Microalgae Cell Wall Research Articles

Microalgae Application in Ruminants Feeds on The Production and Quality of Meat and Milk: A Review

Abstract Research focusing on microalgal as an alternative source of protein and fat in ruminant feed shows a growing trend. Microalgae are rich in carbohydrates, proteins, fats, amino acids, vitamins, minerals, and carotene. Ruminants can digest the cell walls of microalgae, positively affecting their health, growth, metabolism, reproduction, production, and product quality. This paper introduces the latest review of microalgae on ruminant feed and its effect on performance, production, and quality of meat and milk. The results showed that using microalgae does not increase milk production in dairy cows but substitutes protein from corn and soybean meal. Microalgae improves the quality of meat and milk through the changes in fatty acid profiles associated with omega 3, especially DHA and PUFA, which benefit human health. However, some microalgae species reduce palatability, feed consumption, and weight gain. Feeding microalgae to livestock as a supplement or substitute protein for soybean meal protein or other ingredients requires considering the limiting factors of lipid concentration and the economic value of microalgae species.

Natural deep eutectic solvents (NADES) for the extraction of bioactives: emerging opportunities in biorefinery applications

Natural deep eutectic solvents (NADES) have emerged as an eco-friendly alternative for extracting bioactives, avoiding the use of flammable organic solvents and extreme temperatures and pH conditions. NADES rely on intermolecular interactions between hydrogen bonding donors (HBD) and hydrogen bonding acceptors (HBA) to form eutectic mixtures with significantly lower melting points than their individual components. These matrices are influenced by factors like water content, temperature, and component ratios. NADES high viscosity can hinder extractive efficiency, which can be mitigated by adding water or working at higher temperatures. However, excessive dilution with water may disrupt the supramolecular structure of NADES, reducing extraction efficiency. A notable feature of NADES is their fine-tunability for specific purposes. Adjusting physicochemical properties such as polarity, pH, and viscosity optimizes extraction efficiency by promoting the solubility of target molecules and interactions between the NADES and target molecules. NADES, unlike organic solvents, can partially disrupt plant and microalgae cell walls, enhancing permeability and extraction efficiency. Moreover, NADES can have a stabilising effect on bioactives and can enhance their biological activity and bioavailability. These attributes, coupled with their low environmental impact in terms of low toxicity and high biodegradability, make NADES attractive for biorefinery applications.

Microalgae cell wall hydrolysis using snailase and mechanical sand milling

The extraction of intracellular constituents from recalcitrant microalgae strains stands as a significant challenge and a crucial bottleneck in microalgae processing. This study presents a novel enzymatic approach coupling mechanical lysis through sand milling without commercial glass or zirconium beads, with subsequent snailase treatment, resulting in improved cell wall breakdown and increased release of valuable constituents. The selected microalga was Chlorella sp. L06, renowned for its sturdy cell wall structure. Initial experiments involving sand milling unveiled substantial release of proteins (1.19 mg/mL) and chlorophyll (1.80 of absorbance at 680 nm), underscoring effective cell disruption. Remarkably, the application of snailase after sand milling produced noteworthy outcomes, fostering enhanced cell wall degradation and liberating a spectrum of constituents, encompassing soluble reducing sugars (1.13 mg/mL), proteins (2.28 mg/mL), and chlorophyll (2.83 of absorbance at 680 nm).The process was optimized by applying the Box-Behnken design, which revealed distinct operational parameters that significantly improved the release of soluble sugars and proteins by 46 % and 12.7 %, respectively. Moreover, the presence of snailase also showcased a protective antioxidant effect on chlorophyll during the hydrolysis, shedding light on its multifaceted role in the hydrolysis process.This study introduces an advantageous strategy for efficiently valorizing microalgae biomass using the synergistic potential of mechanical lysis and enzymatic treatment. Furthermore, the developed method contributes achieving promising, sustainable microalgae-based biorefineries.

