Increased synthesis of α-tocopherol, paramylon and tyrosine by Euglena gracilis under conditions of high biomass production

Metabolic responses of Euglena gracilis under photoheterotrophic and heterotrophic conditions

The protist Euglena gracilis has various trophic modes including heterotrophy and photoheterotrophy. To investigate how cultivation mode influences metabolic regulation, the chemical composition of cellular metabolites of Euglena gracilis grown under heterotrophic and photoheterotrophic conditions was monitored from the early exponential phase to the mid-stationary phase using two different techniques, i.e, nuclear magnetic resonance (NMR) spectroscopy and high-resolution mass spectrometry (HRMS). The combined metabolomics approach allowed an in-depth understanding of the mechanism of photoheterotrophic and heterotrophic growth for biomolecule production. Heterotrophic conditions promoted the production of polar amino and oxygenated compounds such as proteins and polyphenol compounds, especially at the end of the exponential phase while photoheterotrophic cells enhanced the production of organoheterocyclic compounds, carbohydrates, and alkaloids.

The biomolecules of Euglena gracilis: Harnessing biology for natural solutions to future problems

Over the past decade, the autotrophic and heterotrophic protist Euglena gracilis (E. gracilis) has gained popularity across the studies of environmental science, biosynthesis experiments, and nutritional substitutes. The unique physiology and versatile metabolism of E. gracilis have been a recent topic of interest to many researchers who continue to understand the complexity and possibilities of using E. gracilis biomolecule production. In this review, we present a comprehensive representation of recent literature outlining the various uses of biomolecules derived from E. gracilis across the fields of natural product biosynthesis, as a nutritional substitute, and as bioremediation tools. In addition, we highlight effective strategies for altering metabolite production using abiotic stressors and growth conditions. To better understand metabolite biosynthesis and its role in E. gracilis, integrated studies involving genomics, metabolomics, and proteomics should be considered. Together, we show how the ongoing advancements in E. gracilis related research continue to broaden applications in the biosynthetic sector and highlight future works that would strengthen our understanding of overall Euglena metabolism.

Antares I: a Modular Photobioreactor Suitable for Photosynthesis and Bioenergetics Research

Oxygenic photosynthesis is responsible for most of the fixation of atmospheric CO2. The microalgal community can transport atmospheric carbon into biological cycles in which no additional CO2 is created. This represents a resource to confront the actual climate change crisis. These organisms have evolved to adapt to several environments and different spectral distribution of light that may strongly influence their metabolism. Therefore, there is a need for development of photobioreactors specialized in addressing spectral optimization. Here, a multi-scale modular photobioreactor made from standard glass materials, ad hoc light circuits, and easily accessible, small commercial devices is described. The system is suitable to manage the principal culture variables of research in bioenergetics and photosynthesis. Its performance was tested by growing four evolutionary-distant microalgal species with different endosymbiotic scenarios: Chlamydomonas reinhardtii (Archaeplastida, green primary plastid), Polytomella parva (Archaeplastida, colorless plastid), Euglena gracilis (Discoba, green secondary plastid), and Phaeodactylum tricornutum (Stramenophiles, red secondary plastid). Our results show an improvement of biomass production, as compared to the traditional flask system. The modulation of the incident light spectra allowed us to observe a far-red adaptation in Euglena gracilis with a difference on paramylon production, and it also significantly increased the maximal cell density of the diatom species under green light. Together, these confirm that for photobioreactors with artificial light, manipulation of the light spectrum is a critical parameter for controlling the optimal performance, depending on the downstream goals.

A comprehensive report on valorization of waste to single cell protein: strategies, challenges, and future prospects

The food insecurity due to a vertical increase in the global population urgently demands substantial advancements in the agricultural sector and to identify sustainable affordable sources of nutrition, particularly proteins. Single-cell protein (SCP) has been revealed as the dried biomass of microorganisms such as algae, yeast, and bacteria cultivated in a controlled environment. Production of SCP is a promising alternative to conventional protein sources like soy and meat, due to quicker production, minimal land requirement, and flexibility to various climatic conditions. In addition to protein production, it also contributes to waste management by converting it into food and feed for both human and animal consumption. This article provides an overview of SCP production, including its benefits, safety, acceptability, and cost, as well as limitations that constrains its maximum use. Furthermore, this review criticizes the downstream processing of SCP, encompassing cell wall disruption, removal of nucleic acid, harvesting of biomass, drying, packaging, storage, and transportation. The potential applications of SCP, such as in food and feed as well as in the production of bioplastics, emulsifiers, and as flavoring agents for baked food, soup, and salad, are also discussed.

Microbial meat: A sustainable vegan protein source produced from agri-waste to feed the world

In the modern world, animal and plant protein may not meet the sustainability criteria due to their high need for arable land and potable water consumption, among other practices. Considering the growing population and food shortage, finding alternative protein sources for human consumption is an urgent issue that needs to be solved, especially in developing countries. In this context, microbial bioconversion of valuable materials in nutritious microbial cells represent a sustainable alternative to the food chain. Microbial protein, also known as single-cell protein (SCP), consist of algae biomass, fungi or bacteria that are currently used as food source for both humans and animals. Besides contributing as a sustainable source of protein to feed the world, producing SCP, is important to reduce waste disposal problems and production costs meeting the sustainable development goals. However, for microbial protein as feed or food to become an important and sustainable alternative, addressing the challenges of raising awareness and achieving wider public regulatory acceptance is real and must be addressed with care and convenience. In this work, we critically reviewed the potential technologies for microbial protein production, its benefits, safety, and limitations associated with its uses, and perspectives for broader large-scale implementation. We argue that the information documented in this manuscript will assist in developing microbial meat as a major protein source for the vegan world.

