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This research aimed to model and optimize the growth factors and enhance the lipid yield from Botryococcus braunii microalgae, and to design a system for obtaining biodiesel from these lipids as this does not compromise food security. Botryococcus braunii, grown on a modified Chu‐13 medium, reached the stationary phase after 27 days with a maximum cell count of 265 × 104 cells mL−1 after 27 days and maximum biomass yield of 725 mg L−1 after 30 days on modified Chu‐13 medium, which was higher than growth on Basal SAG medium. The maximum lipid content (18.47%) and lipid yield (4.46 mg L−1day) were obtained when B. braunii was cultivated on modified Chu‐13 medium after 30 days. Gas chromatography (GC) analysis for the lipids indicated that the highest percentages of SFAs (51.03%) and lowest percentages of monounsaturated fatty acids (MUFAs) (36.47%) and polyunsaturated fatty acids (PUFAs) (12.49%) were obtained by culturing B. braunii on modified Chu‐13 medium. The effect of different growth parameters (N2 level, NaHCO3, and CO2 concentrations) on growth yield was modeled by using D‐optimal design response surface methodology (RSM). [ABSTRACT FROM AUTHOR]

The current study examines the phycoremediation potential cum biomass productivity and biomass quality of hitherto uninvestigated five algae in Bold's Basal Medium (BBM) of varying nitrogen (½ to 4 × N), phosphorus (½ to 4 × P), and both together (½ to 2 × NP) with varying N:P. All five algae displayed unique responses in biomass productivity, lipid yield and productivity, and nitrogen (N) and phosphorous (P) removal efficiency. Chlorolobion braunii exhibited the highest biomass productivity (107 to 109.23 mg/L/ day) in N-rich media (3 to 4 × N in BBM), and Monoraphidium contortum exhibited the highest biomass productivity (103.66 mg/L/day) in P-rich media (2 to 4 × P in BBM). All the algae exhibited a higher lipid yield and productivity in BBM with a reduced ratio of N:P (0.85 to 1.47) from a lesser addition of N (½ × N or NP in BBM). Monoraphidium contortum exhibited significantly higher lipid yield (44.38%) and productivity (35.94 mg/L/day) than other species. The lipid content of four species demonstrated high-quality biofuel properties. Halochlorella rubescens exhibited the maximum nitrogen removal efficiency of 96% (in BBM), and Monoraphidium contortum exhibited the maximum phosphorus removal efficiency of 94.4% (2 × NP in BBM). Overall, the experiments stand as a model for understanding the influence of variations in N and P concerning N:P on biomass productivity, lipid content, lipid productivity, and N and P removal rate and efficiency of algae for initial standardization of the culture protocols for further industrial trials. [ABSTRACT FROM AUTHOR]

Algal bioprospecting in ecosystems leads to exploring native microalgae and the competency evaluation of economically producing lipids as biofuel or nutritional applications. In this study, ten microalgae species were screened from the saline water lake. Chlorella vulgaris, Chlorella sorokiniana, Chlamydomonas raudensis, Chlamydomonas hedleyi, Dunaliella salina, Picochlorum bazangan sp. nov., Tetraselmis bazangan sp. nov., Haematococcus lacustris, Nannochloropsis oceanic, and Scenedesmus rubescens were isolated and identified using 18SrDNA and tufA markers. Biodiesel potentials were assayed by the determination of biomass productivity, biochemical components, fatty acid profile, and biodiesel properties. The results showed that the maximum biomass yield (1.22 g/L) belonged to C. vulgaris. The highest protein, carbohydrate, chlorophyll, and carotenoid content were recorded in C. vulgaris, C. raudensis, C. sorokiniana, and D. salina, respectively. N. oceanica accumulated high lipid content and omega-3 fractions (31.09%). However, C. hedleyi had the highest lipid productivity (11.64 g/L/day) compared to other microalgae. The best species for biodiesel production was C. vulgaris, with a specific growth rate of 0.36 day−1, lipid productivity of 7.45 g/L/day, and C16-C18 fatty acid profile of 78.3%. The microalgae C. vulgaris had appropriate biodiesel properties of low viscosity (4.49), high cetane number (55.38), and relatively low cloud point (4.98). Another choice was N. oceanic, with high lipid productivity, cetane number (59.79), oxidative stability (56.43), and low iodine value (47.11). Microalgae T. bazangan sp. nov. had a cetane number (55.24), low cloud point (4.71), and C16-C18 fatty acid profile of 82.34%. Accordingly, C. vulgaris, T. bazangan sp. nov., and N. oceanic can be considered potential species for biodiesel. [ABSTRACT FROM AUTHOR]

The paper provides a review of reports on the results of studies in the field of microalgae biomass cultivation and conversion to marketable chemicals using modern bioengineering approaches. The review discusses approaches to producing biofuels (biodiesel, ethanol, hydrogen) from microalgae. Data on biomass pretreatment methods and various procedures for isolating metabolites and converting them to biofuels are provided. [ABSTRACT FROM AUTHOR]

Microalgae have been recognized as promising competitors for bioenergy production, because of their high lipid content and quick biomass development. In this work, freshwater microalgae Scenedesmus dimorphus was cultivated in a synthetic wastewater media with the object of investigating the bioenergy potential by physicochemical characterization. Batch experiments were performed photoautotrophically for biomass generation supplemented with different levels of CO2 concentration. Maximum biomass production was in the limit of 373 mg/L to 587 mg/L under different CO2 feed concentrations. Cultivation of microalgae along with CO2 supplementation found a substantial impact on buildup of lipid in microalgae biomass. Maximum 29% and 32% lipid content were achieved for 2% and 6% CO2 enrichment respectively, under nitrogen-depleted conditions. Fourier transform infrared spectroscopy, thermogravimetric analysis, and carbon, hydrogen, nitrogen, sulfur elemental analyzer instrumental tools were used to perform physicochemical characterization on biomass in order to determine its proximate analysis, ultimate analysis, higher heating value (HHV), and macromolecular composition, The higher heating value (HHV) of Scenedesmus dimorphus biomass achieved 33.26 MJ/kg with almost zero sulfur content. This HHV value is significantly higher than that of other microalgae sp. Moreover, this HHV value is also even higher than that of bituminous coal (24.3 MJ/kg) and other types of lignocellulosic biomass. Scenedesmus dimorphus biomass indicates that it can be a potential fuel feedstock for environmentally friendly bioenergy production. [ABSTRACT FROM AUTHOR]

Microalgae are regarded as a promising source of biodiesel. In contrast with conventional crops currently used to produce commercial biodiesel, microalgae can be cultivated on non-arable land, besides having a higher growth rate and productivity. However, microalgal biodiesel is not yet regarded as economically competitive, compared to fossil fuels and crop-based biodiesel; therefore, it is not commercially produced. This review provides an overall perspective on technologies with the potential to increase efficiency and reduce the general costs of biodiesel production from microalgae. Opportunities and challenges for large-scale production are discussed. We present the current scenario of Brazilian research in the field and show a successful case in the research and development of microalgal biodiesel in open ponds by Petrobras. This publicly held Brazilian corporation has been investing in research in this sector for over a decade. [ABSTRACT FROM AUTHOR]

