Conversion of sugar beet residues into lipids by Lipomyces starkeyi for biodiesel production

Extraction of biodiesel from vegetable waste hydrolysates and evaluation of its engine performance and emission characteristics

Recently, microbial oil has become one of the promising next-generation feedstocks for producing biodiesel. While microbial oil can be extracted from different sources, there is only limited work on microbial production from fruits and vegetables. In this work, biodiesel was extracted through a two-step process: microbial conversion of vegetable waste into microbial oil using Lipomyces starkeyi, followed by transesterification of microbial oil into biodiesel. The lipid accumulation, composition of microbial oil, and the fuel properties of biodiesel were evaluated. The microbial oil consisted mainly of C16:0, C18:0 and C18:1, which were close to the properties of palm oil. The fuel properties of biodiesel comply with the EN14214:2012 standard. Thus, the vegetable waste can be a good biodiesel feedstock. Three blends (MOB10, MOB20 and MOB30 with 10, 20, and 30% of biodiesel) were tested for engine performance and emission characteristics in a 3.5 kW VCR research engine. At full load, MOB20 reduced the pollutant emissions of CO and HC by 47.8% and 33.2% with the penalty of increased NOx by 3.9%, while BTE reduced by 0.8% with the increased BSFC by 5.2%. Thus, the addition of vegetable waste biodiesel blends reduced the emissions of CO and HC significantly with slight reduction of brake thermal efficiency.

Microbial lipid production from soybean hulls using Lipomyces starkeyi LPB53 in a circular economy

Soybean hulls are lignocellulosic residuesgeneratedinthe industrial processing of soybean, representing about 5 % of the mass of the whole bean. This by-product isan importantsource of polymers suchas cellulose(34 %) and hemicellulose (11 %),which could bevalorizedvia biotechnology to improvethe economic returnof the oilseed chain. In the present work,soybean hulls were evaluated as a carbon sourcefor biolipid productionbyLipomycesstarkeyi LPB 53. Initially the hulls were treated physicochemically and enzymatically to obtain fermentable sugars. Subsequently, biomass growth was evaluated using different nitrogen sources andthe lipid production was optimized, reaching a maximum cell biomass concentration of 26.5 g/L with 42.5 % of lipids. Around 65 % of the xylose content was consumed.The obtained oil wasmajorlycomposed of oleic, palmitic, palmitoleic, linoleic and stearic fatty acids in a proportion of 54 %, 32 %, 4 %, 3 % and 2 %, respectively.

Rewiring of metabolic pathways in yeasts for sustainable production of biofuels

The ever-increasing global energy demand has led world towards negative repercussions such as depletion of fossil fuels, pollution, global warming and climate change. Designing microbial cell factories for the sustainable production of biofuels is therefore an active area of research. Different yeast cells have been successfully engineered using synthetic biology and metabolic engineering approaches for the production of various biofuels. In the present article, recent advancements in genetic engineering strategies for production of bioalcohols, isoprenoid-based biofuels and biodiesels in different yeast chassis designs are reviewed, along with challenges that must be overcome for efficient and high titre production of biofuels.

Enhancement production of lipid and unsaturation of fatty acids in Cryptococcus humicola via addition of calcium ion

Lipids synthesized by oleaginous yeasts are considered to be the best candidates for biodiesel production. Cryptococcus humicola as an oleaginous yeast accumulated lipid in cells. In order to optimize the conditions for lipid production, different carbon and nitrogen sources were used and metals were added into the medium. Ca²⁺ addition increased the lipid production greatly. Xylose and peptone were optimal carbon source and nitrogen source, respectively for lipid accumulation. Response surface experiment results revealed that the accumulation of lipid could be maximized when the xylose, peptone and Ca²⁺ concentration was 61 g/L, 4.31 g/L, 0.67 mmol/L. C16 and C18 fatty acid account for about 91% of the total fatty acids. The most abundant fatty acid was oleic acid (42.68%), followed by palmitic acid (29.7%) and stearic acid (13.87%). The addition of Ca²⁺ increased the content of unsaturated fatty acids (such as C16:1 and C18:1) and improved the unsaturation of fatty acids. Quantitative real time PCR analysis revealed that expression of genes related to lipid biosynthesis showed up-regulated by Ca²⁺ treatment. This study provided a strategy for increase in lipid production and content of unsaturated fatty acids.