Biosorption of Hexavalent Chromium by Freshwater Microalgae Craticula subminuscula from Aqueous Solutions

Recently, microalgae have tended to be used as a biological treatment for wastewater decontamination. The present study aimed to investigate the Cr(VI) removal using the freshwater microalgae ‘Craticula subminuscula’ and their biobased adsorbant, isolated from a Moroccan river in the High Atlas Mountain. The optimum operational conditions for maximum Cr(VI) biosorption by the biobased adsorbent form (95.32%) were determined at (pH = 1.09, adsorbent dose = 10.91 mg L−1, and treatment duration = 129.47 min) using response surface methodology (RSM). Under those optimal conditions, the biosorption process of Cr(VI) by C. subminuscula is endothermic, spontaneous and follows Langmuir and a pseudo-second-order model with a constant rate; the theoretical and experimental biosorption capacity of 0.0004 g/mg/min was 289.01 mg g−1 and 277.57 mg g−1, respectively. Fourier Transform Infrared Spectroscopy (FTIR) analyses of the biomass and scanning electron microscopy (SEM) revealed that the principal mechanism to remove Cr(VI) by C. subminuscula was the affinity of Cr(VI) by the cell walls of microalgae. Thus, the positive results of desorption cycles promise increased potential utilization of these algae in continuous systems within industrial processes. The findings contribute valuable insights into the effectiveness of C. subminuscula as a biobased remediation agent for Cr(VI) in wastewater treatment.

Neochloris oleoabundans cell wall rupture through melittin peptide: a new approach to increase lipid recovery.

Microalgae cell wall affects the recovery of lipids, representing one of the main difficulties in the development of biofuel production. This work aimed to test a new method based on melittin peptide to induce a cellular disruption in N. oleoabundans. Neochloris oleoabundans cells were grown at 32°C in the presence of a high concentration of nitrate-phosphate, causing a cell disruption extent of 83.6%. Further, a two-fold increase in lipid recovery following melittin treatment and solvent extraction was observed. Additionally, it was possible to verify the effects of melittin, both before and after treatment on the morphology of the cells. Scanning electron microscopy (SEM) and confocal images of the melittin-treated microalgae revealed extensive cell damage with degradation of the cell wall and release of intracellular material. Melittin produced a selective cell wall rupture effect in N. oleoabundans under some culture conditions. These results represent the first report on the effect of melittin on lipid recovery from microalgae.

Microalgae as a Sustainable Source of Antioxidants in Animal Nutrition, Health and Livestock Development.

Microalgae are a renewable and sustainable source of bioactive compounds, such as essential amino acids, polyunsaturated fatty acids, and antioxidant compounds, that have been documented to have beneficial effects on nutrition and health. Among these natural products, the demand for natural antioxidants, as an alternative to synthetic antioxidants, has increased. The antioxidant activity of microalgae significantly varies between species and depends on growth conditions. In the last decade, microalgae have been explored in livestock animals as feed additives with the aim of improving both animals' health and performance as well as product quality and the environmental impact of livestock. These findings are highly dependent on the composition of microalgae strain and their amount in the diet. The use of carbohydrate-active enzymes can increase nutrient bioavailability as a consequence of recalcitrant microalgae cell wall degradation, making it a promising strategy for monogastric nutrition for improving livestock productivity. The use of microalgae as an alternative to conventional feedstuffs is becoming increasingly important due to food-feed competition, land degradation, water deprivation, and climate change. However, the cost-effective production and use of microalgae is a major challenge in the near future, and their cultivation technology should be improved by reducing production costs, thus increasing profitability.

Biohydrogen production of a halophytic cyanobacteria Phormidium keutzingium and activated sludge co-culture using different carbon substrates and saline concentrations

Hydrogen (H2) production using a biological pathway such as anaerobic digestion suffers limitations in the survival of microorganisms. Usually, microalgae are used as feedstock but the acidic pH of digestate ruptures the cell wall of microalgae resulting in dead cellular debris. Whereas some cyanobacteria (blue-green microalgae) are very resilient and tolerant to stressful environments such as hypersaline conditions. Therefore, in this study, a microbial consortium (co-culture) of cyanobacteria Phormidium keutzingianum and activated sludge bacteria (ASB) was established to generate H2 production from waste resources. Different co-culturing ratios 2:1, 1:1, and 1:2 v/v (P. keutzingianum: ASB) were analyzed for H2 production with glucose, sorbitol, and mannitol as carbon substrates. In addition, the effect of different concentrations (0, 10, and 20 g/L) of salt (NaCl) on H2 production was also tested. Results indicated that the amount of cumulative H2 produced changed significantly by varying the carbon substrates. Glucose-supplemented co-culture produced the lowest amount of H2 at 278 mL/L as compared to 980 and 562 mL H2/L in sorbitol and mannitol-supplemented co-cultures, respectively. The addition of NaCl negatively affected H2 production by increasing the salinity level from 0 to 20 g/L, and the cumulative H2 reduced from 980 to 176.8 mL/L and 562 to 333 mL/L in sorbitol and mannitol-supplemented co-culture, respectively. Sorbitol showed cyanobacterial growth in terms of chlorophyll from 600 to 1200 μg/L and optical density from 1 to 12 at λ 620 nm. Total organic carbon (TOC) in sorbitol supplemented co-cultures also increased to the peak 5.7, 6.7, and 7.7 g/L in 2:1, 1:2, and 1:1 v/v ratios, respectively, indicating anaerobic growth. Hence, this study signifies that sorbitol appeared to be the significant carbon substrate that helped cyanobacteria grow under anaerobic conditions resulting in higher H2 production. Moreover, cyanobacteria are more tolerant to stressful environments such as hypersaline and acidic conditions compared to microalgae.

