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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]

Microbes are the major source of lipids, which include fatty acids and glycerolipids. Lipids are used as bioplastic and biosurfactants in several industries. Value-added compounds like alpha-linolenic acid, 1,3-propanediol (1,3-PDO), fatty acid methyl esters (FAME), keto-carotenoids, lactic acid, 2,3-butanediol, citric acid, lutein, polyunsaturated fatty acids (PUFAs), 1,3-dihydroxyacetone, oleic acid, propionic acid, and succinic acid have huge applications in textile, cosmetic, food, metallurgy, and pharmaceutical industries. These microbial-based lipids have various industrial and technology applications as printing inks, lubricants, coatings, polymers, solvents, leather processing, hydraulic fluids, surfactants, glycerin (glycerol), pesticide/herbicide adjuvants, and fuels. Biotechnological processes such as medium engineering and metabolic engineering can enhance lipid production in microbes to a certain limit. Integrated biorefinery concept was introduced for cost reduction, efficient utilisation of feedstocks, high yield, zero waste discharges, high productivity, and economically viable technology development. It integrates the conversion of biomass to energy and other high-value products. This review focuses on the bioreactor design; integrated biorefineries; genetic and metabolic engineering prospect of enhanced microbial lipid production; application of microbial lipids in various sectors such as pharmaceuticals, dietary supplement, cosmetics, and biodiesel production; costing; and life cycle assessment. Furthermore, value-added products such as carotenoids, organic acids, polyhydroxyalkanoates, and fatty acids were also discussed. [ABSTRACT FROM AUTHOR]

Background: Metabolic engineering for hyperaccumulation of lipids in vegetative tissues is a novel strategy for enhancing energy density and biofuel production from biomass crops. Energycane is a prime feedstock for this approach due to its high biomass production and resilience under marginal conditions. DIACYLGLYCEROL ACYLTRANSFERASE (DGAT) catalyzes the last and only committed step in the biosynthesis of triacylglycerol (TAG) and can be a rate-limiting enzyme for the production of TAG. Results: In this study, we explored the effect of intron-mediated enhancement (IME) on the expression of DGAT1 and resulting accumulation of TAG and total fatty acid (TFA) in leaf and stem tissues of energycane. To maximize lipid accumulation these evaluations were carried out by co-expressing the lipogenic transcription factor WRINKLED1 (WRI1) and the TAG protect factor oleosin (OLE1). Including an intron in the codon-optimized TmDGAT1 elevated the accumulation of its transcript in leaves by seven times on average based on 5 transgenic lines for each construct. Plants with WRI1 (W), DGAT1 with intron (Di), and OLE1 (O) expression (WDiO) accumulated TAG up to a 3.85% of leaf dry weight (DW), a 192-fold increase compared to non-modified energycane (WT) and a 3.8-fold increase compared to the highest accumulation under the intron-less gene combination (WDO). This corresponded to TFA accumulation of up to 8.4% of leaf dry weight, a 2.8-fold or 6.1-fold increase compared to WDO or WT, respectively. Co-expression of WDiO resulted in stem accumulations of TAG up to 1.14% of DW or TFA up to 2.08% of DW that exceeded WT by 57-fold or 12-fold and WDO more than twofold, respectively. Constitutive expression of these lipogenic "push pull and protect" factors correlated with biomass reduction. Conclusions: Intron-mediated enhancement (IME) of the expression of DGAT resulted in a step change in lipid accumulation of energycane and confirmed that under our experimental conditions it is rate limiting for lipid accumulation. IME should be applied to other lipogenic factors and metabolic engineering strategies. The findings from this study may be valuable in developing a high biomass feedstock for commercial production of lipids and advanced biofuels. [ABSTRACT FROM AUTHOR]

