Metabolic Responses of a Model Green Microalga Euglena gracilis to Different Environmental Stresses

Abstract

Euglena gracilis, a green microalga known as a potential candidate for jet fuel producers and new functional food resources, is highly tolerant to antibiotics, heavy metals, and other environmental stresses. Its cells contain many high-value products, including vitamins, amino acids, pigments, unsaturated fatty acids, and carbohydrate paramylon as metabolites, which change contents in response to various extracellular environments. However, mechanism insights into the cellular metabolic response of Euglena to different toxic chemicals and adverse environmental stresses were very limited. We extensively investigated the changes of cell biomass, pigments, lipids, and paramylon of E. gracilis under several environmental stresses, such as heavy metal CdCl2, antibiotics paromomycin, and nutrient deprivation. In addition, global metabolomics by Ultra-high-performance liquid chromatography tandem mass spectrometry (UHPLC–MS/MS) was applied to study other metabolites and potential regulatory mechanisms behind the differential accumulation of major high-valued metabolites. This study collects a comprehensive update on the biology of E. gracilis for various metabolic responses to stress conditions, and it will be of great value for Euglena cultivation and high-value [154mm][10mm]Q7metabolite production.

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

“…PRM and streptomycin are aminoglycoside antibiotics, and streptomycin has a known inhibitory effect on E. gracilis growth (Kirk, 1962). However, this study showed that low concentrations (1-25 μg/ml) of PRM had little effect on E. gracilis growth, suggesting that E. gracilis is tolerant to low PRM concentrations, consistent with previous reports on Euglena antibiotic tolerance (Kirk, 1962;He et al, 2021). E. gracilis could grow mixotrophically; that is, it can first use organic carbons in the medium or field waters instead of CO 2 via photosynthesis under the light.…”

“…Its cells contain many high-value bioproducts, including vitamins, amino acids, unsaturated fatty acids, and paramylon (Grimm et al, 2015;Zakryś et al, 2017). E. gracilis is of considerable environmental importance and biotechnological value: it can survive a variety of carbon resources, toxic chemicals, and adverse environmental conditions such as heavy metals, antibiotics, acid, salinity, and high levels of ionizing radiation, and can be observed in most waters such as ponds, fish farms and small rivers (Rodríguez-Zavala et al, 2007;Kottuparambil et al, 2012;Mukaida et al, 2016;Moreno-Sánchez et al, 2017;He et al, 2021). Indeed, E. gracilis exhibits remarkable metabolic diversity, blooming as photosynthetic autotrophy, heterotrophy, and photoheterotrophy (Zakryś et al, 2017).…”

Identifying Euglena Gracilis Metabolic and Transcriptomic Adaptations in Response to Mercury Stress

“…Increased metabolism and ATP generation may be a possible mechanisms for recycling oxidized GSH that has already participated in mitigating ROS stress or generating new reduced GSH to sequester Hg(II). The low abundance of fatty acids in Hg treated cells observed in this study is contradictory to other studies where microalgae were exposed to cadmium (Puente-Sánchez et al, 2018), but consistent with fatty acid degradation in E. gracilis after cadmium treatment (He et al, 2021). Essential amino acids also serve as precursors for the generation of ATP through the TCA cycle (Martínez-Reyes & Chandel, 2020), which offers another possible explanation for increased amide and peptide metabolic and biosynthetic processes observed (Table 1).…”

“…Significant fold-changes in amino acids like cysteine, glutamine, proline, and serine; all amino acids were enriched after Hg treatment, especially in extracellular fractions (Figures 1C,F). The increase in transcripts corresponding to ribosomal proteins like RPL21 and RPS10 further suggests a shift towards increased protein synthesis, which could assist E. gracilis with a variety of processes like metal detoxification, mitigation of reactive oxygen species, and repairing cellular damage (He et al, 2021). Many of the intermediates in metabolic processes are involved in reactions that generate amino acids and other metabolites that are linked to both detoxification and biosynthesis processes (Ishikawa et al, 2017).…”

Euglena gracilis Promotes Lactobacillus Growth and Antioxidants Accumulation as a Potential Next-Generation Prebiotic

“…The bacterial media during logarithmic growth was collected for metabolic analysis. The metabolites in the sample were extracted and analyzed according to the method mentioned by He et al ( 16 ). Each sample group included four biological replicates.…”