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

Sustainable production and pharmaceutical applications of β-glucan from microbial sources

β-glucans are a large class of complex polysaccharides found in abundant sources. Our dietary sources of β-glucans are cereals that include oats and barley, and non-cereal sources can consist of mushrooms, microalgae, bacteria, and seaweeds. There is substantial clinical interest in β-glucans; as they can be used for a variety of diseases including cancer and cardiovascular conditions. Suitable sources of β-glucans for biopharmaceutical applications include bacteria, microalgae, mycelium, and yeast. Environmental factors including culture medium can influence the biomass and ultimately β-glucan content. Therefore, cultivation conditions for the above organisms can be controlled for sustainable enhanced production of β-glucans. This review discusses the various sources of β-glucans and their cultivation conditions that may be optimised to exploit sustainable production. Finally, this article discusses the immune-modulatory potential of β-glucans from these sources.

Biofuel production from Euglena: Current status and techno-economic perspectives

Sustainable aviation fuels (SAFs) can contribute reduce greenhouse gas emissions compared to conventional fuel. With the increasing SAFs demand, various generations of resources have been shifted from the 1st generation (oil crops), the 2nd generation (agricultural waste), to the 3rd generation (microalgae). Microalgae are the most suitable feedstock for jet biofuel production than other resources because of their productivity and capability to capture carbon dioxide. However, microalgae-based biofuel has a limitation of high freezing point. Recently, a jet biofuel derived from Euglena wax ester has been paying attention due to its low freezing point. Challenges still remain to enhance production yields in both upstream and downstream processes. Studies on downstream processes as well as techno-economic analysis on biofuel production using Euglena are highly limited to date. Economic aspects for the biofuel production will be ensured via valorization of industrial byproducts such as food wastes.

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.

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.

Assessment of the electrical penetration of cell membranes using four-frequency impedance cytometry

The electrical penetration of the cell membrane is vital for determining the cell interior via impedance cytometry. Herein, we propose a method for determining the conductivity of the cell membrane through the tilting levels of impedance pulses. When electrical penetration occurs, a high-frequency current freely passes through the cell membrane; thus, the intracellular distribution can directly act on the high-frequency impedance pulses. Numerical simulation shows that an uneven intracellular component distribution can affect the tilting levels of impedance pulses, and the tilting levels start increasing when the cell membrane is electrically penetrated. Experimental evidence shows that higher detection frequencies (>7 MHz) lead to a wider distribution of the tilting levels of impedance pulses when measuring cell populations with four-frequency impedance cytometry. This finding allows us to determine that a detection frequency of 7 MHz is able to pass through the membrane of Euglena gracilis (E. gracilis) cells. Additionally, we provide a possible application of four-frequency impedance cytometry in the biomass monitoring of single E. gracilis cells. High-frequency impedance (≥7 MHz) can be applied to monitor these biomass changes, and low-frequency impedance (<7 MHz) can be applied to track the corresponding biovolume changes. Overall, this work demonstrates an easy determination method for the electrical penetration of the cell membrane, and the proposed platform is applicable for the multiparameter assessment of the cell state during cultivation.

Salt Stress Induces Paramylon Accumulation and Fine-Tuning of the Macro-Organization of Thylakoid Membranes in Euglena gracilis Cells

The effects of salt stress condition on the growth, morphology, photosynthetic performance, and paramylon content were examined in the mixotrophic, unicellular, flagellate Euglena gracilis. We found that salt stress negatively influenced cell growth, accompanied by a decrease in chlorophyll (Chl) content. Circular dichroism (CD) spectroscopy revealed the changes in the macro-organization of pigment-protein complexes due to salt treatment, while the small-angle neutron scattering (SANS) investigations suggested a reduction in the thylakoid stacking, an effect confirmed by the transmission electron microscopy (TEM). At the same time, the analysis of the thylakoid membrane complexes using native-polyacrylamide gel electrophoresis (PAGE) revealed no significant change in the composition of supercomplexes of the photosynthetic apparatus. Salt stress did not substantially affect the photosynthetic activity, as reflected by the fact that Chl fluorescence yield, electron transport rate (ETR), and energy transfer between the photosystems did not change considerably in the salt-grown cells. We have observed notable increases in the carotenoid-to-Chl ratio and the accumulation of paramylon in the salt-treated cells. We propose that the accumulation of storage polysaccharides and changes in the pigment composition and thylakoid membrane organization help the adaptation of E. gracilis cells to salt stress and contribute to the maintenance of cellular processes under stress conditions.

Unconventional high-value products from microalgae: A review

Microalgae have gained significant importance in biotechnology development, providing valuable goods and services in multiple applications. Although there is a rising market for most of these applications, the incorporation and introduction of microalgae into new venues will extend in the near future. These advances are due to the vast biodiversity of microalgal species, recent genetic engineering tools, and culture techniques. There are three main possible approaches for novel algal compounds from: (1) recently isolated yet less known microalgae; (2) selectively stressed conditions; and (3) enzymatically adjusted compounds from conventional molecules. All these approaches can be combined in a specific manner. This review discusses the opportunities, potential and limitations of introducing novel microalgae-based products, and how the recent technologies can be deployed to make these products financially viable. To give an outlook to the future, an analysis of the developments and predicted future market that further enlarge the promise of cultivating microalgae for commercial purposes are considered.

Application of electrical treatment on Euglena gracilis for increasing paramylon production

Paramylon also called β-1,3-glucan is a value-added product produced from Euglena gracilis. Recently, researchers have developed various strategies for the enhanced paramylon production, among which electrical treatment for microbial stimulation can be an alternative owing to the applicability to large-scale cultivation. In this study, we applied the electrical treatment for enhanced paramylon production and found the proper treatment conditions. Under the treatment with platinum electrodes at 10 mA, the paramylon production of treated cells was significantly increased about 2.5-fold, compared to those of the untreated cells, although the density of cells was maintained due to considerable stress. The size of treated cells became larger, possibly due to the increased level of paramylon production within the cells. Accordingly, the contents of glucose uptake, glucose-6-phosphate (G6P), glucose-1-phosphate (G1P), and uridine diphosphoglucose (UDPG) were shifted to appropriate states for the process of paramylon synthesis under the treatment. The increased level of transcripts encoding glucan synthase-like 2 (EgGSL2) was also confirmed via droplet digital PCR (ddPCR) under the treatment. Overall, this study makes a major contribution to research on electrical stimulation and provides new insights into E. gracilis metabolism like paramylon synthesis. KEY POINTS: • Electrical treatment induced the paramylon production and morphological change of Euglena gracilis. • The glucose uptake of E. gracilis was increased during the electrical treatment, fueling the paramylon synthesis.

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.

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.

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.