Fatty acid and metabolomic profiling approaches differentiate heterotrophic and mixotrophic culture conditions in a microalgal food supplement 'Euglena'

Effect of ultrafine CO2 bubbles on Euglena gracilis Z growth with CO2 gas bubble size and chlorophyll content

Microalgae have been explored as a viable alternative food source. Among them, Euglena gracilis stands out as a promising single-cell algae. However, the challenge lies in developing more efficient and cost-effective methods for industrial mass production of E. gracilis under controlled culture conditions. Our research aimed to address this by investigating the role of nanotechnology in using fine to ultra-fine bubble CO2 (FB-CO2)-ranging from micrometer to nanometer size-as feeding material to promote cell harvest of E. gracilis Z in autotrophic culture conditions. Our findings suggest that feeding E. gracilis Z with FB-CO2 increased cell growth and chlorophyll content in autotrophic culture conditions. The promotion effect can be attributed to the provision of non-ionized carbon dioxide to the photosynthetic system, which was further enhanced by the dispersion of FB-CO2 in the culture media under acidic conditions.

Riboflavin improves meat quality, antioxidant capacity, muscle development, and lipids composition of breast muscle in pigeon

This study investigated the effects of different dietary riboflavin supplementation levels on riboflavin status, meat quality, antioxidant capacity, breast muscle development, and lipid composition in pigeons. Squabs were fed diets with five riboflavin concentrations ranging from 1.20 to 16.20 mg/kg. Riboflavin, flavin adenine dinucleotide, and flavin mononucleotide concentrations in the liver and breast muscle were significantly lower in the riboflavin-deficient group (P < 0.05) and increased with higher riboflavin levels. Regarding meat quality, riboflavin supplementation improved shear force, redness, breast muscle weight, and percentage (P < 0.05), whereas riboflavin deficiency exhibited poorer meat characteristics. Riboflavin enhanced antioxidant capacity, as shown by reduced MDA and increased T-SOD and GR activity in the supplemented groups (P < 0.05). Histological analysis revealed that riboflavin-deficient pigeons had smaller muscle fiber diameter and greater fiber density (P < 0.05). Riboflavin supplementation also improved lipid composition by reducing saturated fatty acids and increasing polyunsaturated fatty acids, particularly arachidonic acid (P < 0.05). Additionally, riboflavin influenced the expression of key genes involved in lipid metabolism and antioxidant function, with downregulation of ACADL and ACADS in the deficient group (P < 0.05). These results indicate adequate riboflavin supplementation enhances pigeon meat quality, muscle development, antioxidant defense, and lipid metabolism. In conclusion, riboflavin supplements in the pigeon diet can improve the quality of pigeon meat by maintaining muscle development, enhancing antioxidant function, and stabilizing lipid metabolism.

Nuclear mutagenesis and adaptive evolution improved photoautotrophic growth of Euglena gracilis with flue-gas CO2 fixation

To effectively improve biomass growth and flue-gas CO2 fixation of microalgae, acid-tolerant Euglena gracilis was modified with cobalt-60 γ-ray irradiation and polyethylene glycol (PEG) adaptive screening to obtain the mutant strain M800. The biomass dry weight and maximum CO2 fixation rate of M800 were both 1.47 times higher than that of wild strain, which was attributed to a substantial increase in key carbon fixation enzyme RuBisCO activity and photosynthetic pigment content. The high charge separation quantum efficiency in PSII reaction center, efficient light utilization and energy regulation that favors light conversion, were the underlying drivers of efficient photosynthetic carbon fixation in M800. M800 had stronger antioxidant capacity in sufficient high-carbon environment, alleviating lipid peroxidation damage. After adding 1 mM PEG, biomass dry weight of M800 reached 2.31 g/L, which was 79.1 % higher than that of wild strain. Cell proliferation of M800 was promoted, the apoptosis and necrosis rates decreased.