The reuse of the culture media after biomass growth can be a cost-effective strategy for large-scale microalgae production, especially when the target product is biofuel. Therefore, this study aimed to investigate the effect of recycling the microalgae Tetradesmus obliquus culture medium, focusing on the improved production of biomass and lipids, biodiesel properties, and cost reduction. The experiments were carried out in duplicate and three sequential steps with successive recycling (50% of the clarified medium and 50% of the standard). It was found that cells from recycled cultures had a similar overall performance as those from the fresh medium (standard). From this verification, the main findings of this research pointed out that (i) the consumption of the nutrients was efficient, with values in the order of 99% nitrate, 20% phosphate, 64% total iron, and 9% potassium; (ii) the average contents of biomass and lipids in the recycled medium increased around 20% to 24%, respectively, concerning the standard; (iii) the polyunsaturated fatty acids pool present in the microalgal oil dropped from 20.71 to 9.78% in the recycled culture, which represents a high-quality feedstock for biofuel; and (iv) the biodiesel properties evaluated, including iodine and saponification values, were 48 g I2 100 g−1 and 254 mg KOH/goil−1, respectively. Finally, this recyclability bioprocess can reduce overall costs by about 34%, thus improving the economic viability of microalgae production. [ABSTRACT FROM AUTHOR]

Microalgae are a potential source of numerous nutritional products and biofuels. Their applications range from the food industry to the medical and fuel sectors and beyond. Recently, the conversion of biomass into biodiesel and other biofuels has received a lot of positive attention within the fossil fuel arena. The objective of biorefineries is to focus on utilising biomass efficiently to produce quality biofuel products by minimising the input as well as to reduce the use of chemical or thermal pre-treatments. Pre-treatment processes in biorefineries involve cell disruption to obtain lipids. Cell disruption is a crucial part of bioconversion, as the structure and nature of microalgae cell walls are complex. In recent years, many research papers have shown various pre-treatment methods and their advantages. The objective of this paper was to provide a comprehensive in-depth review of various recent pre-treatment techniques that have been used for microalgal biodiesel production and to discuss their advantages, disadvantages, and how they are applied in algal biorefineries. [ABSTRACT FROM AUTHOR]

This scientometric review and bibliometric analysis aimed to characterize trends in scientific research related to algae, photobioreactors and astaxanthin. Scientific articles published between 1995 and 2020 in the Web of Science and Scopus bibliographic databases were analyzed. The article presents the number of scientific articles in particular years and according to the publication type (e.g., articles, reviews and books). The most productive authors were selected in terms of the number of publications, the number of citations, the impact factor, affiliated research units and individual countries. Based on the number of keyword occurrences and a content analysis of 367 publications, seven leading areas of scientific interest (clusters) were identified: (1) techno-economic profitability of biofuels, bioenergy and pigment production in microalgae biorefineries, (2) the impact of the construction of photobioreactors and process parameters on the efficiency of microalgae cultivation, (3) strategies for increasing the amount of obtained lipids and obtaining biodiesel in Chlorella microalgae cultivation, (4) the production of astaxanthin on an industrial scale using Haematococcus microalgae, (5) the productivity of biomass and the use of alternative carbon sources in microalgae culture, (6) the effect of light and carbon dioxide conversion on biomass yield and (7) heterotrophy. Analysis revealed that topics closely related to bioenergy production and biofuels played a dominant role in scientific research. This publication indicates the directions and topics for future scientific research that should be carried out to successfully implement economically viable technology based on microalgae on an industrial scale. [ABSTRACT FROM AUTHOR]

Microalgae are photosynthetic organisms functioning as the green bio-factories for various pharmaceutical and biofuel products. To date, numerous attempts have been carried out to manipulate culture conditions to maximize the production of the desired metabolites. Because light is the energy source of microalgae for their growth and metabolites biosynthesis, it has been one of the most investigated variables emphasized on the deep understanding of how microalgae respond towards light changes as an external stimulus. This review discusses the effects of different light sources, light intensities, light wavelengths and length of photoperiod on various microalgae species, especially in terms of biomass and lipid productivity. Additionally, the relationship between photoregulation processes and lipid productivity of microalgae are also deliberated. The current available approaches of microalgae mass cultivation, including different types of open and closed systems are recapitulated with the intention to highlight the significant insights for the design of future photoreactors. [ABSTRACT FROM AUTHOR]

Freshwater deficiency and growing requests for renewable energy have led to increased concern about water and energy security. Therefore, the present study attempted to evaluate the feasibility of using wastewater (WW) as a culture medium for microalgal cultivation with the aim of nutrient removal and biodiesel production. The green microalga Asterarcys quadricellulare (Chlorophyta) was isolated from a wastewater treatment plant in Menoufia, Egypt, and grown for 24 days in Bold's Basal Medium as a control and at different concentrations of secondary treated WW in distilled water (25%, 50%, 75%, and 100%). The results of 75% WW treatment recorded 96.6%, 98.4%, and 89.9% removal efficiency for nitrate, ammonia, and total phosphorus, respectively. Also, it revealed high biomass yield and biomass productivity (1.44 g L−1 and 69.0 mg L−1 day−1, respectively). In addition, it showed higher lipid production (360.6 mg L−1) and lipid productivity (17.2 mg L−1 day−1). Asterarcys quadricellulare fatty acid profile estimation revealed elevated proportions of oleic (54.92%), palmitic (20.54%), and linoleic acids (13.9%). Most of the properties of biodiesel derived from the studied microalga are consistent with those recommended by the international standards. The current study concluded that A. quadricellulare could be used for wastewater bioremediation and biomass production with high potential as biodiesel feedstock. [ABSTRACT FROM AUTHOR]

Oleaginous microorganisms and the thermal decomposition of their recovered lipids are new attractive research fields for the sustainable production of biofuels from actual biomass. In this work, the thermal decomposition of lipids from C. vulgaris and from L. starkeyi was investigated using a thermogravimetric analyzer coupled to a mass spectrometer (TGA-MS) under non-isothermal conditions. Thermal decomposition was examined using the one-step reaction model. Integral, differential, and advanced isoconversional methods were implemented to analyze the conversion-dependent activation energy. The Friedman method resulted in an accurate and reliable estimation of the kinetic parameters. The activation energy showed a strong dependence on conversion from 123.5 to 246 kJ mol-1 for lipids from C. vulgaris and from 80.3 to 299.9 kJ mol-1 for lipids from L. starkeyi. The generalized master plot approach evidenced that the thermal decomposition of lipids from C. vulgaris proceeds via three-dimensional diffusion (D3—Jander's equation). Also, the kinetic analysis indicated that Valensi's equation (D2), controlled by a two-dimensional diffusion model, is the most likely mechanism for the thermal decomposition of lipids from L. starkeyi. The rate parameters were evaluated via a kinetic compensation plot. Ion temperature evolution was investigated by TGA-MS revealing many of the functional groups evolved in the range of 350–500 °C as C1–C7 aliphatic hydrocarbons, aromatic hydrocarbons, aldehydes, carboxylic acids, and furan derivatives. All these aspects favor the lipid biosynthesis from microbial biomass to potential lipid-based building blocks. [ABSTRACT FROM AUTHOR]

Microalgal biodiesel is technically viable to power diesel engines. This third-generation biofuel has great performance of combustion and can reduce emission of greenhouse gases into the atmosphere. However, its production is currently very expensive, relative to petrochemical diesel. Development and implementation of strategies to optimize productivity and quality of biomass and thus ensure this future-proof biofuel is economically feasible to fabricate and competitive with diesel oil on an industrial scale is challenging. This meta-analytic overview documents the diversity of fastest-growing, oil-accumulating microalgae; performance of cultures and systems; strategies for inducing lipids; and quality and economics of microalgal biodiesel. The microalgae, Neochloris oleoabundans, Scenedesmus obliquus, Desmodesmus sp., and Micractinium sp., are hyperaccumulators of lipids. The genre, Micractinium sp., is a thermophile, and thus it can resist hydrothermal streams. Complementarily, it is the fastest to grow and the most productive in both biomass and biodiesel. This should be of great importance to roll-out sustainable, high-performance algal systems in marginal lands in tropical zones, where the heat often makes the planning and management of projects difficult and expensive. Heat shock, nutritional starvation, and photoperiod are the most effective algae-specific strategies for inducing mechanisms for lipogenesis in Ankistrodesmus dimorphus, Chlorella vulgaris and Leptolyngbya sp., Cylindrotheca closterium and N. oleoabundans, and Amphora subtropica and Dunaliella sp., respectively. Rhodococcus sp. produces a significant amount of biomass at very low cost, relative to diesel oil. The concept of synergistically co-culturing microalgae with this photosynthetically active bacterium may be an option to save the producer the expenditures and uncertainties of third-generation biodiesel. [ABSTRACT FROM AUTHOR]

