Characterization of <i>Euglena gracilis</i> Mutants Generated by Long-Term Serial Treatment with a Low Concentration of Ethyl Methanesulfonate

Abstract

Euglena gracilis is a microalga that has great promise for the production of biofuels, functional foods, and bioactive compounds, and mutagenesis and effective screening methods are required to develop Euglena strains that have industrial use. Ethyl methanesulfonate (EMS) is a widely used mutagen, but is highly lethal to Euglena at typical concentrations. In the present study, low-concentration, long-time EMS exposure combined with serial treatment was introduced for generating Euglena mutants. We then used screening protocols to select cells with altered motility or pigmentation, and isolated two distinct strains of Euglena: Mutant 333 and Mutant 335. Mutant 333 showed increased motility but exhibited a decreased differentiation rate and reduced paramylon content (13.5%), making it unsuitable for industrial applications. However, Mutant 335, which had a deficiency of chlorophyll, had a high paramylon content (31.62%) and a mild and pleasant odor profile due to decreased concentrations of certain volatile compounds, with confirmation by GC-MS analysis. The Mutant 335 strain is suitable for the production of functional food products and renewable jet fuel.