Production of Fatty Acids and Protein by Nannochloropsis in Flat-Plate Photobioreactors

Leveraging microalgae as a sustainable ingredient for meat analogues

As the world's population and income levels continue to rise, there is a substantial increase in the demand for meat, which poses significant environmental challenges due to large-scale livestock production. This review explores the potential of microalgae as a sustainable protein source for meat analogues. The nutritional composition, functional properties, and environmental advantages of microalgae are analyzed. Additionally, current obstacles to large-scale microalgal food production are addressed, such as strain development, contamination risks, water usage, and downstream processing. The challenges associated with creating meat-like textures and flavors using techniques like extrusion and emulsion formation with microalgae are also examined. Lastly, considerations related to consumer acceptance, marketing, and regulation are summarized. By focusing on improvements in cultivation, structure, sensory attributes, and affordability, microalgae demonstrate promise as a transformative and eco-friendly protein source to enhance the next generation of meat alternatives.

Effects of nitrogen starvation on growth and biochemical composition of some microalgae species

Nitrogen is one of the most important nutrient sources for the growth of microalgae. We studied the effects of nitrogen starvation on the growth responses, biochemical composition, and fatty acid profile of Dunaliella tertiolecta, Phaeodactylum tricornutum, and Nannochloropsis oculata. The lack of nitrogen caused changes in carbohydrate, protein, lipid, and fatty acid composition in all examined microalgae. The carbohydrate content increased 59% in D. tertiolecta, while the lipid level increased 139% in P. tricornutum under nitrogen stress conditions compared to the control groups. Nitrogen starvation increased the oligosaccharide and polysaccharide contents of D. tertiolecta 4.1-fold and 3.6-fold, respectively. Furthermore, triacylglycerol (TAG) levels in N. oculata and P. tricornutum increased 2.3-fold and 7.4-fold, respectively. The dramatic increase in the amount of TAG is important for the use of these microalgae as raw materials in biodiesel. Nitrogen starvation increased the amounts of oligosaccharides and polysaccharides of D. tertiolecta, while increased eicosapentaenoic acid (EPA) in N. oculata and docosahexaenoic acid (DHA) content in P. tricornutum. The amount of polyunsaturated fatty acids (PUFAs), EPA, DHA, oligosaccharides, and polysaccharides in microalgal species can be increased without using the too costly nitrogen source in the culture conditions, which can reduce the most costly of living feeding.

Characterization of Selected Microalgae Species as Potential Sources of Nutrients and Antioxidants

Microalgae are exceptional organisms from a nutritional perspective, boasting an array of bioactive compounds that have long justified their incorporation into human diets. In this study, we explored the potential of five microalgae species: Nannochloropsis sp., Tetraselmis chuii, Chaetoceros muelleri, Thalassiosira weissflogii, and Tisochrysis lutea. We conducted comprehensive analyses of their nutritional profiles, encompassing protein content, individual amino acid composition, mineral and trace element levels, fatty acid profiles (including saturated fatty acids (SFAs), monounsaturated fatty acids (MUFAs), and polyunsaturated fatty acids (PUFAs)), polyphenol compositions, and vitamin B content. The antioxidant activity of the ethanolic extracts was evaluated using two methods: ABTS and DPPH radical scavenging assay. The total protein content of the microalgae ranged from 34.09 ± 0.39% to 42.45 ± 0.18%, with the highest concentration observed in T. weissflogii. Essential amino acids such as histidine, threonine, lysine, valine, isoleucine, leucine, phenylalanine, and methionine were present in concentrations ranging from 0.53 ± 0.02 to 12.55 ± 2.21 g/16 g N. Glutamic acid emerged as the most abundant amino acid, with concentrations ranging from 6.73 ± 0.82 to 12.55 ± 2.21 g/16 g N. Among the microalgae species, T. chuii exhibited the highest concentrations of calcium (Ca) and manganese (Mn), while C. muelleri showed prominence in magnesium (Mg), sodium (Na), and iron (Fe). T. weissflogii stood out for its potassium (K) content, and T. lutea contained notable amounts of copper (Cu), zinc (Zn), and lead (Pb). Regarding fatty acid profiles, Nannochloropsis sp. and T. chuii were predominantly composed of SFA, while C. muelleri and T. weissflogii were rich in MUFA. PUFAs dominated the fatty acid profile of T. lutea, which also exhibited the most diverse range of polyphenolic substances. We also analyzed the B vitamin content, with T. lutea displaying the highest concentrations of niacin (B3) and riboflavin (B2). Antioxidant activity was confirmed for all microalgae tested using DPPH and ABTS radical IC50 (mg/mL) converted to Trolox equivalent (TEAC). These findings underscore the substantial potential of the examined microalgae species as sources of biologically valuable substances characterized by rapid growth and relatively undemanding cultivation conditions.