Microalgae are regarded as a promising source of biodiesel. In contrast with conventional crops currently used to produce commercial biodiesel, microalgae can be cultivated on non-arable land, besides having a higher growth rate and productivity. However, microalgal biodiesel is not yet regarded as economically competitive, compared to fossil fuels and crop-based biodiesel; therefore, it is not commercially produced. This review provides an overall perspective on technologies with the potential to increase efficiency and reduce the general costs of biodiesel production from microalgae. Opportunities and challenges for large-scale production are discussed. We present the current scenario of Brazilian research in the field and show a successful case in the research and development of microalgal biodiesel in open ponds by Petrobras. This publicly held Brazilian corporation has been investing in research in this sector for over a decade.

The strong difference between wild and domesticated plants illustrates that gains in yield should be obtainable in other branches of life, keeping in mind that cultivated plants are diploid, whereas the majority of currently cultivated microalgae are haploid. Keywords: microalgae; domestication; algae based bioproducts; lipids; pigments; biofuel; green chemistry EN microalgae domestication algae based bioproducts lipids pigments biofuel green chemistry 1 5 5 09/29/21 20210923 NES 210923 Introduction The term "microalgae" is a practical designation for photosynthetic unicellular cells, embracing organisms from two domains of life, i.e., Bacteria (Cyanobacteria) and various clades of Eukaryota deriving from primary (Archaeplastida) or secondary (e.g., Stramenopile) endosymbiosis events. The phaeodactylum genome reveals the evolutionary history of diatom genomes. Some of the NBTs target genes with a Cas9-coding DNA vector who does not integrate into the plant genome, or even a microinjected Cas9 protein and gRNAs, whereas other NBTs are based on non-targeted random mutations (Holme et al., [24]; Anders et al., [2]). [Extracted from the article]

The production of biofuels using wastewater as a microalgae culture medium is a little explored technology, but with potential for success. In order to contribute to the knowledge of these technologies and their technical feasibility for microalgae growth, in this work the Chlorella sp. strain was cultivated in two types of effluents generated in an experimental farm located in eastern Colombia, before and after a biological treatment process. The consumption of the main nutrients that regulate growth and lipid production was evaluated, in order to extract, quantify, characterize and convert them into biodiesel. The results showed that Chlorella sp. growth and lipid production is more favourable in R2 medium of treated water than in R1 medium of raw water, mainly due to phosphorus limitation and higher N-NO3 concentration in R2 compared to R1. In the R2 medium culture, a percentage of 42.54% of long-chain fatty acids was found, which is necessary to obtain a high quality biodiesel. Finally, the best transesterification experiment allowed reaching a fatty acid methyl esters (FAME) percentage of 90.1 ± 2.7%. In general, the results demonstrated the potential viability of using the wastewater generated in the San Pablo farm to produce biomass with lipid content to obtain biodiesel, finding that where the concentration of nutrients, mainly nitrogen, has a great influence on the microalgal metabolism for lipid accumulation. [ABSTRACT FROM AUTHOR]

In recent years, research initiatives on renewable bioenergy or biofuels have been gaining momentum, not only due to fast depletion of finite reserves of fossil fuels but also because of the associated concerns for the environment and future energy security. In the last few decades, interest is growing concerning microalgae as the third-generation biofuel feedstock. The CO2 fixation ability and conversion of it into value-added compounds, devoid of challenging food and feed crops, make these photosynthetic microorganisms an optimistic producer of biofuel from an environmental point of view. Microalgal-derived fuels are currently being considered as clean, renewable, and promising sustainable biofuel. Therefore, most research targets to obtain strains with the highest lipid productivity and a high growth rate at the lowest cultivation costs. Different methods and strategies to attain higher biomass and lipid accumulation in microalgae have been extensively reported in the previous research, but there are fewer inclusive reports that summarize the conventional methods with the modern techniques for lipid enhancement and biodiesel production from microalgae. Therefore, the current review focuses on the latest techniques and advances in different cultivation conditions, the effect of different abiotic and heavy metal stress, and the role of nanoparticles (NPs) in the stimulation of lipid accumulation in microalgae. Techniques such as genetic engineering, where particular genes associated with lipid metabolism, are modified to boost lipid synthesis within the microalgae, the contribution of "Omics" in metabolic pathway studies. Further, the contribution of CRISPR/Cas9 system technique to the production of microalgae biofuel is also briefly described. [ABSTRACT FROM AUTHOR]

Microalgae has received overwhelming attention worldwide as a sustainable source for energy generation. However, the production of biofuel from microalgae biomass consists of several steps, of which lipid extraction is the most important one. Because of the nature of feedstock, extraction needs special attention. Three different methods were studied to extract algal oil from two different algae variant, Chlorella sp. and Spirulina sp. The highest percentage oil yield was obtained by ultrasonication (9.4% for Chlorella sp., 6.6% for Spirulina sp.) followed by the Soxhlet and solvent extraction processes. Ultrasonication and Soxhlet extraction processes were further optimized to maximize oil extraction as solvent extraction was not effective in extracting lipid. For ultrasonication, an amplitude of 90% recorded the highest percentage yield of oil for Spirulina sp. and a 70% amplitude recorded the highest percentage yield of oil for Chlorella sp. On the other hand, for Soxhlet extraction, a combination of chloroform, hexane, and methanol at a 1:1:1 ratio resulted in the highest yield of algal oil. Afterward, the crude algae oil from the ultrasonication process was transesterified for 5 h using an immobilized lipase (Novozyme 435) at 40 °C to convert triglycerides into fatty acid methyl ester and glycerol. Thus, ultrasonic-assisted lipid extraction was successful in producing biodiesel from both the species. [ABSTRACT FROM AUTHOR]

• Influence of phytohormones on algal biomass and lipid accumulation was investigated. • Auxin and cytokinin exihibited a synergystic effect on biomass and lipid yield. • Phytohormones influenced the activities of antioxidant enzymes SOD, CAT and APX. • Phytohormones modified the FAME contents that were desired for high-grade biofuels. Microalgae are considered as a promising resource for biodiesel. Nevertheless, their commercial exploitation necessitates considerable impetus towards the development of approaches for increased biomass and lipid production. The present work elucidates the impact of exogenously supplemented auxins, i.e., indole-3-acetic acid (IAA), indole-3-butyric acid (IBA) and indole-3-propionic acid (IPA) and cytokinins, i.e., benzylaminopurine (BAP) and thidiazuron (TDZ) on biomass, lipid content and fatty acid profile of Desmodesmus sp. JS07. Among auxins, IBA improved the biomass and lipid content up to 1.96 ± 0.11 g/L and 34.88 ± 3.87 %, respectively while BAP among cytokinins increased the biomass and lipid content up to 1.88 ± 0.061 g/L and 31.84 ± 1.33 % respectively. Further, the cumulative impact of IBA (10 mg/L) and BAP (5 mg/L) resulted in their synergistic effect by stimulating biomass and lipid content up to 2.34 ± 0.032 g/L and 42.43 ± 1.88 % respectively. Auxins stimulated the superoxide dismutase activity, and cytokinins increased the enzymes (catalase and ascorbate peroxidase), scavenging reactive oxidative species, thereby regulating ROS homeostasis in microalgae. A significant alteration in the fatty acid profile owing to the type and dosage of phytohormones was detected. Hence, the strategy employing phytohormones could prove to be a meaningful approach for biofuel production. [ABSTRACT FROM AUTHOR]

