Integrated analysis of using high-value microalgae for tetracycline treatment with biomass utilization: Responses, removal pathway, physiological and metabolomic characterization

Antibiotic-contaminated wastewater poses serious threats to the ecological environment. While using microalgae for antibiotic removal has been extensively studied, this study provides a comprehensive and integrated analysis of the physiological and metabolic response mechanisms of Chlorella sp. HL to tetracycline (TC). The results showed that Chlorella sp. HL exhibited strong TC resistance and high removal efficiencies (98.63–99.95%). Low TC concentrations (<10 mg/L) promoted microalgal growth, while higher concentrations (>20 mg/L) inhibited its growth. Pigment contents (chlorophyll a, chlorophyll b, and carotenoids) generally increased under the stimulation of TC, except for carotenoids at 1 mg/L TC. The photosynthetic activity of Chlorella sp. HL was significantly affected, and it was reduced at higher concentrations of TC. Antioxidant enzyme activities and malondialdehyde (MDA) content increased with TC concentration, indicating TC could cause oxidative stress. In addition, TC altered the high-value substance contents of Chlorella sp. HL, with protein and lipid contents initially declining but subsequently increasing, while polysaccharide content gradually rose. Metabolomic analysis indicated that Chlorella sp. HL responded to TC stress by regulating carbohydrate metabolism and other pathways. This study provides an integrated analysis of the physiological, biochemical, and metabolomic responses of microalgae to TC. This comprehensive analysis provides new insights into how microalgae adapt to and mitigate TC stress, and especially revealing its metabolic response mechanism to TC. In addition, the potential for utilizing microalgal biomass for high-value products production when removing antibiotics has been investigated. This dual focus on bioremediation and resource production is a novel research direction.