Impacts of polyhydroxybutyrate (PHB) microplastic exposure on physiology and metabolic profiles of Litopenaeus vannamei

In light of increasing concerns about microplastic pollution, it is crucial to understand the biological impacts of biodegradable PHB microplastics on marine organisms. This study included a 96-h exposure experiment to assess acute toxicity at PHB concentrations of 0 mg/L, 100 mg/L, 500 mg/L and 1000 mg/L. Additionally, a 60-day feeding trial was conducted with PHB concentrations of 0, 0.5, 1.0 and 2.0 g/kg to evaluate the long-term effects on growth, physiological health and metabolic responses of Litopenaeus vannamei. Results from the exposure experiment indicated that PHB microplastics up to 100 mg/L were non-toxic to shrimp. However, the 60-day feeding trial revealed that higher concentrations led to slight reductions in survival rates and growth performance, indicating a concentration-dependent response. Analysis of antioxidant and immune enzymes showed minimal changes across most parameters. However, increases in malondialdehyde content and lysozyme activity at higher PHB levels suggested a stress response. Microbial analysis indicated higher species richness and greater community diversity in the PHB group compared to controls, as evidenced by Chao1, ACE, Shannon and Simpson indices. Linear discriminant analysis revealed that Enterobacteriales and related taxa were more prevalent in the PHB group, while Rhodobacteraceae and associated taxa dominated the control group. Pathway analysis highlighted enhanced signal transduction, cell mobility and metabolic resource reallocation in response to PHB-induced stress. Integrated transcriptomic and metabolomic analyses revealed significant regulatory changes, especially in lipid metabolism pathways. These findings suggest that while PHB microplastics trigger adaptive metabolic responses in shrimp, they do not cause acute toxicity. Significant variations in intestinal microbiome composition reflect potential shifts in gut health dynamics due to PHB ingestion. This study enhances our understanding of the ecological impacts of microplastics and underscores the necessity for further research into the environmental safety of biodegradable alternatives.