Algal nutraceuticals: A perspective on metabolic diversity, current food applications, and prospects in the field of metabolomics

The current consumers' demand for food naturalness is urging the search for new functional foods of natural origin with enhanced health-promoting properties. In this sense, algae constitute an underexplored biological source of nutraceuticals that can be used to fortify food products. Both marine macroalgae (or seaweeds) and microalgae exhibit a myriad of chemical constituents with associated features as a result of their primary and secondary metabolism. Thus, primary metabolites, especially polysaccharides and phycobiliproteins, present interesting properties to improve the rheological and nutritional properties of food matrices, whereas secondary metabolites, such as polyphenols and xanthophylls, may provide interesting bioactivities, including antioxidant or cytotoxic effects. Due to the interest in algae as a source of nutraceuticals by the food and related industries, novel strategies should be undertaken to add value to their derived functional components. As a result, metabolomics is considered a high throughput technology to get insight into the full metabolic profile of biological samples, and it opens a wide perspective in the study of algae metabolism, whose knowledge is still little explored. This review focuses on algae metabolism and its applications in the food industry, paying attention to the promising metabolomic approaches to be developed aiming at the functional characterization of these organisms.

The potential of Euglena species as a bioindicator for soil ecotoxicity assessment

Currently, there are no standard international test methods for assessing aquatic and soil toxicity, with aquatic toxicity tests based on limited Euglena species. Here, we proposed Euglena species as extended test species, especially as new soil test species for a paper-disc soil method, considering its ecologically important roles in providing highly bioavailable in-vivo nutrients to upper trophic level organisms. We conducted experiments to identify the optimal exposure duration for two Euglena species (Euglena viridis and Euglena geniculata). We demonstrated the toxic effects of nickel (model contaminant) on their photosynthetic parameters and growth in freshwater. The growth and photosynthetic activity of three Euglena species were significantly inhibited in nickel-contaminated soil during paper-disc soil tests, especially the test species adsorbed onto paper-disc soil. Euglena gracilis was more sensitive to nickel than E. viridis and E. geniculata in freshwater and soil. Thus, E. viridis and E. geniculata have potential as additional test species for improving test species diversity, while all three species have potential as new soil test species for soil toxicity assessment. Thus, results these species may be suitable for routine aquatic toxicity testing and new soil toxicity testing, addressing the current paucity of test species in freshwater and soil toxicity assessment.

CO2 gradient domestication improved high-concentration CO2 tolerance and photoautotrophic growth of Euglena gracilis

In order to improve CO₂ biofixation efficiency of microalgae cultivated with coal-chemical flue gas, CO₂ gradient domestication was employed to improve high-concentration CO₂ tolerance and photoautotrophic growth of acid-tolerant Euglena gracilis. The dried biomass yield of photoautotrophic growth of E.gracilis increased from 1.09 g/L (wild-type strain) by 21 % to 1.32 g/L with CO₂ gradient domestication to 15 % CO₂. The RuBisCO activity and biomass production of E.gracilis strain domesticated to 99 % CO₂ were 2.63 and 3.4 times higher, respectively, than those of wild-type strain. The chlorophyll a and b contents were 2.52 and 1.79 times higher, respectively, than those of wild-type strain. Superoxide dismutase and catalase activities of 99 % CO₂-domesticated strain increased to 1.24 and 6 times, which reduced peroxide damage under high carbon stress and resulted in lower apoptotic and necrotic rates of domesticated strain. Thus, this work provides valuable guidance for CO₂ fixation and adaptive evolution of E. gracilis in industrial flue gas.

Microalgal photoautotrophic growth induces pH decrease in the aquatic environment by acidic metabolites secretion

BACKGROUND

Microalgae can absorb CO₂ during photosynthesis, which causes the aquatic environmental pH to rise. However, the pH is reduced when microalga Euglena gracilis (EG) is cultivated under photoautotrophic conditions. The mechanism behind this unique phenomenon is not yet elucidated.