Freshwater microalgae Nannochloropsis limnetica for the production of β-galactosidase from whey powder

This study investigated the first-ever reported use of freshwater Nannochloropsis for the bioremediation of dairy processing side streams and co-generation of valuable products, such as β-galactosidase enzyme. In this study, N. limnetica was found to grow rapidly on both autoclaved and non-autoclaved whey-powder media (referred to dairy processing by-product or DPBP) without the need of salinity adjustment or nutrient additions, achieving a biomass concentration of 1.05-1.36 g L-1 after 8 days. The species secreted extracellular β-galactosidase (up to 40.84 ± 0.23 U L-1) in order to hydrolyse lactose in DPBP media into monosaccharides prior to absorption into biomass, demonstrating a mixotrophic pathway for lactose assimilation. The species was highly effective as a bioremediation agent, being able to remove > 80% of total nitrogen and phosphate in the DPBP medium within two days across all cultures. Population analysis using flow cytometry and multi-channel/multi-staining methods revealed that the culture grown on non-autoclaved medium contained a high initial bacterial load, comprising both contaminating bacteria in the medium and phycosphere bacteria associated with the microalgae. In both autoclaved and non-autoclaved DPBP media, Nannochloropsis cells were able to establish a stable microalgae-bacteria interaction, suppressing bacterial takeover and emerging as dominant population (53-80% of total cells) in the cultures. The extent of microalgal dominance, however, was less prominent in the non-autoclaved media. High initial bacterial loads in these cultures had mixed effects on microalgal performance, promoting β-galactosidase synthesis on the one hand while competing for nutrients and retarding microalgal growth on the other. These results alluded to the need of effective pre-treatment step to manage bacterial population in microalgal cultures on DPBP. Overall, N. limnetica cultures displayed competitive β-galactosidase productivity and propensity for efficient nutrient removal on DPBP medium, demonstrating their promising nature for use in the valorisation of dairy side streams.

Nutritional and immunological evaluation of Nannochloropsis oculata as a potential Nile tilapia-aquafeed supplement

Nannochloropsis oculata (N. oculata) is a marine microalga containing bioactive compounds and a high omega-3 polyunsaturated fatty acid (ω-3 PUFAs). Therefore, it is very promising for nutraceutical and the functional food industry applications. Three groups of Nile tilapia (forty-five fish/group) were fed on basal diets or diets containing 5% (N5) or 10% (N10) of the microalga N. oculata for seven weeks. Fish growth performance, proximate composition, and lipid (fatty acids/ FAs and lipoproteins) profile were estimated. In addition, the expression pattern of some lipid metabolism and immune-relevant genes were assessed. An enhancement in whole body crude protein and growth indices of Nile tilapia was observed on both the supplemented groups N5 and N10. Higher levels of high-density lipoproteins (HDL); and lower levels of the low-density lipoproteins (LDL) were evident in both supplemented groups, while the cholesterol and triglycerides (TG) levels were similar among groups. Ω-3 PUFAs were the significant FAs profile of tilapia fed on N. oculata-supplemented diets in terms of eicosapentaenoic acid, docosahexaenoic acid, and n3/n6 ratio. Concerning the gene expression pattern, heat-shock protein70, glutathione-S-transferase, glutathione peroxidase, and interleukin-1β (IL-1β) were elevated significantly in both supplemented groups. IL-10 is only upregulated in the N10 group. The lipid metabolism-related gene expression showed downregulation of only fatty acid synthase (FAS) in both supplemented groups, with no statistical changes in Peroxisome proliferator-activated receptor alpha (PPARα). Tumor necrosis factor-α (TNF-α), Transforming growth factor-β1 (TGF-β1), and the apoptotic related genes [caspase3 and Proliferating cell nuclear antigen (PCNA)] showed insignificant changes among groups. The histopathological examination of the intestine, liver, and spleen supports our findings and confirms the benefits and safeness of N. oculata dietary inclusion. Collectively, N. oculata is a very promising nutraceutical for improving fish health and sustainability of aquaculture production.

Simultaneous photoautotrophic production of DHA and EPA by Tisochrysis lutea and Microchloropsis salina in co-culture

Marine microalgae have received much attention as a sustainable source of the two health beneficial omega-3-fatty acids docosahexaenoic acid (DHA, C22:6) and eicosapentaenoic acid (EPA, C20:5). However, photoautotrophic monocultures of microalgae can only produce either DHA or EPA enriched biomass. An alternative may be the photoautotrophic co-cultivation of Tisochrysis lutea as DHA-producer with Microchloropsis salina for simultaneous EPA production to obtain EPA- and DHA-rich microalgae biomass in a nutritionally balanced ratio. Photoautotrophic co-cultivation processes of T. lutea and M. salina were studied, applying scalable and fully controlled lab-scale gas-lift flat-plate photobioreactors with LED illumination for dynamic climate simulation of a repeated sunny summer day in Australia [day-night cycles of incident light (PAR) and temperature]. Monocultures of both marine microalgae were used as reference batch processes. Differences in the autofluorescence of both microalgae enabled the individual measurement, of cell distributions in co-culture, by flow cytometry. The co-cultivation of T. lutea and M. salina in artificial sea water with an inoculation ratio of 1:3 resulted in a balanced biomass production of both microalgae simultaneously with a DHA:EPA ratio of almost 1:1 (26 mgDHA gCDW-1, and 23 mgEPA gCDW-1, respectively) at harvest after depletion of the initially added fertilizer. Surprisingly, more microalgae biomass was produced within 8 days in co-cultivation with an increase in the cell dry weight (CDW) concentration by 31%, compared to the monocultures with the same amount of light and fertilizer. What is more, DHA-content of the microalgae biomass was enhanced by 33% in the co-culture, whereas EPA-content remained unchanged compared to the monocultures.

