Ethanol-driven mixotrophic cultivation enhances biomass production and CO2 capture in Euglena gracilis for sustainable bioresource utilisation

Abstract

This study explored the enhancement of biomass production and CO₂ capture in Euglena gracilis through mixotrophic cultivation using ethanol as a high redox potential substrate. Three cultivation strategies were compared: photoautotrophic, heterotrophic, and mixotrophic. The mixotrophic condition yielded the highest biomass production at 1.79 g L⁻¹, markedly exceeding the yields observed in heterotrophic (0.84 g L⁻¹) and photoautotrophic (0.11 g L⁻¹) cultures. Although ethanol consumption was comparable between mixotrophic and heterotrophic conditions, the presence of light in the mixotrophic system appeared to enhance cellular metabolism, presumably by improving cellular energy availability. This led to greater biomass production and CO₂ fixation. Correspondingly, the mixotrophic culture achieved a CO₂ capture rate of 0.07 g CO₂ L⁻¹ day⁻¹, representing a 600 % increase compared to the 0.01 g CO₂ L⁻¹ day⁻¹ observed under photoautotrophic conditions, and exhibited a higher total carbon content in the biomass (41 % versus 28.9 %). These findings provide a proof-of-concept for using ethanol-supplemented mixotrophic cultivation to significantly boost both biomass production and CO₂ capture in E. gracilis, underscoring its potential for applications in carbon capture and sustainable biomass production.