RESULTS

The present study evaluated the growth of EG, compared to Chlorella vulgaris (CV), as the control group; analyzed the dissolved organic matter (DOM) in the aquatic environment; finally revealed the mechanism of the decrease in the aquatic environmental pH via comparative metabolomics analysis. Although the CV cell density was 28.3-fold that of EG, the secreted-DOM content from EG cell was 49.8-fold that of CV (p-value < 0.001). The main component of EG's DOM was rich in humic acids, which contained more DOM composed of chemical bonds such as N-H, O-H, C-H, C=O, C-O-C, and C-OH than that of CV. Essentially, the 24 candidate biomarkers metabolites secreted by EG into the aquatic environment were acidic substances, mainly lipids and lipid-like molecules, organoheterocyclic compounds, organic acids, and derivatives. Moreover, six potential critical secreted-metabolic pathways were identified.

CONCLUSIONS

This study demonstrated that EG secreted acidic metabolites, resulting in decreased aquatic environmental pH. This study provides novel insights into a new understanding of the ecological niche of EG and the rule of pH change in the microalgae aquatic environment.

Heterotrophic Cultivation of Euglena gracilis in Stirred Tank Bioreactor: A Promising Bioprocess for Sustainable Paramylon Production

Paramylon is a valuable intracellular product of the microalgae Euglena gracilis, and it can accumulate in Euglena cells according to the cultivation conditions. For the sustainable production of paramylon and appropriate cell growth, different bioreactor processes and industrial byproducts can be considered as substrates. In this study, a complex medium with corn steep solid (CSS) was used, and various bioreactor processes (batch, fed batch, semicontinuous and continuous) were performed in order to maximize paramylon production in the microalgae Euglena gracilis. Compared to the batch, fed batch and repeated batch bioprocesses, during the continuous bioprocess in a stirred tank bioreactor (STR) with a complex medium containing 20 g/L of glucose and 25 g/L of CSS, E. gracilis accumulated a competitive paramylon content (67.0%), and the highest paramylon productivity of 0.189 g/Lh was observed. This demonstrated that the application of a continuous bioprocess, with corn steep solid as an industrial byproduct, can be a successful strategy for efficient and economical paramylon production.

Fatty Acid Accumulations and Transcriptome Analyses Under Different Treatments in a Model Microalga Euglena gracilis

With the continuous growth of the world’s population and the increasing development of industrialization, the demand for energy by human beings has been expanding, resulting in an increasingly severe energy crisis. Microalgae are considered the most potential alternatives to traditional fossil fuels due to their many advantages, like fast growth rate, strong carbon sequestration capacity, and low growth environment requirements. Euglena can use carbon sources such as glucose, ethanol, and others for heterotrophic growth. Moreover, Euglena is highly adaptable to the environment and has a high tolerance to various environmental stresses, such as salinity, heavy metals, antibiotics, etc. Different treatments of Euglena cells could affect their growth and the accumulation of bioactive substances, especially fatty acids. To expand the industrial application of Euglena as a potential biodiesel candidate, we determine the physiological responses of Euglena against environmental stresses (antibiotics, heavy metals, salinity) or carbon resources (glucose and ethanol), and evaluate the potential for higher quality and yield of fatty acid with a high growth rate. Adding glucose into the culture media increases cell biomass and fatty acid production with high-quality biodiesel characters. The transcriptome analysis helped explore the possible regulation and biosynthesis of fatty acids under different treatments and exploited in the improvement of biodiesel production. This study provides insights for further improvement and various culture treatments for Euglena-based biodiesel and jet fuels.

Metabolomics revealed the photosynthetic performance and metabolomic characteristics of Euglena gracilis under autotrophic and mixotrophic conditions

Photosynthetic and metabolomic performance of Euglena gracilis was examined and compared under autotrophic and mixotrophic conditions. Autotrophic protozoa (AP) obtained greater biomass (about 33% higher) than the mixotrophic protozoa (MP) after 12 days of growth. AP maintained steady photosynthesis, while MP showed a remarkable decrease in photosynthetic efficiency and dropped to an extremely low level at day 12. In MP, low light absorption and photosynthetic electron transport efficiency, and high energy dissipation were reflected by the chlorophyll (chl a) fluorescence (OJIP) of the protozoa. The values of Ψ_O, Φ_Eo, and ET_O/RC of MP decreased to extremely low levels, to 1/15, 1/46, and 1/9 those of AP, respectively, while DI_O/RC increased to approximately 16 times that of AP. A total of 137 metabolites were showed significant differences between AP and MP. AP accumulated more monosaccharide, lipids, and alkaloids, while MP produced more amino acids, peptides, and long-chain fatty acids including poly-unsaturated fatty acids. The top nine most important enriched pathways obtained from KEGG mapping were related to ABC transporters, biosynthesis of amino acids, purine metabolism, and carbohydrate metabolism. There were significant differences between AP and MP in photosynthetic activity, metabolites, and metabolic pathways. This work presented useful information for the production of high value bioproducts in E. gracilis cultured under different nutritional conditions.