Flexibility and Function of Distal Substrate-Binding Tryptophans in the Blue Mussel β-Mannanase MeMan5A and Their Role in Hydrolysis and Transglycosylation

β-Mannanases hydrolyze β-mannans, important components of plant and microalgae cell walls. Retaining β-mannanases can also catalyze transglycosylation, forming new β-mannosidic bonds that are applicable for synthesis. This study focused on the blue mussel (Mytilus edulis) GH5_10 β-mannanase MeMan5A, which contains two semi-conserved tryptophans (W240 and W281) in the distal subsite +2 of its active site cleft. Variants of MeMan5A were generated by replacing one or both tryptophans with alanines. The substitutions reduced the enzyme’s catalytic efficiency (kcat/Km using galactomannan) by three-fold (W281A), five-fold (W240A), or 20-fold (W240A/W281A). Productive binding modes were analyzed by 18O labeling of hydrolysis products and mass spectrometry. Results show that the substitution of both tryptophans was required to shift away from the dominant binding mode of mannopentaose (spanning subsites −3 to +2), suggesting that both tryptophans contribute to glycan binding. NMR spectroscopy and molecular dynamics simulations were conducted to analyze protein flexibility and glycan binding. We suggest that W240 is rigid and contributes to +2 subsite mannosyl specificity, while W281 is flexible, which enables stacking interactions in the +2 subsite by loop movement to facilitate binding. The substitutions significantly reduced or eliminated transglycosylation with saccharides as glycosyl acceptors but had no significant effect on reactions with alcohols.

ANAEROBIC CO-DIGESTION OF MICROALGAE AND RESIDUAL GLYCEROL RECOVERED FROM BIODIESEL: EVALUATION OF PRETREATMENT AND COD/N RATIO

Anaerobic digestion can be a viable alternative for the destination of effluents from stabilization ponds rich in naturally produced microalgae, without the need for concentration processes, however, there are challenges related to the rigid cell wall of microalgae and the low carbon content in its composition, to be overcome. To improve these parameters, this study comparatively evaluated hydrolytic pretreatments in microalgae from effluents from stabilization ponds, aiming to hydrolyze the cell wall of these microorganisms, for co-digestion with residual glycerol from biodiesel. In this case, glycerol is a by-product with limited applicability, acting in this scenario as a carbon supplier, improving the C/N ratio, microalgae biodegradation and biomethane production. Effluents with microalgae submitted to thermal and ultrasonic hydrolysis (for 30 and 90 minutes) were tested to assess their potential in the production of methane-rich biogas, monitored by gauge measurements and gas chromatography, respectively, in co-digestion with residual glycerol from biodiesel. The heat treatment for 30 minutes showed more satisfactory results and was replicated in a benchtop anaerobic reactor (R2), in parallel with a reactor operating untreated microalgae (R1), in a continuous feed system. The effects of pretreatment and COD/N ratio were evaluated on organic matter removal and biomethane production. R2 showed the most satisfactory effect on COD removal, resulting in up to 90% COD removed, with a theoretical biogas production of 0.52 L g-1 COD removed. As for the methane content contained in biogas, R1 reached percentages of up to 84% against 73% in R2.

