Promising Microalga Research Articles

Optimizing the Enzymatic Hydrolysis of Bioflocculated Microalgae for Bioethanol Production

Spirulina platensis is a promising microalga, but biomass harvesting remains a challenge. Fungal bioflocculation offers a potential solution, facilitating the production of valuable bioproducts like bioethanol. Effective cell disruption methods, including physical-chemical and enzymatic treatments, can enhance biomass utilization. However, commercial enzymes are not optimized for microalgae, necessitating research on ideal operational conditions. This study evaluated physical and enzymatic processes to hydrolyze bioflocculated microalgae for bioethanol production. The microalga was harvested using a fungal bioflocculant produced via submerged fermentation. Biomass hydrolysis involved physical methods (autoclaving, ultrasound + autoclaving, ultrasound + gelatinization, and gelatinization) combined with enzymes (amylase, amyloglucosidase, cellulase, and xylanase), optimized for pH, temperature, and enzyme load. Hydrolysates were then used for bioethanol production. Results showed a microalgae harvest efficiency of 99.7% with a 1:8 fungus-to-microalgae ratio. Enzyme optimization identified ideal conditions (e.g., pH 4.5; 60 °C for amylase/amyloglucosidase, 70 °C for cellulase, and 50 °C for xylanase). Combined enzymatic treatments achieved approximately 70% hydrolysis efficiency, yielding 19.06 g/L glucose and 7.29 g/L ethanol (~79% conversion). Ethanol productivity was ~0.6 g per 1 g bioflocculated biomass L−1·hr. These findings highlight the potential of enzymatic hydrolysis for complex biomasses, although further studies are needed to refine enzyme applications for better biomass utilization.

Enhanced carbon dioxide bio-fixation and protein production of Chlorella pyrenoidosa through a highly efficient sequential heterotrophic and photoautotrophic culture strategy

Chlorella pyrenoidosa is one of the most promising microalgae for protein production with carbon dioxide (CO2) bio-fixation. However, the high production cost and low production capability under traditional photoautotrophic culture mode had severely limited its application. Here, a highly efficient sequential heterotrophic and photoautotrophic cultivation strategy was established. Firstly, the heterotrophic seeds culture conditions were optimized with glucose as the carbon source and 1 g L−1 of yeast extract was selected as a useful stimulus to boost cell growth. Then, the heterotrophic cells were transferred to photoautotrophic conditions directly and cultured under varied concentrations of CO2. Moreover, 8 % (v/v) of CO2, high light and high initial cell density were found to be beneficial for cell growth and CO2 sequestration. Finally, different initial nitrogen concentrations and nitrogen feeding strategies were evaluated to increase the protein content to 62.69 % of dry biomass. These results provide feasible strategies for efficient CO2 sequestration and protein production jointly in C. pyrenoidosa.

Removal of arsenic from aqueous solution using magnetic biochar derived from Spirulina platensis

Arsenic contamination in surface waters and groundwater affects millions of people on a daily basis. Oxidation of As(III) to less toxic As(V) is a widely used strategy to enhance the removal of As from solution. This study developed and evaluated a Fe-modified biochar (FeSP600). Spirulina platensis (SP) is one of the most promising microalgae because of its physicochemical properties and potential applications. The high N content of SP may affect the physicochemical properties of the biochar, which could be used as an inherent N source for N doping biochar by carbonization. After Fe modification, the formed Fe species and N-containing components of SP were used to introduce pyridinic N, which can be coordinated with Fe to form Fe-N. We demonstrated that the formed Fe species (Fe0, Fe2+ and Fe3+) and the defective structures in FeSP600 could act as active sites for surface catalytic reactions. FeSP600 not only had magnetic properties but also could effectively remove As from an aqueous solution. These properties were attributed to the release of Fe2+ and the reactive oxygen species (ROSs) generated by the γ-Fe2O3 particles on the crystalline defect structure. As(III) and As(V) removal were affected by the initial pH values. The removal efficiencies for As(III) increased from 57.2 % to 94.9 % as the pH increased from 3 to 9, whereas that for As(V) decreased from 80.1 % to 46.8 %. The presence of coexisting ions either completely (PO43−) or partially (Cl−, CO32− and SO42−) inhibited As removal. The removal of As(V) depended on electrostatic interactions, but As(III) removal was a complex process, including both oxidation and surface adsorption, as the ROSs were able to oxidize As(III) to As(V). Our study demonstrates that FeSP600 has properties that are beneficial for the removal of As(III) and As(V) from aqueous environments. The findings of this study have potential for real-world application in treating As-contaminated water sources, particularly in improving drinking water purification systems in developing countries. More importantly, an assessment of the impact of FeSP600 usage on aquatic ecosystems is required to ensure the safe application of this technology. Therefore, developing methods for mass production of FeSP600 is essential for the commercialization of this technology, necessitating process engineering studies in this area.

