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Mechanism of the Synergistic Toxicity of Ampicillin and Cefazoline on Selenastrum capricornutum
Summary
Researchers studied how two common antibiotics, ampicillin and cefazolin, work together to harm freshwater algae, finding that their combined effect is worse than either antibiotic alone. The antibiotics disrupted the algae's growth, metabolism, and photosynthesis at the genetic level. While focused on antibiotic pollution rather than microplastics, the study is relevant because microplastics can carry antibiotics through waterways, potentially amplifying these toxic effects on aquatic ecosystems.
Ampicillin (AMP) and cefazolin (CZO) are commonly used β-lactam antibiotics which are extensively globally produced. Additionally, AMP and CZO are known to have relatively high ecotoxicity. Notably, the mix of AMP and CZO creates a synergistic effect that is more harmful to the environment, and how exposure to AMP-CZO can induce synergism in algae remains virtually unknown. To yield comprehensive mechanistic insights into chemical toxicity, including dose-response relationships and variations in species sensitivity, the integration of multiple endpoints with de novo transcriptomics analyses were used in this study. We employed <i>Selenastrum capricornutum</i> to investigate its toxicological responses to AMP and CZO at various biological levels, with the aim of elucidating the underlying mechanisms. Our assessment of multiple endpoints revealed a significant growth inhibition in response to AMP at the relevant concentrations. This inhibition was associated with increased levels of reactive oxygen species (ROS) and perturbations in nitrogen metabolism, carbohydrate metabolism, and energy metabolism. Growth inhibition in the presence of CZO and the AMP-CZO combination was linked to reduced viability levels, elevated ROS production, decreased total soluble protein content, inhibited photosynthesis, and disruptions in the key signaling pathways related to starch and sucrose metabolism, ribosome function, amino acid biosynthesis, and the production of secondary metabolites. It was concluded from the physiological level that the synergistic effect of Chlorophyll a (Chla) and Superoxide dismutase (SOD) activity strengthened the growth inhibition of <i>S. capricornutum</i> in the AMP-CZO synergistic group. According to the results of transcriptomic analysis, the simultaneous down-regulation of <i>LHCA4</i>, <i>LHCA1</i>, <i>LHCA5,</i> and <i>sodA</i> destroyed the functions of the photosynthetic system and the antioxidant system, respectively. Such information is invaluable for environmental risk assessments. The results provided critical knowledge for a better understanding of the potential ecological impacts of these antibiotics on non-target organisms.
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