Background: Biofuel research that aims to optimize growth conditions in microalgae is critically important. Chlamydomonas reinhardtii is a green microalga that offers advantages for biofuel production research. This study compares the effects of nitrogen-, sulfur-, and nitrogen and sulfur- deprivations on the C. reinhardtii starchless mutant cc5373-sta6. Specifically, it compares growth, lipid body accumulation, and expression levels of acetyl-CoA carboxylase (ACC) and phosphoenolpyruvate carboxylase (PEPC). Results: Among nutrient-deprived cells, TAP-S cells showed significantly higher total chlorophyll, cell density, and protein content at day 6 (p < 0.05). Confocal analysis showed a significantly higher number of lipid bodies in cells subjected to nutrient deprivation than in the control over the course of six days; N deprivation for six days significantly increased the size of lipid bodies (p < 0.01). In comparison with the control, significantly higher ACC expression was observed after 8 and 24 h of NS deprivation and only after 24 h with N deprivation. On the other hand, ACC and PEPC expression at 8 and 24 h of S deprivation was not significantly different from that in the control. A significantly lower PEPC expression was observed after 8 h of N and NS deprivation (p < 0.01), but a significantly higher PEPC expression was observed after 24 h (p < 0.01). Conclusions: Based on our findings, it would be optimum to cultivate cc5373-sta6 cells in nutrient deprived conditions (-N, -S or –NS) for four days; whereby there is cell growth, and both a high number of lipid bodies and a larger size of lipid bodies produced. [ABSTRACT FROM AUTHOR]

The aim of this study was to evaluate biomass generation and determine the total lipid content of a microalgae isolated from a lagoon of the Ecuadorian Amazon. The morphological identification of the isolated microalgae was done through bibliographic comparisons and molecular identification by PCR followed by DNA sequencing and phylogenetic analysis. A 10-day batch culture was operated in 1-L glass bottles, and nutrient removal was determined daily. After harvesting, biomass was centrifuged to remove most of the water content. Half of the obtained biomass was kept wet and the other half was dried for further analysis. Cell growth, optical density, and dry weight were measured during cultivation time. In addition, total lipid and free fatty acid (FFA) percentages were evaluated. Removal of chemical oxygen demand (COD), nitrates (NO3−), and phosphates (PO43−) was 33.12%, 67.77%, and 76.73%, respectively. The biomass concentration was 2.19 ± 0.12 g/L with a productivity of 0.22 g/L per day. The best extraction percentages of total lipids and FFA were 18.43% and 61.46%, respectively. Although the results of lipids and FFA do not reach the required limits, the productivity of biomass and lipids is comparable with species that are cultivated for biodiesel production. [ABSTRACT FROM AUTHOR]

The study aimed to apply gamma radiation as a cell pretreatment method for lipid extraction and for obtaining astaxanthin from residual biomass of Haematococcus pluvialis. Factor 1 of the two-factor experimental design was represented by cell pretreatment methods: biomass with chloroform:methanol under ultrasound (BCMU), biomass with chloroform:methanol under γ radiation (BCMR), dry biomass under γ radiation (DBR), and control (without pretreatment). Factor 2 considered the vegetative and cystic phases. Cultivation was performed in a mixotrophic system, and biomass was collected in both phases, centrifuged, lyophilized, and submitted to cell pretreatment and lipid extraction. Lipid content and FAMEs were evaluated comparing pretreatment methods and life cycle phases. Total lipid content was higher with the BCMR method in the vegetative (18% DW) and cystic (14% DW) phases. Gamma radiation combined with organic solvent was more efficient for increasing lipid yield, and DBR had a lipid yield similar to BCMU. FAME content differed between phases and pretreatments for most fatty acids, mainly C16:0, C16:1, C18:1n9c, C18:2n6c, C18:2n6t, and C18:3n3. The predominance of saturated or low unsaturated fatty acids makes H. pluvialis, in both phases, suitable for biofuel production. The preservation of astaxanthin from residual cystic biomass was observed when submitted to the DBR method, with a concentration similar to the raw biomass (1.5% DW). Gamma radiation in dry biomass has an antioxidant effect. Therefore, the lipid extraction method preceded by gamma irradiation was efficient for vegetative and cystic cells of H. pluvialis and contributed to the preservation of astaxanthin from residual cystic biomass. [ABSTRACT FROM AUTHOR]

