Exogenous γ-aminobutyric acid alleviates selenite stress and enhances organic selenium and energy-storage compound accumulation in Tribonema minus

Abstract

Tribonema minus, a filamentous microalga, has been shown to effectively remove selenite while accumulating biomass enriched with organic selenium and carbohydrates. However, elevated selenite concentrations markedly inhibit its growth. This study evaluated the potential of γ-aminobutyric acid (GABA; 0.1–10 mg/L) to alleviate selenite-induced stress and enhance the accumulation of value-added products. Supplementation with 10 mg/L GABA yielded optimal results, increasing biomass by 44.72 % and enhancing carbohydrate and lipid productivities by 32.23 % and 71.44 %, respectively. These enhancements were attributed to GABA-mediated activation of antioxidant defences, increased chlorophyll a content, and redirection of carbon flux. GABA also mitigated selenite toxicity by decreasing the apparent selenium removal per unit biomass in the medium and shifting intracellular selenium speciation towards less toxic forms. Within the first six days, expression of two genes involved in toxic selenoprotein synthesis (OsCS and OsSBP1) was significantly downregulated, accompanied by the formation of inert selenium polysaccharides. Meanwhile, selenium volatilisation was suppressed, resulting in a net increase in intracellular selenium accumulation. By day 9, organic selenium productivity rose by 30.75 %, predominantly in the form of selenomethionine. Although biomass-normalised selenium removal declined, the elevated biomass maintained a high selenium removal efficiency of 93.78 %. These findings provide the first mechanistic evidence for GABA's role in alleviating selenite stress and highlight its potential to improve selenium tolerance and bioremediation efficiency of T. minus in selenium-laden wastewater.