Scheffersomyces stipitis ability to valorize different residual biomasses for vitamin B9 production

Sugar beet pulp (SBP), sugar beet molasses (SBM) and unfermented grape marcs (UGM) represent important waste in the agro-food sector. If suitably pre-treated, hexose and pentose sugars can be released in high quantities and can subsequently be used by appropriate cell factories as growth media and for the production of (complex) biomolecules, accomplishing the growing demand for products obtained from sustainable resources. One example is vitamin B₉ or folate, a B-complex vitamin currently produced by chemical synthesis, almost exclusively in the oxidized form of folic acid (FA). It is therefore desirable to develop novel competitive strategies for replacing its current fossil-based production with a sustainable bio-based process. In this study, we assessed the production of natural folate by the yeast Scheffersomyces stipitis, investigating SBM, SBP and UGM as potential growth media. Pre-treatment of SBM and SBP had previously been optimized in our laboratory; thus, here we focused only on UGM pre-treatment and hydrolysis strategies for the release of fermentable sugars. Then, we optimized the growth of S. stipitis on the three media formulated from those biomasses, working on inoculum pre-adaptation, oxygen availability and supplementation of necessary nutrients to support the microorganism. Folate production, measured with a microbiological assay, reached 188.2 ± 24.86 μg/L on SBM, 130.6 ± 1.34 μg/L on SBP and 101.9 ± 6.62 μg/L on UGM. Here, we demonstrate the flexibility of S. stipitis in utilizing different residual biomasses as growth media. Moreover, we assessed the production of folate from waste, and to the best of our knowledge, we obtained the highest production of folate from residual biomasses ever reported, providing the first indications for the future development of this microbial production process.

Recycling industrial food wastes for lipid production by oleaginous yeasts Rhodosporidiobolus azoricus and Cutaneotrichosporon oleaginosum

BACKGROUND

Microbial lipids have been emerging as a sustainable alternative to vegetable oils and animal fat to produce biodiesel and industrial relevant chemicals. The use of wastes for microbial processes can represent a way for upgrading low value feedstock to high value products, addressing one of the main goals of circular economy, the reduction of wastes by recycling. Two oleaginous yeasts, Rhodosporidiobolus azoricus and Cutaneotrichosporon oleaginosum, were used in this study to demonstrate the feasibility of the proposed approach.

RESULTS

In this study wastes from industrial food processing, as pumpkin peels and syrup from candied fruits manufacture, were used for yeast cultivation and for lipids production. Evaluation of growth and sugar consumption revealed marked differences between the yeasts in capacity to utilize the main sugars present in the feedstock. In particular, we observed an unexpected limitation in glucose metabolism on mineral defined media by R. azoricus. Both species showed ability to grow and accumulate lipids on media exclusively composed by undiluted pumpkin peel hydrolysate, and R. azoricus was the best performing. By a two-stage process carried out in bioreactor, this species reached a biomass concentration of 45 g/L (dry weight) containing 55% of lipids, corresponding to a lipid concentration of 24 g/L, with a productivity of 0.26 g/L/h and yield of 0.24 g lipids per g of utilized sugar.

CONCLUSIONS

Wastes from industrial food processing were sufficient to completely support yeast growth and to induce lipid accumulation. This study provides strong evidence that the concept of valorisation through the production of lipids from the metabolism of nutrients present in agro-industrial wastes by oleaginous yeasts is promising for implementation of biotechnological processes in a circular economy contest.

Short-chain alcohols inactivate an immobilized industrial lipase through two different mechanisms

Broadly used in biocatalysis as acyl acceptors or (co)-solvents, short-chain alcohols often cause irreversible loss of enzyme activity. Understanding the mechanisms of inactivation is a necessary step toward the optimization of biocatalytic reactions and the design of enzyme-based sustainable processes. In this work, we explored the functional and structural response of an immobilized enzyme, Novozym 435, exposed to methanol, ethanol, and tert-butanol. N-435 consists of Candida antarctica lipase B (CALB) adsorbed on polymethacrylate beads and finds application in a variety of processes involving the presence of short-chain alcohols. The nature of the N-435 material required the development of an ad hoc method of structural analysis, based on Fourier transform infrared microspectroscopy, which was complemented by catalytic activity assays and by morphological observation by transmission electron microscopy. We found that the inactivation of N-435 is highly dependent on alcohol concentration and occurs through two different mechanisms. Short-chain alcohols induce conformational changes leading to CALB aggregation, which is only partially prevented by immobilization. Moreover, alcohol modifies the texture of the solid support promoting the enzyme release. Overall, knowledge of the molecular mechanisms underlying Novozym 435 inactivation induced by short-chain alcohols promises to overcome the limitations that usually occur during industrial processes. This article is protected by copyright. All rights reserved.