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.

Anti-Inflammatory Activities of Euglena gracilis Extracts

Dietary supplementation with nutrients able to control intestinal and systemic inflammation is of marketable interest. Indeed, gastrointestinal homeostasis plays a significant role in maintaining human health. In this setting, E. gracilis may sustain or promote human health, but the effects on the intestinal inflammatory milieu are not clear. In this study, we investigated the anti-inflammatory activity of E. gracilis and inferred possible mechanisms. Paramylon, crude, and fractionated extracts were obtained from E. gracilis grown in vitro. Phytoconstituents of the extracts were characterized using TLC and HPLC UV-Vis. The anti-inflammatory and antioxidant activities were investigated in primary human macrophages and an intestinal epithelial cell line (HT-29). The analysis of the extracts led to identifying β-carotene, neoxanthin, diadinoxanthin, canthaxanthin, and breakdown products such as pheophytins and pheophorbides. E. gracilis fractionated extracts reduced the production of tumor necrosis factor-α triggered by bacterial lipopolysaccharide (LPS) in the short and long terms. Pheophytin a and b and canthaxanthin increased the intracellular reducing potential and dampened the production of LPS-induced reactive oxygen species and lipid peroxidation, intracellular events usually involved in the perpetuation of chronic inflammatory disorders. This study rationalizes the role of specific extract fractions of E. gracilis in controlling LPS-driven intestinal inflammation.

Metabolomic Study of Heterotrophically Grown Chlorella sp. Isolated from Wastewater in Northern Sweden

There are numerous strains of Chlorella with a corresponding variety of metabolic pathways. A strain we previously isolated from wastewater in northern Sweden can grow heterotrophically as well as autotrophically in light and has higher lipid contents under heterotrophic growth conditions. The aims of the present study were to characterize metabolic changes associated with the higher lipid contents in order to enhance our understanding of lipid production in microalgae and potentially identify new compounds with utility in sustainable development. Inter alia, the amino acids glutamine and lysine were 7-fold more abundant under heterotrophic conditions, the key metabolic intermediate alpha-ketoglutarate was more abundant under heterotrophic conditions with glucose, and maltose was more abundant under heterotrophic conditions with glycerol than under autotrophic conditions. The metabolite 3-hydroxy-butyric acid, the direct precursor of the biodegradable plastic PHB (poly-3-hydroxy-butyric acid), was also more abundant under heterotrophic conditions. Our metabolomic analysis has provided new insights into the alga's lipid production pathways and identified metabolites with potential use in sustainable development, such as the production of renewable, biodegradable plastics, cosmetics, and nutraceuticals, with reduced pollution and improvements in both ecological and human health.

Effect of Protocatechuic Acid on Euglena gracilis Growth and Accumulation of Metabolites

The development of efficient, environmentally friendly, low-cost approaches used to boost the growth of microalgae is urgently required to meet the increasing demands for food supplements, cosmetics, and biofuels. In this study, the growth promotion effects of protocatechuic acid (PCA) in the freshwater microalga Euglena gracilis were confirmed for the first time. PCA is a simple phenolic compound derived from natural plants and has a range of biological functions. The highest biomass yield, 3.1-fold higher than that of the control, used at 1.3 g·L−1, was obtained at 800 mg·L−1 of PCA. The yields of the metabolites chlorophyll a, carotenoids, and paramylon in the presence of PCA at 800 mg·L−1 were 3.1, 3.3, and 1.7 times higher than those of the control group, respectively. The highest paramylon yield was achieved at a lower dosage of PCA (100 mg·L−1), which is considered to be feasible for economic paramylon production. The growth and biosynthesis of metabolites stimulated by phytochemicals such as PCA could be an efficient and cost-effective strategy to enhance the productivity of microalgae in large-scale cultivations.