Optimisation of ultrasonication pretreatment on microalgae Chlorella Vulgaris &Nannochloropsis Oculata for lipid extraction in biodiesel production

A wide variety of nutritious products and biofuels can be produced from microalgae. Their applications span across various sectors such as food, medical, and energy industries. Microalgal cell disruption is a crucial aspect in the production processes as it facilitates the extraction of bio-products stored within them. One of the commonly extracted compounds from microalgae is lipids, which constitute a high percentage of their composition. In this study, we conducted ultrasonic pre-treatment on two different microalgae species, namely Chlorella vulgaris and Nannochloropsis oculata. The pre-treatment involved ultrasonic frequencies of 37 and 80 kHz, exposure times of 10, 15, and 20 min, and extraction times of 2, 3, and 4 h. By utilising ultrasonic frequencies, we induced acoustic cavitation to break the microalgae cell walls and extract lipids. The experimental design followed a Response Surface Methodology (RSM) to evaluate the effect of ultrasonication pretreatment parameters on lipid extraction. In comparison to previously published studies, our findings indicate that higher frequencies of ultrasonication lead to increased lipid extraction from microalgae. The highest lipid yield achieved in our study was 11.54% for Chlorella vulgaris and 17.91% for Nannochloropsis oculata, using the input factors of 80 kHz frequency, 20 min of running time, and 4 h of extraction time. Our results contribute to the existing body of knowledge by demonstrating the efficacy of ultrasonic pre-treatment in lipid extraction from microalgae. By providing a quantitative comparison with previous studies, this study highlight the novel aspects of work and its potential implications for the production of biofuels and other valuable products from microalgae.

Microalgae fractionation and pyrolysis of extracted microalgae biopolymers

In order to maximize the economic return from microalgae production, the feasibility of thermochemically converting microalgae by-products which have had one or more biochemical components extracted (lipids and/or protein) needs to be considered. The extracted microalgae are waste stemming from microalgae biorefineries where biodiesel and/or valuable proteins/peptides have been produced. The biorefinery scheme of maximized microalgae utilization based on isolation of lipids or lipids and proteins combined, and the thermochemical conversion of the remaining fractions are discussed in this study. The biopolymer components of Nannochloropsis gaditana were extracted to form a lipid fraction, a protein fraction and a carbohydrate-rich residue. The lipid extraction efficiency reached 76.9 wt.%, however, the efficiency of protein extraction was 42.2 wt.% due to the inability of the extraction process to remove all protein. The surface functional groups and thermochemical characteristics of extracted components were investigated by FTIR and py-GC/MS, respectively. The FTIR results suggested that the extraction process disrupted the microalgae cell walls and released intracellular components. Lipids are recommended to be extracted for biofuel production by transesterification. For specific high protein-containing microalgae, protein extraction has to be considered to obtain high value proteins and derived chemicals. After the extraction of high value products, the carbohydrate-rich residue which is considered of low value, can be used as a fast pyrolysis feedstock instead of the whole microalgae. The pyrolysis chemical pathways as a function of temperature were schematized in order to better understand the reaction mechanisms in microalgae pyrolysis. The formation of alkanes and alkenes at higher temperatures were stemming from the long-chain alcohols and carboxylic acids. The formation pathways of N-heterocyclic compounds include Maillard reactions, cracking of amino acids and the cyclization of amines and amides.

A Comprehensive Study on DES Pretreatment Application to Microalgae for Enhanced Lipid Recovery Suitable for Biodiesel Production: Combined Experimental and Theoretical Investigations

Cell wall disturbance is an important step in the downstream process of improving the efficiency of lipid extraction from microalgae. Surfactants have been proven to be efficient alternatives to organic solvents in the extraction process. In this study, an effective approach involving deep eutectic solvent (DES) (choline chloride and carboxylic acids) treatment supplemented with surfactants has been developed to disrupt the cell walls of microalgae and increase the extraction of lipids suitable for biodiesel production. A combination of polar and non-polar solvents (ethyl acetate and n-butanol) was used for the lipid extraction process. Microalgae biomass pretreated with choline chloride malonic acid supplemented with the surfactant hexadecyl trimethylammonium chloride (HTAC) showed the best results, improving lipid extraction by 12.365%. Further elucidation of the detailed mechanism behind the cell disruption of the microalga wall by DES was achieved using density functional theory (DFT) methods. The DFT calculations revealed that hydrogen bonds between the chloride ion of the DES and hydrogen bond donor (HBD) molecules are key factors dominating the destruction of the cell wall structure of Chlorella pyrenoidosa. The optimization of lipid extraction was performed through a single-factor experiment, which included the effects of different variables (time, temperature, dosage of surfactant, and ratio of n-butanol to ethyl acetate). An extraction period of 60 min at 80 °C with a surfactant concentration of 0.5% at a 1:2 ratio of n-butanol to ethyl acetate was found to produce the maximum lipid yield (16.97%). Transesterification reactions were used to obtain fatty acid methyl esters from the optimized extracted lipids. Thus, it was determined that C16:0 (20.04%), C18:2 (29.95%), and C18:3 (21.21%) were the most prevalent fatty acids. The potential for producing biodiesel from C. pyrenoidosa was validated by the high yields of C18 fatty acid methyl esters, and the properties of biodiesel are within the European and US standards.