New Angled Twin-layer Porous Substrate Photobioreactors for Cultivation of Nannochloropsis oculata

An angled twin-layer porous substrate photobioreactor (TL-PSBR) using LED light was designed to cultivate Nannochloropsis oculata. Flocculation and sedimentation by modification of pH to 11 were determined as the optimal method for harvesting the N. oculata inoculum. The following optimised parameters were found: tilt angle 15°, Kraft 220 g m^-2 paper as substrate material, initial inoculum density of 12.5 g m^-2, 140 µmol photons m^-2 s^-1 light intensity, and a light/dark cycle of 6:6 (h). Test cultivation for 14 days was performed under optimised conditions. The total dried biomass standing crop was 75.5 g m^-2 growth area with an average productivity of 6.3 g m^-2 d^-1, the productivity per volume of used culture medium was 126.2 mg/L d^-1, total lipid content 21.9% (w/w), and the highest productivity of total lipids was 1.33 g m^-2 d^-1. The dry algal biomass contained 3% eicosapentaenoic acid (w/w), 3.7% palmitoleic acid (w/w), and 513 mg kg^-1 vitamin E. The optimisation of N. oculata cultivation on an angled TL-PSBR system yielded promising results, and applications for commercial products need to be further explored.

Mixotrophy in a Local Strain of Nannochloropsis granulata for Renewable High-Value Biomass Production on the West Coast of Sweden

A local strain of Nannochloropsis granulata (Ng) has been reported as the most productive microalgal strain in terms of both biomass yield and lipid content when cultivated in photobioreactors that simulate the light and temperature conditions during the summer on the west coast of Sweden. To further increase the biomass and the biotechnological potential of this strain in these conditions, mixotrophic growth (i.e., the simultaneous use of photosynthesis and respiration) with glycerol as an external carbon source was investigated in this study and compared with phototrophic growth that made use of air enriched with 1-2% CO₂. The addition of either glycerol or CO₂-enriched air stimulated the growth of Ng and theproduction of high-value long-chain polyunsaturated fatty acids (EPA) as well as the carotenoid canthaxanthin. Bioassays in human prostate cell lines indicated the highest antitumoral activity for Ng extracts and fractions from mixotrophic conditions. Metabolomics detected betaine lipids specifically in the bioactive fractions, suggesting their involvement in the observed antitumoral effect. Genes related to autophagy were found to be upregulated by the most bioactive fraction, suggesting a possible therapeutic target against prostate cancer progression. Taken together, our results suggest that the local Ng strain can be cultivated mixotrophically in summer conditions on the west coast of Sweden for the production of high-value biomass containing antiproliferative compounds, carotenoids, and EPA.

Microalgal Biomass as Feedstock for Bacterial Production of PHA: Advances and Future Prospects

The search for biodegradable plastics has become the focus in combating the global plastic pollution crisis. Polyhydroxyalkanoates (PHAs) are renewable substitutes to petroleum-based plastics with the ability to completely mineralize in soil, compost, and marine environments. The preferred choice of PHA synthesis is from bacteria or archaea. However, microbial production of PHAs faces a major drawback due to high production costs attributed to the high price of organic substrates as compared to synthetic plastics. As such, microalgal biomass presents a low-cost solution as feedstock for PHA synthesis. Photoautotrophic microalgae are ubiquitous in our ecosystem and thrive from utilizing easily accessible light, carbon dioxide and inorganic nutrients. Biomass production from microalgae offers advantages that include high yields, effective carbon dioxide capture, efficient treatment of effluents and the usage of infertile land. Nevertheless, the success of large-scale PHA synthesis using microalgal biomass faces constraints that encompass the entire flow of the microalgal biomass production, i.e., from molecular aspects of the microalgae to cultivation conditions to harvesting and drying microalgal biomass along with the conversion of the biomass into PHA. This review discusses approaches such as optimization of growth conditions, improvement of the microalgal biomass manufacturing technologies as well as the genetic engineering of both microalgae and PHA-producing bacteria with the purpose of refining PHA production from microalgal biomass.

Nannochloropsis sp. Biorefinery: Recovery of Soluble Protein by Membrane Ultrafiltration/Diafiltration

This work proposes a way to maximize the potential of a Nannochloropsis sp. biorefinery process, through membrane technology, producing an extract enriched in soluble proteins, free from the insoluble protein fraction, with a low lipid content and eliminating the colored chlorophyll-a. This procedure, following the principles of a circular economy approach, allows for the valorization of a stream from the biorefining of Nannochloropsis sp. that, otherwise, would be considered a residue without commercial value. The process proposed minimizes fouling phenomena at the membrane surface, making it possible to achieve high permeate fluxes, thus reducing the need for membrane cleaning and, therefore, contributing to an extended membrane lifetime. Supernatant obtained after centrifugation of a suspension of ruptured Nannochloropsis sp. cells was processed by ultrafiltration using a membrane with a cut-off of 100 kDa MWCO. Two different operating approaches were evaluated—controlled transmembrane pressure and controlled permeate flux—under concentration and diafiltration modes. Ultrafiltration operated in a diafiltration mode, under controlled permeate flux conditions, led to the highest soluble protein recovery (78%) with the highest constant permeate flux (12 L·m⁻²·h⁻¹) and low membrane fouling.