R, Shaari K, Ismail IS, Nagao N, Abas F. Mass Spectrometry-Based Metabolomics Combined with Quantitative Analysis of the Microalgal Diatom (Chaetoceros calcitrans)

Although many metabolomics studies of higher land plant species have been conducted, similar studies of lower nonland plant species, which include microalgae, are still developing. The present study represents an attempt to characterize the metabolic profile of a microalgal diatom Chaetoceros calcitrans, by applying high-resolution mass spectrometry detection, via Q-ExactiveTM Plus Orbitrap mass spectrometry. The results showed that 54 metabolites of various classes were tentatively identified. Experimentally, the chloroform and acetone extracts were clearly distinguished from other solvent extracts in chemometric regression analysis using PLS, showing the differences in the C. calcitrans metabolome between the groups. In addition, specific metabolites were evaluated, which supported the finding of antioxidant and anti-inflammatory activities. This study also provides data on the quantitative analysis of four carotenoids based on the identification results. Therefore, these findings could serve as a reliable tool for identifying and quantifying the metabolome that could reflect the metabolic activities of C. calcitrans.

Pre-concentration of microalga Euglena gracilis by alkalescent pH treatment and flocculation mechanism of Ca3(PO4)2, Mg3(PO4)2, and derivatives

BACKGROUND

Microalgae are widely be used in carbon sequestration, food supplements, natural pigments, polyunsaturated fatty acids, biofuel applications, and wastewater treatment. However, the difficulties incurred in algae cell separation and harvesting, and the exorbitant cost required to overcome these challenges, are the primary limitations to large-scale industrial application of microalgae technology.

RESULTS

Herein, we explore the potential of inducing flocculation by adjusting the pH for pre-concentrating Euglena gracilis. Our results demonstrate that flocculation can be induced by increasing the medium pH to 8.5; however, most of the algae cells were broken by increasing the pH > 10. Magnesium phosphate, calcium phosphate, and their derivatives precipitation jointly led to flocculation, although calcium phosphate and its derivatives precipitation had a greater effect.

CONCLUSIONS

This study demonstrates that pH treatment-induced flocculation is efficient and feasible for the pre-concentration of E. gracilis under a pilot-scale culture system. Moreover, it also maintained the microalgae cells' integrity, chlorophyll production, and increased paramylon production. These findings provide a theoretical basis for reducing the cost of large-scale E. gracilis harvesting; as well as provide a reference for harvesting other microalgae.

Metabolomic response of Euglena gracilis and its bleached mutant strain to light

Euglena, a new superfood on the market, is a nutrient-rich, green single-celled microorganism that features the characteristics of both plant and animal. When cultivated under different conditions, Euglena produces different bioactive nutrients. Interestingly, Euglena is the only known microorganism whose chloroplasts are easy to lose under stress and become permanently bleached. We applied gas chromatography-mass spectrometry (GC-MS) to determine the metabolomes of wild-type (WT) Euglena gracilis and its bleached mutant OflB2 under light stimulation. We found a significant metabolic difference between WT and OflB2 cells in response to light. An increase of membrane components (phospholipids and acylamides) was observed in WT, while a decrease of some stimulant metabolites was detected in OflB2. These metabolomic changes after light stimulation are of great significance to the development of Euglena chloroplasts and their communications with the nucleus.

Transcriptome, proteome and draft genome of Euglena gracilis

BACKGROUND

Photosynthetic euglenids are major contributors to fresh water ecosystems. Euglena gracilis in particular has noted metabolic flexibility, reflected by an ability to thrive in a range of harsh environments. E. gracilis has been a popular model organism and of considerable biotechnological interest, but the absence of a gene catalogue has hampered both basic research and translational efforts.

