Microalgae Species Research Articles

Productivity, amino acid profile, and protein bioaccessibility in heterotrophic batch cultivation of Galdieria sulphuraria

The polyextremophilic Galdieria sulphuraria is emerging as a promising microalgal species for food applications. This work explores the potential of heterotrophically cultivated G. sulphuraria as a protein producer for human consumption. To this end, the performances of four G. sulphuraria strains grown under the same conditions were compared. Amino acid profiles varied among strains and growth phases, but all samples met FAO dietary requirements for adults. The specific growth rates were between 1.01 and 1.48 day−1. After glucose depletion, all strains showed an increase of 38–49 % in nitrogen content within 48 h, reaching 7.8–12.0 % w/w. An opposite trend was observed in protein bioaccessibility, which decreased on average from 69 % during the exponential phase to a minimum of 32 % 48 h after stationary phase, with significant differences among the strains. Therefore, selecting the appropriate strain and harvesting time is crucial for successful single-cell protein production.

Space-Efficient 3D Microalgae Farming with Optimized Resource Utilization for Regenerative Food.

Photosynthetic microalgae produce valuable metabolites and are a source of sustainable food that supports life without compromising arable land. However, the light self-shading, excessive water supply, and insufficient space utilization in microalgae farming have limited its potential in the inland areas most in need of regenerative food solutions. Herein, this work develops a 3D polysaccharide-based hydrogel scaffold for vertically farming microalgae without needing liquid media. This liquid-free strategy is compatible with diverse microalgal species and enables the design of living microalgal frameworks with customizable architectures that enhance light and water utilization. This approach significantly increases microalgae yield per unit water consumption, with an 8.8-fold increase compared to traditional methods. Furthermore, the dehydrated hydrogels demonstrate a reduced size and weight (≈70% reduction), but readily recover their vitality upon rehydration. Importantly, valuable natural products can be produced in this system including proteins, carbohydrates, lipids, and carotenoids. This study streamlines microalgae regenerative farming for low-carbon biomanufacturing by minimizing light self-shading, relieving water supply, and reducing physical footprints, and democratizing access to efficient aquatic food production.

Cultivation of microalgae in food processing effluent for pollution attenuation and astaxanthin production: a review of technological innovation and downstream application.

Valorization of food processing effluent (FPE) by microalgae cultivation for astaxanthin production is regarded as a potential strategy to solve the environmental pollution of food processing industry and promote the development of eco-friendly agriculture. In this review paper, microalgal species which have the potential to be employed for astaxanthin in FPE were identified. Additionally, in terms of CO2 emission, the performances of microalgae cultivation and traditional methods for FPE remediation were compared. Thirdly, an in-depth discussion of some innovative technologies, which may be employed to lower the total cost, improve the nutrient profile of FPE, and enhance the astaxanthin synthesis, was provided. Finally, specific effects of dietary supplementation of algal astaxanthin on the growth rate, immune response, and pigmentation of animals were discussed. Based on the discussion of this work, the cultivation of microalgae in FPE for astaxanthin production is a value-adding process which can bring environmental benefits and ecological benefits to the food processing industry and agriculture. Particularly, technological innovations in recent years are promoting the shift of this new idea from academic research to practical application. In the coming future, with the reduction of the total cost of algal astaxanthin, policy support from the governments, and further improvement of the innovative technologies, the concept of growing microalgae in FPE for astaxanthin will be more applicable in the industry.

Strategies to enhance biohydrogen production from microalgae: A comprehensive review

Microalgae represent a promising renewable feedstock for the sustainable production of biohydrogen. Their high growth rates and ability to fix carbon utilizing just sunlight, water, and nutrients make them well-suited for this application. Recent advancements have focused on improving microalgal hydrogen yields and cultivation methods. This review aims to summarize recent developments in microalgal cultivation techniques and genetic engineering strategies for enhanced biohydrogen production. Specific areas of focus include novel microalgal species selection, immobilization methods, integrated hybrid systems, and metabolic engineering. Studies related to microalgal strain selection, cultivation methods, metabolic engineering, and genetic manipulations were compiled and analyzed. Promising microalgal species with high hydrogen production capabilities such as Synechocystis sp., Anabaena variabilis, and Chlamydomonas reinhardtii have been identified. Immobilization techniques like encapsulation in alginate and integration with dark fermentation have led to improved hydrogen yields. Metabolic engineering through modulation of hydrogenase activity and photosynthetic pathways shows potential for enhanced biohydrogen productivity. Considerable progress has been made in developing microalgal systems for biohydrogen. However, challenges around process optimization and scale-up remain. Future work involving metabolic modeling, photobioreactor design, and genetic engineering of electron transfer pathways could help realize the full potential of this renewable technology.