Developing effective, energy-efficient methods to extract lipids from microalgae remains a challenge in bioenergy. This study assesses electric pulse (EP) pretreatments to enhance lipid extraction from Chlorella protothecoides. In tandem with solvent extraction, we applied 10, 50, 100, 200, and 300 60 kV/cm, 60 ns duration EPs or 3, 17, 33, 67, and 100 60 kV/cm, 300 ns duration EPs to match the energy density u applied to the sample for each EP duration. Lipid recovery increased with increasing u for each EP duration until reaching a maximum for 17 300 ns EPs (the second lowest u) and 100 60 ns EPs (the third lowest u) to achieve a 13.3% and 16.1% increase in lipid extraction, respectively. Lipid extraction declined at higher u due to increased cell lysis. The largest net energy released calculated from the difference between the energy available from the extracted lipids and the applied energy of the EPs occurred at the lowest u for each EP duration. Applying trains of 100 μs EPs induced qualitatively similar behavior. These results suggest that a more detailed parametric study may optimize EP parameters for net energy release for specific microalgae and solvents. [ABSTRACT FROM AUTHOR]

Wastewater treatment, along with the simultaneous production of valuable chemical compounds, including lipids by microalgae is a challenging but attractive study. Towards this goal, the candidate microalgae were selected from culture collections or isolated from wastewater in this study. The initial screening test using microalgae revealed that various eukaryotic as well as prokaryotic microalgae showed steady growth in municipal wastewater samples. Among them, Tetraselmis sp. NKG400013 and Parachlorella kessleri NKG021201 from culture collections, and Chloroidium saccharophilum NKH13 from the wastewater sample exhibited high biomass productivity. Furthermore, P. kessleri NKG021201 and C. saccharophilum NKH13 showed high lipid productivity (56 ± 1 mg/L/day for NKG021201, 35 ± 10 mg/L/day for NKH13). During this cultivation, 99% of nitrogen and 82% of phosphorous compounds were removed from the wastewater sample by the strain NKG021201. Analysis of fatty acid compositions of P. kessleri NKG021201 and C. saccharophilum NKH13 revealed that lipids derived from these microalgae were suitable for the application of biodiesel fuels, indicating that these microalgae were promising for wastewater treatment and lipid production. [ABSTRACT FROM AUTHOR]

Background: Nannochloropsis gaditana is a photosynthetic unicellular microalgae considered one of the most interesting marine algae to produce biofuels and food additive due to its rapid growth rate and high lipid accumulation. Although microalgae are attractive platforms for solar energy bioconversion, the overall efficiency of photosynthesis is reduced due to the steep light gradient in photobioreactors. Moreover, accumulation of lipids in microalgae for biofuels production is usually induced in a two-phase cultivation process by nutrient starvation, with additional time and costs associated. In this work, a biotechnological approach was directed for the isolation of strains with improved light penetration in photobioreactor combined with increased lipids productivity. Results: Mutants of Nannochloropsis gaditana were obtained by chemical mutagenesis and screened for having both a reduced chlorophyll content per cell and increased affinity for Nile red, a fluorescent dye which binds to cellular lipid fraction. Accordingly, one mutant, called e8, was selected and characterized for having a 30% reduction of chlorophyll content per cell and an almost 80% increase of lipid productivity compared to WT in nutrient-replete conditions, with C16:0 and C18:0 fatty acids being more than doubled in the mutant. Whole-genome sequencing revealed mutations in 234 genes in e8 mutant among which there is a non-conservative mutation in the dgd1 synthase gene. This gene encodes for an enzyme involved in the biosynthesis of DGDG, one of the major lipids found in the thylakoid membrane and it is thus involved in chloroplast biogenesis. Lipid biosynthesis is strongly influenced by light availability in several microalgae species, including Nannochloropsis gaditana: reduced chlorophyll content per cell and more homogenous irradiance in photobioreactor is at the base for the increased lipid productivity observed in the e8 mutant. Conclusions: The results herein obtained presents a promising strategy to produce algal biomass enriched in lipid fraction to be used for biofuel and biodiesel production in a single cultivation process, without the additional complexity of the nutrient starvation phase. Genome sequencing and identification of the mutations introduced in e8 mutant suggest possible genes responsible for the observed phenotypes, identifying putative target for future complementation and biotechnological application. [ABSTRACT FROM AUTHOR]

Microalgae have been shown as a potential bioresource for food, biofuel, and pharmaceutical products. During the growth phases with corresponding environmental conditions, microalgae accumulate different amounts of various metabolites. We quantified the neutral lipids accumulation and analyzed the swimming signatures (speed and trajectories) of the motile green alga, Dunaliella primolecta, during the lag–exponential–stationary growth cycle at different nutrient concentrations. We discovered significant changes in the neutral lipid content and swimming signatures of microalgae across growth phases. The timing of the maximum swimming speed coincided with the maximum neutral lipid content and both maxima occurred under nutrient stress at the stationary growth phase. Furthermore, the swimming trajectories suggested statistically significant changes in swimming modes at the stationary growth phase when the maximum intracellular neutral lipid content was observed. Our results provide the potential exploitation of microalgal swimming signatures as possible indicators of the cultivation conditions and the timing of microalgal harvest to maximize the lipid yield for biofuel production. The findings can also be implemented to explore the production of food and antibiotics from other microalgal metabolites with low energy costs. [ABSTRACT FROM AUTHOR]

Microalgae based biofuel is an attractive alternative energy source due to its rapid growth rate and high lipid accumulation efficiency. In this study, we screened high lipid content microalga with the favourable fatty acid composition suitable for biodiesel production. Totally twelve different microalgal species were isolated from freshwater habitats. The isolates were identified as Micractinium sp., Chlorella sorokiniana, Scenedesmus bajacalifornicus, Desmodesmus sp., Scenedesmus obliquus, Coelastrum proboscideum, Chlamydomonas moewusii, Chlamydomonas debaryana, Chlamydomonas dorsoventralis, Coelastrum sp., and Ankistrodesmus sp. based on morphological features and ITS region similarity. Among the isolates, highest lipid content (33±0.07%) and lipid productivity (0.27±0.06 g L-1) were obtained from Ankistrodesmus sp. Intracellular lipid droplets of Ankistrodesmus sp. were observed through Nile red staining. The lipid content was enhanced up to 45% under the nitrogen deficient (5 mg L-1) BG-11 medium. Ankistrodesmus sp. fatty acid profile shows the presence of palmitic (16.39%), stearic (15.67%), oleic (25.66%), linolenic (21.62%), and alpha-linoleic acids (14.34%). The oleic acid was the dominant fatty acid 25.66% in the nitrogen deficient condition. [ABSTRACT FROM AUTHOR]

Abstract Background Microalgae are promising sources of lipid triacylglycerol (TAG) for biodiesel production. However, to date, microalgal biodiesel is technically feasible, but not yet economically viable. Increasing TAG content and productivity are important to achieve economic viability of microalgal biodiesel. To increase TAG content, oleaginous microalga Neochloris oleoabundans was genetically engineered with an endogenous key enzyme diacylglycerol acyltransferase 2 (NeoDGAT2) responsible for TAG biosynthesis. Results The integration of NeoDGAT2 expression cassettes in N. oleoabundans transformant was confirmed by PCR. The neutral lipid accumulation in the transformant detected by Nile red staining was accelerated and 1.9-fold higher than in wild type; the lipid bodies in the transformant visualized under fluorescence microscope were also larger. The NeoDGAT2 transcript was two-fold higher in the transformant than wild type. Remarkably higher lipid accumulation was found in the transformant than wild type: total lipid content increased 1.6-to 2.3-fold up to 74.5 ± 4.0% dry cell weight (DCW) and total lipid productivity increased 1.6- to 3.2-fold up to 14.6 ± 2.0 mg/L/day; while TAG content increased 1.8- to 3.2-fold up to 46.1 ± 1.6% DCW and TAG productivity increased 1.6- to 4.3-fold up to 8.9 ± 1.3 mg/L/day. A significantly altered fatty acid composition was detected in the transformant compared to wild type; the levels of saturated fatty acid C16:0 increased double to 49%, whereas C18:0 was reduced triple to 6%. Long-term stability was observed in the transformant continuously maintained in solid medium over 100 generations in a period of about 4 years. Conclusions Our results demonstrate the increased TAG content and productivity in N. oleoabundans by NeoDGAT2 overexpression that may offer the first step towards making microalgae an economically feasible source for biodiesel production. The strategy for genetically improved microalga presented in this study can be applied to other microalgal species possessing desired characteristics for industrial biofuel production.

