Impact of Polystyrene Microplastics on Daphnia magna: Morphological Influence on Toxicity and Microbiome Dynamics

Microplastic pollution poses a significant threat to aquatic ecosystems, yet its effects on freshwater organisms remain inadequately understood. This study investigates the impact of polystyrene (PS) microplastics on the freshwater crustacean Daphnia magna, a vital bioindicator for assessing environmental health. Utilizing microplastics that mimic natural morphologies, we aimed to evaluate the ecological risks associated with PS exposure. Our experimental design assessed mortality rates, reproductive output, generation of reactive oxygen species (ROS), and expression levels of ROS-related genes in D. magna. Following these assessments, we employed metagenomic 16S rRNA amplicon sequencing to analyze the gut microbiome. The sequencing data revealed significant shifts in microbial community composition, with notable changes in relative abundance, alpha diversity, and beta diversity metrics. Functional predictions indicated that the altered microbiome may influence D. magna's health and resilience by modulating metabolic pathways. Additionally, PICRUSt analysis and differential gene expression (DEG) analysis highlighted the biological pathways affected by PS exposure. Overall, these findings underscore the ecological ramifications of microplastic pollution and emphasize the importance of understanding how varying microplastic shapes influence D. magna and its associated microbiome, providing critical insights into the broader implications of microplastic contamination in freshwater ecosystems.