The responses of microbial metabolic activity, bacterial community and resistance genes under the coexistence of nanoplastics and quaternary ammonium compounds in the sewage environment.

Nanoplastics (NPs) and quaternary ammonium compounds (QACs) are frequently detected in sewage. However, little is known about the risks of coexistence of NPs and QACs. In this study, the responses of microbial metabolic activity, bacterial community and resistance genes (RGs) to the exposure of polyethylene (PE), polylactic acid (PLA), silicon dioxide (SiO) and dodecyl dimethyl benzyl ammonium chloride (DDBAC) were focused on 2nd and 30th day of incubation in sewer environment. Bacterial community contributed 25.01 % to shape RGs and mobile genetic elements (MGEs) after two days of incubation in sewage and plastisphere. After 30 days of incubation, the most important individual factor (35.82 %) was turned to microbial metabolic activity. The metabolic capacity of the microbial communities in plastisphere was stronger than that from SiO samples. Moreover, DDBAC inhibited the metabolic capacity of microorganisms in sewage samples, and increased the absolute abundances of 16S rRNA in plastisphere and sewage samples which might be similar to the hormesis effect. After 30 days of incubation, Aquabacterium was the predominant genus in plastisphere. As for SiO samples, Brevundimonas was the predominant genus. QACs RGs (qacEdelta1-01, qacEdelta1-02) and antibiotic RGs (ARGs) (aac(6')-Ib, tetG-1) significantly enriched in plastisphere. There was also co-selection among qacEdelta1-01, qacEdelta1-02 and ARGs. In addition, VadinBC27 which enriched in plastisphere of PLA NPs was positively correlated with the potentially disease-causing genus Pseudomonas. It showed that after 30 days of incubation, plastisphere had an important effect on distribution and transfer of pathogenic bacteria and RGs. Plastisphere of PLA NPs also carried the risk of spreading disease.