A review of paramylon processing routes from microalga biomass to non-derivatized and chemically modified products

Paramylon is a linear β-1,3-glucan, similar to curdlan, produced as intracellular granules by the microalga Euglena gracilis, a highly versatile and robust strain, able to grow under various trophic conditions, with valorization of CO_2, wastewaters, or food byproducts as nutrients. This review focuses in particular on the various processing routes leading to new potential paramylon based products. Due to its crystalline structure, involving triple helices stabilized by internal intermolecular hydrogen bonds, paramylon is neither water-soluble nor thermoplastic. The few solvents able to disrupt the triple helices, and to fully solubilize the polymer as random coils, allow non derivatizing shaping into films, fibers, and even nanofibers by a specific self-assembly mechanism. Chemical modification in homogeneous or heterogeneous conditions is also possible. The non-selective or regioselective substitution of the hydroxyl groups of glucosidic units leads to water-soluble ionic derivatives and thermoplastic paramylon esters with foreseen applications ranging from health to bioplastics.

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.

Organic Carbon Is Ineffective in Enhancing the Growth of Dunaliella

(1) Background: Mixotrophic growth is commonly associated with higher biomass productivity and lower energy consumption. This paper evaluates the impact of using different carbon sources on growth, protein profile, and nutrient uptake for Dunaliella tertiolecta CCAP 19/30 to assess the potential for mixotrophic growth. (2) Methods: Two experimental sets were conducted. The first assessed the contribution of atmospheric carbon to D. tertiolecta growth and the microalgae capacity to grow heterotrophically with an organic carbon source to provide both carbon and energy. The second set evaluated the impact of using different carbon sources on its growth, protein yield and quality. (3) Results: D. tertiolecta could not grow heterotrophically. Cell and optical density, ash-free dry weight, and essential amino acids index were inferior for all treatments using organic carbon compared to NaHCO3. Neither cell nor optical density presented significant differences among the treatments containing organic carbon, demonstrating that organic carbon does not boost D. tertiolecta growth. All the treatments presented similar nitrogen, phosphorus, sulfur recovery, and relative carbohydrate content. (4) Conclusions: Based on the results of this paper, D. tertiolecta CCAP 19/30 is an obligated autotroph that cannot grow mixotrophically using organic carbon.

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.

Microalgal transformation of food processing byproducts into functional food ingredients

Large amounts of food processing byproducts (FPBs) are generated from food manufacturing industries, the second-largest portion of food waste generation. FPBs may require additional cost for post-treatment otherwise cause environmental contamination. Valorization of FPBs into food ingredients by microalgae cultivation can save a high cost for organic carbon sources and nutrients from medium cost. This study reviews FPBs generation categorized by industry and traditional disposal. In contrast with the low-value production, FPBs utilization as the nutrient-abundant medium for microalgae can lead to high-value production. Due to the complex composition in FPBs, various pretreatment methods have been applied to extract the desired compounds and medium preparation. Using the FPB-based medium resulted in cost reduction and a productivity enhancement in previous literature. Although there are still challenges to overcome to achieve economic viability and environmental sustainability, the microalgal transformation of FPBs is attractive for functional food ingredients production.

Probing the Biogenesis of Polysaccharide Granules in Algal Cells at Sub-Organellar Resolution via Raman Microscopy with Stable Isotope Labeling

Phototrophs assimilate CO₂ into organic compounds that accumulate in storage organelles. Elucidation of the carbon dynamics of storage organelles could enhance the production efficiency of valuable compounds and facilitate the screening of strains with high photosynthetic activity. To comprehensively elucidate the carbon dynamics of these organelles, the intraorganellar distribution of the carbon atoms that accumulate at specific time periods should be probed. In this study, the biosynthesis of polysaccharides in storage organelles was spatiotemporally probed via stimulated Raman scattering (SRS) microscopy using a stable isotope (¹³C) as the tracking probe. Paramylon granules (a storage organelle of β-1,3-glucan) accumulated in a unicellular photosynthetic alga, Euglena gracilis, were investigated as a model organelle. The carbon source of the culture medium was switched from NaH¹²CO₃ to NaH¹³CO₃ during the production of the paramylon granules; this resulted in the distribution of the ¹²C and ¹³C constituents in the granules, so that the biosynthetic process could be tracked. Taking advantage of high-resolution SRS imaging and label switching, the localization of the ¹²C and ¹³C constituents inside a single paramylon granule could be visualized in three dimensions, thus revealing the growth process of paramylon granules. We propose that this method can be used for comprehensive elucidation of the dynamic activities of storage organelles.

Exploration and characterization of chemical stimulators to maximize the wax ester production by Euglena gracilis

Euglena gracilis, a phototrophic protist, is a valuable biomass producer that is often employed in sustainable development efforts. E. gracilis accumulates wax esters as byproducts during anaerobic ATP production via the reductive tricarboxylic acid cycle, utilizing the storage carbohydrate β-1,3-glucan paramylon as the carbon source. Here, we report a library screening for chemical stimulators that accelerate both wax ester production and paramylon consumption. Among the 115 compounds tested, we identified nine compounds that increased wax ester production by more than 2.0-fold relative to the solvent control. In the presence of these nine compounds, the paramylon content decreased compared with the control experiment, and the residual paramylon content varied between 7% and 26% of the initial level. The most active compound, 1,4-diaminoanthracene-9,10-dione (OATQ008), stimulated wax ester production up to 2.7-fold within 24 h, and 93% of the cellular paramylon was consumed. In terms of the structural features of the chemical stimulators, we discuss the potential target sites to stimulate wax ester production in mitochondria under anaerobic conditions.

