Ecosystem-specific composition and drivers of plastisphere resistome in freshwater and marine environments

Microplastics in aquatic environments facilitate the formation of specific plastisphere microbiomes and serve as potential hotspots for antibiotic resistance genes (ARGs) propagation. However, the systematic comparisons of ARG profiles on microplastics from different aquatic ecosystems remain limited, particularly the prevalent ARGs and their bacterial hosts. This study performed a comparative meta-analysis of existing metagenomic datasets to investigate the resistome between freshwater and seawater microplastics (FMP and SMP) and their driving factors. Our results revealed that the ARG profiles on both FMP and SMP were significantly distinct from their surrounding waterbody. Moreover, FMP exhibited a higher diversity and abundance of ARGs rather than SMP. Ten core ARGs were shared on FMP and SMP, while 23 core ARGs were exclusively detected on FMP. The bacterial community on microplastics exhibited an ecosystem-specific composition, and was identified as the primary determinant shaping the ARG profiles. Notably, more complex bacteria-ARG co-occurrence pattern was identified on FMP, involving a broader spectrum of core genera and potential pathogenic hosts (e.g., Mycobacterium, Streptomyces). Furthermore, a significant and specific correlation between mobile genetic elements and ARGs was identified on FMP but not SMP, suggesting a markedly elevated horizontal gene transfer potential, with mechanistic support from the concurrent enrichment of oxidative stress and SOS response genes on FMP. These findings provide a comprehensive characterization of ARGs on aquatic microplastics, and especially highlight the role of FMP in the ARG dissemination.