Microalgae-based carbohydrates: A green innovative source of bioenergy

Algal carbohydrates: Sources, biosynthetic pathway, production, and applications

Algae play a significant role in the global carbon cycle by utilizing photosynthesis to efficiently convert solar energy and atmospheric carbon dioxide into various chemical compounds, notably carbohydrates, pigments, lipids, and released oxygen, making them a unique sustainable cellular factory. Algae mostly consist of carbohydrates, which include a broad variety of structures that contribute to their distinct physical and chemical properties such as degree of polymerization, side chain, branching, degree of sulfation, hydrogen bond etc., these features play a crucial role in regulating many biological activity, nutritional and pharmaceutical properties. Algal carbohydrates have not received enough attention in spite of their distinctive structural traits linked to certain biological and physicochemical properties. Nevertheless, it is anticipated that there will be a significant increase in the near future due to increasing demand, sustainable source, biofuel generation and their bioactivity. This is facilitated by the abundance of easily accessible information on the structural data and distinctive characteristics of these biopolymers. This review delves into the different types of saccharides such as agar, alginate, fucoidan, carrageenan, ulvan, EPS and glucans synthesized by various macroalgal and microalgal systems, which include intracellular, extracellular and cell wall saccharides. Their structure, biosynthetic pathway, sources, production strategies and their applications in various field such as nutraceuticals, pharmaceuticals, biomedicine, food and feed, cosmetics, and bioenergy are also elaborately discussed. Algal polysaccharide has huge a scope for exploitation in future due to their application in food and pharmaceutical industry and it can become a huge source of capital and income.

Metabolomics Reveals the Impact of Overexpression of Cytosolic Fructose-1,6-Bisphosphatase on Photosynthesis and Growth in Nannochloropsis gaditana

Nannochloropsis gaditana, a microalga known for its photosynthetic efficiency, serves as a cell factory, producing valuable biomolecules such as proteins, lipids, and pigments. These components make it an ideal candidate for biofuel production and pharmaceutical applications. In this study, we genetically engineered N. gaditana to overexpress the enzyme fructose-1,6-bisphosphatase (cyFBPase) using the Hsp promoter, aiming to enhance sugar metabolism and biomass accumulation. The modified algal strain, termed NgFBP, exhibited a 1.34-fold increase in cyFBPase activity under photoautotrophic conditions. This modification led to a doubling of biomass production and an increase in eicosapentaenoic acid (EPA) content in fatty acids to 20.78-23.08%. Additionally, the genetic alteration activated the pathways related to glycine, protoporphyrin, thioglucosides, pantothenic acid, CoA, and glycerophospholipids. This shift in carbon allocation towards chloroplast development significantly enhanced photosynthesis and growth. The outcomes of this study not only improve our understanding of photosynthesis and carbon allocation in N. gaditana but also suggest new biotechnological methods to optimize biomass yield and compound production in microalgae.

Cultivation of carbohydrate-rich microalgae with great settling properties using cooling tower wastewater

Wastewater treatment and simultaneous production of value-added products with microalgae represent a sustainable alternative. Industrial wastewater, characterized by high C/N molar ratios, can naturally improve the carbohydrate content in microalgae without the need for any external source of carbon while degrading the organic matter, macro-nutrients, and micro-nutrients. This study aimed to understand the treatment, reuse, and valorization mechanisms of real cooling tower wastewater (CWW) from a cement-processing industry mixed with domestic wastewater (DW) to produce microalgal biomass with potential for synthesis of biofuels or other value-added products. For this purpose, three photobioreactors with different hydraulic retention times (HRT) were inoculated simultaneously using the CWW-DW mixture. Macro- and micro-nutrient consumption and accumulation, organic matter removal, algae growth, and carbohydrate content were monitored for 55 days. High COD (> 80%) and macronutrient removals (> 80% of N and P) were achieved in all the photoreactors, with heavy metals below the limits established by local standards. The best results showed maximum algal growth of 1.02 g SSV L-1 and 54% carbohydrate accumulation with a C/N ratio of 31.24 mol mol-1. Additionally, the harvested biomass presented a high Ca and Si content, ranging from 11 to 26% and 2 to 4%, respectively. Remarkably, big flocs were produced during microalgae growth, which enhanced natural settling for easy biomass harvesting. Overall, this process represents a sustainable alternative for CWW treatment and valorization, as well as a green tool for generating carbohydrate-rich biomass with the potential to produce biofuels and fertilizers.