Enhancing the Protein, Mineral Content, and Bioactivity of Wheat Bread through the Utilisation of Microalgal Biomass: A Comparative Study of Chlorella vulgaris, Phaeodactylum tricornutum, and Tetraselmis chuii

At present, the incorporation of microalgae into bread and related cereal products has attracted attention due to their potential for enhancing nutritional profiles and their impact on health. In this study, 4% of Chlorella vulgaris, Phaeodactylum tricornutum, and Tetraselmis chuii were added into wheat flour to produce bread and assesses their impact on the dough rheology behaviour, quality performance, nutritive value, and bioactive profile of bread. The results showed that T. chuii strengthened the dough network, whereas P. tricornutum exerted minimal influence. Notably, the incorporation of C. vulgaris induced a pronounced weakening of the protein network within the dough matrix, leading to disruptions in dough structure and subsequent alterations in starch gelatinisation and retrogradation. These changes lead to a reduction in the bread volume (22.7%) and a corresponding increase in its firmness when C. vulgaris was added. In contrast, T. chuii and P. tricornutum had no significant effect on bread volume. All microalgae species caused the dark green colour of the bread and enhanced the bread nutritional composition, namely in terms of protein content (14.7% increase in C. vulgaris bread) and mineral profile. The breads containing T. chuii exhibited a noticeable increase in both total phenolic content (from 7.22 in the control to 38.52 (µg GAE/g)) and antioxidant capacity (from 117.29 to 591.96 (µg TEAC/g) measured by FRAP).

Unwrapping the (glyco-)lipidome in the microalgae Microchloropsis gaditana: Effects of eco-friendly extraction methods

Microalgae have recently captivated worldwide attention because of their extraordinary lipid composition, which includes essential omega-3 and omega-6 long-chain polyunsaturated fatty acids (LC-PUFA), neutral lipids, and more complex lipids (glycolipids and phospholipids), as well as eicosanoids. To explore this further, we present a novel (glyco-)lipidomics strategy, including a green chemistry extraction approach, liquid chromatography high-resolution mass spectrometry (LC-HRMS) lipid profiling, and a comprehensive data evaluation workflow. Using untargeted lipidomics based on LC-HRMS approaches, we studied the lipid composition up to the molecular species level of the microalgae Microchloropsis gaditana (formerly Nannochloropsis gaditana), focusing on the distribution of saturated, monounsaturated, and polyunsaturated fatty acids in different lipid classes. Our analysis successfully identified 520 lipid molecular species from 18 lipid classes. Regarding fatty acid composition, our primary focus was on elucidating the distribution of LC-PUFA across the different microalgal lipid classes. This particular strategy holds potential as it may unravel the use of microalgal lipids as innovative sources of food ingredients. Our findings show that LC-PUFA are relatively elevated in membrane lipids, in which cholesterol esters (ChE) have the highest PUFA share (94 %), followed by polar membrane lipids (glycolipids and phospholipids), with phosphatidylethanolamines (PE) up to 67 %, phosphatidylglycerols (PG) up to 47 %, and monogalactosyldiacylglycerols (MGDG) up to 47 % PUFA content. This highlights the high percentage of PUFA in the structural parts of microalgae and the importance of these lipid classes as a reservoir for PUFA. Finally, we also compared a classical Folch extraction method with environmentally friendly ultrasound-assisted extraction approaches and enzymatic pre-treatments to investigate the lipid composition and enrichment of valuable lipid classes. Thus, this extensive analysis of the (glyco-)lipidome of Microchloropsis gaditana provides valuable insights into the existing knowledge about this microalgae species, enhancing our understanding of the complex lipid composition and opening up new opportunities for potential applications in the biotechnology and food industry.

A Review of Cyclic Imines in Shellfish: Worldwide Occurrence, Toxicity and Assessment of the Risk to Consumers.