Isolation, molecular identification of lipid-producing Rhodotorula diobovata: optimization of lipid accumulation for biodiesel production

Background

The increased demand for oil and fats to satisfy the ever-increasing human needs has enhanced the research in this field. Single-cell oils or microbial lipids produced by oleaginous microorganisms are being utilized as an alternative to traditional oil sources. Oleaginous yeasts can accumulate lipids above 20% of their biomass when they are grown under controlled conditions.

Results

In the present study, sixty-five yeasts were isolated from different sources. Using Sudan Black B staining technique, five yeast isolates were selected. Under nitrogen-limited cultivation conditions, the Co1 isolate was the best lipid accumulation potential of 39.79%. Isolate (Co1) was characterized morphologically and identified using the ribosomal DNA internal transcribed spacers regions (rDNA-ITS) from their genomic DNA. The sequence alignment revealed a 99.2% similarity with Rhodotorula diobovata. Under the optimized conditions, Rhodotorula diobovata accumulated lipids up to 45.85% on a dry biomass basis. R. diobovata, when grown on different raw materials, accumulated lipid up to 46.68% on sugar beet molasses medium, and the lipid had a high degree of monounsaturated fatty acids which gives biodiesel better quality.

Conclusions

The data suggest that the potent oleaginous yeast, R. diobovata, together with the use of cheap feedstock raw materials such as sugar beet molasses, can be considered as a promising feedstock for biodiesel production.

Enhancing microbial lipids yield for biodiesel production by oleaginous yeast Lipomyces starkeyi fermentation: A review

The enhanced production of microbial lipids suitable for manufacturing biodiesel from oleaginous yeast Lipomyces starkeyi is critically reviewed. Recent advances in several aspects involving the biosynthetic pathways of lipids, current conversion efficiencies using various carbon sources, intensification strategies for improving lipid yield and productivity in L. starkeyi fermentation, and lipid extraction approaches are analyzed from about 100 papers for the past decade. Key findings on strategies are summarized, including (1) optimization of parameters, (2) cascading two-stage systems, (3) metabolic engineering strategies, (4) mutagenesis followed by selection, and (5) co-cultivation of yeast and algae. The current technical limitations are analyzed. Research suggestions like examination of more gene targets via metabolic engineering are proposed. This is the first comprehensive review on the latest technical advances in strategies from the perspective of process and metabolic engineering to further increase the lipid yield and productivity from L. starkeyi fermentation.

Two-Stage Fermentation of Lipomyces starkeyi for Production of Microbial Lipids and Biodiesel

The high operating cost is currently a limitation to industrialize microbial lipids production by the yeast Lipomyces starkeyi. To explore economic fermentation technology, the two-stage fermentation of Lipomyces starkeyi using yeast extract peptone dextrose (YPD) medium, orange peel (OP) hydrolysate medium, and their mixed medium were investigated for seven days by monitoring OD₆₀₀ values, pH values, cell growth status, C/N ratios, total carbon concentration, total nitrogen concentration, residual sugar concentration, lipid content, lipid titer, and fatty acids profiles of lipids. The results showed that two-stage fermentation with YPD and 50% YPD + 50% OP medium contributed to lipid accumulation, leading to larger internal lipid droplets in the yeast cells. However, the cells in pure OP hydrolysate grew abnormally, showing skinny and angular shapes. Compared to the one-stage fermentation, the two-stage fermentation enhanced lipid contents by 18.5%, 27.1%, and 21.4% in the flasks with YPD medium, OP medium, and 50%YPD + 50%OP medium, and enhanced the lipid titer by 77.8%, 13.6%, and 63.0%, respectively. The microbial lipids obtained from both one-stage and two-stage fermentation showed no significant difference in fatty acid compositions, which were mainly dominated by palmitic acid (33.36–38.43%) and oleic acid (46.6–48.12%). Hence, a mixture of commercial medium and lignocellulosic biomass hydrolysate could be a promising option to balance the operating cost and lipid production.