Reaction of Pyrrolobenzothiazines with Schiff Bases and Carbodiimides: Approach to Angular 6/5/5/5-Tetracyclic Spiroheterocycles

1H-Pyrrole-2,3-diones, fused at [e]-side with a heterocycle, are suitable platforms for the synthesis of various angular polycyclic alkaloid-like spiroheterocycles. Recently discovered sulfur-containing [e]-fused 1H-pyrrole-2,3-diones (aroylpyrrolobenzothiazinetriones) tend to exhibit unusual reactivity. Based on these peculiar representatives of [e]-fused 1H-pyrrole-2,3-diones, we have developed an approach to an unprecedented 6/5/5/5-tetracyclic alkaloid-like spiroheterocyclic system of benzo[d]pyrrolo[3',4':2,3]pyrrolo[2,1-b]thiazole via their reaction with Schiff bases and carbodiimides. The experimental results have been supplemented with DFT computational studies. The synthesized alkaloid-like 6/5/5/5-tetracyclic compounds have been tested for their biotechnological potential as growth stimulants in the green algae Chlorella vulgaris.

Growth, nutrient removal, and lipid productivity promotion of Chlorella sorokiniana by phosphate solubilizing bacteria Bacillus megatherium in swine wastewater: Performances and mechanisms

Effects of a phosphorus-solubilizing bacteria (PSB) Bacillus megatherium on growth and lipid production of Chlorella sorokiniana were investigated in synthesized swine wastewater with dissolved inorganic phosphorus (DIP), insoluble inorganic phosphorus (IIP), and organic phosphorus (OP). The results showed that the PSB significantly promoted the algal growth in OP and IIP, by 1.10 and 1.78-fold, respectively. The algal lipid accumulation was also greatly triggered, respectively by 4.39, 1.68, and 1.38-fold in DIP, IIP, and OP. Moreover, compared with DIP, OP improved the oxidation stability of algal lipid by increasing the proportion of saturated fatty acids (43.8 % vs 27.9 %), while the PSB tended to adjust it to moderate ranges (30.2-41.6 %). Further, the transcriptome analysis verified the OP and/or PSB-induced up-regulated genes involving photosynthesis, lipid metabolism, signal transduction, etc. This study provided novel insights to enhance microalgae-based nutrient removal combined with biofuel production in practical wastewater, especially with complex forms of phosphorus.

Effect of light intensity and photoperiod on high-value production and nutrient removal performance with bacterial-algal coupling system

Direct discharge of mariculture wastewater can lead to eutrophication, posing a threat to aquatic ecosystems. A novel Bacteria-Algae Coupled Reactor (BACR) offers advantages in treating mariculture wastewater, which can effectively remove pollutants while simultaneously obtaining microalgal products. However, there is limited information available on how illumination affects the cultivation of mixotrophic microalgae in this bacteria-algae coupling system. Therefore, a combined strategy of photoperiod and light intensity regulation was employed to improve the biological mariculture wastewater remediation, promote microalgae biomass accumulation, and increase the high-value product yield in this study. Optimal light conditions could effectively enhance microalgal carbohydrate, protein, lipid accumulation and photosynthetic activity, with the carbohydrate, protein and lipid contents reached 44.11, 428.57 and 399.68 mg/L, respectively. Moreover, excellent removal rates were achieved for SCOD, NH4+-N and TP, reaching 86.68%, 87.35% and 95.13% respectively. This study proposes a comprehension of BACR processes in mariculture wastewater under different light conditions.

Cultivating photosynthetic microorganisms in cooling water waste and urban effluents as a strategy of water regeneration and valorization

Contaminants from cooling water waste (CWW) generated by industries represent an environmental hazard if discharged into aquatic bodies and soil without treatment. Most treatment strategies are energy-demanding and costly; hence, low-cost and sustainable treatment alternative technologies are needed. The present study proposed cyanobacteria culture as a low-cost biological method to treat cooling water waste (CWW) while simultaneously producing carbohydrates. For this purpose, CWW from a cooling tower was evaluated in different dilutions with domestic wastewater (DW) (DW25% -CWW75%, DW50% -CWW50%, DW25% -CWW75%, DW100%, and CWW100%) (v/v). The CWW provided a high content of inorganic carbon and low content of N and P, which resulted in a high C/N ratio promoting a fast carbohydrate accumulation but low biomass production. In contrast, cultures with higher DW concentrations achieved similar results in 14 days. The best results were obtained with DW25% -CWW75%, achieving up to 52 ± 18% carbohydrate content on day 8, with the highest biomass concentration of 1.7 ± 0.12 g L-1 on day 14. This culture removed >94% of TAN, N-NO3- and P-PO43-, and 84 ± 10.82% of COD. This strategy could be a promising approach to treating CWW and DW from the same industry and producing value-added products and bioenergy.