Cyclic imines are a class of lipophilic shellfish toxins comprising gymnodimines, spirolides, pinnatoxins, portimines, pteriatoxins, prorocentrolides, spiro-prorocentrimine, symbiomines and kabirimine. They are structurally diverse, but all share an imine moiety as part of a bicyclic ring system. These compounds are produced by marine microalgal species and are characterized by the rapid death that they induce when injected into mice. Cyclic imines have been detected in a range of shellfish species collected from all over the world, which raises the question as to whether they present a food safety risk. The European Food Safety Authority (EFSA) considers them to be an emerging food safety issue, and in this review, the risk posed by these toxins to shellfish consumers is assessed by collating all available occurrence and toxicity data. Except for pinnatoxins, the risk posed to human health by the cyclic imines appears low, although this is based on only a limited dataset. For pinnatoxins, two different health-based guidance values have been proposed at which the concentration should not be exceeded in shellfish (268 and 23 µg PnTX/kg shellfish flesh), with the discrepancy caused by the application of different uncertainty factors. Pinnatoxins have been recorded globally in multiple shellfish species at concentrations of up to 54 times higher than the lower guidance figure. Despite this observation, pinnatoxins have not been associated with recorded human illness, so it appears that the lower guidance value may be conservative. However, there is insufficient data to generate a more robust guidance value, so additional occurrence data and toxicity information are needed.

Evaluation of prokaryotic and eukaryotic microbial communities on microplastic‐associated biofilms in marine and freshwater environments

AbstractMicroplastics (MPs) are major concern due to their potential harm to ecosystems and most research has focused on their presence and fate, with limited attention to their biodegradation in aquatic ecosystems. Nevertheless, MPs act as hotspots for the colonization by a diverse range of microorganisms that can adhere to plastic surfaces, resulting in the subsequent formation of biofilms—a potential threat especially in terms of pathogenicity. This study employed 16S rRNA and 18S rRNA sequencing metagenomic analyses to investigate microbial communities within biofilms on plastic materials exposed to long‐term marine and freshwater environments. Three Arcobacter species (Arcobacter nitrofigilis, Arcobacter acticola, and Arcobacter suis) emerged as dominant species in M_MP sample, while Flavobacterium tructae was the predominant species within the F_MP sample. The 18S rRNA sequencing revealed the presence of the fungal phylum Ascomycota and the microalgal species Pseudocharaciopsis ovalis in F_MP. Although, the primary species detected on M_MP and F_MP samples include bacteria previously implicated as pathogen, the predominant species identified in this study were unconnected to MP‐associated biofilms or MP degradation. Their presence constitutes a novel discovery, opening promising avenues for the exploration of their potential involvement in the biodegradation of MPs within aquatic environments.

Myco-Phycobiont Interactions within the "Ramalina farinacea Group": A Geographical Survey over Europe and Macaronesia.

Ramalina farinacea is a widely distributed epiphytic lichen from the Macaronesian archipelagos to Mediterranean and Boreal Europe. Previous studies have indicated a specific association between R. farinacea and Trebouxia microalgae species. Here, we examined the symbiotic interactions in this lichen and its closest allies (the so-called "R. farinacea group") across ten biogeographic subregions, spanning diverse macroclimates, analyzing the climatic niche of the primary phycobionts, and discussing the specificity of these associations across the studied area. The most common phycobionts in the "R. farinacea group" were T. jamesii and T. lynnae, which showed a preference for continentality and insularity, respectively. The Canarian endemic R. alisiosae associated exclusively with T. lynnae, while the other Ramalina mycobionts interacted with both microalgae. The two phycobionts exhibited extensive niche overlap in an area encompassing Mediterranean, temperate Europe, and Macaronesian localities. However, T. jamesii occurred in more diverse climate types, whereas T. lynnae preferred warmer and more humid climates, often close to the sea, which could be related to its tolerance to salinity. With the geographical perspective gained in this study, it was possible to show how the association with different phycobionts may shape the ecological adaptation of lichen symbioses.

