Bead milling for lipid recovery from thraustochytrid cells and selective hydrolysis of Schizochytrium DT3 oil using lipase

Extraction methods of algae oils for the production of third generation biofuels - A review

Microalgae are the main source of third-generation biofuels because they have a lipid content of 20-70%, can be abundantly produced and do not compete in the food market besides other benefits. Biofuel production from microalgae is a promising option to contribute for the resolution of the eminent crisis of fossil energy and environmental pollution specially in the transporting sector. The choice of lipid extraction method is of relevance and associated to the algae morphology (i.e., rigid cells). Therefore, it is essential to develop suitable extraction technologies for economically viable and environment-friendly lipid recovery processes with the aim of achieving a commercial production of biofuels from this biomass. This review presents an exhaustive analysis and discussion of different methods and processes of lipid extraction from microalgae for the subsequent conversion to biodiesel. Physical methods based on the use of supercritical fluids, ultrasound and microwaves were reviewed. Chemical methods using solvents with different polarities, aside from mechanical techniques such as mechanical pressure and enzymatic methods, were also analyzed. The advantages, drawbacks, challenges and future prospects of lipid extraction methods from microalgae have been summarized to provide a wide panorama of this relevant topic for the production of economic and sustainable energy worldwide.

Geobacter sulfurreducens' Unique Metabolism Results in Cells with a High Iron and Lipid Content

Geobacter sulfurreducens is a ubiquitous iron-reducing bacterium in soils, and in engineered systems, it can respire an electrode to produce measurable electric current. Its unique metabolism, heavily dependent on an extensive network of cytochromes, requires a unique cell composition. In this work, we used metallomics, cell fraction and elemental analyses, and transcriptomics to study and analyze the cell composition of G. sulfurreducens. Elemental composition studies (C, H, O, N, and ash content) showed high C:O and H:O ratios of approximately 1.7:1 and 0.25:1, indicative of more reduced cell composition that is consistent with high lipid content. Our study shows that G. sulfurreducens cells have a large amount of iron (2 ± 0.2 μg/g dry weight) and lipids (32 ± 0.5% dry weight/dry weight) and that this composition does not change whether the cells are grown with a soluble or an insoluble electron acceptor. The high iron concentration, higher than similar microorganisms, is attributed to the production of cytochromes that are abundant in transcriptomic analyses in both solid and soluble electron acceptor growth. The unique cell composition of G. sulfurreducens must be considered when growing this microorganism for lab studies and commercial applications. IMPORTANCE Geobacter sulfurreducens is an electroactive microorganism. In nature, it grows on metallic minerals by transferring electrons to them, effectively "breathing" metals. In a manmade system, it respires an electrode to produce an electric current. It has become a model organism for the study of electroactive organisms. There are potential biotechnological applications of an organism that can bridge the gap between biology and electrical signal and, as a ubiquitous iron reducer in soils around the world, G. sulfurreducens has an impact on the global iron cycle. We measured the concentrations of metals, macromolecules, and basic elements in G. sulfurreducens to define this organism's composition. We also used gene expression data to discuss which proteins those metals could be associated with. We found that G. sulfurreducens has a large amount of lipid and iron compared to other bacteria-these observations are important for future microbiologists and biotechnologists working with the organism.

Coupling with in-situ electrochemical reactive chlorine species generation and two-phase partitioning method for enhanced microalgal biodiesel production

Microalgal-based biofuel production is of great significance in alleviating energy crisis and achieving carbon neutrality. However, the excessive costs and high solvent consumption in lipids extraction from microalgal obstruct the widespread application of biodiesel in practice. Reported herein is the construction of facile strategy for lipids extraction via electrocatalytic pretreatment and a subsequent two-phase partitioning method. Electrocatalytic pretreatment method adopts the solar as power source and avoids the drying of microalgal biomass, in favor of carbon neutrality requirement. During this process, eco-friendly electrode with high specific surface area could contribute to the sufficient generation of reactive chlorine species (RCS), facilitating the outflows of intracellular lipid. As a result, assisted with two-phase partitioning method, a satisfied performance of lipid recovery (86.72 %) was obtained. Notably, compared with traditional solvent method, two-phase partitioning method greatly reduced the dosage of organic solvent, which is an economical or environmental technique.