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.

Valorization of microalgae biomass into bioproducts promoting circular bioeconomy: a holistic approach of bioremediation and biorefinery

The need for alternative source of fuel has demanded the cultivation of 3rd generation feedstock which includes microalgae, seaweed and cyanobacteria. These phototrophic organisms are unique in a sense that they utilise natural sources like sunlight, water and CO₂ for their growth and metabolism thereby producing diverse products that can be processed to produce biofuel, biochemical, nutraceuticals, feed, biofertilizer and other value added products. But due to low biomass productivity and high harvesting cost, microalgae-based production have not received much attention. Therefore, this review provides the state of the art of the microalgae based biorefinery approach to define an economical and sustainable process. The three major segments that need to be considered for economic microalgae biorefinery is low cost nutrient source, efficient harvesting methods and production of by-products with high market value. This review has outlined the use of various wastewater as nutrient source for simultaneous biomass production and bioremediation. Further, it has highlighted the common harvesting methods used for microalgae and also described various products from both raw biomass and delipidified microalgae residues in order to establish a sustainable, economical microalgae biorefinery with a touch of circular bioeconomy. This review has also discussed various challenges to be considered followed by a techno-economic analysis of the microalgae based biorefinery model.

A strategic approach to apply bacterial substances for increasing metabolite productions of Euglena gracilis in the bioreactor

Bacterial extracellular polymeric substances (EPS) are promising materials that have a role in enhancing growth, metabolite production, and harvesting efficiency. However, the validity of the EPS effectiveness in scale-up cultivation of microalgae is still unknown. Therefore, in order to verify whether the bacterial metabolites work in the scale-up fermentation of microalgae, we conducted a bioreactor fermentation following the addition of bacterial EPS derived from the marine bacterium, Pseudoalteromonas sp., to Euglena gracilis. Various culture strategies (i.e., batch, glucose fed-batch, and glucose and EPS fed-batch) were conducted to maximize metabolite production of E. gracilis in scale-up cultivation. Consequently, biomass and paramylon concentrations in the continuous glucose and EPS-treated culture were enhanced by 3.0-fold and 4.2-fold (36.1 ± 1.4 g L^-1 and 25.6 ± 0.1 g L^-1), respectively, compared to the non-treated control (12.0 ± 0.3 g L^-1 and 6.1 ± 0.1 g L^-1). Also, the supplementation led to the enhanced concentrations of α-tocopherols and total fatty acids by 3.7-fold and 2.8-fold, respectively. The harvesting efficiency was enhanced in EPS-supplemented cultivation due to the flocculation of E. gracilis. To the best of our knowledge, this is the first study that verifies the effect of bacterial EPS in scale-up cultivation of microalgae. Also, our results showed the highest paramylon productivity than any other previous reports. The results obtained in this study showed that the scale-up cultivation of E. gracilis using bacterial EPS has the potential to be used as a platform to guide further increases in scale and in the industrial environment. KEY POINTS: Effect of EPS on Euglena gracilis fermentation was tested in bioreactor scale. EPS supplement was effective for the paramylon, α-tocopherol, and lipid production. EPS supplement induced the flocculation of E. gracilis.

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.

Environmental determinants of the distribution of planktonic diplonemids and kinetoplastids in the oceans

We analysed a widely used barcode, the V9 region of the 18S rRNA gene, to study the effect of environmental conditions on the distribution of two related heterotrophic protistan lineages in marine plankton, kinetoplastids and diplonemids. We relied on a major published dataset (Tara Oceans) where samples from the mesopelagic zone were available from just 32 of 123 locations, and both groups are most abundant in this zone. To close sampling gaps and obtain more information from the deeper ocean, we collected 57 new samples targeting especially the mesopelagic zone. We sampled in three geographic regions: the Arctic, two depth transects in the Adriatic Sea, and the anoxic Cariaco Basin. In agreement with previous studies, both protist groups are most abundant and diverse in the mesopelagic zone. In addition to that, we found that their abundance, richness, and community structure also depend on geography, oxygen concentration, salinity, temperature, and other environmental variables reflecting the abundance of algae and nutrients. Both groups studied here demonstrated similar patterns, although some differences were also observed. Kinetoplastids and diplonemids prefer tropical regions and nutrient-rich conditions and avoid high oxygen concentration, high salinity, and high density of algae.

Molecular tools and applications of Euglena gracilis: From biorefineries to bioremediation

Euglena gracilis is a promising source of commercially important metabolites such as vitamins, wax esters, paramylon, and amino acids. However, the molecular tools available to create improved Euglena strains are limited compared to other microorganisms that are currently exploited in the biotechnology industry. The complex poly-endosymbiotic nature of the Euglena genome is a major bottleneck for obtaining a complete genome sequence and thus represents a notable shortcoming in gaining molecular information of this organism. Therefore, the studies and applications have been more focused on using the wild-type strain or its variants and optimizing the nutrient composition and cultivation conditions to enhance the production of biomass and valuable metabolites. In addition to producing metabolites, the E. gracilis biorefinery concept also provides means for the production of biofuels and biogas as well as residual biomass for the remediation of industrial and municipal wastewater. Using Euglena for bioremediation of environments contaminated with heavy metals is of special interest due to the strong ability of the organism to accumulate and sequester these compounds. The published draft genome and transcriptome will serve as a basis for further molecular studies of Euglena and provide a guide for the engineering of metabolic pathways of relevance for the already established as well as novel applications.