Use of hydroponic fertilizers in growth media for Chlorella vulgaris for producing affordable protein in developing countries

ABSTRACT Chlorella vulgaris (Chlorophyta) stands out as a promising microalga for single-cell protein production, particularly due to its potential to address the need for affordable nutrition in less-developed regions. Given this context, the quest for more economic fertilization methods is essential. Among the viable alternatives, hydroponic fertilizer (HF) emerges as a widely available option, particularly in regions such as Indonesia. Typically, HF is supplied in two distinct forms, powdered Mix-A and Mix-B, to prepare the stock solutions. This study investigates the impact of varying concentrations and stock solution ratios on both the growth rate and biomass yield of C. vulgaris. Additionally, an economic analysis of cultivation activities is conducted, with a specific focus on comparing the feasibility of utilizing hydroponic fertilizer against conventional methods. The findings reveal that specific ratios and concentrations of the tested growth media outperform standard media in promoting the growth rate and biomass yield of cultivated C. vulgaris. Furthermore, the economic analysis assesses two primary cost components: fertilizer and energy. All tested hydroponic media offered a more cost-effective cultivation solution compared to conventional methods, primarily attributed to the lower cost of the hydroponic fertilizers.

Physiological response and carbon dioxide sequestration mechanisms during photosynthesis in Mychonastes rotundus

Carbon sequestration by microalgae is a simple and easy-to-operate process, without secondary pollution that has broad application prospects due to rapid growth, efficient photosynthesis, and high lipid content produced. In this study, the potential of Mychonastes rotundus for CO2 fixation, and its growth pattern, enzyme activity, lipid production, and cellular microstructure were investigated with changes in CO2 input. The results showed that when the inlet CO2 concentration was 20% (v/v), stable carbon sequestration ability was obtained after a 590 min reaction with an outlet CO2 concentration of 0.32%. The algal cellular structure was intact when the lowest contents of malondialdehyde and reactive oxygen species (ROS) were 7.08 and 17.79 nmol/mg, respectively, indicating the highest cell activity. In addition, 20% CO2 effectively promoted the synthesis of C18:2n6c and C20:0 in M. rotundus. When the inlet CO2 concentration was increased to 30%, the average pH dropped to 5.7, resulting in the death of M. rotundus. 1O2 was identified as the major ROS damaging microalgal cells during carbon sequestration. This study determined the optimal CO2 concentration for carbon capture by M. rotundus as a raw material for biodiesel production. The results indicate that M. rotundus is a promising microalgae for carbon fixation and CO2 capture of power plant flue gas and biodiesel production for low-cost bioenergy production.

A critical review on hydrothermal liquefaction screening using Microalgae as a two-way approach to sewage water treatment and biofuel production

<p>Hydrothermal liquefaction (HTL) is involved in concurrently treating both sewage water and generating biofuels. It involves the analysis of various operating parameters, such as pressure, catalyst temperature, and reaction time, to determine the productivity and physiochemical properties of the resulting bio-oil. The critical assessment of over 100 algal strains, compared on the basis of their growth kinetics in different wastewater environments and their HTL-based yields, identified Auxenochlorella pyrenoidosa and Microchaete spirulina strains as the most suitable ones for optimised municipal wastewater treatment. Additionally, other strains like Chlorella sorokiniana, Tetradesmus obliquus, and Desmodesmus abundance are found to be effective for heavy metal remediation in municipal wastewater due to their high biosorption capacities. Furthermore, certain microalgal strains, namely Auxenochlorella pyrenoidosa, Botryococcus braunii, Microchloropsis gaditana, and Microchaete spirulina, were described as promising microalgae in the production of high crude oil yields through the HTL technique. The current review highlights the integrated approach of sustainable and economical HTL techniques using the best microalgal strains as a technologically and environmentally feasible solution selected through a systematic protocol for sewage water treatment and biofuel production.</p>