RESULTS

We report a detailed transcriptome and partial genome for E. gracilis Z1. The nuclear genome is estimated to be around 500 Mb in size, and the transcriptome encodes over 36,000 proteins and the genome possesses less than 1% coding sequence. Annotation of coding sequences indicates a highly sophisticated endomembrane system, RNA processing mechanisms and nuclear genome contributions from several photosynthetic lineages. Multiple gene families, including likely signal transduction components, have been massively expanded. Alterations in protein abundance are controlled post-transcriptionally between light and dark conditions, surprisingly similar to trypanosomatids.

CONCLUSIONS

Our data provide evidence that a range of photosynthetic eukaryotes contributed to the Euglena nuclear genome, evidence in support of the 'shopping bag' hypothesis for plastid acquisition. We also suggest that euglenids possess unique regulatory mechanisms for achieving extreme adaptability, through mechanisms of paralog expansion and gene acquisition.

Euglena gracilis growth and cell composition under different temperature, light and trophic conditions

Background

Euglena gracilis, a photosynthetic protist, produces protein, unsaturated fatty acids, wax esters, and a unique β-1,3-glucan called paramylon, along with other valuable compounds. The cell composition of E. gracilis was investigated in this study to understand how light and organic carbon (photo-, mixo- and heterotrophic conditions) affected growth and cell composition (especially lipids). Comparisons were primarily carried out in cultures grown at 23 °C, but the effect of growth at higher temperatures (27 or 30 °C) was also considered.

Cell growth

Specific growth rates were slightly lower when E. gracilis was grown on glucose in either heterotrophic or mixotrophic conditions than when grown photoautotrophically, although the duration of exponential growth was longer. Temperature determined the rate of exponential growth in all cultures, but not the linear growth rate during light-limited growth in phototrophic conditions. Temperature had less effect on cell composition.

Cell composition

Although E. gracilis was not expected to store large amounts of paramylon when grown phototrophically, we observed that phototrophic cells could contain up to 50% paramylon. These cells contained up to 33% protein and less than 20% lipophilic compounds, as expected. The biomass contained about 8% fatty acids (measured as fatty acid methyl esters), most of which were unsaturated. The fatty acid content of cells grown in mixotrophic conditions was similar to that observed in phototrophic cells, but was lower in cells grown heterotrophically. Heterotrophic cells contained less unsaturated fatty acids than phototrophic or mixotrophic cells. α-Linolenic acid was present at 5 to 18 mg g^-1 dry biomass in cells grown in the presence of light, but at < 0.5 mg g^-1 biomass in cells grown in the dark. Eicosapentaenoic and docosahexaenoic acids were detected at 1 to 5 mg g^-1 biomass. Light was also important for the production of vitamin E and phytol.

Characterization of an easy-to-use method for the routine analysis of the central metabolism using an affordable low-resolution GC-MS system: application to Arthrospira platensis

We developed an easy-to-use method for the routine analysis of the central metabolism using an affordable low-resolution GC-MS system run in SIM mode. The profiling approach was optimized for the derivatization protocol of some 60 targeted metabolites. The performance of two silylation reagents (MSTFA and BSTFA) that allowed the comprehensive derivatization of 42 key intermediary metabolites of the 60 initially targeted (organic acids, phosphate derivatives, monosaccharides and amino acids) was measured. The experimental results unequivocally showed that the MSTFA reagent met mandatory criteria including ease of handling (a very simple one-step protocol was developed), comprehensiveness of derivatization (the 42 compounds covered the extended metabolic pathways of the central carbon metabolism, with a coverage percentage ranging from 17% for the worst to 90% for the best result), optimized response coefficient of the whole derivatives (median value greater than the others by one order of magnitude) and repeatability of the protocol (RSD value below 25% for the whole procedure). When tested in real conditions (cyanobacteria polar extract), the experimental results showed that the profiling methodology was adequately repeatable (RSD = 35%) to ensure quantification results comparable with much more sensitive analytical techniques (capillary electrophoresis/mass spectrometry and liquid chromatography/triple quadrupole mass spectrometry system), while needing only about twice the quantity of biomass. Graphical abstract Schematic overview of an easy-to-use profiling method for the routine analysis of the central metabolism using a low-resolution GC-MS system.