# Synergistic Enhancement of Paramylon Production in Edible Microalga Euglena gracilis via Ethanol-Guaiacol Co-Regulation

## TL;DR

Researchers found that combining ethanol and guaiacol boosts biomass and paramylon production in the microalga Euglena gracilis, offering a sustainable method for biorefineries.

## Contribution

The study introduces a novel ethanol-guaiacol co-regulation strategy to enhance paramylon biosynthesis in Euglena gracilis.

## Key findings

- Ethanol mixotrophy increased biomass and paramylon production by 12.68 and 6.43 times compared to autotrophic control.
- At 10 mg·L−1 GA, chlorophyll a, carotenoids, and paramylon increased by 8.96%, 11.75%, and 16.67% respectively.
- Higher GA concentrations reduced biomass and paramylon yield, indicating a hormesis effect.

## Abstract

Biomass-derived growth stimulants are widely recognized as green and economical solutions that can significantly enhance microalgae culture efficiency and optimize the biomanufacturing process of target products. In this paper, we investigated the effect of ethanol synergized with guaiacol (GA) on biomass and β-1,3 glucan accumulation in edible microalgae, namely Euglena gracilis. The ethanol-induced mixotrophic mode significantly increased biomass and paramylon production by 12.68 and 6.43 times, respectively, compared to the autotrophic control group. GA further exerted toxic excitatory effects (hormesis) on top of ethanol mixotrophic nutrition. At the optimal concentration of 10 mg·L−1 GA, chlorophyll a, carotenoids, and paramylon production increased by 8.96%, 11.75%, and 16.67%, respectively, compared to the ethanol-treated group. However, at higher concentrations, the biomass and paramylon yield decreased significantly. This study not only establishes an effective combinatorial strategy for enhancing paramylon biosynthesis but also provides novel insights into the hormesis mechanism of phenolic compounds in microalgae cultivation. The developed approach demonstrates promising potential for sustainable production of high-value algal metabolites while reducing cultivation costs, which could significantly advance the commercialization of microalgae-based biorefineries in food and pharmaceutical industries.