Water extract from Euglena gracilis prevents lung carcinoma growth in mice by attenuation of the myeloid-derived cell population

The partially purified water extract from Euglena gracilis (EWE) was evaluated for its antitumor and immunomodulatory effects in cell cultures and in a mouse orthotopic lung carcinoma allograft model. In two-dimensional cell culture, the EWE treatment inhibited cell growth of both murine Lewis lung carcinoma (LLC) and human lung carcinoma cells (A549 and H1299) in a dose- and time-dependent manner. In contrast, the growth of mouse bone marrow cells (BMCs), but not mouse splenocytes (SPLs), was stimulated by the treatment with EWE. In three-dimensional spheroid culture, spheroid growth of LLC cells was significantly attenuated by EWE treatment. In a mouse LLC orthotopic allograft model, pretreatment with EWE (150-200 mg/kg/day, via drinking water) three weeks prior to the LLC cell inoculation, but not post-treatment after LLC cell inoculation, significantly attenuated the growth of LLC tumors in immunocompetent syngeneic mouse lung. This tumor growth attenuation coincided with a significant decrease in the population of myeloid-derived cells, primarily neutrophils. Flow cytometric analysis revealed that the EWE treatment significantly attenuated growth of granulocytic myeloid-derived suppressor cells (gMDSC) in BMCs and that this decrease was due to induction of gMDSC-specific apoptosis and differentiation of monocytic MDSCs (mMDSC) to macrophages. The present study provides evidence that EWE pretreatment inhibits lung carcinoma growth mainly by stimulating host antitumor immunity through attenuation of growth of gMDSCs and decreasing the number of peripheral granulocytes. This study suggests that the partially purified extract derived from Euglena gracilis contains significant bioactive materials that prevent lung carcinoma growth.

Possibility of co-culturing Euglena gracilis and Lactuca sativa L. with biogas digestate

The goal of this study was to establish a system for co-culturing microalgae and crop plants with biogas digestate. We examined growth performances of E. gracilis and L. sativa co-cultured using a commercial liquid fertilizer designed for soilless culture supplemented with vitamins and ammonium. This solution simulated the filtrate of nitrified biogas digestate derived from the organic fraction of municipal solid waste but was supplemented with insufficient plant nutrients (Mg, Fe and Mn). The specific growth rate of the co-cultured E. gracilis was 0.761 ± 0.081 d-1 (mean ± SE), which was the same rate that E. gracilis achieved when grown as a sole culture. There were no significant differences between L. sativa cultured with E. gracilis until the stationary growth phase of E. gracilis was reached and those cultured alone relative to biomass, RGRs (relative growth rates), or relative to SPAD values of leaves. These results suggest that E. gracilis and L. sativa could be co-cultured with the biogas digestate after being nitrified and filtered. In addition, considering concentrations of plant macronutrients in the residual solution after the co-culturing E. gracilis and L. sativa, it could be re-used as the nutrient solution for co-culturing E. gracilis and L. sativa.

Probing the Role of the Chloroplasts in Heavy Metal Tolerance and Accumulation in Euglena gracilis

The E. gracilis Zm-strain lacking chloroplasts, characterized in this study, was compared with the earlier assessed wild type Z-strain to explore the role of chloroplasts in heavy metal accumulation and tolerance. Comparison of the minimum inhibitory concentration (MIC) values indicated that both strains tolerated similar concentrations of mercury (Hg) and lead (Pb), but cadmium (Cd) tolerance of the Z-strain was twice that of the Zm-strain. The ability of the Zm-strain to accumulate Hg was higher compared to the Z-strain, indicating the existence of a Hg transportation and accumulation mechanism not depending on the presence of chloroplasts. Transmission electron microscopy (TEM) showed maximum accumulation of Hg in the cytosol of the Zm-strain and highest accumulation of Cd in the chloroplasts of the Z-strain indicating a difference in the ability of the two strains to deposit heavy metals in the cell. The highly abundant heavy metal transporter MTP2 in the Z-strain may have a role in Cd transportation to the chloroplasts. A multidrug resistance-associated protein highly increased in abundance in the Zm-strain could be a potential Hg transporter to either cytosol or mitochondria. Overall, the chloroplasts appear to have major role in the tolerance and accumulation of Cd in E. gracilis.

Safety assessment of Euglena gracilis ATCC 12894 whole cell biomass

A safety assessment of the dried whole cell biomass of Euglena gracilis ATCC 12894 was performed by the bacterial reverse mutation (Ames) assay, an in vitro micronucleus assay, and a 90-day repeat oral toxicity study in Wistar rats. E. gracilis ATCC 12894 whole cell biomass has no added excipients and contains 33.8% protein, 28.8% β-glucans, 19.8% fat, 7.1% ash, and 2.8% moisture. The bacterial reverse mutation assay found no evidence of mutagenicity after exposure to E. gracilis ATCC 12894 whole cell biomass, with or without metabolic activity, at levels up to 1581 µg/plate, the limit dose for the assay. Similarly, no evidence of genotoxicity was observed in the micronucleus assay, with or without metabolic activation, up to 320 µg/mL, the limit dose for the assay. The subchronic toxicity study was performed with the following test article dose groups: 0 (control), 1250, 2500, and 5000 mg/kg/day, administered to male and female Wistar rats via oral gavage for 90 days. No test article-related mortalities or adverse events were reported during the study. Histopathological examination revealed some vacuolation in the livers of males in the 5000 mg/kg/day group. This finding was considered adaptive, due to the approximately 20% fat content of whole cell biomass, and was therefore test article-related, but not adverse. No such findings were reported in female rats in the study. The results of the subchronic toxicity study describe a no observed adverse effect level of at least 5000 mg/kg/day.

