Low-temperature plasma priming enhances nutrient removal and astaxanthin production in Haematococcus pluvialis: Transcriptomic responses during controlled aquaculture wastewater cultivation.

Microalgal cultivation can recover dissolved nutrients from aquaculture wastewater while generating value-added biomass, but wastewater stress and slow growth limit the performance of Haematococcus pluvialis. This study investigated low-temperature plasma (LTP) pretreatment as a novel priming strategy to enhance nutrient removal and astaxanthin production by H. pluvialis in a controlled, sterilized aquaculture wastewater system. Dosage optimization revealed a biphasic response: 30 kV for 60 s induced a sublethal oxidative stimulus, increased antioxidant enzyme activities, and improved subsequent biomass accumulation, whereas excessive exposure caused irreversible cytotoxicity. At this optimal dosage, LTP-treated H. pluvialis showed progressive recovery of photosystem II efficiency, electron transport rate, and non-photochemical quenching, indicating strengthened population-level photosynthetic acclimation. In sterilized 2-fold diluted aquaculture wastewater, LTP-treated H. pluvialis reduced dissolved nitrogen and phosphorus concentrations to below their respective method detection limits and increased biomass and astaxanthin yields by 25.6 % and 28.6 %, respectively, relative to the untreated control. Comparative transcriptomic analysis and RT-qPCR indicated that LTP consistently activated a nitrate/nitrite reduction module, whereas wastewater cultivation further shaped phosphorus-associated metabolism, lipid remodeling, and energy metabolism during the green growth stage. These results suggest that improved nutrient removal and biomass valorization may arise from the interaction between LTP-induced nitrogen-metabolic priming and wastewater-dependent acclimation. This study provides proof-of-concept evidence for LTP-assisted H. pluvialis cultivation in controlled sterilized aquaculture wastewater, while further validation in non-sterile systems remains necessary.