The present study demonstrates the potential of freshwater algal species collected from the natural habitats of Central India for biofuel production. Algal samples were collected from different waterbodies and were microscopically examined in the laboratory. Based on the morphological features using the taxonomic keys, a total of 51 algal species (18 Cyanophyta, 22 Chlorophyta, 7 Bacillariophyta, and 4 Charophyta) were identified. Among them, 18 algal species were successfully purified in the laboratory and tested for their ability to produce biomass and lipid, which are the essential criteria to be qualified as suitable feedstock for biofuel production. The data on specific growth rates suggest that Chlorella vulgaris, Scenedesmus bijugatus, and Nitzschia recta were the fastest growing species, whereas all the members of Cyanophyta showed relatively slower growth. The biomass productivity was higher in C. vulgaris, S. bijugatus, and Anabaena sp., but the lipid production was highest in C. vulgaris followed by Haematococcus sp., whereas the members of Cyanophyta showed the lowest lipid production. Furthermore, we assessed the ability of biomass and lipid production and biochemical parameters of four selected algal species, C. vulgaris, S. bijugatus, Anabaena sp., and N. recta, due to their faster growth, higher biomass and lipid production, and abundance. Based on the cluster analyses of the values of lipid and biomass production of these species against internal N:P ratio, three distinct clusters were noticed, cluster 1: near 50:1, cluster 2: between 30:35, and cluster 3 between 15:20 cellular N:P ratios. High lipid and biomass productivity were observed between the 30:35 N:P ratio. Despite the metabolic significance of N and P for algae, more research is warranted to conclude anything precisely.

Background: The promising use of lignocellulosic materials as a substrate for the synthesis of biochemical and biofuels has long been recognized. The bioconversion of all lignocellulosic sugars into useful products results in high sugar yields, which makes lignocelluloses appealing for use. Pretreatment and hydrolysis of lignocelluloses at high solids loadings are vital throughout industrial processes, making them more cost-effective and ecologically friendly by lowering the need for capital expenditures, energy use, and water use. The high expense of fermentation medium hinders heterotrophic oleaginous microorganisms' ability to metabolically synthesize single-cell oils for biodiesel use. This study's objective was to ascertain whether bagasse hydrolysate could be used as a cost-effective feedstock for oleaginous Rhodococcus opacus to produce microbial lipids. Methods: R. opacus a strain was used in this study. The culture was first of all maintained at soytone nutrient growth medium (i.e. GROTH MEDIUM 56) and subcultured at regular intervals and as well as preserved at 4°C. For the production media, a minimal salt medium is used. Sugarcane bagasse is pretreated by acidic hydrolysis followed by detoxification of hydrolysate and lipid extraction is done by Folch's extraction process. Results: After a brief adaptation/lag phase, the strain showed a viable growth pattern once the nutrients were detoxicated through the removal of inhibitors (e.g. hydroxymethyl-furfural [HMF]). R. opacus was grown via shake flask fermentation in bagasse hydrolysate with different sugar concentrations. When cultivated in S2 experiment, R. opacus obtained over 50% of its dry cell weight as a lipid with a lipid yield of 64.47% and productivity is 0.015 g/L/h. Conclusions: Depending on the available substrates, different microbial oils had different compositions. These findings suggest that lignocellulosic hydrolysate can be utilized as an inexpensive fermentation substrate for the R. opacus to produce microbial lipids. As a result, the range of uses for aqueous liquors produced by lignocellulosic pretreatment has increased, enabling further improvement.

Background: The promising use of lignocellulosic materials as a substrate for the synthesis of biochemical and biofuels has long been recognized. The bioconversion of all lignocellulosic sugars into useful products results in high sugar yields, which makes lignocelluloses appealing for use. Pretreatment and hydrolysis of lignocelluloses at high solids loadings are vital throughout industrial processes, making them more cost-effective and ecologically friendly by lowering the need for capital expenditures, energy use, and water use. The high expense of fermentation medium hinders heterotrophic oleaginous microorganisms' ability to metabolically synthesize single-cell oils for biodiesel use. This study's objective was to ascertain whether bagasse hydrolysate could be used as a cost-effective feedstock for oleaginous Rhodococcus opacus to produce microbial lipids. Methods: R. opacus a strain was used in this study. The culture was first of all maintained at soytone nutrient growth medium (i.e. GROTH MEDIUM 56) and subcultured at regular intervals and as well as preserved at 4°C. For the production media, a minimal salt medium is used. Sugarcane bagasse is pretreated by acidic hydrolysis followed by detoxification of hydrolysate and lipid extraction is done by Folch's extraction process. Results: After a brief adaptation/lag phase, the strain showed a viable growth pattern once the nutrients were detoxicated through the removal of inhibitors (e.g. hydroxymethyl-furfural [HMF]). R. opacus was grown via shake flask fermentation in bagasse hydrolysate with different sugar concentrations. When cultivated in S2 experiment, R. opacus obtained over 50% of its dry cell weight as a lipid with a lipid yield of 64.47% and productivity is 0.015 g/L/h. Conclusions: Depending on the available substrates, different microbial oils had different compositions. These findings suggest that lignocellulosic hydrolysate can be utilized as an inexpensive fermentation substrate for the R. opacus to produce microbial lipids. As a result, the range of uses for aqueous liquors produced by lignocellulosic pretreatment has increased, enabling further improvement. [ABSTRACT FROM AUTHOR]

