Physiological and transcriptomic responses of Chlorella vulgaris to novel antibacterial nanoparticles of ethyl cyanoacrylate polymer

The ethyl cyanoacrylate nanoparticles (ECA-NPs) have recently been reported as promising novel antibacterial NPs capable of inhibiting the growth of several Gram-positive and Gram-negative bacteria. However, the effects of ECA-NPs on microalgae, which are primary producers in aquatic ecosystems, remain unknown. In this study, we examined the effects of ECA-NPs on the microalga Chlorella vulgaris (Chlorella) at both cellular and molecular levels. A high concentration of ECA-NPs (100 μg/mL) exhibited strong growth inhibitory effects on Chlorella. In the ECA-NPs-treated cells, transmission electron microscope (TEM) observations showed the prominent internalization of ECA-NPs in the periplasmic space and vacuoles. Moreover, notable morphological changes such as a thinner cell wall, stacked thylakoid structure, and plasmolysis were observed. ECA-NPs exposed Chlorella secreted more extracellular polymeric substances (EPS) and accumulated more storage lipids (mainly triacylglycerol, TAG) compared to the control. However, the contents of total fatty acids and starch were decreased, and photosynthetic activity was reduced. In addition, the content of intracellular reactive oxygen species (ROS) and the activities of antioxidant enzymes in ECA-NPs-treated cells were significantly higher than in the control. Transcriptomic analysis revealed the downregulation of genes that are involved in drug binding/catabolic process, chemical stimulus detection, and cell wall component catabolic process (chitin catabolism), while genes involved in photosynthetic membrane and plastid thylakoid were upregulated. These results indicated that the effects of ECA-NPs exposure are not limited to specific metabolic pathways, but rather influence metabolic pathways across the entire cell. This study also provided new insights into the potential toxic effects associated with cyanoacrylate NPs in phytoplankton.