Microplastics disrupt energy metabolism in the brackish water flea Diaphanosoma celebensis

Energy metabolism is crucial for normal biological processes, such as growth, development, and reproduction. Microplastics disrupt energy homeostasis by modulating the digestive capacity and contents of energy reserves to overcome stress. This study investigated the modulation of digestive enzyme activity and energy reserves in the brackish water flea Diaphanosoma celebensis exposed to polystyrene (PS) beads (0.05-, 0.5-, 6-μm) for 48 h, and examined transcriptional changes in digestive enzyme-coding genes and AMP-activated protein kinase (AMPK) signaling pathway genes. PS particle size differentially modulated digestive enzyme activity, energy molecule content (glycogen, protein, and lipids), and metabolism-related gene expression. In particular, the 0.5-μm PS had the most significant effect on digestive enzyme activity. In contrast, the 0.05-μm PS caused significant metabolic disorder following a decrease in total energy budget (E_a). These findings suggest that PS beads can modulate energy metabolism through different modes depending on the bead size.