Emerging prospects of microbial production of omega fatty acids: Recent updates

Healthy foods containing omega-3/omega-6 polyunsaturated fatty acids (PUFAs) have been in great demand because of their unique dietary and health properties. Reduction in chronic inflammatory and autoimmune diseases has shown their therapeutic and health-promoting effects when consumed under recommended ratio 1:1-1:4, however imbalanced ratios (>1:4, high omega-6) enhance these risks. The importance of omega-6 is apparent however microbial production favors larger production of omega-3. Current research focus is prerequisite to designing omega-6 production strategies for better application prospects, for which thraustochytrids could be promising due to higher lipid productivity. This review provides recent updates on essential fatty acids production from potential microbes and their application, especially major insights on omega research, also discussed the novel possible strategies to promote omega-3 and omega-6 accumulation via engineering and omics approaches. It covers strategies to block the conversion of omega-6 into omega-3 by enzyme inhibition, nanoparticle-mediated regulation and/or metabolic flux regulation, etc.

Water-plasma-enhanced and phase-separation-assisted extraction of microalgal lipid for biodiesel production

Traditional methods for lipid extraction from microalgal biomass usually involve harsh reaction conditions or the use of contaminant reagents, which lead to enormous energy consumption and wastage. Hence, a novel strategy was presented, which combined water-plasma and three-phase partitioning (TPP) techniques. Benefiting from its unique advantages such as rapid and low cost, water-plasma strategy can disrupt microalgal cell wall and can thus greatly affect lipid extraction. As a result, assisted with the TPP method, excellent performance lipid recovery (74.34%) was obtained at 200 W in 10 min. The performance was superior to that achieved through cell disruption via water-plasma pretreatment. Importantly, the whole process of lipid extraction prevented the drying of microalgal biomass, contributing to reduced energy consumption in large-scale biodiesel production. Moreover, the high fatty acids content suggested that the extracted lipids are great potential candidate for biodiesel production.

In-situ transesterification of single-cell oil for biodiesel production: a review

In recent years, biodiesel synthesis and production demands have increased because of its high degradability, cleaner emissions, non-toxicity, and an alternative to petroleum diesel. In this context, Single Cell Oil (SCO) has been identified as an alternative feedstock, having the advantage of accumulating high intracellular lipid. SCO/microbial lipids are potential alternatives for sustainable biodiesel production. The traditional technique for biodiesel production from the oils obtained from microbes generally requires two steps: lipid extraction and transesterification. In-situ transesterification is an innovative and renewable process for biodiesel production. It rules out the need to isolate and refine the feedstock lipid, as it directly uses biomass in a single step, i.e., the pretreated biomass will be subjected to in-situ transesterification in the presence of catalysts. Hence, the production cost can be reduced by eliminating the lipid extraction procedure. The current review focuses on the basic features and advantages of in-situ transesterification of SCO for biodiesel production with the aid of short-chain alcohols along with different acid, base, and enzyme catalysts. In addition, a comparative study was carried out to highlight the merits of in-situ transesterification over conventional transesterification.

Multiproduct biorefinery from marine thraustochytrids towards a circular bioeconomy

Microalgal biotechnology research continues to expand due to largely unexplored marine environments and growing consumer interest in healthy products. Thraustochytrids, which are marine oleaginous protists, are known for their production of bioactives with significant applications in nutraceuticals, pharmaceuticals, and aquaculture. A wide range of high-value biochemicals, such as nutritional supplements (omega-3 fatty acids), squalene, exopolysaccharides (EPSs), enzymes, aquaculture feed, and biodiesel and pigment compounds, have been investigated. We discuss thraustochytrids as potential feedstocks to produce various bioactive compounds and advocate developing a biorefinery to offset production costs. We anticipate that future advances in cell manufacturing, lipidomic analysis, and nanotechnology-guided lipid extraction would facilitate large-scale cost-competitive production through these microbes.