Lipid extraction from fresh Nannochloropsis oceanica using semi-hydrophobic eutectic solvents

Conventional lipid extraction from microalgae involves energy-intensive pretreatments and the use of non-renewable organic solvents. Eutectic solvents (ES), a new class of designer solvents, hold the potential to improve lipid extraction. Hydrophilic ES have been reported to impair the cell wall of microalgae, bypassing the need for pretreatments. However, other hydrophobic solvents were still required as extraction medium. Recently, ES imidazole and hexanoic acid was discovered to exhibit tuneable hydrophobicity, i.e., dissolving both water and lipids depending on their molar composition. In this work, we evaluated the feasibility of imidazole/hexanoic ES as a single solvent for lipid extraction from intact wet and dried microalga Nannochloropsis oceanica. Single-factor multilevel design of experiments is used to evaluate the yield under different conditions (ES composition, temperature, time, solvent/biomass ratio, and water content). Interestingly, the extractions from wet algae paste were higher than dried biomass, reaching a comparable yield to the traditional chloroform/methanol method. From wet biomass, >80 % lipids were extracted by the imidazole/hexanoic acid ES (15:85 mol/mol) at 50 °C within 2 h. Whereas, the extraction yield of dry biomass was lower, reaching only 65 % even after 12 h under the same condition. Supplementation of water during the dry extraction resulted in the same yield as the wet extraction. This research demonstrated that ES can be used to replace non-renewable organic solvents without the need of using mechanical disruption and can be applied directly on wet biomass.

Combining AFM, XPS and chemical hydrolysis to understand the complexity and dynamics of C. vulgaris cell wall composition and architecture

The microalgae cell wall represents its interface with its environment, and is a dynamic and complex structure that evolves depending on the growth phase or culture conditions. To apprehend this complexity, an experimental approach combining AFM, XPS, and chemical hydrolysis followed by HPAEC-PAD was developed to understand the cell wall of Chlorella vulgaris, a biotechnologically-relevant green microalgae species. Exponential and stationary growth stages were investigated, as well as saline stress condition inducing lipid production. Results showed that both the cell wall composition and architecture changes in stationary phase, with an increase of the lipidic fraction at the expense of the proteic fraction, changes in the polysaccharidic composition, and a significant increase of its rigidity. Under saline stress, cell wall architecture seems to be affected as importantly, its rigidity is reduced. Altogether, this study demonstrates the power of combining these three techniques to give new insights into C. vulgaris cell wall, in terms of composition and architecture, and of its dynamics in different conditions.

Optimized infrared-assisted extraction to obtain total lipid from microalgae Scenedesmus obliquus: a green approach

Abstract Microalgae oil has great potential to address the growing energy demand and dependence on fossil fuels. However, the multilayered cell walls of microalgae hinder efficient extraction and enhanced lipid recovery. In this study, we develop a novel protocol based on near infrared-assisted extraction (NIRAE) technology to extract efficiently total lipids from Scenedesmus obliquus. Under a greener solvent extraction approach, the effect of nine non-polar/polar solvent systems in various ratios on lipid yield was tested, and the results were compared with Soxhlet, Folch, and Bligh–Dyer methods. The highest oil yields were NIRAE 15.43%, and Soxhlet 22.24%, using AcoEt/MeOH (1:2 v/v). For Folch and Bligh–Dyer, 9.11 and 10%, respectively. The optimized NIRAE conditions obtained using response surface methodology (RSM): 43.8 min, solvent/biomass 129.90:1 (m/v), and AcOEt/MeOH 0.57:2.43 (v/v) increased the oil yield significantly to 24.20%. In contrast to conventional methods, the overall optimized NIRAE process satisfied the requirements of a green extraction because of the simple and safe operation, less solvent toxicity, lower extraction time, and solvent and energy consumption.