Improvement of Euglena gracilis Paramylon Production through a Cocultivation Strategy with the Indole-3-Acetic Acid-Producing Bacterium Vibrio natriegens

We investigated the putative effects on the growth and paramylon production of Euglena gracilis of cocultivation with Vibrio natriegensE. gracilis heterotrophically cocultivated with V. natriegens displayed significant increases in biomass productivity and paramylon content. In addition, the effects of the bacterial inoculum density and the timing of inoculation on the growth of E. gracilis were examined, to determine the optimal conditions for cocultivation. With the optimal deployment of V. natriegens, biomass productivity and paramylon content were increased by more than 20% and 35%, respectively, compared to those in axenic E. gracilis cultures. Interestingly, indole-3-acetic acid biosynthesized by V. natriegens was responsible for these enhancements of E. gracilis The morphology of cocultured E. gracilis cells was assessed. Paramylon granules extracted from the cocultivation were significantly larger than those from axenic culture. Our study showed that screening for appropriate bacteria and subsequent cocultivation with E. gracilis represented an effective way to enhance biomass and metabolite production.IMPORTANCEEuglena gracilis has attracted special interest due to its ability to excessively accumulate paramylon. Paramylon is a linear β-1,3-glucan polysaccharide that is the principal polymer for energy storage in E. gracilis The polysaccharide features high bioactive functionality in the immune system. This study explored a new method to enhance the production of paramylon by E. gracilis, through cocultivation with the indole-3-acetic acid-producing bacterium Vibrio natriegens The enhanced production was achieved indirectly with the phytohormone-producing bacteria, instead of direct application of the hormone. The knowledge obtained in this study furthers the understanding of the effects of V. natriegens on the growth and physiology of E. gracilis.

Enhancement of growth and paramylon production of Euglena gracilis by co-cultivation with Pseudoalteromonas sp. MEBiC 03485

This study investigated the putative effects of co-cultivation of Euglena gracilis with Pseudoalteromonas sp. MEBiC 03485 on the growth of E. gracilis and its paramylon production. The strain MEBiC 03485 had beneficial effects on the growth and paramylon contents of E. gracilis. To determine the optimal conditions for co-cultivation, the effects of algal to bacterial inoculum ratios and E. gracilis growth stages were examined. Under optimal conditions, the biomass productivity and paramylon production were increased by more than 23% and 34%, respectively. These effects were attributed to the extracellular polymeric substances (EPS) from the strain MEBiC 03485. GC-MS and HPAEC were carried out to analyze the composition of EPS. It was found that the EPS consisted of rhamnose, galactose, glucose, and mannose. These results suggest a novel approach for potentially enhancing the growth of E. gracilis as well as its paramylon production, via co-culturing with the symbiotic strain MEBiC 03485.

Bioproducts From Euglena gracilis: Synthesis and Applications

In recent years, the versatile phototrophic protist Euglena gracilis has emerged as an interesting candidate for application-driven research and commercialisation, as it is an excellent source of dietary protein, pro(vitamins), lipids, and the β-1,3-glucan paramylon only found in euglenoids. From these, paramylon is already marketed as an immunostimulatory agent in nutraceuticals. Bioproducts from E. gracilis can be produced under various cultivation conditions discussed in this review, and their yields are relatively high when compared with those achieved in microalgal systems. Future challenges include achieving the economy of large-scale cultivation. Recent insights into the complex metabolism of E. gracilis have highlighted unique metabolic pathways, which could provide new leads for product enhancement by genetic modification of the organism. Also, development of molecular tools for strain improvement are emerging rapidly, making E. gracilis a noteworthy challenger for microalgae such as Chlorella spp. and their products currently on the market.

Microalgae metabolites: A rich source for food and medicine

Microalgae are one of the important components in food chains of aquatic ecosystems and have been used for human consumption as food and as medicines. The wide diversity of compounds synthesized from different metabolic pathways of fresh and marine water algae provide promising sources of fatty acids, steroids, carotenoids, polysaccharides, lectins, mycosporine-like amino acids, halogenated compounds, polyketides, toxins, agar agar, alginic acid and carrageenan. This review discusses microalgae used to produce biological substances and its economic importance in food science, the pharmaceutical industry and public health.

Particulate and solubilized β-glucan and non-β-glucan fractions of Euglena gracilis induce pro-and anti-inflammatory innate immune cell responses and exhibit antioxidant properties

Purpose

The purpose of this work was to determine the pro-and anti-inflammatory properties of the single-cell organism Euglena gracilis (EG) and various fractions of its whole biomass.

Methods

Heterotrophically grown EG was tested, along with its aqueous fraction (E-AQ), the intact linear β-glucan paramylon granules (PAR), and alkaline-solubilized paramylon. Peripheral blood mononuclear cell cultures were treated with the test products and analyzed for a variety of cellular responses. Immune cell activation was evaluated by flow cytometry detection of CD69 levels on CD3^-CD56⁺ NK cells, CD3⁺CD56⁺ NKT cells, and monocytes, and cytokines were analyzed from the cell culture supernatants. Antioxidant capacity was measured by Folin-Ciocalteu assay and cellular antioxidant protection and MTT assays.