Enzymatic enrichment of n-3 polyunsaturated fatty acid glycerides by selective hydrolysis

Most natural oils are low in n-3 polyunsaturated fatty acids (n-3 PUFAs) content, which limits their application in health products. In this study, n-3 PUFAs in glyceride form were selectively enriched by lipase-mediated hydrolysis of n-3 PUFA-containing oils. First, commercial lipases were screened, and the lipase AY "Amano" 400SD from Candida cylindracea was the best choice in producing n-3 PUFA glycerides from tuna oil. Subsequently, the hydrolysis conditions were optimized. Under the optimal conditions, the highest n-3 PUFA content in the glyceride fraction was found to be 57.7% after enzymatic hydrolysis. Addition of Ca²⁺ to the system significantly shortened the reaction time from 10 to 4 h. When algal oil was used as substrate, total PUFA contents in the glyceride fraction were 89.9%. This study provides an efficient enzymatic process to produce n-3 PUFA-enriched glyceride concentrates and demonstrates that AY "Amano" 400SD can effectively discriminate against n-3 PUFAs during hydrolysis.

Effect of Nitrogen Sources on Omega-3 Polyunsaturated Fatty Acid Biosynthesis and Gene Expression in Thraustochytriidae sp

The molecular mechanism that contributes to nitrogen source dependent omega-3 polyunsaturated fatty acid (n-3 PUFA) synthesis in marine oleaginous protists Thraustochytriidae sp., was explored in this study. The fatty acid (FA) synthesis was significantly influenced by the supplement of various levels of sodium nitrate (SN) (1–50 mM) or urea (1–50 mM). Compared with SN (50 mM) cultivation, cells from urea (50 mM) cultivation accumulated 1.16-fold more n-3 PUFAs (49.49% docosahexaenoic acid (DHA) (w/w, of total FAs) and 5.28% docosapentaenoic acid (DPA) (w/w, of total FAs)). Strikingly higher quantities of short chain FAs (<18 carbons) (52.22-fold of that in urea cultivation) were produced from SN cultivation. Ten candidate reference genes (RGs) were screened by using four statistical methods (geNorm, NormFinder, Bestkeeper and RefFinder). MFT (Mitochondrial folate transporter) and NUC (Nucleolin) were determined as the stable RGs to normalize the RT-qPCR (real-time quantitative polymerase chain reaction) data of essential genes related to n-3 PUFAs-synthesis. Our results elucidated that the gene transcripts of delta(3,5)-delta(2,4)-dienoyl-CoA isomerase, enoyl-CoA hydratase, fatty acid elongase 3, long-chain fatty acid acyl-CoA ligase, and acetyl-CoA carboxylase were up-regulated under urea cultivation, contributing to the extension and unsaturated bond formation. These findings indicated that regulation of the specific genes through nitrogen source could greatly stimulate n-3 PUFA production in Thraustochytriidae sp.

Characterization and comparison of lipid and PUFA production by native thraustochytrid strains using complex carbon sources

The thraustochytrid are marine heterotrophic protists that are widely distributed in the marine world. They are characterized by producing and accumulating great amount of lipids in their cells, especially long chain polyunsaturated fatty acids (LC-PUFA), highlighting the docosahexaenoic acid (DHA, 22:6, n-3), eicosapentaenoic acid (EPA, 20:5, n-3) and arachidonic acid (ARA, 20:4, n-6), as well as pigments of interest for human health and animal nutrition, such as carotenoids. Therefore, the objective of this study was to isolate and characterize three natives isolated of thraustochytrids and assess the potential of the by-products of the manufacture of beer (RB) and protein extraction of Lupine flour (RL) as complex carbon sources to produce biomass, lipid and polyunsaturated fatty acids. Three native strains of thraustochytrid (AS5-B2, IQ81 y VAL-B1), isolated from Chilean coastal waters were morphologically and genetically identified as thraustochytrid. For the determination of biomass production cultures were quantified by gravimetry and the fatty acids quantification and identification were carried out by gas chromatography (GC-FID). Our results show that the culture with any sources of complex carbon used, increased significantly the production of both biomass and total lipids in the strains IQ81 and VAL-B1, compared to glucose as pure carbon source. On the other hand, strain AS5-B2 showed a decrease in the total production of lipids in RB compared to the pure carbon source. For the production of fatty acids, the strains IQ81 and VAL-B1 showed a significant increase in DHA when growing in RB. In conclusion strains IQ81 and VAL-B1 can be used to biotransform industrial waste, such as RB and RL, into a more valuable product such as DHA, EPA, ARA and lipids.