Mechanical processing of Phaeodactylum tricornutum and Tetraselmis chui biomass affects phenolic and antioxidant compound availability, nutrient digestibility and deposition of carotenoids in Atlantic salmon

Cell walls of microalgae differ both in terms of chemical composition and architecture. Certain characteristics of cell walls limit both the effectiveness of extraction of valuable constituents and nutrient bioavailability and bioaccessibility in fish. We first investigated the potential of bead milling to disrupt cell walls to improve extractability of bioactive compounds from Phaeodactylum tricornutum and Tetraselmis chui. We also evaluated the effect of the mechanical treatment on i) digestibility of nutrients in the two microalgae and ii) fatty acid and pigment content of fillet of Atlantic salmon fed the algae diets.Cell wall disruption facilitated efficient release of total phenolic compounds (TPC), chlorophyll A, chlorophyll B and total carotenoids from both microalgae species, but increased only the total antioxidant capacity (TAC) of T. chuii. The polyphenol profile varied between the two species; we identified 2 and 6 polyphenols from P. tricornutum and T. chui, respectively.For the feeding experiment, microalgae biomass, intact or cell wall disrupted (90.7 and 76.4% disruption degree for T. chui and P. tricornutum, respectively), were mixed with the other feed ingredients. Atlantic salmon (315 g start weight / 55 fish per tank) were fed one of the five extruded experimental diets (a fishmeal-based reference diet and four feeds with 30% of the whole or broken microalgae biomass added to the reference diet). The digestibility of protein in the P. tricornutum was significantly higher compared to that of T. chui. Breaking the cell walls by bead milling caused a significant improvement in digestibility of protein in T. chui. The apparent digestibility coefficient of lipid was higher in P. tricornutum and bead milling improved the digestibility of the two algae. However, bead milling did not favourably change the fatty acid profile of Atlantic salmon. At the end of the feeding trial, P. tricornutum-fed fish had significantly improved pigmentation, probably due to the higher content of fucoxanthin and fucoxanthinol compared to the fish fed the reference diet. The main conclusion from the mechanical processing of the microalgae is that bead milling can increase i) the extractability of polyphenols and pigments, ii) the digestibility of lipid in both algae while the effect on protein was improved only for T. chui. Furthermore, P. tricornutum can be considered a natural pigment source in the feeds of Atlantic salmon.

Extraction of total carbohydrates by solvents from the microalgae <em>Chlorella</em> vulgaris and analysis of the influence of NaNO3 and photoperiods on microalgae cell growth

The development of new resources for ethanol production has been changing over the years, and microalgae use has become one of the most ecological alternatives. Microalgae are increasingly being used due to their biochemical composition, rich in carbohydrates and proteins, in addition to several properties such as high CO2 absorption capacity. One of the most cultivated and studied microalgae today is Chlorella vulgaris since it has high growth rates and can be cultivated in different environments and conditions. Therefore, microalgae biomass is composed of potential ingredients for the production of biofuels. Considering the above, the objective of this work is to extract the total carbohydrates stored in the cellular structure of the microalgae by the organic solvent extraction method, hexane/ethanol (1:2) and by ionic liquid/ethanol (1:2), evaluating different conditions of microalgae cultivation. For this, 9 experiments were carried out, varying according to the culture medium in which the microalgae were introduced, containing BG-11 medium with different concentrations of NaNO3 (sodium nitrate) and forced aeration, in addition to different cultivation photoperiods. The reading of the results showed that the breakdown of the microalgae cell wall was better with acid hydrolysis and extraction with hexane. Thus, the highest efficiency in the extraction of carbohydrates was with a sodium nitrate concentration of 2300 and a photoperiod of 16 hours, during the entire period evaluated.

Synthesis and Characterization of Innovative Microgels Based on Polyacrylic Acid and Microalgae Cell Wall and Their Potential as Antigen Delivery Vehicles.