Doxorubicin-Loaded Microalgal Delivery System for Combined Chemotherapy and Enhanced Photodynamic Therapy of Osteosarcoma

Osteosarcoma (OS) is considered the most frequent type of primary malignant bone tumor. Currently, radiotherapy, photodynamic (PDT), and other therapies for osteosarcoma are limited by tumor hypoxia and single efficacy and serve side-effects. Herein, we reported a microalgal drug delivery system (SpiD), doxorubicin (DOX)-loaded Spirulina platensis (Spi) for OS therapy. The specific surface of Spirulina platensis allowed for effective loading of DOX via surface channels and electrostatic interactions. Under 650 nm laser irradiation, SpiD enabled high oxygen production by photosynthesis and enhanced reactive oxygen species (ROS) generation via chlorophyll-assisted photosensitization, synergistically killing tumor cells with the released DOX. Combined chemotherapy and enhanced PDT mediated by SpiD exerted synergic antitumor effects and resulted in potent therapeutic efficacy in orthotopic osteosarcoma mice. Furthermore, SpiD could reduce the side-effects of chemotherapy, showing excellent blood and tissue safety. Taken together, this microalgal drug delivery system provided a natural, efficient, safe, and inexpensive strategy for OS treatment.

Exploring the diverse applications of Carbohydrate macromolecules in food, pharmaceutical, and environmental technologies

Carbohydrates are a class of macromolecules that has significant potential across several domains, including the organisation of genetic material, provision of structural support, and facilitation of defence mechanisms against invasion. Their molecular diversity enables a vast array of essential functions, such as energy storage, immunological signalling, and the modification of food texture and consistency. Due to their rheological characteristics, solubility, sweetness, hygroscopicity, ability to prevent crystallization, flavour encapsulation, and coating capabilities, carbohydrates are useful in food products. Carbohydrates hold potential for the future of therapeutic development due to their important role in sustained drug release, drug targeting, immune antigens, and adjuvants. Bio-based packaging provides an emerging phase of materials that offer biodegradability and biocompatibility, serving as a substitute for traditional non-biodegradable polymers used as coatings on paper. Blending polyhydroxyalkanoates (PHA) with carbohydrate biopolymers, such as starch, cellulose, polylactic acid, etc., reduces the undesirable qualities of PHA, such as crystallinity and brittleness, and enhances the PHA's properties in addition to minimizing manufacturing costs. Carbohydrate-based biopolymeric nanoparticles are a viable and cost-effective way to boost agricultural yields, which is crucial for the increasing global population. The use of biopolymeric nanoparticles derived from carbohydrates is a potential and economically viable approach to enhance the quality and quantity of agricultural harvests, which is of utmost importance given the developing global population. The carbohydrate biopolymers may play in plant protection against pathogenic fungi by inhibiting spore germination and mycelial growth, may act as effective elicitors inducing the plant immune system to cope with pathogens. Furthermore, they can be utilised as carriers in controlled-release formulations of agrochemicals or other active ingredients, offering an alternative approach to conventional fungicides. It is expected that this review provides an extensive summary of the application of carbohydrates in the realms of food, pharmaceuticals, and environment.

Effects of light quality on microalgae cultivation: bibliometric analysis, mini-review, and regulation approaches

The ever-increasing concern for energy shortages and greenhouse effect has triggered the development of sustainable green technologies. Microalgae have received more attention due to the characteristics of biofuel production and CO2 fixation. From the perspective of autotrophic growth, the optimization of light quality has the potential to promote biomass production and bio-component accumulation in microalgae at low cost. In this study, bibliometric analysis was used to describe the basic features, identify the hotspots, and predict future trends of the research related to the light quality on microalgae cultivation. In addition, a mini-review referring to regulation methods of light quality was provided to optimize the framework of research. Results demonstrated that China has the greatest interest in this area. The destination of most research was to obtain biofuels and high-value-added products. Both blue and red lights were identified as the crucial spectrums for microalgae cultivation. However, sunlight is the most affordable light resource, which could not be fully utilized by microalgae through the photosynthetic process. Hence, some regulation approaches (e.g., dyes, plasmonic scattering, and carbon-based quantum dots) are proposed to increase the proportion of beneficial spectrum for enhancement of photosynthetic efficiency. In summary, this review introduces state-of-the-art research and provides theoretical guidance for light quality optimization in microalgae cultivation to obtain more benefits.