Sustainable production of EPA-rich oil from microalgae: Towards an algal biorefinery

Utilization of sustainable natural resources such as microalgae has been considered for the production of biofuels, aquaculture feed, high-value bioactives such as omega-3 fatty acids, carotenoids, etc. Eicosapentaenoic acid (EPA) is an omega-3 fatty acid present in fish oil, which is of physiological importance to both humans and fishes. Marine microalgae are sustainable sources of lipid rich in EPA and different species have been explored for the production of EPA as a single product. There has been a rising interest in the concept of a multi-product biorefinery, focusing on maximum valorization of the algal biomass. Targeting one or more value-added compounds in a biorefinery scenario can improve the commercial viability of low-value products like triglycerides for biofuel. This approach has been viewed by technologists and experts as a sustainable and economically feasible possibility for the large-scale production of microalgae for its potential applications in biodiesel and jet fuel production, nutraceuticals, animal and aquaculture feeds, etc. In this review paper, we describe the recent developments in the production of high-value EPA-rich oil from microalgae, emphasizing on the upstream and downstream bioprocess techniques, and the advantages of considering an EPA-rich oil based biorefinery.

Nutraceutical productions from microalgal derived compounds via circular bioeconomy perspective

Circular bioeconomy has become a sustainable business model for commercial production that promises to reuse, recycle & recover while considering less environmental footprints in nutraceutical industries. Microalgae biotechnology has the synergy to bioremediate waste stream while generating high-value-added compounds such as astaxanthin, protein and polyunsaturated fatty acids that are potential compounds used in various industries, thus, the integration of this approach provides economic advantages. However, since the industrial production of these compounds is costly and affected byunstable climate in the Nordic regions such as low temperature, light intensity, and polar circle, the focus of biosynthesis has shifted from less tolerant commercial strains towards indigenous strains. Nutraceutical productions such as polyunsaturated fatty acids and protein can now be synthesized at low temperatures which significantly improve the industry's economy. In this review, the above-mentioned compounds with potential strains were discussed based on a Nordic region's perspective.

The effect of cell disruption on the extraction of oil and protein from concentrated microalgae slurries

Novel cell-disruption combinations (autolytic incubation and hypotonic osmotic shock combined with HPH or pH12) were used to investigate the fundamental mass transfer of lipids and proteins from Nannochloropsis slurries (140 mg biomass/g slurry). Since neutral lipids exist as cytosolic globules, their mass transfer was directly dependent on disintegration of cell walls. Complete recovery was obtained with complete physical disruption. HPH combinations exerted more physical disruption and led to higher yields than pH12. In contrast, proteins exist as both cytosolic water-soluble fractions and cell-wall/membrane structural fractions and have a complex extraction behaviour. Mass transfer of cytosolic proteins was dependent on cell-wall disintegration, while that of structural proteins was governed by cell-wall disintegration and severance of protein linkage from the wall/membrane. HPH combinations exerted only physical disruption and were limited to releasing soluble proteins. pH12 combinations hydrolysed chemical linkages in addition to exerting physical disruption, releasing both soluble and structural proteins.

Molecular analysis of sugar transporters and glycolysis pathways in Ettlia sp. under heterotrophy using fructose and glucose

Fructophilic behavior in microalgae is a rare trait that could benefit biorefineries by enabling substitution of carbon source with fructose, and our previous study identified that Ettlia sp. prefers fructose relative to glucose. In this study, by analyzing the transcription levels of genes related to sugar transport and the glycolysis pathway, the fructose utilization of Ettlia sp. was investigated. In a fructose-containing medium, the expression levels of fructokinase (EttFRK3) and glucokinase (EttGCK1 and EttGCK2) genes were significantly upregulated in heterotrophic cultivation of Ettlia sp. under fructose supplementation conditions. Further, a sugar transporter (EttSTF11) was significantly upregulated by 3.2-fold in 1 day, and this increase was analogous to the specific growth rate exhibited by the species. Subsequent cultivation tests with multi-sugar sources also showed a significant upregulation of EttSTF11 relative to other treatments without fructose. A phylogenetic tree derived from the analysis of different transporters of interest identified that EttSTF11 was adjacent to reference fructose transporters with a high bootstrap value of 71. Given that the transmembrane domains of EttSTF11 were analogous to those of reference fructose transporter genes, EttSTF11 appeared to play a critical role in fructose consumption and metabolism in Ettlia sp.

Fucoxanthin and docosahexaenoic acid production by cold-adapted Tisochrysis lutea

Tisochrysis lutea is an important microalgal species for fucoxanthin and docosahexaenoic acid (DHA) production with an optimum cultivation temperature of approximately 30 °C. The aim of the present work was to develop a winter strain with high productivity at 15 °C. The response of the original strain to a decrease in temperature from 30 °C to 15 °C was investigated in continuous turbidostat experiments. This was followed by adaptation for >180 days at 15 °C and 2 rounds of sorting for cells with high chlorophyll fluorescence (top 5%) using fluorescence-activated cell sorting (FACS). For the original strain the productivity of biomass, fucoxanthin, and DHA decreased by 92 %, 98 % and 85 % respectively when decreasing the temperature from 30 °C to 15 °C. In the sorted cold-adapted 'winter strain', biomass, fucoxanthin, and DHA productivities were similar to those at 30 °C. In addition, the fucoxanthin concentration increased from 1.11 to 4.24 mg g^-1 dry weight and the polar lipid fraction in total fatty acids increased from 21 % to 55 %. The winter strain showed a robust and stable phenotype after one year of cultivation, expanding the outdoor fucoxanthin and lipid production seasons for this species.