Comparative dynamic optimization study of batch hydrothermal liquefaction of two microalgal strains for economic bio-oil production

This work presents dynamic optimization strategies of batch hydrothermal liquefaction of two microalgal species, Aurantiochytrium sp. KRS101 and Nannochloropsis sp. to optimize the reactor temperature profiles. Three dynamic optimization problems are solved to maximize the endpoint biocrude yield, minimize the final time, and minimize the reactor thermal energy. The biocrude maximization and time minimization problems demonstrated 11% and 6.18% increment in the optimal biocrude yields and reduction of 78.2% and 61.66% in batch times compared to the base cases for the microalgae with higher lipid and protein fractions, respectively. The energy minimization problem revealed a significant reduction in the reactor thermal energies to generate the targeted biocrude yields compared to the biocrude maximization. Therefore, the identified optimal temperature trajectories outperformed the conventional fixed temperature profiles and could improve the overall economics of the batch bio-oil production from the algal-based biorefineries by significantly enhancing the reactor performance.

Botryococcus braunii autolysate for the production of deuterium-labeled recombinant protein

Deuterated biomolecules such as proteins, lipids, and DNA are widely used in neutron scattering experiments. This is due to the unique scattering properties of 2H, including a strong positive neutron scattering length while contributing very little background compared to the more abundant 1H isotope. Deuteration is therefore an indispensable component in the study of structure, function, and dynamic behaviour of biomolecules by neutron scattering. In the past we compared multiple microalgae species for their ability to grow under deuterated conditions and in our hands Botryococcus braunii proved the easiest and most resilient to long-term culturing in D2O. In this study we describe how to culture B. braunii cells under deuterated conditions followed by preparation of an aqueous extract. The procedure is based on autolysis where cells are incubated at 50 °C for 24 h and clarified by centrifugation and filtration. The product, deuterated algal autolysate, is then used in minimal media for deuterated recombinant protein production in bacteria. We demonstrate that in-house produced deuterated algal autolysate can fully substitute for glycerol-d8 in minimal media without a reduction in expressed protein yield while obtaining ~98 % deuterium incorporation in the final product, suitable for neutron scattering and other types of experiments.

Физико-химические характеристики и альгологический состав снежного покрова в устьях рек бассейна юго‑восточной части Баренцева моря

The composition of the snow cover in the Arctic characterizes the winter atmosphere, when long-range and ultra-long-range transport becomes dominant in the influx of aerosols. In addition, when snow occurs on the ice of a water body, the “snow — ice — under-ice water” cryosystem is formed. The components of this system mutually influence each other. In March 2023, to research the ionic and algological composition of the snow cover snow samples were taken in the estuaries of three rivers in the Nenets Autonomous Area (the Indiga River, the Pyosha River and the Pechora River). In the field, the characteristics of snow cover were identified. Snow samples were melted at room temperature, after which the pH level and mineralization were determined. Further, the concentrations of the major ions and nutrients were identified in the filtrate, as well as the species composition and abundance of microalgae. It is shown that the snow cover in the river estuaries of the southern-eastern Barents Sea has a unique composition. It is formed in conditions of close interaction with both air and water environments. In winter, in addition to the atmospheric transport of marine aerosol, seawater seeping through the ice can enrich the snow cover with salts, thereby increasing mineralization and pH levels. This effect is most clearly seen in the estuary of the Indiga River, a little less — in the estuary of the Pyosha River. Marine arctic species of diatom microalgae were found in the snow cover in the estuaries of both rivers. The development of diatoms was promoted by the concentration of nutrients, which exceeded the values limiting the development of microalgae. The main channel for the entry of microalgae can be seawater seeping through the ice during high tide.

Pollutant Gases to Algal Animal Feed: Impacts of Poultry House Exhaust Air on Amino Acid Profile of Algae.