Results

EG and E-AQ were the most effective in driving immune cell responses as measured by CD69 upregulation on NK and NKT cells and proinflammatory (tumor necrosis factor, IL-6, IL-1β) cytokine production. None of the test products effectively stimulated monocyte. EG and PAR inhibited reactive oxygen species under conditions of oxidative stress. E-AQ contained antioxidants capable of providing cellular antioxidant protection from oxidative damage and protection of mitochondrial function under inflammatory conditions.

Conclusion

The effects of EG on immune function are only partially attributable to the content of the β-glucan, paramylon. The regulation of additional cellular responses, such a reactive oxygen species production and resistance to oxidative stress, is likely mediated by currently unknown molecules found in the EG cell.

Development of screening strategies for the identification of paramylon-degrading enzymes

Enzymatic degradation of the β-1,3-glucan paramylon could enable the production of bioactive compounds for healthcare and renewable substrates for biofuels. However, few enzymes have been found to degrade paramylon efficiently and their enzymatic mechanisms remain poorly understood. Thus, the aim of this work was to find paramylon-degrading enzymes and ways to facilitate their identification. Towards this end, a Euglena gracilis-derived cDNA expression library was generated and introduced into Escherichia coli. A flow cytometry-based screening assay was developed to identify E. gracilis enzymes that could hydrolyse the fluorogenic substrate fluorescein di-β-D-glucopyranoside in combination with time-saving auto-induction medium. In parallel, four amino acid sequences of potential E. gracilis β-1,3-glucanases were identified from proteomic data. The open reading frame encoding one of these candidate sequences (light_m.20624) was heterologously expressed in E. coli. Finally, a Congo Red dye plate assay was developed for the screening of enzyme preparations potentially able to degrade paramylon. This assay was validated with enzymes assumed to have paramylon-degrading activity and then used to identify four commercial preparations with previously unknown paramylon degradation ability.

Comparative assessment of the Euglena gracilis var. saccharophila variant strain as a producer of the β-1,3-glucan paramylon under varying light conditions

Euglena gracilis Z and a "sugar loving" variant strain E. gracilis var. saccharophila were investigated as producers of paramylon, a β-1,3-glucan polysaccharide with potential medicinal and industrial applications. The strains were grown under diurnal or dark growth conditions on a glucose-yeast extract medium supporting high-level paramylon production. Both strains produced the highest paramylon yields (7.4-8 g · L^-1 , respectively) while grown in the dark, but the maximum yield was achieved faster by E. gracilis var. saccharophila (48 h vs. 72 h). The glucose-to-paramylon yield coefficient Y_par/glu  = 0.46 ± 0.03 in the E. gracilis var. saccharophila cultivation, obtained in this study, is the highest reported to date. Proteomic analysis of the metabolic pathways provided molecular clues for the strain behavior observed during cultivation. For example, overexpression of enzymes in the gluconeogenesis/glycolysis pathways including fructokinase-1 and chloroplastic fructose-1,6-bisphosphatase (FBP) may have contributed to the faster rate of paramylon accumulation in E. gracilis var. saccharophila. Differentially expressed proteins in the early steps of chloroplastogenesis pathway including plastid uroporphyrinogen decarboxylases, photoreceptors, and a highly abundant (68-fold increase) plastid transketolase may have provided the E. gracilis var. saccharophila strain an advantage in paramylon production during diurnal cultivations. In conclusion, the variant strain E. gracilis var. saccharophila seems to be well suited for producing large amounts of paramylon. This work has also resulted in the identification of molecular targets for future improvement of paramylon production in E. gracilis, including the FBP and phosophofructokinase 1, the latter being a key regulator of glycolysis.

β-1,3 glucan derived from Euglena gracilis and Algamune™ enhances innate immune responses of red drum (Sciaenops ocellatus L.)

To reduce susceptibility to stressors and diseases, immune-modulators such as β-glucans have been proven effective tools to enhance the innate immune responses of fish. Consequently, commercial sources of this polysaccharide are becoming increasingly more available. Algamune™ is a commercial additive produced from Euglena gracilis, as a source of linear β-1,3-glucan. In order to evaluate the immunomodulatory effects of this β-glucan product, the present study assessed the innate immune parameters of red drum (Sciaenops ocellatus) exposed to Algamune™ ex vivo and in vivo. Isolated kidney phagocytes were incubated with graded concentrations (0, 0.2, 0.4, 0.8, 1.6 and 3.2 mg L^-1) of dried Euglena gracilis (Algamune™) as well as purified Paramylon (linear β-1,3 glucan). Increased bactericidal activity against Streptococcus iniae, and production of intracellular O₂^- anion superoxide were stimulated by both β-glucan sources. A reduced activity of extracellular anion superoxide was observed by the phagocytes incubated with Algamune ™. After corroborating the effectiveness of the glucan source ex vivo, a feeding trial was conducted using red drum juveniles (∼26.6 g initial weight). Fish were fed diets with graded levels of Algamune™ (0, 100, 200, 400 and 800 mg kg^-1) twice daily for 21 days. No significant differences were detected regarding production performance parameters. At the end of the feeding trial, blood, intestinal content, and kidney were sampled. Intestinal microbiota from fecal material was analyzed through denaturing gradient gel electrophoresis (DGGE) and found to be similar among all treatments. No significant differences were detected for oxidative radical production from whole blood, and isolated phagocytes, and plasma lysozyme activity. However, the total hemolytic activity of red drum plasma was increased in fish fed 100 and 200 mg kg^-1 of dietary Algamune™ when compared to fish fed the basal diet. Based on results from both ex vivo and in vivo trials, β-glucan from Algamune™ was demonstrated to have a moderate immunostimulatory effects on red drum.

