Combined effects of microplastics and methylmercury on the activity of ATP-binding cassette (ABC) transporter in the brackish water flea Diaphanosoma celebensis

Objectives Due to their widespread presence, persistence, and bioaccumulation in living organisms, microplastics (MP) and methylmercury (MeHg) pollution pose a threat to aquatic organisms. ATP cassette-binding (ABC) protein plays a key role in the efflux of these contaminants from the cell. Although MP and MeHg co-exist in the ocean, their toxicological interaction in marine small crustacean remained to be poorly understood. This study aimed to investigate the combined effects of MP and MeHg on ABC transporter.Methods In this study, (1) ABCB and ABCC subfamily genes were identified and characterized in the Diaphanosoma celebensis, (2) the effects of MeHg alone and MeHg + PS MP mixture on ABC transporter activity were examined, and subsequently, (3) the transcriptional modulation of ABCB and ABCC subfamily genes was investigated using quantitative real-time polymerase chain reaction.Results Sequence analysis showed that D. celebensis ABCB and ABCC subfamily genes had conserved domains. Efflux assay revealed that MP inhibited the function of ABCB and ABCC transporter under MeHg co-exposure in a size-dependent manner. The expression of ABCC1-1 and ABCC1-2 was upregulated in the mixture of MeHg and MP higher than MeHg alone.Conclusions ABCB and ABCC subfamilies in D. celebensis likely serve as evolutionarily conserved efflux pumps. PS NMPs can enhance the toxicity of MeHg by interrupting the efflux activity of ABC transporters in a particle size-dependent manner.