Algae provide a rich source of proteins, lipids, vitamins, and minerals, making them valuable feed ingredients in animal nutrition. Beyond their nutritional benefits, algae have been recognized for their potential to mitigate the negative environmental impacts of poultry production. Poultry production is crucial for the global food supply but contributes to environmental concerns, particularly in terms of ammonia and carbon dioxide gas emissions. This study emphasizes the importance of reducing greenhouse gas and ammonia production in poultry operations by utilizing algae species suitable for animal consumption, highlighting the need for sustainable feed sources. This study investigated the effects of poultry exhaust air and culture conditions on the amino acid profiles of three microalgae species, namely, Scenedesmus sp. (AQUAMEB-60), Ankistrodesmus sp. (AQUAMEB-33), and Synechococcaceae (AQUAMEB 32). The experiments were conducted in a commercial broiler farm in Bursa, Turkey, focusing on reducing pollutant gas emissions and utilizing poultry exhaust air in algae cultivation. The highest protein content of 50.4% was observed in the biomass of Synechococcaceae with BBM and DI water. Scenedesmus sp. had the highest carbohydrate content of 33.4% cultivated with DI water. The algae biomass produced from Synechococcaceae growth with DI water was found to have the highest content of essential and nonessential amino acids, except for glutamic acid and glycine. The arsenic, cadmium, and mercury content showed variations within the following respective ranges: 1.076-3.500 mg/kg, 0.0127-0.1210 mg/kg, and 0.1330-0.0124 mg/kg. The overall operating costs for producing 1.0 g L-1 d-1 of dry algal biomass with the existing PBR system were $0.12-0.35 L-1 d-1, $0.10-0.26 L-1 d-1, and $0.11-0.24 L-1 d-1 for Scenedesmus sp., Ankistrodesmus sp., and Synechococcaceae, respectively. The operating cost of producing 1.0 g L-1 d-1 of protein was in the range of $0.25-0.88 L-1 d-1 for the three algae species. The results provide insights into the potential of algae as a sustainable feed ingredient in animal diets, emphasizing both environmental and economic considerations. The results demonstrated a considerable reduction in the production costs of dry biomass and protein when utilizing poultry house exhaust air, highlighting the economic viability and nutritional benefits of this cultivation method.

Enhancing bioremediation potential of microalgae Chlorella vulgaris and Scenedesmus acutus by NaCl for pyrene degradation.

Microalgae are increasingly recognized as promising organisms for bioremediation of organic pollutants. This study investigates the potential of enhancing the bioremediation efficiency of pyrene (PYR), a polycyclic aromatic hydrocarbon (PAH), through NaCl induced physiological and biochemical alterations in two microalgae species, Chlorella vulgaris and Scenedesmus acutus. Our findings reveal significant improvement in PYR removal when these microalgae were cultivated in the presence of 0.1% NaCl where PYR removal increased from 54 to 74% for C. vulgaris and from 26 to 75% for S. acutus. However, it was observed that NaCl induced stress had varying effects on the two species. While C. vulgaris exhibited increased PYR removal, it experienced reduced growth and biomass production, as well as lower photosynthetic efficiency when exposed to PYR and PYR + NaCl. In contrast, S. acutus displayed better growth and biomass accumulation under PYR + NaCl conditions, making it a more efficient candidate for enhancing PYR bioremediation in the presence of NaCl. In addition to assessing growth and biochemical content, we also investigated stress biomarkers, such as lipid peroxidation, polyphenol and proline contents. These findings suggest that S. acutus holds promise as an alternative microalgae species for PYR removal in the presence of NaCl, offering potential advantages in terms of bioremediation efficiency and ecological sustainability. This study highlights the importance of understanding the physiological and biochemical responses of microalgae to environmental stressors, which can be harnessed to optimize bioremediation strategies for the removal of organic pollutants like PYR.

Challenges in Functional Food Products with the Incorporation of Some Microalgae.

Much attention has been given to the use of microalgae to produce functional foods that have valuable bioactive chemicals, including essential amino acids, polyunsaturated fatty acids, vitamins, carotenoids, fiber, and minerals. Microalgal biomasses are increasingly being used to improve the nutritional values of foods because of their unique nutrient compositions that are beneficial to human health. Their protein content and amino acid composition are the most important components. The microalgal biomass used in the therapeutic supplement industry is dominated by bio-compounds like astaxanthin, β-carotene, polyunsaturated fatty acids like eicosapentaenoic acid and docosahexaenoic acid, and polysaccharides such as β-glucan. The popularity of microalgal supplements is growing because of the health benefits of their bioactive substances. Moreover, some microalgae, such as Dunaliella, Arthrospira (Spirulina), Chlorella, and Haematococcus, are commonly used microalgal species in functional food production. The incorporation of microalgal biomass leads not only to enhanced nutritional value but also to improved sensory quality of food products without altering their cooking or textural characteristics. Microalgae, because of their eco-friendly potential, have emerged as one of the most promising and novel sources of new functional foods. This study reviews some recent and relevant works, as well as the current challenges for future research, using different methods of chemical modification in foods with the addition of a few commercial algae to allow their use in nutritional and sensory areas. It can be concluded that the production of functional foods through the use of microalgae in foods has become an important issue.