In this study, a new microalgal strain, Asterarcys quadricellulare R-56, was isolated for biomass and lipid production. The effects of carbon and nitrogen sources and initial pH on the cell growth and lipid accumulation of strain R-56 were investigated. At 10 g L−1 glucose, 0.6 g L−1 sodium nitrate, and pH 7, the highest biomass of 4.18 g L−1 and lipid content of 43.66% were obtained. Microalgae had a broad pH tolerance in the range of 5–11, and the pH of the culture medium was close to neutral at the end of cultivation. The maximum contents of chlorophyll, carbohydrate, and protein under the recommended culture conditions were 19.47 mg mL−1, 21.80%, and 29.94%, respectively. Palmitic and palmitoleic acid contents in strain R-56 accounted for as high as 83.73% of total fatty acids. This study suggested that strain R-56 was a promising lipid producer for high-quality biodiesel production. [ABSTRACT FROM AUTHOR]

The lipid, fatty acid, protein, and carbohydrate contents in cyanobacterial strains and biomass can vary by orders of magnitude. Many publications (thousands of peer-reviewed articles) require more work to extract their precise concentration values (i.e., different units, inaccurate data), which makes them not easily exploitable. For this purpose, tables have been compiled from the literature data, including lipids, fatty acids, proteins, and carbohydrates composition and quantities in cyanobacteria. A lot of data (323) were collected after careful a literature search, according to selected criteria in order to distinguish separately cyanobacteria, and according to categories of genus and species and generate average values of the contents of these cell components. These data are exploited in a first systematic analysis of the content in types of strains. Our database can be a powerful tool for biologists, chemists, and environmental agencies to determine the potential concentration of high-value chemical building blocks directly from low-value bloom biomass, cell cultures, or debris in the sediment, offering the potential to minimize environmental waste and add value to the agro-industrial residues. The database can also support strategies for food manufacturers to develop new products with optimized properties for veterinarian applications. [ABSTRACT FROM AUTHOR]

Exploration of alternative and sustainable sources of fuel production has become vital for a couple of decades because of the increase in demand, shortages in inexpensive fossil fuel production, and environmental pollution caused by their derivatives. Although a variety of renewable energy alternatives are currently available, energy derived from natural microalgae associated with bacteria seems promising because it flourishes in all natural environments, along with contributing to the carbon cycle. Lipid extraction from different microalgae cells is a significant boundary for the biofuel business because of the multifaceted nature of the procedure and cell structure of the microalgae. Although the current existing dry extraction methods for lipid extraction from algae are in use, the drying of microalgae is consuming more energy than the extraction itself. There is still lack of technology to optimize the extraction of biodiesel from microalgae in a cost-effective and quick way. Studies show that eliminating the drying step and extracting lipids in one step can be optimal by adding mechanisms like supercritical method, ionic liquids, Eutectic solvents, and transesterification. A major constraint in this process is effective lipid extraction technique. Fuel production from wet microalgae biomass is significantly desirable because it would eliminate at least two lengthy processes (dewatering and drying) that consume much energy. In this study, wet extraction techniques are comprehended. For implementing and optimizing this application, further research and exploration are much needed. [ABSTRACT FROM AUTHOR]

