Ethanol Elucidates Mitigation of Glucose Stress in Euglena

A research group consisting of Minami Makimoto (Master's program graduate) and Associate Professor Takashi Osanai from the Environmental Biotechnology Laboratory, Graduate School of Agriculture, Meiji University, has elucidated that the addition of ethanol alleviates the growth inhibition of the eukaryotic microalga Euglena gracilis under high-concentration glucose conditions.

<Key Points of Research Findings>

• Euglena performs photosynthesis and has the ability to produce useful components such as paramylon, proteins, and lipids.

• Glucose is a carbon source that promotes the growth and paramylon accumulation of Euglena. However, excessive glucose can, conversely, reduce growth.

• This study discovered that adding ethanol alleviates the growth inhibition caused by high-concentration glucose. It is believed that ethanol addition mitigated glucose stress by altering respiration and cell membrane composition, thereby suppressing cell enlargement.

Abstract

Euglena^{Note 1)}, a microalga, can be cultured under photoautotrophic, heterotrophic, and mixotrophic conditions, and can produce proteins, vitamins, and lipids. Paramylon, a storage polysaccharide of Euglena and a type of β-1,3-glucan, has been reported to be effective in suppressing the onset of skin diseases and preventing influenza.

Culturing Euglena with glucose addition promotes the growth and paramylon accumulation of Euglena. However, it had been reported that excessive glucose reduces Euglena growth due to high osmotic pressure.

In this study, it was revealed that Euglena cells cultured with high-concentration glucose do not dehydrate and shrink, but rather enlarge.

Furthermore, it was clarified that adding ethanol at a concentration of 0.5% alleviates the growth inhibition of Euglena under high-concentration glucose conditions of 400 mM. In addition, under conditions where ethanol was added in addition to high-concentration glucose, spindle-shaped cells similar to those under conditions without glucose addition were observed.

These results indicate that ethanol alleviates glucose stress in Euglena, clarifying the physiological aspects of Euglena under heterotrophic conditions.

This research was conducted by a research group including Minami Makimoto (Master's program graduate) and Associate Professor Takashi Osanai from the Environmental Biotechnology Laboratory, Graduate School of Agriculture, Meiji University. This research was supported by the JST Mirai Program for Innovative GX Technologies (Representative: Moriya Okuma) and the Asahi Glass Foundation (Representative: Takashi Osanai). The results of this research were published online in the international journal “Journal of Biotechnology” on March 18, 2026.

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*Research Group

Environmental Biotechnology Laboratory, Graduate School of Agriculture, Meiji University

Associate Professor Takashi Osanai

Master's Program Graduate Minami Makimoto

1. Background

Euglena is edible and is attracting attention as an effective alternative protein source. It also contains proteins, vitamins, lipids, and paramylon, a β-1,3-glucan found only in Euglena, which is marketed as an immune stimulant.

Among various carbon sources such as galactose, lactic acid, and glycerol, Euglena shows the highest growth when glucose is used as a carbon source. Furthermore, culturing Euglena with glucose addition also promotes Euglena's paramylon accumulation. However, when glucose concentration becomes high (60 g/L), it conversely inhibits growth. This growth inhibition is thought to be caused by osmotic stress.

Euglena can also utilize ethanol as a carbon source. Ethanol is metabolized via the glyoxylate pathway through acetic acid and acetyl-CoA. It has been revealed that Euglena cells cultured under 0.5% or 1.0% ethanol addition conditions show increased paramylon accumulation and increased cell size compared to cells cultured without ethanol. Furthermore, it was suggested that it may help maintain the normal morphology of Euglena.