Effects of aeration and centrifugation conditions on omega-3 fatty acid production by the mixotrophic dinoflagellate Gymnodinium smaydae in a semi-continuous cultivation system on a pilot scale

High production and efficient harvesting of microalgae containing high omega-3 levels are critical concerns for industrial use. Aeration can elevate production of some microalgae by providing CO2 and O2. However, it may lower the production of others by generating shear stress, causing severe cell damage. The mixotrophic dinoflagellate Gymnodinium smaydae is a new, promising microalga for omega-3 fatty acid production owing to its high docosahexaenoic acid content, and determining optimal conditions and methods for high omega-3 fatty acid production and efficient harvest using G. smaydae is crucial for its commercial utilization. Therefore, to determine whether continuous aeration is required, we measured densities of G. smaydae and the dinoflagellate prey Heterocapsa rotundata in a 100-L semi-continuous cultivation system under no aeration and continuous aeration conditions daily for 9 days. Furthermore, to determine the optimal conditions for harvesting through centrifugation, different rotational speeds of the continuous centrifuge and different flow rates of the pump injecting G. smaydae + H. rotundata cells into the centrifuge were tested. Under continuous aeration, G. smaydaeproduction gradually decreased; however, without aeration, the production remained stable. Harvesting efficiency and the dry weights of omega-3 fatty acids of G. smaydae + H. rotundata cells at a rotational speed of 16,000 rpm were significantly higher than those at 2,000–8,000 rpm. However, these parameters did not significantly differ at injection pump flow rates of 1.0–4.0 L min-1. The results of the present study provide a basis for optimized production and harvest conditions for G. smaydae and other microalgae.

Characterization of a uranium-tolerant green microalga of the genus Coelastrella with high potential for the remediation of metal-polluted waters

Uranium (U) contamination of terrestrial and aquatic ecosystems poses a significant threat to the environment and human health due to the chemotoxicity of this actinide. The characterization of organisms that tolerate and accumulate U is crucial to decipher the mechanisms evolved to cope with the radionuclide and to propose new effective strategies for the bioremediation of U-contaminated environments. Here, we isolated a unicellular green microalga of the genus Coelastrella from U-contaminated wastewater. We showed that Coelastrella sp. PCV is much more tolerant to U than Chlamydomonas reinhardtii and Chlorella vulgaris. Coelastrella sp. PCV is able to accumulate U very rapidly and then gradually release it into the medium, behaving as an excluder to limit the toxic effects of U. The ability of Coelastrella sp. PCV to accumulate U is remarkably high, with up to 240 mg of tightly bound U per g of dry biomass. Coelastrella sp. PCV is able to grow and maintain high photosynthesis in natural metal-contaminated waters from a wetland near a reclaimed U mine. In a single one-week growth cycle, Coelastrella sp. PCV is able to capture 25–55 % of the U from the contaminated waters and shows lipid droplet accumulation. Coelastrella sp. PCV is a very promising microalga for the remediation of polluted waters with valorization of algal biomass that accumulates lipids.

Continuous extraction and application potential of value-added products from a promising microalga Coelastrella sp. SDEC-28 for green microalgae-based industry

Microalgae are emerging as a good source of various high-value bio-active compounds and nowadays are applied in several fields. Here we proposed a new extraction method, continuous extraction, to attain crude polysaccharides (CP), methanol extracts (ME) and crude lipid (CL) of a newly isolated soil microalgae, Coelastrella sp. SDEC-28, which improved the yield (amount to 40.60%, by dry weight) and application potential of these products simultaneously. The CP (at 2 mg/mL) from SDEC-28 showed the better antioxidant activity with 96.17% scavenging rates on 2, 2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) free radical. ME extracted from continuous extraction displayed potent anti-proliferative effects on melanoma cancer cells A375, and the inhibition efficiency was up to 99.62% at high dose (1000 μg/mL) after 24 h exposure. The proportion of neutral lipid in CL obtained from continuous extraction was 1.38 times higher than that of one-step extraction. These results suggest that continuous extraction assists to fully utilize microalgal biomass and makes microalgae-based products industry more sustainable and greener for the future development.