Realization process of microalgal biorefinery: The optional approach toward carbon net-zero emission

Increasing carbon dioxide (CO2) emission has already become a dire threat to the human race and Earth's ecology. Microalgae are recommended to be engineered as CO2 fixers in biorefinery, which play crucial roles in responding climate change and accelerating the transition to a sustainable future. This review sorted through each segment of microalgal biorefinery to explore the potential for its practical implementation and commercialization, offering valuable insights into research trends and identifies challenges that needed to be addressed in the development process. Firstly, the known mechanisms of microalgal photosynthetic CO2 fixation and the approaches for strain improvement were summarized. The significance of process regulation for strengthening fixation efficiency and augmenting competitiveness was emphasized, with a specific focus on CO2 and light optimization strategies. Thereafter, the massive potential of microalgal refineries for various bioresource production was discussed in detail, and the integration with contaminant reclamation was mentioned for economic and ecological benefits. Subsequently, economic and environmental impacts of microalgal biorefinery were evaluated via life cycle assessment (LCA) and techno-economic analysis (TEA) to lit up commercial feasibility. Finally, the current obstacles and future perspectives were discussed objectively to offer an impartial reference for future researchers and investors.

Identification and Characterization of a Novel Microalgal Strain from the Antofagasta Coast Tetraselmis marina AC16-MESO (Chlorophyta) for Biotechnological Applications

The wide rocky coastline of the Antofagasta hosts an intertidal ecosystem in which the species that inhabit it are routinely exposed to a wide range of physical and chemical conditions and have therefore evolved to tolerate extremes. In the search for new species of potential biotechnological interest with adaptations to a wide range of environmental conditions, the isolation and characterization of microalgae from these ecosystems is of great interest. Here, a new microalgal strain, Tetraselmis marina AC16-MESO, is described, which was isolated from a biofilm collected on the intertidal rocks of the Antofagasta coast (23°36'57.2″ S, 70°23'33.8″ W). In addition to the morphological characterization, 18S and ITS sequence as well as ITS-2 secondary structure analysis revealed an identity of 99.76% and 100% with the species Tetraselmis marina, respectively. The analyses of the culture characteristics and biochemical content showed similarities with other strains that are frequently used in aquaculture, such as the species Tetraselmis suecica. In addition, it is tolerant of a wide range of salinities, thus allowing its culture in water of varying quality. On the other hand, added to these characteristics, the results of the improvement of the lipid content in stressful situations of salinity observed in this study, together with other antecedents such as the potential in bioremediation already published for this strain by the same research group, present a clear example of its biotechnological plasticity. It is noteworthy that this strain, due to its characteristics, allows easy collection of its biomass by decantation and, therefore, a more cost-efficient harvesting than for other microalgal strains. Therefore, this new strain of Tetraselmis marina, first report of this species in Chile, and its morphologically, molecularly and biochemically description, presents promising characteristics for its use in biotechnology and as feed for aquaculture.

Genetic engineering for biohydrogen production from microalgae

The development of biohydrogen as an alternative energy source has had great economic and environmental benefits. Hydrogen production from microalgae is considered a clean and sustainable energy production method that can both alleviate fuel shortages and recycle waste. Although algal hydrogen production has low energy consumption and requires only simple pretreatment, it has not been commercialized because of low product yields. To increase microalgal biohydrogen production several technologies have been developed, although they struggle with the oxygen sensitivity of the hydrogenases responsible for hydrogen production and the complexity of the metabolic network. In this review, several genetic and metabolic engineering studies on enhancing microalgal biohydrogen production are discussed, and the economic feasibility and future direction of microalgal biohydrogen commercialization are also proposed.