Cutaneotrichosporon oleaginosus is a highly efficient single cell oil producer, which in addition to hexoses and pentoses can metabolize organic acids. In this study, fed-batch cultivation with consumption-based acetic acid feeding was further developed to integrate the transformation of an industrial paper mill lignocellulosic hydrolysate (LCH) into yeast oil. Employing pentose-rich LCH as a carbon source instead of glucose significantly improved both biomass formation and lipid titer, reaching 55.73 ± 5.20 g/L and 42.1 ± 1.7 g/L (75.5% lipid per biomass), respectively. This hybrid approach of using acetic acid and LCH in one process was further optimized to increase the share of bioavailable carbon from LCH using a combination of consumption-based and continuous feeding. Finally, the techno-economic analysis revealed a 26% cost reduction when using LCH instead of commercial glucose. In summary, we developed a process leading to a holistic approach to valorizing a pentose-rich industrial waste by converting it into oleochemicals. [ABSTRACT FROM AUTHOR]

Industrial crops are becoming increasingly relevant as raw materials for different goods and services. Although there are many oilseed crops with industrial purposes, data about their production in Chile are scarce because the definition used by the Office of Agricultural Studies and Policies places agro‐industrial and industrial crops in the same category. Here, we review the available information about 12 industrial oleaginous crops at different levels of development (four native, two adventive and six introduced crops). Most of these crops have been evaluated for or are related to biodiesel production, despite the lack of commercial biodiesel production in Chile. Jojoba was the first industrial oilseed produced commercially in Chile; however, every year its production area decreases, and currently it does not exceed 100 ha. Sunflower and rapeseed, which are the first generation of raw materials for biodiesel production, have been poorly studied in Chile despite the large number of studies available on them worldwide. Camelina and castor bean have recently been studied; the former is produced in the south, while the latter is produced on the coastline in northern Chile. Further research is needed to improve the production and adaptation of these oilseed crops to climatic conditions in Chile; moreover, a new market must be opened to produce and commercialize their oils. Oilseed species native to Chile have not been extensively studied, and they represent an interesting option suitable for production under Chilean climatic conditions; this is particularly true for guindilla and chañar, because both can grow under different abiotic stresses. © 2022 Society of Chemical Industry and John Wiley & Sons, Ltd. [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]

The present study aimed to optimize synthetic wastewater composition as a mixotrophic medium for enhanced growth and lipid accumulation coupled with high nitrogen removal by the green microalga Chlorella sp. Individual effects of the three main independent variables (nitrate concentration, seawater ratio, and glycerol supplementation) were tested initially, then response surface methodology (RSM) was subsequently performed to explore the optimum combined conditions. The highest lipid productivity of 37.60 mg/L day was recorded at 25% seawater. Glycerol supplementation enhanced both lipid content and biomass production, which resulted in the highest recorded lipid productivity of 42.61 mg/L day at 4 g/L glycerol. Central composite design followed by numerical optimization was further applied which suggested NaNO3 concentration at 101.5 mg/L, seawater ration of 23.8%, and glycerol supplementation of 0.25 g/L as the optimum conditions for dual maximum lipid productivity and nitrogen removal of 46.9 mg/L day and 98.0%, respectively. Under the optimized conditions, dry weight and lipid content increased by 31.9% and 20.3%, respectively, over the control, which resulted in increase in lipid productivity by 71.5%. In addition, optimization process resulted in pronounced changes in fatty acid proportions where saturated fatty acids increased by 7.4% in the optimized culture with simultaneous reduction of polyunsaturated fatty acids. The estimated biodiesel characteristics calculated from the fatty acid methyl ester (FAMEs) profile showed agreement with the international standards, while optimized cultures showed an 8.5% lower degree of unsaturation, which resulted in higher cetane numbers and lower iodine values. This study provides economical approach for optimization and efficient nutrient recycling through cultivation of Chlorella sp. for further enhanced biodiesel production. [ABSTRACT FROM AUTHOR]

Microalgae are an attractive source of biomass for fossil fuel alternatives and renewable energy sources. Regardless of their potential, the development of microalgal biofuels has been limited due to the associated economic and environmental costs. We followed and compared the biomass properties of six Chlorellaceae strains with a specific interest in lipid-based biofuels. The strains were cultivated under balanced nutrient limitation inducing a gradual limitation of nutrients that triggered reserve accumulation. The final biomass of each strain was characterized by its elemental and biochemical composition. Due to its high lipid content and overall composition, Chlorella vulgaris NIES 227 was identified as an ideal feedstock for biofuels with the best energy-content biomass. Its fatty acid profile also showed superior qualities for biodiesel production. Balanced nutrient limitation promoted not only the accumulation of storage compounds in all strains, but also resulted in a low content of heteroatom precursors and ashes for biofuel applications. [ABSTRACT FROM AUTHOR]

