Bacterial community assembly and beta-lactamase (bla) genes regulation in a full-scale chloraminated water

Beta-lactamases (bla) are the largest class of antibiotic resistance genes (ARGs) and can survive drinking water treatment processes. However, the key influencing factors of bla genes and the control measures in drinking water supply systems (DWSSs) remain unclear. Quantitative PCR, metagenomic, and 16S rRNA gene sequencing assays were performed to investigate the bla genes in the DWSS. The main carriers of bla genes are genera Caenimonas and Sphingomonas, which were the dominant bacterial genera in the DWSS. The abundance of bla genes was associated with bacterial community assembly events. When the heterotrophic plate count (HPC) in water was below 500 CFU/mL, stochastic assembly was the major contributor to bacterial community assembly and the bacterial community was less affected by the environment. When the HPC in water was above 500 CFU/ mL, deterministic assembly played an important role and decreasing the organic matter improved the efficiency of bla genes control. Organic matter can affect bla genes by shifting the diversity of the microbial community, and less organic matter appeared to be beneficial to reducing the bacterial niche width in the DWSS. Nanofiltration (NF) can decrease the effluent organic matter in waterworks and slow the dissemination of bacteria carrying bla genes in the DWSS.