Untargeted metabolomic analysis of heterotrophic Euglena gracilis cells in response to the organic carbon source

Abstract

Euglena gracilis is a single-celled, free-living flagellate that grows in a variety of cultivation conditions. In this study, we investigated the effects of calcium acetate, glucose, glutathione (GSH), glutamic acid, and malic acid additions on the growth and metabolism of heterotrophic E. gracilis cells. To analyze the metabolic changes, size exclusion liquid chromatography-mass spectrometry was employed, enabling the comprehensive examination of the metabolomics changes in response to the carbon sources. The addition of glucose and GSH led to relatively high cell count production, whereas moderate cell count production was observed with the use of calcium acetate, glutamic acid, and malic acid, synonymous with less favorable growth conditions. Common enriched pathways (i.e., cysteine and methionine metabolism, purine metabolism, pentose phosphate pathway (PPP), and glyoxylate and dicarboxylate metabolism) were found in all carbon treatments, highlighting their critical role in the basic Euglena gracilis metabolism. Moreover depending on the carbon source, some metabolites associated with the amino acid, lipid, and vitamin metabolisms were significantly enriched. These findings provided valuable insights into the metabolism of E. gracilis regarding its diverse metabolic responses to carbon source changes.