In situ monitoring of chlorophyll a fluorescence in Nannochloropsis oceanica cultures to assess photochemical changes and the onset of lipid accumulation during nitrogen deprivation

In situ chlorophyll a fluorescence measurements were applied to monitor changes in the photochemical variables of Nannochloropsis oceanica cultures under nitrogen-deplete and nitrogen-replete (control) conditions. In addition, growth, lipid, fatty acid, and pigment contents were also followed. In the control culture, growth was promoted along with pigment content, electron transport rate (ETR), and polyunsaturated fatty acids, while total lipid content and fatty acid saturation level diminished. Under nitrogen-deplete conditions, the culture showed a higher de-epoxidation state of the xanthophyll cycle pigments. Fast transients revealed a poor processing efficiency for electron transfer beyond Q_A , which was in line with the low ETR due to nitrogen depletion. Lipid content and the de-epoxidation state were the first biochemical variables triggered by the change in nutrient status, which coincided with a 20% drop in the in situ effective quantum yield of PSII (ΔF'/F_m '), and a raise in the V_j measurements. A good correlation was found between the changes in ΔF'/F_m ' and lipid content (r = -0.96, p < 0.01). The results confirm the reliability and applicability of in situ fluorescence measurements to monitor lipid induction in N. oceanica.

A Newly Designed Automatically Controlled, Sterilizable Flat Panel Photobioreactor for Axenic Algae Culture

In context of the global climate change, microalgae processes are gaining momentum as a biotechnological tool for direct fixation and valorization of greenhouse gases. Algae have the metabolic capacity to photosynthetically convert CO₂ into high value products, such as food additives, under economic boundary conditions. High cost, commercial flat panel gas-lift bioreactors for microalgae cultivation at laboratory scale provide either small volumes or no sterile operation, which limits academic research. This brief report presents initial data for a new type of sterile operating flat panel gas-lift bioreactor with a unique asymmetrical U-shape. It utilizes automatable process control technologies that adhere to industrial standards to enhance data reproducibility and aid industrial scale up. The practicability was demonstrated using a Chlorella sorokiniana cultivation, which showed the typical growth behavior. Due to the sophisticated implemented control engineering technology, pivotal parameters as pH and temperature can be determined within a range of ±0.1 units, which was confirmed experimentally. The new flat panel gas-lift photobioreactor presented in this brief report fills the technology gap at laboratory scale with an autoclavable volume of 7.2 L. Moreover, it is easy to rebuild by means of the hereby provided blueprint, while exhibiting a six-fold cost reduction compared to commercially available flat panel photobioreactors.

Organic Matter Type Defines the Composition of Active Microbial Communities Originating From Anoxic Baltic Sea Sediments

Carbon cycling in anoxic marine sediments is dependent on uncultured microbial communities. Niches of heterotrophic microorganisms are defined by organic matter (OM) type and the different phases in OM degradation. We investigated how OM type defines microbial communities originating from organic-rich, anoxic sediments from the Baltic Sea. We compared changes in the sediment microbial community, after incubation with different stable isotope labeled OM types [i.e., particulate algal organic matter (PAOM), protein, and acetate], by using DNA stable isotope probing (DNA-SIP). Incorporation of 13C and/or 15N label was predominantly detected in members of the phyla Planctomycetes and Chloroflexi, which also formed the majority (>50%) of the original sediment community. While these phylum-level lineages incorporated label from all OM types, phylogenetic analyses revealed a niche separation at the order level. Members of the MSBL9 (Planctomycetes), the Anaerolineales (Chloroflexi), and the class Bathyarchaeota, were identified as initial degraders of carbohydrate-rich OM, while other uncultured orders, like the CCM11a and Phycisphaerales (Planctomycetes), Dehalococcoidia, and JG30-KF-CM66 (Chloroflexi), incorporated label also from protein and acetate. Our study highlights the importance of initial fermentation of complex carbon pools in shaping anoxic sediment microbial communities and reveals niche specialization at the order level for the most important initial degraders in anoxic sediments.

Improved fucoxanthin and docosahexaenoic acid productivities of a sorted self-settling Tisochrysis lutea phenotype at pilot scale

This work aimed to select a Tisochrysis lutea phenotype with higher biomass and fucoxanthin productivities using fluorescence-activated cell sorting (FACS). A novel phenotype was obtained after 2 rounds of selection, based on high-fucoxanthin fluorescence. The resulting phenotype forms cell aggregates, has no flagella, and was stable after 15 months. Optimal temperature (30 °C) and light (300 µmol m^-2 s^-1) were obtained at laboratory scale, identical to the original strain. The biomass productivity was higher than the original strain: 1.9× at laboratory scale (0.4 L), and 4.5× under outdoor conditions (190 L). Moreover, compared to the original strain, the productivity of fucoxanthin increased 1.6-3.1× and docosahexaenoic acid 1.5-1.9×. These are the highest ever reported outdoor productivities, obtained with a robust new phenotype from a T. lutea monoculture isolated with FACS without genetic manipulation. The resulting phenotype shows high potential for industrial production.

Light spectra as triggers for sorting improved strains of Tisochrysis lutea

It is known that microalgae respond to different light colors, but not at single-cell level. This work aimed to assess if different light colors could be used as triggers to sort over-producing cells. Six light spectra were used: red + green + blue (RGBL), blue (BL), red (RL), green (GL), blue + red (BRL) and blue + green (BGL). Fluorescence-activated cell sorting method was used to analyse single-cell fluorescence and sort cells. BGL and RGBL lead to the highest fucoxanthin production, while RL showed the lowest. Therefore, it was hypothesized that hyper-producing cells can be isolated efficiently under the adverse condition (RL). After exposure to all light colors for 14 days, the top 1% fucoxanthin producing cells were sorted. A sorted strain from RL showed higher (16-19%) growth rate and fucoxanthin productivity. This study showed how light spectra affected single-cell fucoxanthin and lipid contents and productivities. Also, it supplied an approach to sort for high-fucoxanthin or high-lipid cells.