Growth promotion of Euglena gracilis by ferulic acid from rice bran

A significant growth promotion of Euglena gracilis was achieved by simply adding ferulic acid from rice bran without diminishing the accumulation of valuable products like paramylon. E. gracilis is a freshwater microalga that is widely applied in cosmetics, food, medicine, and supplements, and it is considered a potential source of biofuel. It is therefore important to enhance its yield at a lower cost for its commercial viability. Introducing a growth regulator derived from agro waste is considered a cheaper and safer strategy to improve biomass productivity compared with other alternatives such as implementing genetic engineering or adding nutrients and plant hormones as growth stimulator. The effect of ferulic acid derived from rice bran on the growth and metabolism of E. gracilis was investigated in this study. To aid in the dissolution of ferulic acid, 1% dimethyl sulfoxide (DMSO) was added to Cramer–Myers medium. Ferulic acid could alleviate the inhibitory effect of DMSO and significantly promoted the growth of E. gracilis. It was found that cell density was 2.5 times greater than that of the control group and 3.6 times greater than that of the negative control group when 500 mg/L of ferulic acid was added. In addition, the photosynthetic pigment content, especially chlorophyll a, increased with increasing ferulic acid concentrations. The total paramylon production would also be enhanced by ferulic acid since the number of cells increased without reducing the cellular content of paramylon.

Nickel accumulation by the green algae-like Euglena gracilis

Nickel accumulation and nickel effects on cellular growth, respiration, photosynthesis, ascorbate peroxidase (APX) activity, and levels of thiols, histidine and phosphate-molecules were determined in Euglena gracilis. Cells incubated with 0.5-1mM NiCl₂ showed impairment of O₂ consumption, photosynthesis, Chl a+b content and APX activity whereas cellular integrity and viability were unaltered. Nickel accumulation was depressed by Mg²⁺ and Cu²⁺, while Ca²⁺, Co²⁺, Mn²⁺ and Zn²⁺ were innocuous. The growth half-inhibitory concentrations for Ni²⁺ in the culture medium supplemented with 2 or 0.2mM Mg²⁺ were 0.43 or 0.03mM Ni²⁺, respectively. Maximal nickel accumulation (1362mg nickel/Kg DW) was achieved in cells exposed to 1mM Ni²⁺ for 24h in the absence of Mg²⁺ and Cu²⁺; accumulated nickel was partially released after 72h. GSH polymers content increased or remained unchanged in cells exposed to 0.05-1mM Ni²⁺; however, GSH, cysteine, γ-glutamylcysteine, and phosphate-molecules all decreased after 72h. Histidine content increased in cells stressed with 0.05 and 0.5mM Ni²⁺ for 24h but not at longer times. It was concluded that E. gracilis can accumulate high nickel levels depending on the external Mg²⁺ and Cu²⁺ concentrations, in a process in which thiols, histidine and phosphate-molecules have a moderate contribution.

Exploring the Glycans of Euglena gracilis

Euglena gracilis is an alga of great biotechnological interest and extensive metabolic capacity, able to make high levels of bioactive compounds, such as polyunsaturated fatty acids, vitamins and β-glucan. Previous work has shown that Euglena expresses a wide range of carbohydrate-active enzymes, suggesting an unexpectedly high capacity for the synthesis of complex carbohydrates for a single-celled organism. Here, we present an analysis of some of the carbohydrates synthesised by Euglena gracilis. Analysis of the sugar nucleotide pool showed that there are the substrates necessary for synthesis of complex polysaccharides, including the unusual sugar galactofuranose. Lectin- and antibody-based profiling of whole cells and extracted carbohydrates revealed a complex galactan, xylan and aminosugar based surface. Protein N-glycan profiling, however, indicated that just simple high mannose-type glycans are present and that they are partially modified with putative aminoethylphosphonate moieties. Together, these data indicate that Euglena possesses a complex glycan surface, unrelated to plant cell walls, while its protein glycosylation is simple. Taken together, these findings suggest that Euglena gracilis may lend itself to the production of pharmaceutical glycoproteins.

Single Cell Protein-State-of-the-Art, Industrial Landscape and Patents 2001-2016

By 2050, the world would need to produce 1,250 million tonnes of meat and dairy per year to meet global demand for animal-derived protein at current consumption levels. However, growing demand for protein will not be met sustainably by increasing meat and dairy production because of the low efficiency of converting feed to meat and dairy products. New solutions are needed. Single cell protein (SCP), i.e., protein produced in microbial and algal cells, is an option with potential. Much of the recent interest in SCP has focused on the valorisation of side streams by using microorganisms to improve their protein content, which can then be used in animal feed. There is also increased use of mixed populations, rather than pure strains in the production of SCP. In addition, the use of methane as a carbon source for SCP is reaching commercial scales and more protein-rich products are being derived from algae for both food and feed. The following review addresses the latest developments in SCP production from various organisms, giving an overview of commercial exploitation, a review of recent advances in the patent landscape (2001–2016) and a list of industrial players in the SCP field.