Current and novel approaches to downstream processing of microalgae: A review

Biotechnological application of microalgae cultures at large scale has significant potential in the various fields of biofuels, food and feed, cosmetic, pharmaceutic, environmental remediation and water treatment. Despite this great potential application, industrialisation of microalgae culture and valorisation is still faced with serious remaining challenges in culture scale-up, harvesting and extraction of target molecules. This review presents a general summary of current techniques for harvesting and extraction of biomolecules from microalgae, their relative merits and potential for industrial application. The cell wall composition and its impact on microalgae cell disruption is discussed. Additionally, more recent progress and promising experimental methods and studies are summarised that would allow the reader to further investigate the state of the art. A final survey of energetic assessments of the different techniques is also made. Bead milling and high-pressure homogenisation seem to give clear advantages in terms of target high value compounds extraction from microalgae, with enzyme hydrolysis as a promising emerging technique. Future industrialisation of microalgae for high scale biotechnological processing will require the establishment of universal comparison-standards that would enable easy assessment of one technique against another.

Suitability of Novel Algal Biomass as Fish Feed: Accumulation and Distribution of Omega-3 Long-Chain Polyunsaturated Fatty Acid in Zebrafish

A 28-day feeding experiment with formulated feed using docosahexaenoic acid (DHA)-rich whole cells of freeze-dried marine microalgae Schizochytrium sp. to understand the distribution of fatty acids in a laboratory model zebrafish was conducted. Three feeds, commercial feed, 50:50 feed (50% commercial and 50% algae), and pure algae, were investigated. All feeds were consumed by zebrafish and showed optimal growth and weight gain with a survival rate of 100%. Lipids were extracted from four different tissues, brain, liver, muscle, and blood, to understand the distribution of fatty acids with respect to the feed. Maximum lipid was observed in zebrafish fed with 50:50 feed in all tissue samples. An increasing concentration of fatty acids was observed upon increasing the experimental time. Algae feed supported the DHA accumulation in all tissue samples compared to other feeds and resulted in an overall increment of polyunsaturated fatty acid content. To understand the role of fatty acids during zebrafish embryogenesis, eggs were collected at the end of the experiment and fatty acid content was analyzed. However, no significant difference was observed in fatty acid composition of embryos fed with algae. This provides a base for the understanding of fatty acid distribution in zebrafish with commercial and algae feeds and support the utilization of Schizochytrium biomass as a potential replacement for fishmeal.

Optimization of lipid extraction from the oleaginous yeasts Rhodotorula glutinis and Lipomyces kononenkoae

The constant growing demand for vegetable oil for biodiesel and food is raising many environmental concerns about the sustainability of its production based on crops. Oleaginous yeasts show great potential to end with those concerns due to their high lipid productivity in small areas. To evaluate their productivity in lipids, an efficient and reproducible extraction process should be used. As no standard extraction process is available for the extraction of yeast lipids, an optimized extraction process is presented. In this work, the lipids extraction process for the yeasts Rhodotorula glutinis and Lipomyces kononenkoae is optimized using bead beating for cell rupture and introducing adaptations of the two most used extraction methods (Bligh and Dyer and Folch). For Rhodotorula g. the optimum extraction conditions are obtained by the Bligh and Dyer method applying 4.8 cycles of 47 s with 0.7 g of glass beads. For Lipomyces k. the optimum extraction conditions make use of the Folch method applying seven cycles of 42 s with 0.54 g of glass beads. These results reinforce the idea that, for each yeast, different extraction processes may be needed to correctly determine the lipid yield. The extraction procedure was further evaluated with less harmful solvents. Toluene was tested as a possible substitute of chloroform, and ethanol as a possible substitute of methanol. With the optimized extraction process, better results for Lipomyces k. were obtained using toluene and ethanol, while for Rhodotorula g. toluene proved to be a valid substitute of chloroform but ethanol is far less effective than methanol.