Nannochloropsis spp. as Feed Additive for the Pacific White Shrimp: Effect on Midgut Microbiology, Thermal Shock Resistance and Immunology

This work aimed to evaluate Nannochloropsis spp. as feed additive in the diet of Pacific white shrimp for their effect on midgut microbiology, thermal shock resistance and immunological parameters. Initially, the digestibility of the microalgae meal was assessed, and the apparent digestibility coefficient (ADC) was determined. The ADC was, in general, high in lipids (78.88%) and eicosapentaenoic fatty acid (73.86%). Then, Nannochloropsis spp. were included in diets at four levels (0, 0.5, 1 and 2% inclusion). The shrimp were reared in 500 L clear water tanks containing 20 shrimp per tank with an initial weight of 6.05 ± 0.06 g and fed four times a day. Shrimp fed with supplemented diets containing Nannochloropsis spp. (0.5 and 2%) presented higher resistance to thermal shock when compared to the non-supplemented group (control). Shrimp fed with 1 and 2% of algae inclusion had a higher production of reactive oxygen species (ROS) when compared to other treatments. No statistical difference was observed in the immunological parameters and microbiology of the intestinal tract. Thus, the inclusion of Nannochloropsis spp. in shrimp diets at 0.5 and 2% levels increases resistance to thermal shock and ROS production in shrimp.

Temperature-Dependent Lipid Accumulation in the Polar Marine Microalga Chlamydomonas malina RCC2488

The exploration of cold-adapted microalgae offers a wide range of biotechnological applications that can be used for human, animal, and environmental benefits in colder climates. Previously, when the polar marine microalga Chlamydomonas malina RCC2488 was cultivated under both nitrogen replete and depleted conditions at 8°C, it accumulated lipids and carbohydrates (up to 32 and 49%, respectively), while protein synthesis decreased (up to 15%). We hypothesized that the cultivation temperature had a more significant impact on lipid accumulation than the nitrogen availability in C. malina. Lipid accumulation was tested at three different temperatures, 4, 8, and 15°C, under nitrogen replete and depleted conditions. At 4°C under the nitrogen replete condition C. malina had the maximal biomass productivity (701.6 mg L-1 day-1). At this condition, protein content was higher than lipids and carbohydrates. The lipid fraction was mainly composed of polyunsaturated fatty acids (PUFA) in the polar lipid portion, achieving the highest PUFA productivity (122.5 mg L-1 day-1). At this temperature, under nitrogen deficiency, the accumulation of carbohydrates and neutral lipids was stimulated. At 8 and 15°C, under both nitrogen replete and depleted conditions, the lipid and carbohydrate content were higher than at 4°C, and the nitrogen stress condition did not affect the algal biochemical composition. These results suggest that C. malina is a polar marine microalga with a favorable growth temperature at 4°C and is stressed at temperatures ≥8°C, which directs the metabolism to the synthesis of lipids and carbohydrates. Nevertheless, C. malina RCC2488 is a microalga suitable for PUFA production at low temperatures with biomass productivities comparable with mesophilic strains.

Flashing light emitting diodes (LEDs) induce proteins, polyunsaturated fatty acids and pigments in three microalgae

As the periodic emission of light pulses by light emitting diodes (LEDs) is known to stimulate growth or induce high value biocompounds in microalgae, this flashing light regime was tested on growth and biochemical composition of the microalgae Nannochloropsis gaditana, Koliella antarctica and Tetraselmis chui. At low flashing light frequencies (e.g., 5 and 50 Hz, Duty cycle = 0.05), a strain-dependent growth inhibition and an accumulation of protein, polyunsaturated fatty acids, chlorophyll or carotenoids (lutein, β-carotene, violaxanthin and neoxanthin) was observed. In addition, a 4-day application of low-frequency flashing light to concentrated cultures increased productivities of eicosapentaenoic acid (EPA) and specific carotenoids up to three-fold compared to continuous or high frequency flashing light (500 Hz, Duty cycle = 0.05). Therefore, applying low-frequency flashing light as finishing step in industrial production can increase protein, polyunsaturated fatty acids or pigment contents in biomass, leading to high-value algal products.

Growth-promoting bacteria double eicosapentaenoic acid yield in microalgae

High-yielding microalgae present an important commodity to sustainably satisfy burgeoning food, feed and biofuel demands. Because algae-associated bacteria can significantly enhance or reduce yields, we isolated, identified and selected highly-effective "probiotic" bacterial strains associated with Nannochloropsis oceanica, a high-yielding microalga rich in eicosapentaenoic acid (EPA). Xenic algae growth was significantly enhanced by co-cultivation with ten isolated bacteria that improved culture density and biomass by 2.2- and 1.56-fold, respectively (1.39 × 10⁸ cells mL^-1; 0.82 g L^-1). EPA contents increased up to 2.25-fold (to 39.68% of total fatty acids). Added probiotic bacteria possessed multiple growth-stimulating characteristics, including atmospheric nitrogen fixation, growth hormone production and phosphorous solubilization. Core N. oceanica-dominant bacterial microbiomes at different cultivation scales included Sphingobacteria, Flavobacteria (Bacteroidetes), and α, γ-Proteobacteria, and added probiotic bacteria could be maintained. We conclude that the supplementation with probiotic algae-associated bacteria can significantly enhance biomass and EPA production of N. oceanica.