• Passive lipid extraction techniques that skip conventional cell lysis step for microalgal biofuel production. • Energy consumption by passive methods are compared with physical methods. • In-situ transesterification, saponification-acidification, and switchable solvents have low energy consumption. • Passive methods suitable for lipid-based biorefinery is presented. The conventional method of lipid extraction mandatorily includes cell lysis which is considered an essential process for the enhancement of extraction efficiency. However, cell lysis method especially those incorporating mechanical and physical methods such as homogenization, sonication, microwave techniques, etc., are energy intensive and drastically escalates the biofuel production cost. Therefore, the development of an alternate route of extraction skipping the conventional mechanical cell lysis step remains a challenge to be accomplished. In this context, we discuss the reports involving passive techniques that are able to extract lipid from microalgae without significant cell wall shearing. This includes methods such as in-situ transesterification, direct saponification, supercritical fluid extraction, organic solvent extraction, etc. Moreover, the review discusses the employment of passive lipid extraction methods in a biorefinery set-up, outlining the various bioproducts that could be generated along with lipid. The review concludes with the analysis of the economics of microalgal lipid extraction using passive disruption methods and compares with the processes incorporating cell lysis steps. [ABSTRACT FROM AUTHOR]

Discovery of high-yielding microalgae rich in valuable lipids, proteins, pigments, or carbohydrates is essential to the growth of nutraceutical and biofuel industries. Therefore, bioprospecting of microalgae from diverse environmental conditions has become highly significant to meet the demand of such bioresources globally. In this context, bioprospecting of three species of microalgae isolated from bloomed freshwaters of Kerala, India, was carried out; morphological and molecular characterizations revealed two of the algae as new species to science and named accordingly. The industrial potentials of these algae (Fasciculochloris boldii (MH992105.1), Sphaerocystis antoni-kadavilaii Ray & Prasanth sp. nov. (MK005299.1), and Chlorella zachariaii Ray & Prasanth sp. nov. (MH930447.1)) were assessed in terms of biomass yield and biochemical profile. The alga Sphaerocystis antoni-kadavilaii with a biomass yield of 176.8 ± 2.0% increase L−1 day−1, lipid productivity of 4.4 ± 0.3 mg L−1 day−1, the protein content of 46.1%, is found promising, in comparison with the known species such as Spirulina sp. and Chlorella sp. It is high in chlorophyll a, and total carotenoid content as well. The alga Fasciculochloris boldii showed high lipid content of 26.8 ± 1.1% and the alga Chlorella zachariaii showed 30.1% of omega-3 fractions in its total fatty acids. The Fourier transform infrared spectroscopy confirmed biodiesel feasibility of lipids from all these algae. However, the alga Fasciculochloris boldii with high proportions of saturated fatty acids in its lipid (71.2%) can be considered as a potential species for biodiesel as the biodiesel from the same also shows the required cetane number (63.3) and low iodine value (38.9). [ABSTRACT FROM AUTHOR]

The ultra-high Cd polluted environment is a special habitat in nature. Analysis of the biological adaptation and resistance mechanism of Auxenochlorella protothecoides UTEX234 to ultra-high Cd stress would offer some inspiring understanding on Cd detoxification mechanism and help discovering highly active bioremediation agents. In this study, integrated analyses of the transcriptome, multi-physiological and biochemical data and fatty acid profilings of UTEX2341 were performed for the first time. It was found that exogenous Ca ions could alleviate Cd stress. Manganese-dependent superoxide dismutase and peroxidase also participated in intracellular detoxification. And non-enzymatic antioxidants rather than one specific enzymatic antioxidant were suggested to be used as "core antioxidants", which witnessed better performance in Cd detoxification. In addition, Cd stress improved sixteen alkane value and biofuel yield and quality. Image 1 • Non-enzymatic antioxidants played more important roles than enzymatic antioxidants. • Exogenous Ca ions could alleviate Cd stress. • Nramp, MATE, ZIP, CE, ABC family and Ca2+-ATPase participated in Cd transport. • Cd stress improved the sixteen alkane value, the yield and quality of biodiesel. Under ultra-high Cd stress, non-enzymatic antioxidants were suggested to be as "core antioxidants" in microalgae's detoxification. [ABSTRACT FROM AUTHOR]

BACKGROUND The effects of the initial nitrogen concentration, as well as of two‐stage and prolonged cultivation on the growth rate, lipid and protein content of Chlorella vulgaris were examined. Additionally, a kinetic model of specific growth rate in the exponential growth phase (µexp) was developed as a function of initial nitrogen concentration. RESULTS: As the initial nitrogen concentration in the culture medium increased, the total biomass production and µexp went through a maximum at 300 mg N L−1 and at 200 mg N L−1, respectively. The lipid content was found to be highly dependent on the initial nitrogen concentration and increased from 9.0% to 29.6% as the nitrogen concentration varied from 800 to 10 mg N L−1, respectively. Cultivation in two stages resulted in an increase of the lipid content of the biomass from 15.4% to 24.9%, while prolonged cultivation led to an increase of the lipid content from 15.4% to 23.0%. CONCLUSION: Cultivation under optimum nitrogen concentration can lead to increased biomass production. In addition, optimization of lipid production can be carried out by a two‐stage cultivation mode or by prolonged cultivation. © 2018 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Commercial production of biofuel from oleaginous microalgae is often impeded by their slow growth rate than other fast-growing algal species. A promising strategy is to genetically engineer the fast-growing algae to accumulate lipids by expressing key lipogenic genes from oleaginous microalgae. However, lacking of strong expression cassette to transform most of the algal species and potential metabolic target to engineer lipid metabolism has hindered its biotechnological applications. In this study, we engineered the oxidative pentose phosphate pathway (PPP) of green microalga Chlorella pyrenoidosa for lipid enhancement by expressing a glucose-6-phosphate dehydrogenase (G6PD) from oleaginous diatom Phaeodactylum tricornutum. Molecular characterization of transformed lines revealed that heterologous PtG6PD was transcribed and expressed successfully. Interestingly, subcellular localization analyses revealed that PtG6PD was targeted to chloroplasts of C. pyrenoidosa. PtG6PD expression remarkably elevated NADPH content and consequently enhanced the lipid content without affecting growth rate. Collectively, this report represents a promising candidate to engineer lipid biosynthesis in heterologous hosts with notable commercial significance, and it highlights the potential role of plastidial PPP in supplying lipogenic NADPH in microalgae. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Microalgae incubation after PEF-treatment improves water-soluble components release. • Microalgae incubation after PEF-treatment improves lipid extraction yields. • With 20 h of incubation, energy of PEF-treatment can be reduced to 0.25 MJ/kg DW. • Incubation is also efficient at 4 °C but less than at 25 °C. Abstract Pulsed Electric Field (PEF) pre-treatment, applied on fresh microalgae Auxenochlorella protothecoides, induces spontaneous release of a substantial water fraction and enables subsequent lipid extraction using ethanol-hexane blends. In this study, fresh microalgae suspensions were treated with PEF and incubated under inert conditions. Incubation promotes the release of ions and carbohydrates and increases the yields of subsequent lipid extraction thus enabling a considerable reduction of PEF-treatment energy. With a 20 h incubation period at 25 °C, almost total lipid extraction is achieved with a specific PEF-treatment energy of only 0.25 MJ/kg DW. Incubation on ice remains beneficial but less efficient than at 25 °C. Additionally, incubating microalgae cells in suspension at 100 g DW /L or in a dense paste, was almost equally efficient. Correlation between the different results suggests that spontaneous release of ions and carbohydrates facilitates more successful lipid extraction. A direct causality between the two phenomena remains to be demonstrated. [ABSTRACT FROM AUTHOR]