Screening of microalgae strains for efficient biotransformation of small molecular organic acids from dark fermentation biohydrogen production wastewater

Dark fermentation biohydrogen production is a rapidly advancing and well-established field. However, the accumulation of volatile organic acid (VFAs) byproducts hinder its practical applications. Microalgae have demonstrated the ability to efficiently utilize VFAs while also treating waste gases and other nutrient elements. Integrating microalgae cultivation with dark fermentation is a promising approach. However, low VFAs tolerance and slow VFAs consumption restrict their application. To find suitable wastewater treatment microalgae, this work screened eight microalgae strains from five family. The results demonstrated that Chlamydomonas reinhardtii exhibited significant advantages in VFAs utilization, achieving a maximum removal of 100% for acetate and 52.5% for butyrate. Among the tested microalgae strains, CW15 outperformed in terms of photobioreactor adaptability, VFAs utilization, biomass productivity, and nutrient removal, making it the most promising microalgae for practical applications. This research demonstrates the feasibility of integrating microalgae cultivation with dark fermentation and providing a viable technical solution for integrated-biorefining.

Circular economy approaches for the production of high-value polysaccharides from microalgal biomass grown on industrial fish processing wastewater: A review

The discharge of high-strength wastewater from the fish-processing industries, comprising undefined blends of toxic and organic compounds, has always been a subject of great disquiet worldwide. Despite a large number of effluent treatment methodologies known to date, biosorption with the aid of naturally grown microalgae has been recognized recently to possess promising outcomes in eradicating pollutants comprising organic compounds from liquid effluents. Interestingly, the microalgal biomass harvested from phytoremediation of fish effluent was identified to be abundant in bio compounds that exhibited potential application in pharmaceutical, nutraceutical, and, aquaculture feed, generating a circular economy. In this context, the focus of the review is to emphasize the applications of microalgal species as naturally occurring and zero-cost adsorbents for the elimination of organic contaminants from fish liquid effluents. The summary of the literature encompassed in this work is supposed to benefit the readers to comprehend the primary mechanisms by which microalgae uptakes the organic matter from fish processing effluents and converts them into various biological molecules. From the scientific works assessed through this review, the most promising microalgae species regards to nutrient uptake and removal efficiency from fish effluent, were identified as Chlorella sp. >Spirulina sp. >Scenedesmus sp. The review further revealed supercritical fluid extraction as the robust extraction tool for the extraction of targeted bioproducts from microalgal biomass grown within fish effluents. Eventually, the information presented through this review establishes phytoremediation using microalgal biomass to be a natural cost-effective, sustainable circular bio-economy approach that could be robustly applied for the efficient treatment of wastewater discharged from food processing industries.

Salinity-Induced Physiochemical Alterations to Enhance Lipid Content in Oleaginous Microalgae Scenedesmus sp. BHU1 via Two-Stage Cultivation for Biodiesel Feedstock.

In the recent past, various microalgae have been considered a renewable energy source for biofuel production, and their amount and extent can be enhanced by applying certain types of stress including salinity. Although microalgae growing under salinity stress result in a higher lipid content, they simultaneously reduce in growth and biomass output. To resolve this issue, the physiochemical changes in microalgae Scenedesmus sp. BHU1 have been assessed through two-stage cultivation. In stage-I, the maximum carbohydrate and lipid contents (39.55 and 34.10%) were found at a 0.4 M NaCl concentration, while in stage-II, the maximum carbohydrate and lipid contents (42.16 and 38.10%) were obtained in the 8-day-old culture. However, under increased salinity, Scenedesmus sp. BHU1 exhibited a decrease in photosynthetic attributes, including Chl-a, Chl-b, Fv/Fm, Y(II), Y(NPQ), NPQ, qP, qL, qN, and ETRmax but increased Y(NO) and carotenoids content. Apart from physiological attributes, osmoprotectants, stress biomarkers, and nonenzymatic antioxidants were also studied to elucidate the role of reactive oxygen species (ROS) facilitated lipid synthesis. Furthermore, elemental and mineral ion analysis of microalgal biomass was performed to evaluate the biomass quality for biofuel and cell homeostasis. Based on fluorometry analysis, we found the maximum neutral lipids in the 8-day-old grown culture at stage-II in Scenedesmus sp. BHU1. Furthermore, the use of Fourier-transform infrared (FT-IR) and nuclear magnetic resonance (NMR) spectroscopy analyses confirmed the presence of higher levels of hydrocarbons and triacylglycerides (TAGs) composed of saturated fatty acids (SFAs) and monounsaturated fatty acids (MUFAs) in the 8-day-old culture. Therefore, Scenedesmus sp. BHU1 can be a promising microalga for potential biodiesel feedstock.