Proteomic and Transcriptomic Patterns during Lipid Remodeling in Nannochloropsis gaditana

Nutrient limited conditions are common in natural phytoplankton communities and are often used to increase the yield of lipids from industrial microalgae cultivations. Here we studied the effects of bioavailable nitrogen (N) and phosphorus (P) deprivation on the proteome and transcriptome of the oleaginous marine microalga Nannochloropsis gaditana. Turbidostat cultures were used to selectively apply either N or P deprivation, controlling for variables including the light intensity. Global (cell-wide) changes in the proteome were measured using Tandem Mass Tag (TMT) and LC-MS/MS, whilst gene transcript expression of the same samples was quantified by Illumina RNA-sequencing. We detected 3423 proteins, where 1543 and 113 proteins showed significant changes in abundance in N and P treatments, respectively. The analysis includes the global correlation between proteomic and transcriptomic data, the regulation of subcellular proteomes in different compartments, gene/protein functional groups, and metabolic pathways. The results show that triacylglycerol (TAG) accumulation under nitrogen deprivation was associated with substantial downregulation of protein synthesis and photosynthetic activity. Oil accumulation was also accompanied by a diverse set of responses including the upregulation of diacylglycerol acyltransferase (DGAT), lipase, and lipid body associated proteins. Deprivation of phosphorus had comparatively fewer, weaker effects, some of which were linked to the remodeling of respiratory metabolism.

Effective Harvesting of Nannochloropsis Microalgae Using Mushroom Chitosan: A Pilot-Scale Study

For efficient downstream processing, harvesting remains as one of the challenges in producing Nannochloropsis biomass, a microalga with high-value omega-3 oils. Flocculation is an effective, low-energy, low-cost method to harvest microalgae. Chitosan has been shown to be an effective food-grade flocculant; however, commercial chitosan is sourced from crustaceans, which has disadvantages including concerns over heavy-metal contamination. Thus, this study tests the flocculation potential of mushroom chitosan. Our results indicate a 13% yield of chitosan from mushroom. The identity of the prepared chitosan was confirmed by Fourier-transform infrared (FTIR) spectroscopy. Furthermore, results show that mushroom chitosan can be an alternative flocculant with >95% flocculation efficiency when tested in 100-mL jar and 200-L vertical column photobioreactor. Applications in a 2000-L raceway pond demonstrated that thorough mixing of mushroom chitosan with the algal culture is required to achieve efficient flocculation. With proper mixing, mushroom chitosan can be used to produce food-grade Nannochloropsis biomass suitable for the production of vegan omega-3 oils as a fish oil alternative.

Experimental and Model-Based Analysis to Optimize Microalgal Biomass Productivity in a Pilot-Scale Tubular Photobioreactor

A dynamic coarse-grained model of microalgal growth considering light availability and temperature under discontinuous bioprocess operation was parameterized using experimental data from 15 batch cultivations of Nannochloropsis granulata in a pilot-scale tubular photobioreactor. The methodology applied consists of a consecutive two-step model parameter estimation using pooled, clustered and reorganized data to obtain initial estimates and multi-experiment fitting to obtain the final estimates, which are: maximum specific growth rate μ_max = 1.56 d⁻¹, specific photon half-saturation constant K_S,ph = 1.89 molphgX-1d-1, specific photon maintenance coefficient m_ph = 0.346 molphgX-1d-1 and the cardinal temperatures T_min = 2.3°C, T_opt = 27.93°C and T_max = 32.59°C. Biomass productivity prediction proved highly accurate, expressed by the mean absolute percent error MAPE = 7.2%. Model-based numerical optimization of biomass productivity for repeated discontinuous operation with respect to the process parameters cultivation cycle time, inoculation biomass concentration and temperature yielded productivity gains of up to 35%. This optimization points to best performance under continuous operation. The approach successfully applied here to small pilot-scale confirms an earlier one to lab-scale, indicating its transferability to larger scale tubular photobioreactors.

Evaluation of Microbial Load, Formation of Odorous Metabolites and Lipid Stability during Wet Preservation of Nannochloropsis gaditana Concentrates

Wet preservation of algae allows us to bridge the time period between algae harvest and processing while avoiding the costs and nutritional losses associated with algae drying. This study aimed to identify suitable storage conditions for the wet preservation of Nannochloropsis gaditana concentrates. The impact of storage temperature, time and the way of closing the storage recipient was evaluated using a full factorial design. The effect of acetic acid addition was tested for one storage condition. Storage temperature was the main factor determining the microbial count and had a vast impact on the formation of odorous metabolites. Storage at 20 °C in closed recipients led to rapid O2 consumption, accumulation of malodorous short-chain fatty acids above their odor thresholds, and the production of H2S and methanethiol. These odorous metabolites were not formed or to a much lower extent during 4 °C and 8 °C storage in closed recipients. Acetic acid supplementation (50 mM) suppressed the formation of short-chain fatty acids during 8 °C storage in unsealed recipients and reduced the aerobic microbial count and the number of yeasts and molds by approximately one log unit after 14 days. Yet, acetic acid addition also induced lipid hydrolysis and decreased chlorophyll levels when algae were stored for more than one week. This study demonstrated that temperature control is needed and that acetic acid addition is a promising approach when N. gaditana concentrates are stored for less than one week.

