Florfenicol impairs photosynthesis and triggers oxidative stress in Phaeodactylum tricornutum: Physiological and transcriptomic evidence.

Florfenicol (FFC) is a broad-spectrum antibiotic that is used in aquaculture to effectively control bacterial infections in animals by inhibiting bacterial protein synthesis. However, its widespread application in aquaculture has increased environmental residues, posing potential toxic effects on non-target organisms in aquatic ecosystems. In this study, we evaluated the toxic effects of FFC on the marine diatom Phaeodactylum tricornutum and the associated underlying mechanisms. The results showed that FFC significantly inhibited cell proliferation in a dose-dependent manner, reduced photosynthetic pigment content, and impaired photosynthetic performance, as evidenced by decreased chlorophyll fluorescence parameters. At the same time, FFC exposure induced oxidative stress, characterized by suppressed antioxidant enzyme activities, decreased soluble sugar and protein contents, and elevated malondialdehyde (MDA) levels. Transcriptomic analysis revealed that short-term exposure (24 h) primarily disrupted nitrogen metabolism-related gene expression, while prolonged exposure (96 h) significantly suppressed photosynthetic pathways. qPCR analysis further validated the downregulation of key genes involved in porphyrin metabolism and ribosome biogenesis in eukaryotes. Collectively, FFC inhibited P. tricornutum growth by disrupting the photosynthetic electron transport chain, inducing oxidative damage, and interfering with critical biological processes, including nitrogen metabolism and protein synthesis.