Growth Behavior, Biomass Composition and Fatty Acid Methyl Esters (FAMEs) Production Potential of Chlamydomonas reinhardtii, and Chlorella vulgaris Cultures

The production of biomolecules by microalgae has a wide range of applications in the development of various materials and products, such as biodiesel, food supplements, and cosmetics. Microalgae biomass can be produced using waste and in a smaller space than other types of crops (e.g., soja, corn), which shows microalgae's great potential as a source of biomass. Among the produced biomolecules of greatest interest are carbohydrates, proteins, lipids, and fatty acids. In this study, the production of these biomolecules was determined in two strains of microalgae (Chlamydomonas reinhardtii and Chlorella vulgaris) when exposed to different concentrations of nitrogen, phosphorus, and sulfur. Results show a significant microalgal growth (3.69 g L-1) and carbohydrates (163 mg g-1) increase in C. reinhardtii under low nitrogen concentration. Also, higher lipids content was produced under low sulfur concentration (246 mg g-1). It was observed that sulfur variation could affect in a negative way proteins production in C. reinhardtii culture. In the case of C. vulgaris, a higher biomass production was obtained in the standard culture medium (1.37 g L-1), and under a low-phosphorus condition, C. vulgaris produced a higher lipids concentration (248 mg g-1). It was observed that a low concentration of nitrogen had a better effect on the accumulation of fatty acid methyl esters (FAMEs) (C16-C18) in both microalgae. These results lead us to visualize the effects that the variation in macronutrients can have on the growth of microalgae and their possible utility for the production of microalgae-based subproducts.

Prospects of microalgae in nutraceuticals production with nanotechnology applications

Nutraceutical supplements provide health benefits, such as fulfilling the lack of nutrients in the human body or being utilized to treat or cure certain diseases. As the world population is growing, certain countries are experiencing food crisis challenges, causing natural foods are not sustainable to be used for nutraceutical production because it will require large-scale of food supply to produce enriched nutraceutics. The high demand for abundant nutritional compounds has made microalgae a reliable source as they can synthesize high-value molecules through photosynthetic activities. However, some microalgae species are limited in growth and unable to accumulate a significant amount of biomass due to several factors related to environmental conditions. Therefore, adding nanoparticles (NPs) as a photocatalyst is considered to enhance the yield rate of microalgae in an energy-saving and economical way. This review focuses on the composition of microalgal biomass for nutraceutical production, the health perspectives of nutritional compounds on humans, and the application of nanotechnology on microalgae for improved production and harvesting. The results obtained show that microalgal-based compounds indeed have better nutrients content than natural foods. However, nanotechnology must be further comprehended to make them non-hazardous and sustainable.

Glucose Conversion for Biobutanol Production from Fresh Chlorella sorokiniana via Direct Enzymatic Hydrolysis

Microalgae, which accumulate considerable carbohydrates, are a potential source of glucose for biofuel fermentation. In this study, we investigated the enzymatic hydrolysis efficiency of wet microalgal biomass compared with freeze-dried and oven-dried biomasses, both with and without an acidic pretreatment. With the dilute sulfuric acid pretreatment followed by amy (α-amylase and amyloglucosidase) and cellulase hydrolysis, approximately 95.4% of the glucose was recovered; however, 88.5% was released by the pretreatment with 2% (w/v) sulfuric acid, which indicates the potential of the acids for direct saccharification process. There were no considerable differences in the glucose yields among the three kinds of materials. In the direct amy hydrolysis without any pretreatment, a 78.7% glucose yield was obtained, and the addition of cellulase had no significant effect on the hydrolysis to glucose. Compared with the oven-dried biomass, the wet biomass produced a substantially higher glucose yield, which is possibly because the cross-linked cells of the oven-dried biomass prevented the accessibility of the enzymes. According to the results, the fresh microalgal biomass without cell disruption can be directly used for enzymatic hydrolysis to produce glucose. The enzymatic hydrolysate of the wet microalgal biomass was successfully used for acetone–butanol–ethanol (ABE) fermentation, which produced 7.2 g/L of ABE, indicating the application potential of wet microalgae in the bioalcohol fuel fermentation process.

