High-dose 2-phenoxyethanol exposure induces transient growth arrest, respiratory suppression, and oxidative-stress-associated response in mixotrophic Euglena gracilis
Description
2‑Phenoxyethanol (PhE) is a widely used preservative and solvent in cosmetics, pharmaceuticals, and other consumer products, leading to its continuous release into aquatic environments. This study examined the toxic effects of PhE on the freshwater protist Euglena gracilis by assessing growth dynamics, respiratory activity, medium acidification, and oxidative stress responses. Mixotrophic E. gracilis cultures were exposed to PhE concentrations ranging from 2 to 10 mM. PhE induced a concentration‑dependent delay in growth and partial cell death. These effects were accompanied by decreased respiration rates and reduced medium acidification reflecting the delayed metabolism of ethanol into acidic products such as acetate, in cultures with ≥6 mM PhE during the initial cultivation period compared to the control and lower-dose treatments. Cultures treated with 2–4 mM PhE recovered growth within 3–6 days, whereas those exposed to 6–10 mM PhE required 6–12 days for recovery. Elevated polyphenol accumulation during the first day of exposure indicated the onset of oxidative stress. Although high PhE concentrations caused severe damage and death in a portion of the cells, the remaining population retained the ability to proliferate, enabling culture recovery. These findings demonstrate that PhE at concentrations ≥ 2 mM acts as an abiotic stress factor for E. gracilis and highlight the resilience of this protist to transient chemical stress, while underscoring the need for further studies on the mechanisms underlying PhE toxicity and tolerance in aquatic microorganisms.