We report the cultivation of Chlorella sorokiniana str. SLA-04 in media containing trace amounts of Ca and Mg. The differences in productivities of biomass, lipids and carbohydrates were assessed relative to cultures grown in standard media (BG-11) that contain approximately 8 × higher concentration of Ca and 30 × higher concentration of Mg. Culture performance in N-limited standard media was also investigated. In addition to growth and accumulation of storage products (lipid and carbohydrate), we measured the utilization of N, Ca and Mg and monitored changes in cell size and photosynthetic activity. Our results showed that limitation of Ca or Mg did not inhibit cell replication and culture growth. On the contrary, Ca-limited (Ca L ) cultures had ∼30% higher biomass productivity relative to the control with excessive nutrients possibly due to improvement in cell wall flexibility and cell division. We also observed that Ca L and Mg-limited (Mg L ) cultures had nearly 3-fold higher lipid concentration (measured as fatty acid methyl ester) and 50% higher carbohydrate concentration than the nutrient excess control cultures. Simultaneous culture growth and lipid accumulation in Ca L and Mg L cultures suggest that de novo synthesis was the primary mechanism for lipid accumulation in Ca/Mg-limited media. Overall, our study demonstrates that micro nutrient optimization, in addition to optimization of macronutrients, could significantly improve microalgal biorefinery yields. [ABSTRACT FROM AUTHOR]

Switchable solvents (SS), also termed smart solvents, have the unique ability to change their polarity/hydrophilicity through a protonation reaction using CO 2. Recently, a novel method employing the use of SS for lipid extraction in microalgae has shown promising results. In this study the efficiency of the tertiary amine N, N-dimethyl cyclohexylamine (DMCHA) to extract lipids from the eukaryotic microalgae Chlorella vulgaris and Haematococcus pluvialis , was investigated using traditional hexane as a control under wet conditions. The results revealed that high lipid yields using DMCHA can be achieved in both species, however the extraction procedure is significantly more complex compared with hexane. This study found that lipid extraction of H. pluvialis , using DMCHA to be an efficient solvent, achieving a maximum lipid yield of 64.84%. Furthermore, DMCHA achieved a maximum lipid yield of 63.85% with C. vulgaris. The practicalities of DMCHA for lipid recovery are considerably more complex at larger volumes compared with hexane. • DMCHA is biocompatible with Haematococcus pluvialis for lipid extraction. • Switchable solvents form globules with neutral lipids through Van-der Waal forces. • Microalgae cell wall rigidity reduces lipid extraction efficiency. • Switchable hydrophobic solvents are a more environmentally friendly alternative. • H. pluvialis and C. vulgaris maximum lipid recovery using DMCHA of 64.84% and 63.85%. [ABSTRACT FROM AUTHOR]

[Display omitted] • Sodium oleate (NaOL) enhances both biomass and lipid productivity in algae. • Optimum NaOL augmented with light irradiance governed the metabolite accumulation. • Total carotenoid and lipid content were significantly increased. • NaOL ameliorated the antioxidant potential of microalgae during the stationary phase. • NaOL orchestrated the metabolite overproduction in a dose-dependent manner. Microalgal metabolites have emerged as potential commodity components due to their notable beneficial nutritional and economic properties, and thus, their overproduction is of paramount importance to combat the existing ecological and dietary issues. However, the production titer of these metabolites by the algal systems at optimal cultivation conditions is inadequate to meet the burgeoning global demand for those metabolites. Therefore, a pressing demand remains to concurrently co-produce valuable metabolites without compromising cellular biomass production. Here, we report an effective strategy that simultaneously overproduces lipids, biomass and carotenoids in Chlorella vulgaris by providing sodium oleate (NaOL) in the cultivation medium. Supplement of sodium oleate at the optimal concentration (50 µg/mL) at increased light intensity enhances cellular growth rate in a dose-dependent manner. Total lipid content was quantified, which showed that lipid content was significantly increased in the NaOL-treated cells by 2.08-fold than that of the control cells. Interestingly, spectrophotometric determination of total carotenoids showed that carotenoid content was increased by 2.48-fold in the T5 (50 µg/mL) NaOL treated cells compared to the control. Interestingly antioxidant analysis showed that NaOL provision alleviated the antioxidant potential of the algal cells. Together, this report exemplifies the potential strategy to preclude the existing intricacies of co-producing metabolites in C. vulgaris by supplementing NaOL, thereby highlighting the viable chemical engineering approach for the biological production of commercially essential metabolites in microalgae. [ABSTRACT FROM AUTHOR]

Acetate and ammonium were used as organic carbon and nitrogen sources, respectively, during mixotrophic cultivation of Chlorella pyrenoidosa . Cell growth, content of neutral lipid (NL), productivity of biomass and total lipid, and fatty acid profiles were investigated. Results showed that C. pyrenoidosa could endure high concentrations of NH 4 + -N (100–200 mg/L) and immediately entered logarithmic growth, when the culture media contained 2.0–10.0 g/L NaAc. The 2.0–10.0 g/L NaAc in the media also resulted in the NL content of 1.87–3.05 mg/10 9 cells, much higher than 0.5 mg/10 9 cells of the controls. The maximum productivities of biomass and total lipid were achieved under 50 and 10 mg/L NH 4 + -N respectively when the 2.0 g/L NaAc was dosed. The fatty acids were mainly composed of C16:0, C16:1, C18:0, and C18:1 under the mixotrophic cultivation, with the higher saturation compared to the controls. [ABSTRACT FROM AUTHOR]

SUMMARY: Microalgae are considered a very promising alternative for biofuel production. Several strategies were developed to modulate and improve algae metabolites production to meet the requirements for biodiesel production. Most previous research evidenced that the increase of the lipid content is accompanied by a decrease of the biomass production, which increases the cost of the downstream processing. Hence, the challenge is to find special culture conditions that increase the lipid and the biomass productivities simultaneously. In the present work, we developed a strategy for the improvement of biomass and lipid productivities in a novel local microalga isolate, Chlorocystis sp. QUCCCM14, which was not previously known as a promising strain. Indeed, culturing QUCCCM14 using f/2 medium with 10× NaH2PO4 (0.15 g L−1 NaNO3 and 5.6 mg L−1 NaH2PO4) resulted in an improvement of 3.178 folds the lipid productivity reaching 56.121 mg L−1 day−1 and enhanced the biomass productivity reaching 141.363 mg L−1 day−1, simultaneously. Comparative analyses of the FAME profiles demonstrated that fed‐batch culture with phosphate or nitrate separately leads to a high production of the omega 3 fatty acids (Linolenic acid), whereas fed‐batch culture with phosphate and nitrate simultaneously increased the production of fatty acids suitable for biodiesel production. [ABSTRACT FROM AUTHOR]