Oleaginous yeasts respond differently to carbon sources present in lignocellulose hydrolysate

BACKGROUND

Microbial oils, generated from lignocellulosic material, have great potential as renewable and sustainable alternatives to fossil-based fuels and chemicals. By unravelling the diversity of lipid accumulation physiology in different oleaginous yeasts grown on the various carbon sources present in lignocellulose hydrolysate (LH), new targets for optimisation of lipid accumulation can be identified. Monitoring lipid formation over time is essential for understanding lipid accumulation physiology. This study investigated lipid accumulation in a variety of oleaginous ascomycetous and basidiomycetous strains grown in glucose and xylose and followed lipid formation kinetics of selected strains in wheat straw hydrolysate (WSH).

RESULTS

Twenty-nine oleaginous yeast strains were tested for their ability to utilise glucose and xylose, the main sugars present in WSH. Evaluation of sugar consumption and lipid accumulation revealed marked differences in xylose utilisation capacity between the yeast strains, even between those belonging to the same species. Five different promising strains, belonging to the species Lipomyces starkeyi, Rhodotorula glutinis, Rhodotorula babjevae and Rhodotorula toruloides, were grown on undiluted wheat straw hydrolysate and lipid accumulation was followed over time, using Fourier transform-infrared (FTIR) spectroscopy. All five strains were able to grow on undiluted WSH and to accumulate lipids, but to different extents and with different productivities. R. babjevae DVBPG 8058 was the best-performing strain, accumulating 64.8% of cell dry weight (CDW) as lipids. It reached a culture density of 28 g/L CDW in batch cultivation, resulting in a lipid content of 18.1 g/L and yield of 0.24 g lipids per g carbon source. This strain formed lipids from the major carbon sources in hydrolysate, glucose, acetate and xylose. R. glutinis CBS 2367 also consumed these carbon sources, but when assimilating xylose it consumed intracellular lipids simultaneously. Rhodotorula strains contained a higher proportion of polyunsaturated fatty acids than the two tested Lipomyces starkeyi strains.

CONCLUSIONS

There is considerable metabolic diversity among oleaginous yeasts, even between closely related species and strains, especially when converting xylose to biomass and lipids. Monitoring the kinetics of lipid accumulation and identifying the molecular basis of this diversity are keys to selecting suitable strains for high lipid production from lignocellulose.

Complete Utilization of the Major Carbon Sources Present in Sugar Beet Pulp Hydrolysates by the Oleaginous Red Yeasts Rhodotorula toruloides and R. mucilaginosa

Agro-industrial residues are low-cost carbon sources (C-sources) for microbial growth and production of value-added bioproducts. Among the agro-industrial residues available, those rich in pectin are generated in high amounts worldwide from the sugar industry or the industrial processing of fruits and vegetables. Sugar beet pulp (SBP) hydrolysates contain predominantly the neutral sugars d-glucose, l-arabinose and d-galactose, and the acidic sugar d-galacturonic acid. Acetic acid is also present at significant concentrations since the d-galacturonic acid residues are acetylated. In this study, we have examined and optimized the performance of a Rhodotorula mucilaginosa strain, isolated from SBP and identified at the molecular level during this work. This study was extended to another oleaginous red yeast species, R. toruloides, envisaging the full utilization of the C-sources from SBP hydrolysate (at pH 5.0). The dual role of acetic acid as a carbon and energy source and as a growth and metabolism inhibitor was examined. Acetic acid prevented the catabolism of d-galacturonic acid and l-arabinose after the complete use of the other C-sources. However, d-glucose and acetic acid were simultaneously and efficiently metabolized, followed by d-galactose. SBP hydrolysate supplementation with amino acids was crucial to allow d-galacturonic acid and l-arabinose catabolism. SBP valorization through the production of lipids and carotenoids by Rhodotorula strains, supported by complete catabolism of the major C-sources present, looks promising for industrial implementation.