Lipid droplets are cytoplasmic organelles that store lipids for energy and membrane synthesis. The oleaginous yeast Lipomyces starkeyi is one of the most promising lipid producers and has attracted attention as a biofuel source. It is known that the expansion of lipid droplets is enhanced under nutrient-poor conditions. Therefore, we prepared a novel nitrogen-depleted medium (N medium) in which to culture L. starkeyi cells. Lipid accumulation was rapidly induced, and this was reversed by the addition of ammonium. In this condition, cell proliferation stopped, and cells with giant lipid droplets were arrested in G1 phase. We investigated whether cell cycle arrest at a specific phase is required for lipid accumulation. Lipid accumulation was repressed in hydroxyurea-synchronized S phase cells and was increased in nocodazole-arrested G2/M phase cells. Moreover, the enrichment of G1 phase cells seen upon rapamycin treatment induced massive lipid accumulation. From these results, we conclude that L. starkeyi cells store lipids from G2/M phase and then arrest cell proliferation in the subsequent G1 phase, where lipid accumulation is enhanced. Cell cycle control is an attractive approach for biofuel 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]

Cutaneotrichosporon oleaginosus is a highly efficient single cell oil producer, which in addition to hexoses and pentoses can metabolize organic acids. In this study, fed-batch cultivation with consumption-based acetic acid feeding was further developed to integrate the transformation of an industrial paper mill lignocellulosic hydrolysate (LCH) into yeast oil. Employing pentose-rich LCH as a carbon source instead of glucose significantly improved both biomass formation and lipid titer, reaching 55.73 ± 5.20 g/L and 42.1 ± 1.7 g/L (75.5% lipid per biomass), respectively. This hybrid approach of using acetic acid and LCH in one process was further optimized to increase the share of bioavailable carbon from LCH using a combination of consumption-based and continuous feeding. Finally, the techno-economic analysis revealed a 26% cost reduction when using LCH instead of commercial glucose. In summary, we developed a process leading to a holistic approach to valorizing a pentose-rich industrial waste by converting it into oleochemicals.

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]

The nature of global dietary supplements is transitioning from animal derivatives to plant based. Industries around the world are seeking vegan alternatives to animal-derived supplements. The microalgal industry is expected to undergo a market boom in the current decade. Microalgal supplements (power based and extracts) as well as microalgal fuels are expected to show a significant increase in market value. Microalgae are an under-utilized source of high-value products. They are rich reservoirs of multiple compounds capable of enhancing immunity, fortifying nutritional diets and improving cardiovascular health. Microalgae are also high lipid producing organisms, which make them viable candidates in the global search for energy alternatives. However, the inability to translate in vitro results onto the industrial scale is a major drawback of the microalgal research landscape. It is therefore, vital to find a robust microalgal species capable of producing a feasible quantity of high-value compounds. This paper investigates the potential of four microalgae sourced from the coastal town of Mangalore, India as candidates for nutraceutical industries and the clean energy industry. Desmodesmus komareikii (MK990101) was found to be rich in total lipid, while the three Chlorella species were found to be relatively richer in total protein yields. Chlorella thermophila (MN006612) is capable of yielding harvests up to nearly 280 tonnes/acre/year. Chlorella thermophila (MN006612) yielded the highest amount of both mono and polyunsaturated fatty acids. The fatty acid profiles of Chlorella thermophila (MN006612), Chlorella vulgaris (MN252517-18) and Chlorella sorokiniana (MN011568) can be explored as an alternative edible oil. Desmodesmus komareikii (MK990101) yielded the highest amount of saturated fatty acids, which are used in the production of clean and quality biofuels.

