment are introduced, the potential of industrial application and issues (relatively low COD removal, low lipid yield, cost of operation, and lack of scale up application) of this technology are presented, and some critical outlook mainly on co-culture method, combination with other treatments, process controlling and adjusting are discussed systematically. By this article, some important information to develop this technology can be obtained.

T, Das P, Meng X, Stoklosa RJ, Bhalla A, Hodge DB, Yuan JS, Ragauskas AJ. Conversion of corn stover alkaline pre-treatment waste streams into biodiesel via Rhodococci

The bioconversion of second-generation cellulosic ethanol waste streams into biodiesel via oleaginous bacteria, Rhodococcus, is a novel optimization strategy for biorefineries with substantial potential for rapid development.

Isolation, identification and characterization of Cystobasidium oligophagum JRC1: A cellulase and lipase producing oleaginous yeast

Oleaginous yeast closely related to Cystobasidium oligophagum was isolated from soil rich in cellulosic waste. The yeast was isolated based on its ability to accumulate intracellular lipid, grow on carboxymethylcellulose (CMC) and produce lipase. It could accumulate up to 39.44% lipid in a glucose medium (12.45±0.97g/l biomass production). It was able to grow and accumulate lipids (36.46%) in the medium containing CMC as the sole carbon source. The specific enzyme activities obtained for endoglucanase, exoglucanase, and β-glucosidase were 2.27, 1.26, and 0.98IU/mg respectively. The specific enzyme activities obtained for intracellular and extracellular lipase were 2.16 and 2.88IU/mg respectively. It could grow and accumulate lipids in substrates including glycerol (42.04%), starch (41.54%), xylose (36.24%), maltose (26.31%), fructose (24.29%), lactose (21.91%) and sucrose (21.72%). The lipid profile of the organism was suitable for obtaining biodiesel with desirable fuel properties.