In this study, hybrid polyacrylic acid and Schizochytrium sp. microalgae (PAA/Schizo) microgels were synthesized by inverse emulsion assisted by ultrasound using the cell wall fraction as crosslinker. Physicochemical characterization of PAA/Schizo microgels revealed polymeric spherical particles (288 ± 39 nm) and were deemed stable and negatively charged. The produced microgels are not inherently toxic as cell viability was sustained above 80% when mice splenocytes were exposed to concentrations ranging 10-900 µg/mL. PAA/Schizo microgels were evaluated as antigen delivery nanovehicle by adsorbing bovine serum albumin (BSA); with a loading efficiency of 72% and loading capacity of 362 µg/mg. Overall, intranasally-immunized BALB/c mice showed null IgG or IgA responses against PAA/Schizo microgel-BSA, whereas soluble BSA induced significant humoral responses in systemic and mucosal compartments. Splenocytes proliferation assay upon BSA stimulus revealed positive CD4+ T cells-proliferation response in PAA/Schizo microgels-BSA group. Thus, PAA/Schizo microgels constitute functional antigen delivery vehicles of simple and ecofriendly synthesis. Moreover, the use of cell wall fraction as cross-linker agent provides an alternative use for the generation of high-value products using residual algae biomass from the oil industry. Our data suggests that the PAA/Schizo microgels are potential antigen delivery vehicles for immunotherapy development.

Recovery of lipids and carotenoids from Dunaliella salina microalgae using deep eutectic solvents

Microalgae are natural sources of bioactive compounds used for numerous applications such as pharmaceutical, nutraceutical, cosmetic, and recently in the production of biofuels. Achieving sustainability in some biotechnological processes still requires overcoming important challenges including the fatty acid biomass extraction processes. Methanol and chloroform are generally used in the traditional extraction processes, which are toxic and present environmental risks. Thus, studies involving environmentally sustainable solvents which are less aggressive to health are necessary. In this context, deep eutectic solvents (DESs) have shown attractive characteristics. DESs stand out as adjuvants in cell disruption and biomolecule extraction stages, working as non-toxic, non-volatile, and renewable agents. This work aimed to evaluate the effect of different DESs (pure and aqueous based on choline chloride) on extracting lipids and carotenoids from Dunaliella salina. The best total lipid recovery was 67.41 % ± 6.07 achieved using a DES synthetized with choline chloride and urea (Ch-U treatment) from dry biomass by two-step extraction. On the other hand, a significant migration to the DES phase (pre-treatment) was observed for carotenoids, and consequently lower recovery values. Thus, the one-pot method was evaluated to solve this problem and reduce the process steps, and 84.06 ± 1.22 % of carotenoids were recovered from wet biomass with Ch-U treatment and ethyl acetate and ethanol (EAE) solvent. It was also observed that the treatment performed with choline chloride and oxalic acid (Ch-Ox treatment) presented one of the highest reductions in carbohydrate content among the evaluated treatments, and the most in protein content of the microalgal biomass. Finally, the strategies tested herein were validated by comparing the results with traditional methodologies (ultrasonic and ball mill). It was generally found that DESs enhanced the solvent permeability in the microalgae cell wall and the efficiency and sustainability of the extractive process can be increased depending on the chosen strategy.

Interactive adverse effects of low-density polyethylene microplastics on marine microalga Chaetoceros calcitrans

Low-density polyethylene (LDPE) is broadly utilized worldwide, increasing more dramatically during the COVID-19 pandemic, and the majority ends up in the aquatic environment as microplastics. The influence of polyethylene microplastics (LDPE-MPs) on aquatic ecosystems still needs further investigation, especially on microalgae as typical organisms represented in all aquatic systems and at the base of the trophic chain. Thereby, the biological and toxicity impacts of LDPE-MPs on Chaetoceros calcitrans were examined in this work. The results revealed that LDPE-MPs had a concentration-dependent adverse effect on the growth and performance of C. calcitrans. LDPE-MPs contributed the maximum inhibition rates of 85%, 51.3%, 21.49% and 16.13% on algal growth chlorophyll content, φPSII and Fv/Fm, respectively. The total protein content, superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) activities were significantly increased at 25 mg L−1 LDPE-MPs by 1.37, 3.52, 2.75 and 1.84 folds higher than those of the controls to sustain the adverse effects of LDPE-MPs. Extracellular polymeric substance (EPS) and monosaccharides contents of C. calcitrans were improved under low concentration of LDPE-MPs, which could facilitate the adsorption of MPs particles on the microalgae cell wall. This adsorption caused significant physical damage to the algal cell structure, as observed by SEM. These results suggest that the ecological footprint of MPs may require more attention, particularly due to the continuing breakdown of plastics in the ecosystem.