The demand for renewable energy has risen rapidly due to the depletion of petroleum oil. Biodiesel has attracted potential interest to be utilized as an alternative to petroleum oil since it is produced from renewable resources with minimal environmental impact. However, the production and quality of biodiesel potentially influence several factors including physicochemical properties of lipids, selection of feedstock, and technology utilized for lipids extraction. Candlenut contains the highest amount of oil among the oilseed crops. Supercritical carbon dioxide (scCO2) is viewed as an effective alternative method over conventional solvent extraction methods for the extraction and separation of lipids from various plant matrices. The distinct properties of the fluid CO2, such as nonflammability, nontoxicity, environmental friendliness, and its ability to solubilize lipophilic substance led to the wide application of the scCO2 in various industrial applications. Hence, the present study attempts to review the influence of the supercritical carbon dioxide (scCO2) technology for the extraction of lipids from candlenut as a potential feedstock for biodiesel production. The limitations of existing technologies in candlenut oil extraction and the potential scCO2 technology for the extraction of lipids from candlenut were also reviewed. [ABSTRACT FROM AUTHOR]

This research aims to evaluate the effect of molasses as a source of organic carbon on the growth and lipid profile of Dunaliella salina cultivated under different light regimes to determine its strategy and potential use to produce biodiesel. Two sources of nutrients (F/2 medium, F/2; molasses, M) and two light conditions (12 h light: 12 h darkness, 12L:12D) conformed four treatments (F/2 12L:12D, F/2 D, M 12L:12D, and MD) that were investigated with three replicates each. The concentration of microalgae produced by the groups under light conditions was more than double that of those grown in darkness. The highest biomass produced (46.91 ± 6.47 g L-1) was obtained in the F/2 medium with 12L:12D treatment, while the lowest (18.99 ± 0.78 g L-1) was in the M 12L:12D group. Regardless of the culture conditions, the lipids were mainly composed of the C16:0 and C18 fatty acids. The use of molasses as a culture medium produced the highest amount of C18:1, regardless of the light regime. Molasses promoted the highest production of fatty acids methyl esters. Depending on the culture medium, D. salina cells showed different percentages of saturated (SFA), monounsaturated (MFA), and polyunsaturated (PUFA) fatty acids. The highest amount of saturated fatty acids was obtained in F/2 12L:12D. The highest amount of polyunsaturated fatty acids was presented in the mixotrophic culture (molasses and light). The cultures grown with molasses were rich in monounsaturated fatty acids. An inexpensive industrial by-product, Cane molasses could be a low-cost feedstock for biodiesel in cultivating D. salina. [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]

Microalgae are an attractive source of biomass for fossil fuel alternatives and renewable energy sources. Regardless of their potential, the development of microalgal biofuels has been limited due to the associated economic and environmental costs. We followed and compared the biomass properties of six Chlorellaceae strains with a specific interest in lipid-based biofuels. The strains were cultivated under balanced nutrient limitation inducing a gradual limitation of nutrients that triggered reserve accumulation. The final biomass of each strain was characterized by its elemental and biochemical composition. Due to its high lipid content and overall composition, Chlorella vulgaris NIES 227 was identified as an ideal feedstock for biofuels with the best energy-content biomass. Its fatty acid profile also showed superior qualities for biodiesel production. Balanced nutrient limitation promoted not only the accumulation of storage compounds in all strains, but also resulted in a low content of heteroatom precursors and ashes for biofuel applications.

The bioenergy crops such as energycane, miscanthus, and sorghum are being genetically modified using state of the art synthetic biotechnology techniques to accumulate energy‐rich molecules such as triacylglycerides (TAGs) in their vegetative cells to enhance their utility for biofuel production. During the initial genetic developmental phase, many hundreds of transgenic phenotypes are produced. The efficiency of the production pipeline requires early and minimally destructive determination of oil content in individuals. Current screening methods require time‐intensive sample preparation and extraction with chemical solvents for each plant tissue. A rapid screen will also be needed for developing industrial extraction as these crops become available. In the present study, we have devised a proton relaxation nuclear magnetic resonance (1H‐NMR) method for single‐step, non‐invasive, and chemical‐free characterization of in‐situ lipids in untreated and pretreated lignocellulosic biomass. The systematic evaluation of NMR relaxation time distribution provided insight into the proton environment associated with the lipids in the biomass. It resolved two distinct lipid‐associated subpopulations of proton nuclei that characterize total in‐situ lipids into bound and free oil based on their "molecular tumbling" rate. The T1T2 correlation spectra also facilitated the resolution of the influence of various pretreatment procedures on the chemical composition of molecular and local 1H population in each sample. Furthermore, we show that hydrothermally pretreated biomass is suitable for direct NMR analysis unlike dilute acid and alkaline pretreated biomass which needs an additional step for neutralization. [ABSTRACT FROM AUTHOR]

