MIL-101(Cr) disrupts algal carbon fixation by intercepting photosynthetic electron flow: Implications for aquatic...

Microalgal photosynthetic carbon fixation is pivotal to the global carbon cycle, yet it is increasingly threatened by emerging pollutants. Metal organic frameworks (MOFs), a class of functional materials with rapidly expanding applications, are inevitably being released into the environment. However, the impact of MOFs on microalgal photosynthesis remains poorly understood. Herein, we systematically investigated the effects of MIL-101(Cr), one of representative MOFs, on the photosynthetic performance of Chlorella vulgaris (C. vulgaris). Our results demonstrated that MIL-101(Cr) significantly inhibited C. vulgaris photosynthesis and impaired its carbon dioxide (CO₂) fixation capacity, evidenced by shrunken thylakoid interlayer spaces, compromised photosynthetic efficiency, reduced carbon fixation rates, and perturbed levels of key metabolites involved in the TCA and CBB cycles. Mechanistically, owing to the abundance of unsaturated Cr³⁺ active sites, MIL-101(Cr) competitively trapped electrons from the photosynthetic electron transport chain of C. vulgaris, hindering the synthesis of ATP and NADPH. The reduced NADPH sink further led to increased electron leakage to molecular oxygen, triggering excessive reactive oxygen species generation, thus forming a vicious self-reinforcing cycle that ultimately exacerbated the impairment of CO₂ fixation, evidenced by ¹³C-bicarbonate tracing experiment. Collectively, these findings identify photosynthetic electron interception as a previously overlooked mechanism by which MOFs can impair microalgal carbon fixation. This mechanism provides new insight into the ecological risk of MOFs residues in aquatic environments, particularly their potential impacts on algal primary productivity.