Simultaneous cell disruption and lipid extraction of wet aurantiochytrium sp. KRS101 using a high shear mixer

Microalgae are regarded as a promising source of biofuels, and the concept of a microalgae-based biorefinery has attracted increasing attention in recent years. From an economic perspective, however, the process remains far from competitive with fossil fuels. This is particularly true of lipid extraction, due in part to the energy-intensive drying step. As a result, wet extraction methods have been studied as an economic alternative. In the present study, a novel extraction approach which utilizes high shear stress mixing was adopted and demonstrated for simultaneous lipid extraction and cell disruption to enable the retrieval of lipids directly from concentrated wet biomass. When a high shear mixer (HSM) was used to extract lipid from a dense biomass (> 350 g/L) of the oleaginous algae Aurantiochytrium sp., it exhibited a yield of esterifiable lipids which exceeded 80% in 10 min at 15,000 rpm with various solvent types. The HSM was found to improve the lipid yields substantially with solvents less miscible with either lipids or water, such that the range of Hansen solubility parameters for the usable solvents became 3.3 times wider (14.9-26.5 MPa^1/2). The HSM, which appeared effectively to loosen the water barrier that prevents solvent molecules from penetrating through the cell envelope, was found to be more efficient with hexane, hexane/isopropanol, and ethanol, all of which showed nearly identical lipid yields compared to the dry extraction process. The HSM can, indeed, offer a powerful mechanical means of lipid extraction with non-polar and less toxic solvents from wet biomass.

Enzymatic Processes in Marine Biotechnology

In previous review articles the attention of the biocatalytically oriented scientific community towards the marine environment as a source of biocatalysts focused on the habitat-related properties of marine enzymes. Updates have already appeared in the literature, including marine examples of oxidoreductases, hydrolases, transferases, isomerases, ligases, and lyases ready for food and pharmaceutical applications. Here a new approach for searching the literature and presenting a more refined analysis is adopted with respect to previous surveys, centering the attention on the enzymatic process rather than on a single novel activity. Fields of applications are easily individuated: (i) the biorefinery value-chain, where the provision of biomass is one of the most important aspects, with aquaculture as the prominent sector; (ii) the food industry, where the interest in the marine domain is similarly developed to deal with the enzymatic procedures adopted in food manipulation; (iii) the selective and easy extraction/modification of structurally complex marine molecules, where enzymatic treatments are a recognized tool to improve efficiency and selectivity; and (iv) marine biomarkers and derived applications (bioremediation) in pollution monitoring are also included in that these studies could be of high significance for the appreciation of marine bioprocesses.

Algal biotechnology for pursuing omega-3 fatty acid (bioactive) production

Algae are spread in diversified ecosystems that include marine, freshwater, desert and hot springs and even snow and ice environments. Algae are classified as multicellular large sea weeds (macroalgae) or unicellular microalgae. Macroalgae are targeted for mining of natural biologically active components, which include proteins, linear peptides, cyclic peptides, and amino acids1. Recently, microalgae have been exploited for the production of high-value compounds such as lipids (omega-3 fatty acids), enzymes, polymers, toxins, antioxidants, and pigments (carotenoids)2. Thus, algal biotechnology is defined as ‘the technology developed using algae (macro or micro) to make or modify bioactive compounds, or products (nutritional supplements, fine chemicals) and renewable fuels for specific use’.

A new approach of microalgal biomass pretreatment using deep eutectic solvents for enhanced lipid recovery for biodiesel production

The biomass of Chlorella sp. was pretreated with three different aqueous deep eutectic solvents (aDESs), i.e. aqueous choline chloride-oxalic acid (aCh-O), aqueous choline chloride-ethylene glycol (aCh-EG) and aqueous urea-acetamide (aU-A). The effect of aDESs pretreatment of microalgae biomass was evaluated in terms of lipid recovery rate, total carbohydrate content, fatty acid composition, and thermal chemical behavior of biomass. Results indicated that, lipid recovery rate was increased from 52.03% of untreated biomass to 80.90%, 66.92%, and 75.26% of the biomass treated by aCh-O, aCh-EG and aU-A, respectively. However, there were no major changes observed in fatty acid profiles of both untreated and treated biomass, specifically palmitic acid, palmitoleic acid and stearic acid under various pretreatments. Furthermore, characterizations of untreated and treated biomass were carried out using Fourier transform infrared (FTIR), thermogravimetry analysis (TGA) and scanning electron microscope (SEM) to understand the enhanced lipids recovery.