Progress on the biological characteristics and physiological activities of fucoxanthin produced by marine microalgae

BackgroundFucoxanthin is a carotenoid found in seaweed. Its unique chemical structure gives it a variety of properties. Thus fucoxanthin have attracted the attention of companies and researchers.MethodsScientific papers were collected from the database. Duplicates and unavailable literature were excluded first. Then the remaining literature was categorized for referencing in the review.ResultsThis article contains a summary of the microalgae species producing fucoxanthin and their progress in breeding and cultivation modes. Additionally, the review summarized the progress of research on physiological activities and organized the experimental models used in these studies.ConclusionsThese present findings may provide information for the upstream production of fucoxanthin from algal species selection to process optimization. The analysis of the physiological activity results will help advance subsequent physiological and biochemical experiments. Furthermore, it intends to pique researchers’ enthusiasm for fucoxanthin and enrich related research data to accelerate the development of this natural product.

Methylmercury Effect and Distribution in Two Extremophile Microalgae Strains Dunaliella salina and Coccomyxa onubensis from Andalusia (Spain).

The main entrance point of highly toxic organic Hg forms, including methylmercury (MeHg), into the aquatic food web is phytoplankton, which is greatly represented by various natural microalgal species. Processes associated with MeHg fate in microalgae cells such as uptake, effects on cells and toxicity, Hg biotransformation, and intracellular stability are detrimental to the process of further biomagnification and, as a consequence, have great importance for human health. The study of MeHg uptake and distribution in cultures of marine halophile Dunaliella salina and freshwater acidophilic alga Coccomyxa onubensis demonstrated that most of the MeHg is imported inside the cell, while cell surface adhesion is insignificant. Almost all MeHg is removed from the culture medium after 72 h. Significant processes in rapid MeHg removal from liquid medium are its abiotic photodegradation and volatilization associated with algal enzymatic activity. The maximum intracellular accumulation for both species was in 80 nM MeHg-exposed cultures after 24 h of exposure for D. salina (from 27 to 34 µg/gDW) and at 48 h for C. onubensis (up to 138 µg/gDW). The different Hg intakes in these two strains could be explained by the lack of a rigid cell wall in D. salina and the higher chemical ability of MeHg to pass through complex cell wall structures in C. onubensis. Electron microscopy studies on the ultrastructure of both strains demonstrated obvious microvacuolization in the form of many very small vacuoles and partial cell membrane disruption in 80 nM MeHg-exposed cultures. Results further showed that Coccomyxa onubensis is a good candidate for MeHg-contaminated water reclamation due to its great robustness at nanomolar concentrations of MeHg coupled with its very high intake and almost complete Hg removal from liquid medium at the MeHg levels tested.

Formation and adaptation of algal–bacterial granular sludge in real Chinese liquor brewing wastewater treatment

The intricate pollutant composition and pronounced water fluctuations of Chinese liquor brewing wastewater (CLBW) pose formidable challenges for effective treatment, thereby raising significant environmental concerns. This study for the first time delves into the exploration of algal–bacterial granular sludge (ABGS) development and its efficacy in the removal of organic matter and nitrogen and phosphorus over a 100–day investigation of real CLBW treatment. Mature ABGS emerged after approximately 40 days of treating wastewater with 20% real CLBW, exhibiting exceptional settling performance and significant removal of COD (86.2%), NH4+–N (98.0%), and TP (51.5%). As the real CLBW proportion increased to 40% or higher, a stable granular structure and excellent settleability persisted, primarily attributed to the consistent content of tightly bound extracellular polymeric substances, the sustained protein–to–polysaccharide ratio, and the proliferation of microalgae within the granules. Microbial community analysis revealed the dominance of microalgal species, including Sphaeropleales, Scenedesmaceae, and Chloromonas. Moreover, the observed decline in nitrification efficiency with increasing CLBW ratio was linked to reductions in Nitrosomonas and Nitrospira populations. Conversely, the recovered TN removal was primarily associated with the accumulation of denitrifiers, including Azoarcus and Thauera, especially when the real CLBW ratio reached 100%. The findings from this study are anticipated to offer a practical reference for optimizing and promoting the treatment of real CLBW.