Growth performances and changes of macronutrient ion concentrations in the culture medium when Euglena gracilis was cultured with nitrified digestate

We investigated the possibility of using Euglena gracilis to convert digestate from methane fermentation of organic wastes into a medium for soilless crop culture. The growth of E. gracilis cultured with aqueous solutions containing filtrate of raw digestate at 1-30% (v/v) and nitrified digestate at 10-100% (v/v) was examined. Concentrations of plant macronutrient ions in nitrified digestate before and after culturing E. gracilis were also examined. Specific growth rates in aqueous solutions containing filtrate of raw digestate at 1-10% and nitrified digestate at 10-100% showed no significant differences, respectively (0.781 ± 0.031 d^-1 and 0.925 ± 0.033 d^-1, mean ± standard error). The rates in the filtrate of nitrified digestate were significantly higher than those in the filtrate of raw digestate. Moreover, there were no significant differences between the concentrations of plant macronutrient ions other than [Formula: see text] in the filtrate of nitrified digestate before and after culturing E. gracilis. The concentration of [Formula: see text] decreased significantly by 10.5% of the initial concentration. As a result, the constituent ratio of plant macronutrient ions other than magnesium in the solution after culturing E. gracilis was similar to that in a standard nutrient solution for soilless culture.

Effect of Organic Solvents on Microalgae Growth, Metabolism and Industrial Bioproduct Extraction: A Review

In this review, the effect of organic solvents on microalgae cultures from molecular to industrial scale is presented. Traditional organic solvents and solvents of new generation-ionic liquids (ILs), are considered. Alterations in microalgal cell metabolism and synthesis of target products (pigments, proteins, lipids), as a result of exposure to organic solvents, are summarized. Applications of organic solvents as a carbon source for microalgal growth and production of target molecules are discussed. Possible implementation of various industrial effluents containing organic solvents into microalgal cultivation media, is evaluated. The effect of organic solvents on extraction of target compounds from microalgae is also considered. Techniques for lipid and carotenoid extraction from viable microalgal biomass (milking methods) and dead microalgal biomass (classical methods) are depicted. Moreover, the economic survey of lipid and carotenoid extraction from microalgae biomass, by means of different techniques and solvents, is conducted.

Temporal change of photophobic step-up responses of Euglena gracilis investigated through motion analysis

The adaptation to a strong light is one of the essential characteristics of green algae, yet lacking relatively the information about the photophobic responses of Eukaryotic microalgae. We investigated the photophobic step-up responses of Euglena gracilis over a time course of several hours with alternated repetition of blue-light pulse illumination and spatially patterned blue-light illumination. Four distinctive photophobic motions in response to strong blue light were identified in a trace image analysis, namely on-site rotation, running and tumbling, continuous circular swimming, and unaffected straightforward swimming. The cells cultured in autotrophic conditions under weak light showed mainly the on-site rotation response at the beginning of blue-light illumination, but they acquired more blue-light tolerant responses of running and tumbling, circular swimming, or straightforward swimming. The efficiency of escaping from a blue-light illuminated area improved markedly with the development of these photophobic motions. Time constant of 3.0 h was deduced for the evolution of photophobic responses of E. gracilis. The nutrient-rich metabolic status of the cells resulting from photosynthesis during the experiments, i.e., the accumulation of photosynthesized nutrient products in balance between formation and consumption, was the main factor responsible for the development of photophobic responses. The reduction-oxidation status in and around E. gracilis cells did not affect their photophobic responses significantly, unlike the case of photophobic responses and phototaxis of Chlamydomonas reinhardtii cells. This study shows that the evolution of photophobic motion type of E. gracilis is dominated mainly by the nutrient metabolic status of the cells. The fact suggests that the nutrient-rich cells have a higher threshold for switching the flagellar motion from straightforward swimming to rotation under a strong light.

Biochemistry and Physiology of Heavy Metal Resistance and Accumulation in Euglena

Free-living microorganisms may become suitable models for removal of heavy metals from polluted water bodies, sediments, and soils by using and enhancing their metal accumulating abilities. The available research data indicate that protists of the genus Euglena are a highly promising group of microorganisms to be used in bio-remediation of heavy metal-polluted aerobic and anaerobic acidic aquatic environments. This chapter analyzes the variety of biochemical mechanisms evolved in E. gracilis to resist, accumulate and remove heavy metals from the environment, being the most relevant those involving (1) adsorption to the external cell pellicle; (2) intracellular binding by glutathione and glutathione polymers, and their further compartmentalization as heavy metal-complexes into chloroplasts and mitochondria; (3) polyphosphate biosynthesis; and (4) secretion of organic acids. The available data at the transcriptional, kinetic and metabolic levels on these metabolic/cellular processes are herein reviewed and analyzed to provide mechanistic basis for developing genetically engineered Euglena cells that may have a greater removal and accumulating capacity for bioremediation and recycling of heavy metals.

Succinate and Lactate Production from Euglena gracilis during Dark, Anaerobic Conditions

Euglena gracilis is a eukaryotic, unicellular phytoflagellate that has been widely studied in basic science and applied science. Under dark, anaerobic conditions, the cells of E. gracilis produce a wax ester that can be converted into biofuel. Here, we demonstrate that under dark, anaerobic conditions, E. gracilis excretes organic acids, such as succinate and lactate, which are bulk chemicals used in the production of bioplastics. The levels of succinate were altered by changes in the medium and temperature during dark, anaerobic incubation. Succinate production was enhanced when cells were incubated in CM medium in the presence of NaHCO₃. Excretion of lactate was minimal in the absence of external carbon sources, but lactate was produced in the presence of glucose during dark, anaerobic incubation. E. gracilis predominantly produced L-lactate; however, the percentage of D-lactate increased to 28.4% in CM medium at 30°C. Finally, we used a commercial strain of E. gracilis for succinate production and found that nitrogen-starved cells, incubated under dark, anaerobic conditions, produced 869.6 mg/L succinate over a 3-day incubation period, which was 70-fold higher than the amount produced by nitrogen-replete cells. This is the first study to demonstrate organic acid excretion by E. gracilis cells and to reveal novel aspects of primary carbon metabolism in this organism.