A low temperature-adapted Euglena gracilis ecotype for outdoor biomass production in colder climates

Euglena gracilis strain Z is currently used for industrial purposes such as the production of the polysaccharide paramylon, lipids, and carotenoids. This strain shows promise for sustainable bioproduction, but its growth is inhibited at temperatures below 20°C, limiting its geographic range for outdoor cultivation. Here, we discovered a new low temperature-adapted E. gracilis ecotype, strains min34 and min41, in freshwater from a northern prefecture of Japan. These strains were isolated during the participatory science project "Everyone's Euglena Project." Strain min41 thrives at 15°C, achieving cell densities and dry weights of 5.2- and 7.5-times higher than those of strain Z, respectively. Strain min34 also showed high growth ability at 15°C but was inferior to strain min41. Whereas strain Z exhibits reduced bioproduction capacity at 15°C (as evidenced by decreased paramylon, lipid, and carotenoid production), strain min41 maintains high bioproductivity at low temperature. Our findings underscore the rich genetic potential within E. gracilis for adaptation to diverse conditions and offer a valuable bioresource for exploring temperature-adapted systems, broadening the prospects for biomass production.IMPORTANCEOutdoor cultivation of microorganisms for bioproduction is often limited by temperature. Industrially useful E. gracilis strain cannot grow well in colder climates, restricting their use in sustainable industries such as food and biofuel production. In this study, we identified a new low temperature-adapted strain of E. gracilis that can thrive and remain productive at 15°C. This strain could enable year-round biomass production in regions with colder weather, expanding the potential of environmentally friendly biomanufacturing. Our discovery also highlights the untapped natural diversity of this microorganism, which may hold the key to developing more resilient and efficient bioproduction systems.