A robust multinutrient kinetic model for enhanced lutein and biomass yields in mixotrophic microalgae cultivation: A step towards successful large-scale productions.

Mixotrophic cultivation holds great promise to significantly enhance the productivities of biomass and valuable metabolites from microalgae. In this study, a new kinetic model is developed, explicitly describing the effect of the most influential environmental factors on both biomass growth and the production of the high-value product lutein. This extensive study of multinutrient kinetics for Tetradesmus obliquus in a mixotrophic regime covers various nutritional conditions. Crucial nutrients governing the model include nitrate, phosphate, and glucose. Using seven state variables and 13 unknown parameters, the model's accuracy was ensured through a well-designed two-factor, four-level experimental setup, providing ample data for reliable calibration and validation. Results accurately predict dynamic concentration profiles for all validation experiments, revealing broad applicability. Optimizing nitrogen availability led to significant increases in biomass (up to fourfold) and lutein production (up to 12-fold), with observed maximum biomass concentration of 6.80 g L-1 and lutein reaching 25.58 mg L-1. Noticeably, the model exhibits a maximum specific growth rate of 4.03 day-1, surpassing reported values for photoautotrophic and heterotrophic conditions, suggesting synergistic effects. Valuable guidance is provided for applying the method to various microalgal species and results are large-scale production-ready. Future work will exploit these results to develop real-time photobioreactor operation strategies.

Lipid Yields and Fatty Acid Composition if Indigenous Microalgae, Isolated from the Beira, and Diyawanna Urban Lakes, for Sustainable Biofuel Production in Sri Lanka


 Biofuels are carbon-neutral combustibles produced from renewable biomass. Third generation biofuels, derived from microalgal biomass, are distinctly superior to their preceding generations, due to higher productivity and resource use efficiency of microalgae compared to conventional energy crops. It is a viable source of sustainable energy for our country due to the availability of water, ambient temperatures and year-round sunlight needed for microalgae cultivation, and most importantly, the abundance of diverse microalgae species. However, these native microalgae are relatively unexplored for their productivities and thereby, greatly underutilized. This research was aimed to investigate the lipid yields and fatty acid compositions of local freshwater microalgae, and to identify their potential for biodiesel production. This was carried out by (1) microalgae isolation and morphological identification (2) microalgae cultivation (3) biomass harvesting, lipid extraction, gravimetric measurement of extracted lipids and (4) acid-catalysed transesterification, followed by GCMS analysis of the biodiesel product. Chlorella sp., Chlorococcum sp. and Chlamydomonas sp. were isolated from Beira/ Diyawanna Lakes using streak plate technique in solid standard BBM media. They were next cultivated under axenic conditions in liquid standard BBM media under 16: 8 (light: dark), at 25°C for 20 days in duplicates. The biomass was then harvested using alum, dried to reach a constant weight and the Bligh and Dyer lipid extraction was done in triplicate. The extracted lipids were trans-esterified with methanol, using sulfuric acid catalyst at 90° C for 60 minutes. The separated product was analysed by GCMS. Chlorella sp., Chlorococcum sp. and Chlamydomonas sp. cultivated under standard conditions gave average lipid yields of 11.34±1.01%, 15.00±1.40% and 2.10±0.50% respectively. Average lipid yield of Chlamydomonas sp. was significantly lower than the other two species at 95% confidence level (Two-sample T test on SPSS Version 21). GCMS analysis of the biodiesel product from Chlorella sp. indicated significant levels of saturated fatty acids including palmitic and stearic acids, monounsaturated fatty acids like cis-11- eicosenoic acid and polyunsaturated fatty acids including linoleic and linolenic acids. The fatty acid ratios were used to calculate the saturation value, cetane number, density, iodine value and pour point of the produced biodiesel. These quality parameters were in accordance with the ASTM D6751- 20a standards. Therefore, with a substantial yield and fatty acid composition of intracellular lipids, this local species of Chlorella can be a prospective candidate for sustainable bioenergy production in Sri Lanka.
 
 Keywords: Chlorella, Chlorococcum, Chlamydomonas, Microalgal lipids, Biodiesel