Influence of polyethylene microplastics on carbendazim degradation by Rhodococcus sp. XY-1: Molecular mechanisms and soil bioremediation effects.

Abstract

Carbendazim persists in soil, causing harm to the environment. Microbial degradation is a main way to remove carbendazim from soil, and polyethylene (PE), as a kind of microplastics, widely exists in soil. However, the mechanism by which PE influences carbendazim biodegradation is still unclear. This study isolated Rhodococcus sp. XY-1, a highly efficient carbendazim-degrading bacterium capable of completely degrading 50 mg·L^-1 carbendazim, as its sole carbon and nitrogen source within 4 d. Scanning electron microscopy revealed that PE (700 µm, 5 %) depressed XY-1 cell surfaces but induced protective intercellular substance adhesion. According to cellular reactive oxygen species (ROS) assays and Fourier transform infrared spectroscopy, PE exposure increased intracellular ROS levels in XY-1 and enhanced the absorption intensity of characteristic protein and nucleic acid peaks, indicating metabolic stimulation. Consequently, PE accelerated carbendazim degradation by strain XY-1, achieving a 79.0 % removal of 50 mg·L^-1 carbendazim within 60 h. Furthermore, PE itself underwent oxidation and hydrolysis, as evidenced by the simulated soil experiments at an increased carbon-to-oxygen ratio (from 0.016 to 0.072) and the emergence of -OH functional groups. PE also enhanced soil microbial activity, regulated organic carbon content, and influenced carbendazim adsorption, collectively promoting its degradation. Under PE (700 µm, 5 %) amendment, strain XY-1 achieved a degradation rate of 58.0 % for 5.0 mg·kg^-1 carbendazim within 7 d in soil. This study elucidates the mechanism by which microplastics influence the microbial degradation of soil organic pollutants.