Beta-glucan production of Phaeodactylum tricornutum, Monodopsis subterranea and Cylindrotheca fusiformis during nitrogen depletion

Beta-glucans are polysaccharides that can be used for different applications, for example as an immunomodulator in food or feed or for managing high cholesterol levels. Certain microalgae species use beta-glucans as energy storage, accumulating them during nutrient depletion. In this study, we examined and compared beta-glucan production during nitrogen depletion in three different algae species, Phaeodactylum tricornutum, Monodopsis subterranea and Cylindrotheca fusiformis, grown in artificially illuminated flat panel airlift reactors, in order to determine the most promising microalgae species for beta-glucan production. Co-products such as fatty acids (especially eicosapentaenoic acid) and the carotenoid fucoxanthin (not produced by M. subterranea) were also considered. Biomass analysis showed that P. tricornutum cultures reached a maximal beta-glucan content of 317 ± 9 mg gDW−1, M. subterranea cultures reached 188 ± 6 mg gDW−1 and C. fusiformis cultures reached 129 ± 13 mg gDW−1. Furthermore, beta-glucan production was faster in P. tricornutum cultures. However, the maximum volumetric beta-glucan concentration reached was higher in M. subterranea cultures compared to P. tricornutum cultures as M. subterranea cultures produced more biomass during nitrogen depletion. In terms of possible co-products, P. tricornutum produced fucoxanthin and EPA, whereas M. subterranea did not produce fucoxanthin. However, M. subterranea exhibited a higher EPA content, which remained above 45 mg g−1 even after several days of nitrogen depletion. Overall, our results suggest that P. tricornutum and M. subterranea are both suitable species for beta-glucan production in flat panel airlift reactors.

Microalgae Oil-Based Metal Working Fluids for Sustainable Minimum Quantity Lubrication (MQL) Operations—A Perspective

This article presents a perspective on the potential use of microalgae oils in the production of metal working fluids (MWFs) used for minimum quantity lubrication (MQL) operations. The generalities of MQL operations and requirements of MWFs, and current advances in the development of the most promising microalgae oils with high contents of saturated, monounsaturated, and polyunsaturated fatty acids were reviewed and discussed. The analysis of data, discussions, and conclusions of numerous studies published recently and combined with the experience of the multidisciplinary team of authors strongly suggest that microalgae oils do indeed have great potential as sustainable and eco-friendly base oils for producing semi-synthetic MWFs, soluble oils and straight cutting fluids for MQL operations. Additionally, gaps and challenges focused on the use of agro-industry wastewater in microalgae production, green harvesting and oil extraction methods, and replacement of toxic additives in MWFs by green nanoparticles and biopolymers were identified and highlighted for achieving massive microalgae oil-based MWFs production and truly green machining processes.

Enhancing Urban Wastewater Treatment through Isolated Chlorella Strain-Based Phytoremediation in Centrate Stream: An Analysis of Algae Morpho-Physiology and Nutrients Removal Efficiency.

