Interactions between microplastics and organic contaminants: The microbial mechanisms for priming effects of organic compounds on microplastic biodegradation

The co-presence of plastics and other organic contaminants is pervasive in various ecosystems, particularly in areas with intensive anthropogenic activities. Their interactions inevitably impact the composition and functions of the plastisphere microbiome, which in turn determines the trajectory of these contaminants. Antibiotics are a group of organic contaminants that warrant particular attention due to their wide presence in environments and significant potential to disseminate antibiotic resistance genes (ARGs) within the plastisphere. Therefore, this study investigated the impacts of sulfadiazine (SDZ), a prevalent environmental antibiotic, on the composition and function of the plastisphere microbial community inhabiting micro-polyethylene (mPE), one of the most common microplastic contaminants. Our findings indicated that the presence of SDZ increased the overall plastisphere microbial abundance and enriched populations that are capable of degrading both SDZ and mPE. The abundance of Aquabacterium, a dominant plastisphere population that is capable of degrading both SDZ and mPE, increased over the course of SDZ exposure, while another abundant mPE-degrading population, Ketobacter, remained stable. Accordingly, the removal of SDZ was enhanced in the presence of mPE. Moreover, the results further revealed that not only SDZ but also other labile organic contaminants (e.g., aniline and hexane) could accelerate mPE biodegradation through a priming effect. This investigation underscores the complex dynamics among microplastics, organic contaminants, and the plastisphere microbiome, offering insights into the environmental fate of plastic and antibiotic pollutants.