Cell disruption and lipid extraction from Chlorella species for biorefinery applications: Recent advances

Chlorella is a promising microalga for CO₂-neutral biorefinery that co-produces drop-in biofuels and multiple biochemicals. Cell disruption and selective lipid extraction steps are major technical bottlenecks in biorefinement because of the inherent robustness and complexity of algal cell walls. This review focuses on the state-of-the-art achievements in cell disruption and lipid extraction methods for Chlorella species within the last five years. Various chemical, physical, and biological approaches have been detailed theoretically, compared, and discussed in terms of the degree of cell wall disruption, lipid extractability, chemical toxicity, cost-effectiveness, energy use, scalability, customer preferences, environment friendliness, and synergistic combinations of different methods. Future challenges and prospects of environmental-friendly and efficient extraction technologies are also outlined for practical applications in sustainable Chlorella biorefineries. Given the diverse industrial applications of Chlorella, this review may provide useful information for downstream processing of the advanced biorefineries of other algae genera.

Nitrogen recovery from wastewater by microbial assimilation - A review

The increased nitrogen (N) input with low utilization rate in artificial N management has led to massive reactive N (Nr) flows, putting the Earth in a high-risk state. It is essential to recover and recycle Nr during or after Nr removal from wastewater to reduce N input while simultaneously mitigate Nr pollution in addressing the N stress. However, mechanisms for efficient Nr recovery during or after Nr removal remain unclear. Here, the occurrence of N risk and progress in wastewater treatment in recent years as well as challenges of the current technologies for N recovery from wastewater were reviewed. Through analyzing N conversion fluxes in biogeochemical N-cycling networks, microbial N assimilation through photosynthetic and heterotrophic microorganisms was highlighted as promising alternative for synergistic N removal and recovery in wastewater treatment. In addition, the prospects and gaps of Nr recovery from wastewater through microbial assimilation are discussed.

Reducing culture medium nitrogen supply coupled with replenishing carbon nutrient simultaneously enhances the biomass and lipid production of Chlamydomonas reinhardtii

Chlamydomonas reinhardtii is a model strain to explore algal lipid metabolism mechanism, and exhibits great potentials in large-scale production of lipids. Completely lacking nitrogen is an efficient strategy to trigger the lipid synthesis in microalgal cells, while it always leads to the obvious reduction in the biomass. To illustrate the optimal culture substrate carbon (C) and nitrogen (N) levels to simultaneously stimulate the growth and lipid production of C. reinhardtii, cells were cultivated under altered C and N concentrations. Results showed that replenishing 6 g/L sodium acetate (NaAc) could increase 1.50 and 1.53 times biomass and lipid productivity compared with 0 g/L NaAc treatment (the control), but total lipid content slightly decreased. Reducing 75% of basic medium (TAP) N level (0 g/L NaAc + 0.09 g/L NH₄Cl treatment) could promote 21.57% total lipid content in comparison with the control (containing 0.38 g/L NH₄Cl), but decrease 44.45% biomass and 34.15% lipid productivity. The result of the central composite design (CCD) experiment suggested the optimum total lipid content together with higher biomass and lipid productivity could be obtained under the condition of 4.12 g/L NaAc and 0.20 g/L NH₄Cl. They reached 32.14%, 1.68 g/L and 108.21 mg/L/d, and increased by 36.77%, 93.10% and 1.75 times compared with the control, respectively. It suggests moderately increasing C supply and decreasing N levels could synchronously improve the biomass and lipid content of C. reinhardtii.

Update on the application of magnetic fields to microalgal cultures

Several studies have shown that any magnetic field (MF) applied to microalgae modifies its cultivation conditions and may favor biomolecule production since it interacts with the microorganisms and affect their growth. As a result, there are changes in concentrations and compositions of biomass and biomolecules. This review aims at updating MF applications to microalga cultures that were reported by studies conducted in the last 5 years. It shows the main studies that reached positive results of carbohydrate, lipid, protein and pigment production. Effects of MFs may be positive, negative or null, depending on some factors, such as intensity, exposure time, physiological state of cells and application devices. Therefore, this review details cultivation conditions used for reaching high concentration of biomolecules, explains the action of MFs on microalgae and describes their applicability to the biorefinery concept.