Thermally coupled dark-anoxia incubation: A platform technology to induce auto-fermentation and thus cell-wall thinning in both nitrogen-replete and nitrogen-deplete Nannochloropsis slurries

Nitrogen-deprived Nannochloropsis cells invested their fixed carbon into the accumulation of triacylglycerol and cell wall cellulose (thickness of N-replete cell walls = 27.8 ± 5.8, N-deplete cell walls = 51.0 ± 10.2 nm). In this study, the effect of nitrogen depletion on the ability of the cells to weaken their own cell walls via autolysis was investigated. Autolytic cell wall thinning was achieved in both N-replete and N-deplete biomass by incubating highly concentrated slurries in darkness at 38 °C. The incubation forced cells to anaerobically ferment their intracellular cellulose and resulted in 30-40% reduction in cell wall thickness for both biomass types. This wall depletion weakened the cells and increased the extent of cell rupture by mechanical force (from 42 to 78% for N-replete biomass, from 36 to 62% for N-deplete biomass). Importantly, autolysis did not adversely impact the amino acid content of protein-rich N-replete biomass or the fatty acid content of lipid-rich N-deplete biomass.

High-efficiency nuclear transformation of the microalgae Nannochloropsis oceanica using Tn5 Transposome for the generation of altered lipid accumulation phenotypes

BACKGROUND

One of the major problems in the production of lipids for biotechnological purposes using microalgae is maintaining a high productivity of these molecules without reducing cellular biomass. High production rates are usually obtained by cultivating microalgae under different stress conditions. However, many of these changes usually result in lower biomass productivity. Therefore, the optimization of the culture conditions and genetic modification techniques in these organisms is needed to generate robust new strains for profitable economic use.

RESULTS

In this work, we describe a new strategy for random mutation of genomic DNA in the microalgae Nannochloropsis oceanica by insertion of a Transposome complex Tn5. This complex contains an antibiotic-resistance cassette commanded by a CMV viral promoter that allows high efficiency of transformation and the generation of mutants. This strategy, complemented with a large-scale identification and selection system for mutants, such as flow cytometry with cell selection, allowed us to obtain clonal cultures of mutants with altered phenotypes in the accumulation of intracellular lipids. The characterization of some of these mutants uncovered new genes that are likely to be involved in the regulation of lipid synthesis, revealing possible cellular responses that influence the intracellular homeostasis of lipids.

CONCLUSION

The strategies proposed here are easy to implement in different types of microalgae and provide a promising scenario for improving biotechnological applications.

Microencapsulated diets to improve growth and survivorship in juvenile European flat oysters (Ostrea edulis)

Sustainable expansion of aquaculture is critical to global food security, and bivalve shellfish aquaculture represents a sustainable method to provide people with affordable nutritious food. Oysters represent 54% of the global bivalve market by value, with propagation of juveniles within hatcheries critical to allow the industry to grow. Growth and survival of juvenile oysters in hatchery systems is constrained by suboptimal feed. The live algal feed currently used is expensive, of variable quality, contamination prone, and the high level of skill and equipment required limits where hatcheries can be located. We demonstrate how a novel microencapsulated diet can increase the growth and survivorship of Ostrea edulis (European flat oyster) juveniles in both the laboratory and hatchery setting. The microcapsules are easily produced in large quantities, stable for long term storage, and can be customised to have exceptionally high levels of nutrients key for oyster growth. O. edulis larvae fed a combined diet of microcapsules and algae for 8 days had a 46% greater increase in maximum size, 171% greater increase in minimum size, and 5% higher survival than larvae fed algae alone. O. edulis spat of 4 mm fed the combined diet for 7 weeks also had significantly greater survivorship (16% greater in hatchery, 58% greater in laboratory) and growth comparable (hatchery) or better (laboratory experiments) than algae alone. Further tailoring of the nutritional composition of microcapsules to specific bivalve species or growth stages could allow microcapsules to replace a greater proportion of or even completely replace algal diets. There is potential for these diets to revolutionise bivalve shellfish farming globally.

Potential of Microalgae Carotenoids for Industrial Application

Microalgae cultivation, when compared to the growth of higher plants, presents many advantages such as faster growth, higher biomass productivity, and smaller land area requirement for cultivation. For this reason, microalgae are an alternative platform for carotenoid production when compared to the traditional sources. Currently, commercial microalgae production is not well developed but, fortunately, there are several studies aiming to make the large-scale production feasible by, for example, employing different cultivation systems. This review focuses on the main carotenoids from microalgae, comparing them to the traditional sources, as well as a critical analysis about different microalgae cultivation regimes that are currently available and applicable for carotenoid accumulation. Throughout this review paper, we present relevant information about the main commercial microalgae carotenoid producers; the comparison between carotenoid content from food, vegetables, fruits, and microalgae; and the great importance and impact of these molecule applications, such as in food (nutraceuticals and functional foods), cosmetics and pharmaceutical industries, feed (colorants and additives), and healthcare area. Lastly, the different operating systems applied to these photosynthetic cultivations are critically discussed, and conclusions and perspectives are made concerning the best operating system for acquiring high cell densities and, consequently, high carotenoid accumulation.