Euglena cultivation with the addition of ethanol was found to contribute to increased productivity of biomass and valuable substances, as well as improved cell recovery efficiency, according to a joint study by Euglena Co., Meiji University, and the Microalgae Production Control Technology Laboratory at the RIKEN institute. The research results were published in the international journal "Applied Microbiology and Biotechnology" on March 21, 2023.

■The key points of the study are as follows

Euglena has been considered for industrial applications due to its ability to produce various valuable substances. However, the cost of cell production is high, necessitating the exploration of cell recovery methods to reduce costs.

When Euglena was cultured with the addition of ethanol, it was found that both cell and paramylon production increased, and the settling rate of cells also improved.

The study suggests the potential usefulness of ethanol utilization in Euglena cell production and recovery through gravity sedimentation.

Background:

The global increase in population and depletion of fossil fuels have raised concerns about food and energy shortages. Microalgae are being seen as a promising solution for sustainable supply, particularly Euglena gracilis, which possesses rapid growth and independence from soil fertility, making it capable of synthesizing numerous valuable substances. Industrial applications require cell recovery, and gravity sedimentation is commonly used; however, it faces challenges in terms of efficiency.

■Research Methods and Results

In this study, E. gracilis NIES-48 strain was cultivated for eight days in four different media with 0 (control), 0.5, 1.0, and 2.0% ethanol concentrations. The cultures were bubbled with 1% (v/v) CO2 in air, maintained at 25°C, and subjected to a 12-hour light/12-hour dark cycle.

Comparison between ethanol-added cultivation and control conditions revealed that Euglena cultured with ethanol showed approximately 3.6 times higher growth promotion. Furthermore, image analysis of Euglena cells obtained under different culture conditions showed that 97% of cells settled 60 minutes after sedimentation started under the 0.5% EtOH condition, while nearly 100% of cells settled within 60 minutes under the 1.0% EtOH condition. In contrast, the control condition exhibited 71% cell sedimentation after 24 hours. The sedimentation rates of the 0.5% and 1.0% EtOH conditions were consistent with previous studies.

Moreover, investigations into cell size, dry weight, paramylon content, cell morphology, and cell motility were conducted. The results showed that average cell size increased under the 0.5% and 1.0% EtOH conditions, and the dry weight per cell increased only under the 0.5% EtOH condition compared to the control. Paramylon content was higher in all ethanol conditions than in the control. Additionally, cells cultured under ethanol conditions exhibited spherical or elliptical shapes, while control cells were elongated. Time-lapse analysis revealed convection in the control condition but not in the ethanol condition.

■Future Perspectives

The study demonstrated the potential of ethanol addition in enhancing the rapid cell recovery of Euglena. The ethanol-added cultivation resulted in increased cell yield and paramylon production, as well as the benefit of utilizing gravity sedimentation for cell recovery without special treatments. This could lead to the acquisition of more valuable biomass and cost-effectiveness in harvesting and biomass production. However, it is important to further investigate various Euglena species and conduct large-scale cultivation studies, as the current results were verified using E. gracilis NIES-48 in laboratory-scale experiments.