Biosynthesis of microalgal lipids, proteins, lutein, and carbohydrates using fish farming wastewater and forest biomass under photoautotrophic and heterotrophic cultivation

Biorefineries enable the circular, sustainable, and economic use of waste resources if value-added products can be recovered from all the generated fractions at a large-scale. In the present studies the comparison and assessment for the production of value-added compounds (e.g., proteins, lutein, and lipids) by the microalga Chlorella sorokiniana grown under photoautotrophic or heterotrophic conditions was performed. Photoautotrophic cultivation generated little biomass and lipids, but abundant proteins (416.66 mg/g_CDW) and lutein (6.40 mg/g_CDW). Heterotrophic conditions using spruce hydrolysate as a carbon source favored biomass (8.71 g/L at C/N 20 and 8.28 g/L at C/N 60) and lipid synthesis (2.79 g/L at C/N 20 and 3.61 g/L at C/N 60) after 72 h of cultivation. Therefore, heterotrophic cultivation of microalgae using spruce hydrolysate instead of glucose offers a suitable biorefinery concept at large-scale for biodiesel-grade lipids production, whereas photoautotrophic bioreactors are recommended for sustainable protein and lutein biosynthesis.

Exploring agricultural waste biomass for energy, food and feed production and pollution mitigation: A review

Globally agricultural production system generates a huge amount of solid waste. Improper agri-waste management causes environmental pollution which resulted in economic losses and human health-related problems. Hence, there is an urgent need to design and develop eco-friendly, cost-effective, and socially acceptable agri-waste management technologies. Agri-waste has high energy conversion efficiency as compared to fossil fuel-based energy generation materials. Agri-waste can potentially be exploited for the production of second-generation biofuels. However, composted agri-waste can be an alternative to energy-intensive chemical fertilizers in organic production systems. Furthermore, value-added agri-waste can be a potential feedstock for livestock and industrial products. But comprehensive information concerning agri-waste management is lacking in the literature. Therefore, the present study reviewed the latest advancements in efficient agri-waste management technologies. This latest review will help the researchers and policy planners to formulate environmentally robust residue management practices for achieving a green economy in the agricultural production sector.

Microalgae-derived polysaccharides: Potential building blocks for biomedical applications

In recent years, the increasing concern about human health well-being has strongly boosted the search for natural alternatives that can be used in different fields, especially in biomedicine. This has put microalgae-based products in evidence since they contain many bioactive compounds, of which polysaccharides are attractive due to the diverse physicochemical properties and new or improved biological roles they play. Polysaccharides from microalgae, specially exopolysaccharides, are critically important for market purposes because they can be used as anti-inflammatory, immunomodulatory, anti-glycemic, antitumor, antioxidant, anticoagulant, antilipidemic, antiviral, antibacterial, and antifungal agents. Therefore, to obtain higher productivity and competitiveness of these naturally available compounds, the cultivation parameters and the extraction/purification processes must be better optimized in order to bring perspectives for the exploitation of products in commercial and clinical practice. In this sense, the objective of the present review is to elucidate the potential biomedical applications of microalgae-derived polysaccharides. A closer look is taken at the main polysaccharides produced by microalgae, methods of extraction, purification and structural determination, biological activities and their applications, and current status.

Microalgae-Based PUFAs for Food and Feed: Current Applications, Future Possibilities, and Constraints

Microalgae are currently considered an attractive source of highly valuable compounds for human and animal consumption, including polyunsaturated fatty acids (PUFAs). Several microalgae-derived compounds, such as ω-3 fatty acids, pigments, and whole dried biomasses are available on the market and are mainly produced by culturing microalgae in open ponds, which can be achieved with low setup and maintenance costs with respect to enclosed systems. However, open tanks are more susceptible to bacterial and other environmental contamination, do not guarantee a high reproducibility of algal biochemical profiles and productivities, and constrain massive cultivation to a limited number of species. Genetic engineering techniques have substantially improved over the last decade, and several model microalgae have been successfully modified to promote the accumulation of specific value-added compounds. However, transgenic strains should be cultured in closed photobioreactors (PBRs) to minimize risks of contamination of aquatic environments with allochthonous species; in addition, faster growth rates and higher yields of compounds of interest can be achieved in PBRs compared to open ponds. In this review, we present information collected about the major microalgae-derived commodities (with a special focus on PUFAs) produced at industrial scale, as well genetically-engineered microalgae to increase PUFA production. We also critically analyzed the main bottlenecks that make large-scale production of algal commodities difficult, as well as possible solutions to overcome the main problems and render the processes economically and environmentally safe.