The release of inadequately treated urban wastewater is the main cause of environmental pollution of aquatic ecosystems. Among efficient and environmentally friendly technologies to improve the remediation process, those based on microalgae represent an attractive alternative due to the potential of microalgae to remove nitrogen (N) and phosphorus (P) from wastewaters. In this work, microalgae were isolated from the centrate stream of an urban wastewater treatment plant and a native Chlorella-like species was selected for studies on nutrient removal from centrate streams. Comparative experiments were set up using 100% centrate and BG11 synthetic medium, modified with the same N and P as the effluent. Since microalgal growth in 100% effluent was inhibited, cultivation of microalgae was performed by mixing tap-freshwater with centrate at increasing percentages (50%, 60%, 70%, and 80%). While algal biomass and nutrient removal was little affected by the differently diluted effluent, morpho-physiological parameters (FV/FM ratio, carotenoids, chloroplast ultrastructure) showed that cell stress increased with increasing amounts of centrate. However, the production of an algal biomass enriched in carotenoids and P, together with N and P abatement in the effluent, supports promising microalgae applications that combine centrate remediation with the production of compounds of biotechnological interest; for example, for organic agriculture.

Effect of specific irradiance on productivity and pigment and protein production of Porphyridium purpureum (Rhodophyta) semi-continuous culture

Porphyridium purpureum is a promising microalga species due to the content of various valuable compounds. In this study, specific irradiance parameter, representing the amount of light energy per unit of microalgae biomass, was introduced. The growth characteristics and pigments and protein accumulation of P. purpureum culture were investigated under semi-continuous mode. Varying dilution rate and surface irradiance resulted in a specific irradiance of 0.2–6.7 W g−1. Using mathematical modeling, we determined the patterns of changes in biomass, pigments, protein content and productivity of P. purpureum culture depending on specific irradiance. The content of target compounds was maximized under the lowest level of specific irradiance (0.2–1.2 W g−1), while the highest productivity of this components was reached under 1.2–1.7 W g−1. Overall, lower irradiance levels were favorable for P. purpureum cultivation based on the energy consumption and production characteristics of this species.

DISCOVR strain screening pipeline – Part III: Strain evaluation in outdoor raceway ponds

In our previous studies, as described in the corresponding Part I and II manuscripts in this Special issue, we selected 12 promising microalgae strains from 38 strains for high biomass productivity based on their salinity preferences, temperature profiles, and biomass growth under simulated outdoor conditions. The 12 strains include 6 cold season strains (Micractium reisseri NREL14-F2, Monoraphidium minutum 26B-AM, Monoraphidium sp. MONOR1, Chlorella vulgaris LRB-AZ-1201, Tetraselmis striata LANL1001, Phaeodactylum tricornutum UTEX646) and 6 warm seasons strains (Scenedesmus obliquus DOE0152.z, Scenedesmus obliquus UTEX393, Chlorella sorokiniana DOE1116, Picochlorum renovo NREL39-A8, Picochlorum celeri TG2-WT-CSM/EMRE, Porphyridium cruentum CCMP7765). Because the preceding screening efforts were completed in indoor systems, this study focuses on quantitatively assessing these strains in outdoor raceway ponds to further eliminate those perform poorly under outdoor conditions. The trials presented in this study, categorized as either cold or warm season experiments based on water temperature, were carried out between February and June in 2018, 2019 and 2020. For each season, a benchmark strain, M. minutum 26B-AM for the cold season and S. obliquus UTEX393 for the warm season, was grown side-by-side with the new strains to provide a baseline for comparing strains cultivated under different weather conditions. The results showed that the cold season benchmark, M. minutum 26B-AM, remained the most productive cold season strain, but two new strains, P. triconutum UTEX646 and T. striata LANL1001, demonstrated robust growth in the presence of weather changes and biological contaminants. For the warm season trials, P. celeri TG2-WT-CSM/EMRE and P. cruentum CCMP675 were 39 % and 11 % more productive than the benchmark with substantially improved culture stability. Biomass compositional analyses of the strains showed that the carbohydrate, lipid (measured as fatty acid methyl esters) and protein account for 5.2–20.6 %, 7.2–11.9 %, and 21.7–53 %, of the ash-free dry matter, respectively.