Background: In the wake of rising energy demands, microalgae have emerged as potential sources of sustainable and renewable carbon-neutral fuels, such as bio-hydrogen and bio-oil. Purpose: For rational metabolic engineering, the elucidation of metabolic pathways in fine detail and their manipulation according to requirements is the key to exploiting the use of microalgae. Emergence of site-specific nucleases have revolutionized applied research leading to biotechnological gains. Genome engineering as well as modulation of the endogenous genome with high precision using CRISPR systems is being gradually employed in microalgal research. Further, to optimize and produce better algal platforms, use of systems biology network analysis and integration of omics data is required. This review discusses two important approaches: systems biology and gene editing strategies used on microalgal systems with a focus on biofuel production and sustainable solutions. It also emphasizes that the integration of such systems would contribute and compliment applied research on microalgae. Conclusions: Recent advances in microalgae are discussed, including systems biology, gene editing approaches in lipid bio-synthesis, and antenna engineering. Lastly, it has been attempted here to showcase how CRISPR/Cas systems are a better editing tool than existing techniques that can be utilized for gene modulation and engineering during biofuel production. [ABSTRACT FROM AUTHOR]

For the disintegration and extraction of microalgae to produce lipids and biofuels, a novel processing technology was investigated. The utilization of a hydrothermal treatment was tested on four different microalgae species (Scenedesmus rubescens, Chlorella vulgaris, Nannochloropsis oculata and Arthorspira platensis (Spirulina)) to determine whether it has an advantage in comparison to other disintegration methods for lipid extraction. It was shown, that hydrothermal treatment is a reasonable opportunity to utilize microalgae without drying and increase the lipid yield of an algae extraction process. For three of the four microalgae species, the extraction yield with a prior hydrothermal treatment elevated the lipid yield up to six times in comparison to direct extraction. Only Scenedesmus rubescens showed a different behaviour. Reason can be found in the different cell wall of the species. The investigation of the differences in cell wall composition of the used species indicate that the existence of algaenan as a cell wall compound plays a major role in stability. [ABSTRACT FROM AUTHOR]

Heterotrophic microalgae, capable of converting organic carbons to biofuel, as well as assimilating nutrients, have a great prospective in wastewater treatment. Meanwhile, the knowledge about heterotrophic microalgae is still far less than the autotrophic conterpart. Hence, in this study, 20 heterotrophic microalgal strains were isolated from a domestic wastewater treatment plant, and identified according to morphology and partial 18S and 23S rRNA gene sequences. Further, their biological traits were assessed in terms of N, P, TOC removal efficiencies, growth parameters, self-settleability and lipids production, expressed through a comprehensive selection index. By such, the optimal strains were chosen and applied back to treat the real wastewater, with or without pretreatment of sterilization. An organic-adaptable strain, i.e., Botryococcus sp. NJD-1, was ultimately recommended to achieve the concurrent biofuel production (up to 61.7% lipid content) and pollutants removal (up to 64.5%, 89.8% and 67.9% for N, P and TOC) in pristine wastewater. [ABSTRACT FROM AUTHOR]

Autotrophic microalgae are a promising bioproducts platform. However, the fundamental requirements these organisms have for nitrogen fertilizer severely limit the impact and scale of their cultivation. As an alternative to inorganic fertilizers, we investigated the possibility of using amino acids from deconstructed biomass as a nitrogen source in the genus Dunaliella. We found that only four amino acids (glutamine, histidine, cysteine, and tryptophan) rescue Dunaliella spp. growth in nitrogen depleted media, and that supplementation of these amino acids altered the metabolic profile of Dunaliella cells. Our investigations revealed that histidine is transported across the cell membrane, and that glutamine and cysteine are not transported. Rather, glutamine, cysteine, and tryptophan are degraded in solution by a set of oxidative chemical reactions, releasing ammonium that in turn supports growth. Utilization of biomass-derived amino acids is therefore not a suitable option unless additional amino acid nitrogen uptake is enabled through genetic modifications of these algae. [ABSTRACT FROM AUTHOR]

This paper reviews some of the most important aspects of microalgae as a potential source for biodiesel production. Microalgae are photosynthetic microorganisms that can grow rapidly in a variety of environments because of their unicellular or multicellular structure depending on the species. They have the advantage of self-reproduction using solar energy and converting it into chemical energy via photosynthesis. This process concludes a full cycle in a few days, obtaining higher lipid yields than terrestrial crops. This review shows several techniques and some methodologies used in the biodiesel production process from microalgae as well as the challenges that must be overcome for large-scale process and in bio-refineries. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The paper is dedicated to new unconventional sources of non-food renewable feedstock for third generation biofuel – microalgae biomass. Methods of lipid induction in microalgae have been considered. It represents the results of advanced microalgae strains state-of-the-art investigations – lipid producers. The paper discusses selection of stressors at two-stage culturing, where 1st stage includes culturing under most optimal conditions to produce maximum amount of biomass, and at 2nd stage biosynthesis and accumulation of lipids in biomass occurs. Types of stressors used for lipid induction have been briefly reviewed on the basis of foreign studies. Proper experimental results on isolation of new candidate microalgae strains from natural sources, as well as on selection of stressors for lipid induction have been shown and discussed. Nitrogen and phosphoric starvation, high and low illuminance, along with temperature conditions have been studied as stressors. Effectiveness of lipid-containing microalgae screening technique by fluorescent dye Nile red staining has been determined. Processible fast-growing Arhtrospira platensis microalgae/cyanobacteria use perspectiveness as a model for selection of stressors and overall lipid-containing microalgae culturing mode have been verified. Method of various microalgae heat-treated biomass conversion into biohydrogen by anaerobic acetone-butanol fermentation using cellular immobilized catalysts based on Clostridium acetobutylicum has been considered. Ultimate hydrogen efficiency has been found for Chlorococcum sp. rsemsu Ccc-7/11 strain biomass (8.4 и 6.1 mmol/l of medium/day); while hydrogen production is 23.7% and 18.6% of notionally possible level, A. platensis strains cultivated under the influence of stressors ( rsemsu 1/02-P – 5.6 mmol/l of medium/day, 32.3%; rsemsu 1/02-Т – 3.3 mmol/of medium/day, 28.8%) rank slightly below them in efficiency, outperforming in hydrogen production. [ABSTRACT FROM AUTHOR]

The manipulation of nutritional and culture parameters is one of the most promising methods for enhancing microalgal biomass and biofuel production. An earlier study analysed the ability of eight locally isolated microalgae to utilize standard nutrient sources in culture media to produce lipids. Four microalgae, Ankistrodesmus falcatus, Chlorella emersonii, Chaetoceros muelleri , and Isochrysis galbana , showed the desired biofuel properties (lipid/mass productivity, lipid content, and fatty acid profiles) and were selected for the present study. In this study, light intensity and nitrogen concentration were optimised to increase the growth rate, biomass, and lipid content of the four selected microalgae. Under optimal conditions of 135 μmol/m2/s light intensity and 5 g/l nitrogen, the isolates exhibited biomass productivity of 0.31–0.56 g/l/day, lipid content of 20.30–40.95% dry weight, and lipid productivity of 85.26–180.18 mg/l/day. Using the optimised parameters, the microalgae was further cultured with an upscaled volume of 5 L. The study found that C. muelleri and I. galbana produced the most promising results, with the highest lipid content, up to 43.40% dry weight, and the desired fatty acid profiles, which included a high concentration of saturated fatty acids (43.89–48.00%) and monounsaturated fatty acids (35.30–38.44%). Regardless, C. muelleri was chosen as a promising candidate for biodiesel application because of its high oleic acid proportion (27.68%), which was significantly higher than the other three microalgae (only 2.37–3.62% oleic acid). The study demonstrates the potential use of the tropical marine microalga C. muelleri as a feedstock for the production of biofuels. [Display omitted] • Four native microalgal strains were used in this study. • Lipid/biomass productivity, lipid content, and fatty acid profiles were analysed. • Optimised parameters were 135 μmol/m2/s illumination and 5 g/l nitrate. • The microalgae produced satisfactory lipid results under optimal conditions. • The microalga Chaetoceros muelleri is a promising biodiesel producer candidate. [ABSTRACT FROM AUTHOR]