Microalgae Polysaccharides: An Alternative Source for Food Production and Sustainable Agriculture

Carbohydrates or polysaccharides are the main products derived from photosynthesis and carbon fixation in the Calvin cycle. Compared to other sources, polysaccharides derived from microalgae are safe, biocompatible, biodegradable, stable, and versatile. These polymeric macromolecules present complex biochemical structures according to each microalgal species. In addition, they exhibit emulsifying properties and biological characteristics that include antioxidant, anti-inflammatory, antitumor, and antimicrobial activities. Some microalgal species have a naturally high concentration of carbohydrates. Other species can adapt their metabolism to produce more sugars from changes in temperature and light, carbon source, macro and micronutrient limitations (mainly nitrogen), and saline stress. In addition to growing in adverse conditions, microalgae can use industrial effluents as an alternative source of nutrients. Microalgal polysaccharides are predominantly composed of pentose and hexose monosaccharide subunits with many glycosidic bonds. Microalgae polysaccharides can be structural constituents of the cell wall, energy stores, or protective polysaccharides and cell interaction. The industrial use of microalgae polysaccharides is on the rise. These microorganisms present rheological and biological properties, making them a promising candidate for application in the food industry and agriculture. Thus, microalgae polysaccharides are promising sustainable alternatives for potential applications in several sectors, and the choice of producing microalgal species depends on the required functional activity. In this context, this review article aims to provide an overview of microalgae technology for polysaccharide production, emphasizing its potential in the food, animal feed, and agriculture sector.

Emerging biological wastewater treatment using microalgal-bacterial granules: A review

Aiming at deepening the understanding of the formation and evolution of emerging microalgal-bacterial granule (MBG)-based wastewater treatment systems, the recent advances regarding the formation processes, transfer phenomena, innovative bioreactors development and wastewater treatment performance of MBG-based systems are comprehensively reviewed in this work. Particularly, the successful establishments of MBG-based systems with various inocula are summarized. Besides, as the indispensable factors for biochemical reactions in MBGs, the light and substrates (organic matters, inorganic nutrients, etc) need to undergo complicated and multi-scale transfer processes before being assimilated by microorganisms within MBGs. Therefore, the involved transfer phenomena and mechanisms in MBG-based bioreactors are critically discussed. Subsequently, some recent advances of MBG-based bioreactors, the application of MBG-based systems in treating various synthetic and real wastewater, and the future development directions are discussed. In short, this review helps in promoting the development of MBG-based systems by presenting current research status and future perspectives.

Evaluation of Euglena gracilis 815 as a New Candidate for Biodiesel Production

Euglena comprises over 200 species, of which Euglena gracilis is a model organism with a relatively high fatty acid content, making it an excellent potential source of biodiesel. This study isolated and characterized a new strain named E. gracilis 815. E. gracilis 815 cells were cultivated under light and dark conditions, with either ethanol or glucose as an external carbon source and an autotrophic medium as control. To achieve maximum active substances within a short period i.e., 6 days, the effects of the light condition and carbon source on the accumulation of bioactive ingredients of E. gracilis 815 were explored, especially fatty acids. In comparison with the industrially used E. gracilis Z strain, E. gracilis 815 exhibited high adaptability to different carbon sources and light conditions, with a comparable biomass and lipid yield. The content and composition of fatty acids of E. gracilis 815 were further determined to assess its potential for biodiesel use. Results suggested that E. gracilis 815 has biodiesel potential under glucose addition in dark culture conditions and could be a promising source for producing unsaturated fatty acids. Therefore, E. gracilis 815 is a candidate for short-chain jet fuel, with prospects for a wide variety of applications.

Low temperature combined with high inoculum density improves alpha-linolenic acid production and biochemical characteristics of Chlamydomonas reinhardtii

Chlamydomonas reinhardtii grows fast and is rich in polyunsaturated fatty acids. To explore whether the alpha-linolenic acid (ALA) content can be further enhanced, the cultures were incubated under different culture temperatures, light intensities and inoculum densities. Results showed that temperature exhibited more great impact on ALA synthesis of C. reinhardtii than light intensity and inoculum size. The changes of light intensity and inoculum size displayed non-significant effects on ALA content. The optimal ALA proportion in cells was obtained under the condition of 10 °C, 50 μE/m²/s and 5% inoculum density, which reached ∼ 39%.The augmented initial inoculum density could markedly improve the biomass of C. reinhardtii under 10 °C. The maximum ALA productivity (16.42 mg/L/d) was gained under 10 °C coupled with 25% inoculum size, where higher intracellular sugar and protein yield were observed. These results suggest C. reinhardtii would be an alternative feedstock for the industrial production of ALA.