Amino acid profile and protein bioaccessibility of two Galdieria sulphuraria strains cultivated autotrophically and mixotrophically in pilot-scale photobioreactors

Galdieria sulphuraria is considered one of the most promising microalgae for food applications. In this study, we compared two strains of G. sulphuraria cultivated autotrophically and mixotrophically over 35 days in pilot-scale photobioreactors under nonsterile conditions. The low pH (<1.9) used for cultivation successfully prevented microbial contamination. The two strains had similar autotrophic and mixotrophic biomass productivities, the latter being 2.3 times higher than autotrophic productivity. Comparing the two strains, G. sulphuraria SAG 108.79 and ACUF 064 had 51% and 64% (w/w) protein and 4% and 9% (w/w) C-phycocyanin content, respectively. Interestingly, G. sulphuraria SAG 108.79 showed a protein bioaccessibility of 62%, in line with other microalgal species, whereas G. sulphuraria ACUF 064 had a protein bioaccessibility of only 14%. No differences in the amino acid profile were found between the two strains or between trophic modes. Stable and well-balanced protein profiles are encouraging results for future applications of this species. Industrial relevanceThe main focus of this study was the production of single-cell proteins using two strains of the polyextremophilic microalgae Galdieria sulphuraria. The acidic cultivation condition was sufficient to guarantee axenic production in not sterile conditions, even in the presence of glucose. Both strains were rich in proteins with a similar amino acid profile rich in all of the essential amino acids. Interestingly, there was a 4.4-fold difference in protein bioaccessibility between the two strains. Simple production of axenic microalgal biomass rich in protein is an encouraging result for future food applications of this species.

Flashing lights affect the photophysiology and expression of carotenoid and lipid synthesis genes in Nannochloropsis gaditana

Nannochloropsis gaditana is a promising microalga for biotechnology. One of the strategies to stimulate its full potential in metabolite production is exposure to flashing lights. Here, we report how N. gaditana adapts to different flashing light regimes (5, 50, and 500 Hz) by changing its cellular physiology and the relative expression of genes related to critical cellular functions. We analyzed the differential mRNA abundance of genes related to photosynthesis, nitrogen assimilation and biosynthesis of chlorophyll, carotenoids, lipids, fatty acids and starch. Analysis of photosynthetic efficiency and high mRNA abundance of photoprotection genes supported the inference that excess excitation energy provided by light absorbance during photosynthesis was produced under low frequency flashing lights and was dissipated by photopigments via the xanthophyll-cycle. Increased relative expression levels of genes related to the synthesis of carotenoids and chlorophyll confirmed the accumulation of photopigments previously observed at low frequency flashing lights. Higher differential mRNA abundance of genes related to the triacylglycerol biosynthesis were observed at lower frequency flashing lights, possibly triggered by a poor nitrogen assimilation caused by low mRNA abundance of a nitrate reductase gene. This study advances a new understanding of algal physiology and metabolism leading to improved cellular performance and metabolite production.

Approach to microalgal biodiesel production: Insight review on recent advancements and future outlook

AbstractThe environmental concerns about fossil energy and rising oil prices are regular global phenomena. In such an exigency where fossil fuel sources are dwindling, carbon‐neutral biodiesel derived from microalgae lipid seems to be an important renewable energy resource. In recent years, microalgae have become a lucrative feedstock for economically viability of commercial‐scale biofuel production owing to its high biomass growth and high oil yield compared with other crops. The screening and selection of promising microalgae strain should be based on their fatty acid profile and culture conditions. The laboratory to pilot scale culture of microalgae species requires systematic experimental designs to maximize microalgal growth using open or raceway ponds, closed photo bioreactors and hybrid systems. The pros and cons of each harvesting technique, including filtration, centrifugation, sedimentation and flocculation as well cell disruption by thermal, mechanical, chemical and biological techniques, are deliberated in details. Furthermore, the application of homogeneous, heterogeneous and enzyme catalysts in transesterification processes as well as purification technologies are emphasized to ensure high‐quality biodiesel production as per ASTM norms. Microalgae comprise a potential feedstock and biodiesel synthesis from them requires a series of complex up‐streaming and down‐stream processes which are inherently disadvantageous in technology transfer from laboratory to industrial scale. This review paper is mainly focused on microalgal cultivation, harvesting, oil extraction, biodiesel production and purification technologies, and each vital process is critically reviewed in each step. © 2022 Society of Chemical Industry and John Wiley &amp; Sons, Ltd.