• Methyl esterification targets lipids of coccolithophore. • Coccolithophore lipids were methyl-esterified at lower temperature than green alga. • Coccolithophore cell wall, composed of CaCO 3 , acted as a catalyst. • Effect of CaCO 3 on the methyl esterification by supercritical methanol was examined using green alga. • CaCO 3 is more effective than CaSO 4 -0.5H 2 O, which was previously considered effective. The methyl esterification of lipids employing supercritical methanol is an environmentally benign method since it does not produce alkaline wastewater, as is the case with conventional methods employing sodium hydroxide. Previous studies have shown that solid base catalysts are effective in decreasing reaction temperatures in the supercritical methanol methyl esterification. We focused on the coccolithophore Pleurochrysis carterae , which exhibits coccolith, i.e., CaCO 3 cell walls, and confirmed that the coccoliths acted as a catalyst in the methyl esterification of lipids in P. carterae employing supercritical methanol. To confirm the catalytic effect of the coccolith, the results of the supercritical methanol reaction of extracted lipids from P. carterae without coccolith were compared. The results showed that significant differences occurred, confirming that coccolith of P. carterae acts as a catalyst. To confirm the catalytic effect of CaCO 3 , the main component of coccolith, the green alga Chlorella vulgaris with cellulose cell walls was used to compare non-catalyst, addition of CaCO 3 and addition of CaSO 4 –0.5H 2 O, which is reported to be effective. The results revealed that the amount of the product obtained from the methyl esterification of fatty acids in C. vulgaris employing CaCO 3 was more significant than those obtained without any catalyst or with CaSO 4 –0.5H 2 O, indicating the effectiveness of CaCO 3 as a catalyst for methyl esterification by supercritical methanol. Coccolithophores, which exhibit CaCO 3 cell walls, are desirable raw materials for biofuels because they can function as catalysts. [ABSTRACT FROM AUTHOR]

High moisture content in wet algal biomass hinders effective performance of current lipid extraction methods. An improved aqueous extraction method combing thermal and enzymatic lysis was proposed and performed in algal slurry of Nannochloropsis oceanica (96.0% moisture) in this study. In general, cell-wall of N. oceanica was disrupted via thermal lysis and enzymatic lysis and lipid extraction was performed using aqueous surfactant solution. At the optimal conditions, high extraction efficiencies for both lipid (88.3%) and protein (62.4%) were obtained, which were significantly higher than those of traditional hexane extraction and other methods for wet algal biomass. Furthermore, an excessive extraction of polar lipid was found for wet biomass compared with dry biomass. The advantage of this method is to efficiently extract lipids from high moisture content algal biomass and avoid using organic solvent, indicating immense potential for commercial microalgae-based biofuel production. [ABSTRACT FROM AUTHOR]

Taxonomy and phylogeny of twenty two microalgal isolates were examined using both universal and newly designed molecular primers. Among the isolates, Scenedesmus bijugus , Coelastrella sp., Auxenochlorella protothecoides , and Chlorella sp. were particularly promising in terms of producing lipids as measured by fatty acid methyl esters (FAME) analysis and significant concentration of carotenoids. A comparative experiment showed that S. bijugus and Chlorella sp. were the most promising candidates (L − 1 d − 1 , with biomass) 174.77 ± 6.75, 169.81 ± 5.22 mg, lipids 40.14 ± 3.31, 39.72 ± 3.89 mg, lutein 0.47, 0.36 mg, and astaxanthin 0.27, 0.18 mg respectively. The fatty acids produced by these microalgal isolates were mainly palmitic, stearic, oleic, linoleic, and linolenic acid. The freshwater microalgal isolate S. bijugus be the most suitable isolate for producing biodiesel and carotenoids, due to high productivity of biomass, lipids, metabolites, and its suitable fatty acid profile. [ABSTRACT FROM AUTHOR]

Biofuel production from microalgae requires energy efficient processes for extracting and converting triacylglyceride lipids to fuel, compatible with coproduction of protein feeds and nutraceuticals. Wet solvent extraction involves mechanical cell rupture, lipid extraction via solvent contacting, physical phase separation, thermal solvent recovery, and transesterification. A detailed analysis of the effect of key process parameters on the parasitic energy demand of this process was performed. On a well-to-pump basis, between 16% and 320% of the resultant biodiesel energy was consumed depending solely on the process parameters. Highly positive energy balances can be achieved, but only if a correctly designed process is used. This requires processing concentrated biomass ( ca 25% w/w) with a high triacylglyceride content ( ca 30% w/w), and an efficient extraction process employing a non-polar solvent, low solvent-to-paste ratio, and efficient energy recovery. These requirements preclude many laboratory scale processes and polar co-solvents as viable options for large-scale biofuel production. [ABSTRACT FROM AUTHOR]

In the present investigation, the application of NMR spectroscopic techniques was extensively used with an objective to explore the biodiesel potential of biomass cultivated on a lab scale using strains of Chlorella vulgaris and Scenedesmus ecornis. The effect of variation in the composition of culturing medium on the neutral and polar lipids productivity, and fatty acid profile of solvent extracts of microalgae biomass was studied. Determination of unsaturated fatty acid composition (C18:N = 1-3, ω3 C20:5, ω3 C22:6), polyunsaturated fatty esters (PUFEs), saturated fatty acids (SFAs), unsaturated fatty acids (UFAs), free fatty acids (FFAs), and iodine value were achieved from a single H NMR spectral analysis. The results were validated by C NMR and GC-MS analyses. It was demonstrated that newly developed methods based on H and C NMR techniques are direct, rapid, and convenient for monitoring the microalgae cultivation process for enhancement of lipid productivity and their quality aspects in the solvent extracts of microalgal biomasses without any sample treatment and prior separation compared to other methods. The fatty acid composition of algae extracts was found to be similar to vegetable and fish oils, mostly rich in C16:0, C18:N (N = 0 to 3), and n-3 omega polyunsaturated fatty acids (PUFAs). The lipid content, particularly neutral lipids, as well as most of the quality parameters were found to be medium specific by both the strains. The newly developed methods based on NMR and ultrasonic procedure developed for efficient extraction of neutral lipids are cost economic and can be an effective aid for rapid screening of algae strains for modulation of lipid productivity with desired biodiesel quality and value-added products including fatty acid profile. [ABSTRACT FROM AUTHOR]

Currently microalgae are considered as an efficient biological producer of oil. Present study was conducted to explore the lipid yield percentage of three microalgal strains Chlorella sp., Oedogonium sp. and Spirogyra sp. Bligh and Dyer, Soxhlet, Folch and Microwave assisted extraction methods were employed for oil extraction. It was observed that Bligh and Dyer method with Chloroform-methanol (1:2, v/v) gave maximum extraction yield (15.46 ± 0.240%) for Chlorella sp. whereas Folch method with chloroform-methanol (2:1, v/v) gave more lipid yield as compared to Bligh and Dyer method i.e 5.53 ± 0.240% for Spirogyra sp., 13.67 ± 0.240% and 19.69 ± 0.667% for Oedogonium sp. and Chlorella sp. respectively. Soxhlet extraction resulted in less (14.5± 0.45) percentage yield as compared to Bligh and Dyer and Folch method (16.7± 0.24). Microwave assisted extraction with chloroform- methanol resulted in highest lipid yield (30%) with Chlorella sp. indicating that it contained the maximum lipid content among all the three species. [ABSTRACT FROM AUTHOR]