Microbial lipid production has been studied extensively for years; however, lipid metabolic engineering in many of the extraordinarily high lipid-accumulating yeasts was impeded by inadequate understanding of the metabolic pathways including regulatory mechanisms defining their oleaginicity and the limited genetic tools available. The aim of this review is to highlight the prominent oleaginous yeast genera, emphasizing their oleaginous characteristics, in conjunction with diverse other features such as cheap carbon source utilization, withstanding the effect of inhibitory compounds, commercially favorable fatty acid composition--all supporting their future development as economically viable lipid feedstock. The unique aspects of metabolism attributing to their oleaginicity are accentuated in the pretext of outlining the various strategies successfully implemented to improve the production of lipid and lipid-derived metabolites. A large number of in silico data generated on the lipid accumulation in certain oleaginous yeasts have been carefully curated, as suggestive evidences in line with the exceptional oleaginicity of these organisms. The different genetic elements developed in these yeasts to execute such strategies have been scrupulously inspected, underlining the major types of newly-found and synthetically constructed promoters, transcription terminators, and selection markers. Additionally, there is a plethora of advanced genetic toolboxes and techniques described, which have been successfully used in oleaginous yeasts in the recent years, promoting homologous recombination, genome editing, DNA assembly, and transformation at remarkable efficiencies. They can accelerate and effectively guide the rational designing of system-wide metabolic engineering approaches pinpointing the key targets for developing industrially suitable yeast strains. [ABSTRACT FROM AUTHOR]

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]

Objective: The extraction of the hemicellulose fraction of sugarcane bagasse (SCB) by acid hydrolysis was evaluated in an autoclave and a Parr reactor aiming the application of the hydrolysate as a carbon source for lipid production by Lipomyces starkeyi. Results: The hydrolysis that resulted in the highest sugar concentration was obtained by treatment in the Parr reactor (HHR) at 1.5% (m/v) H2SO4 and 120 °C for 20 min, reaching a hemicellulose conversion of approximately 82%. The adaptation of the yeast to the hydrolysate provided good fermentability and no lag phase. The fermentation of hemicellulose-derived sugars (HHR) by L. starkeyi resulted in a 27.8% (w/w) lipid content and YP/S of 0.16 g/l.h. Increasing the inoculum size increased the lipid content by approximately 61%, reaching 44.8% (w/w). Conclusion: The hemicellulose hydrolysate from SCB is a potential substrate for L. starkeyi to produce lipids for biodiesel synthesis based on the biorefinery concept. [ABSTRACT FROM AUTHOR]

Abstract Background The regulation of genes related to lipid metabolism by genetic engineering is an important way to increase the accumulation of lipids in microalgae. DNA binding with one finger (DOF) is a plant-specific transcription factor in higher plants, where it regulates carbon and nitrogen metabolic pathways by regulating key genes involved in these pathways. Overexpression of DOF can increase lipid production in plants; however, it is not clear whether overexpression of DOF can increase lipids in microalgae. Results In this study, we cloned a DOF transcription factor, crDOF, from Chlamydomonas reinhardtii. The sequence of this transcription factor is 1875 bp and encodes a peptide of 624 amino acids with a conserved DOF domain. Overexpression of crDOF in C. reinhardtii significantly increased the intracellular lipid content. The content of total fatty acids in the transgenic algae line Tranc-crDOF-12 was 126.01 μg/mg (dry weight), which was 23.24% higher than that of the wild type. Additionally, the content of unsaturated fatty acids in the transgenic Tranc-crDOF-12 line increased significantly. Fluorescence quantitative PCR analysis showed that in the transgenic line Tranc-crDOF-12, the expression levels of BCC1, FAT1, SQD1, MGD1, DGD1 and PGP1 genes were significantly upregulated, while the expression levels of ACP1, ACS1, CIS1 and SQD2 were downregulated. Conclusions Our results confirm that crDOF increases intracellular lipids in C. reinhardtii by regulating key genes involved in lipid metabolism. According to these findings, we propose that enhancing the lipid content in microalgae by overexpressing DOF may be achieved in other industrial strains of microalgae and be employed for the industrial production of biodiesel.