Polystyrene microplastics induce microbial dysbiosis and dysfunction in surrounding seawater.

Microplastics are ubiquitously present in the environment, accumulate in aquaculture water, and cause toxicological effects on aquatic organisms. Besides, microplastics provide ecological niches for microorganisms in aquatic environments. However, the effects of microplastics on microbial balance and function in surrounding water are still unclear, especially for aquaculture water. Therefore, 16S rRNA gene sequencing was employed to uncover polystyrene microplastics (PS)-induced microbial dysbiosis in surrounding seawater cultivating marine medaka (Oryzias melastigmas) and to screen related potential bacterial biomarkers. We found that Proteobacteria and Bacteroidetes were the dominant phyla in each group, accounting for more than 95% of the total abundance, and that 26 bacterial taxa belonging to Proteobacteria and Bacteroidetes were significantly altered in surrounding seawater after 10- and 200-µm PS exposure. Functional analysis revelated that photosynthesis, carbon metabolism (such as carbon fixation, glycolysis, tricarboxylic acid cycle, and glycan biosynthesis and metabolism), amino acid metabolism, lipid synthesis, and nucleotide metabolism were decreased, while environmental stress responses, such as xenobiotics biodegradation and metabolism, glutathione metabolism, and taurine and hypotaurine metabolism, were increased in surrounding seawater microbiota after separate 10- and 200-µm PS exposure. Pathway analysis and correlation networks demonstrated that changes in relative abundances of bacterial taxa belonging to Proteobacteria and Bacteroidetes were highly correlated with those in the liver metabolism of marine medaka. Subsequently, 8 bacterial taxa were discovered to be able to be used separately as the potential biomarker for assessing the surrounding seawater microbial dysbiosis and metabolic responses of marine medaka, with a diagnostic accuracy of 100.0%. This study provides novel insights into toxicological effects of microplastics on microbial dysbiosis and function in surrounding water and ecosystems, and suggests potential roles of biomarkers involved in surrounding microbial dysbiosis in assessing microplastic ecotoxicology, microbial dysbiosis, and the health status of organisms at higher trophic levels.