Enhanced removal efficiency of Tetradesmus obliquus for nevirapine removal via co-substrate supplementation: removal mechanisms, relative gene expression and metabolomics†

The bioremediation of pharmaceutical wastewater by microalgae has gained scientific attention due to its cost-effectiveness and environmental friendliness. However, limited information is available regarding the influence of co-substrates on the removal of antiretroviral (ARV) drugs by microalgae. This study was aimed at evaluating the NVP removal efficiency and antioxidant gene expression of microalga Tetradesmus obliquus under different cultivation modes (autotrophic, heterotrophic, and mixotrophic). The removal mechanism, biotransformation products, and changes in key algal metabolites were also investigated. The maximum removal of NVP (80.13%) was achieved on the 8th day of cultivation. Fourier-transform infrared (FTIR) spectroscopy confirmed the adsorption of NVP on the microalgae cell surface. The highest NVP removal was observed in the mixotrophic mode, followed by the heterotrophic and autotrophic cultivation. Gene expression analysis showed elevated antioxidant enzyme activity in autotrophic, heterotrophic and mixotrophic growth. Metabolomic analysis identified significant changes in key metabolites of T. obliquus in treatments compared to the control (p < 0.05). Additionally, a potential degradation pathway of NVP was predicted by using computation tools, eMolecules and EAWAG-BBD PPS database and discussed. The overall findings of this study suggest that T. obliquus can be used as a promising agent for environmental remediation and ARV drug removal.