title: Reduction in horizontal transfer of conjugative plasmid by UV irradiation and low-level chlorination.
abstract: The widespread presence of antibiotic resistance genes (ARGs) and antibiotic resistant bacteria (ARB) in the drinking water system facilitates their horizontal gene transfer among microbiota. In this study, the conjugative gene transfer of RP4 plasmid after disinfection including ultraviolet (UV) irradiation and low-level chlorine treatment was investigated. It was found that both UV irradiation and low-level chlorine treatment reduced the conjugative gene transfer frequency. The transfer frequency gradually decreased from 2.75 × 10(-3) to 2.44 × 10(-5) after exposure to UV doses ranging from 5 to 20 mJ/cm(2). With higher UV dose of 50 and 100 mJ/cm(2), the transfer frequency was reduced to 1.77 × 10(-6) and 2.44 × 10(-8). The RP4 plasmid transfer frequency was not significantly affected by chlorine treatment at dosages ranging from 0.05 to 0.2 mg/l, but treatment with 0.3-0.5 mg/l chlorine induced a decrease in conjugative transfer to 4.40 × 10(-5) or below the detection limit. The mechanisms underlying these phenomena were also explored, and the results demonstrated that UV irradiation and chlorine treatment (0.3 and 0.5 mg/l) significantly reduced the viability of bacteria, thereby lowering the conjugative transfer frequency. Although the lower chlorine concentrations tested (0.05-0.2 mg/l) were not sufficient to damage the cells, exposure to these concentrations may still depress the expression of a flagellar gene (FlgC), an outer membrane porin gene (ompF), and a DNA transport-related gene (TraG). Additionally, fewer pili were scattered on the bacteria after chlorine treatment. These findings are important in assessing and controlling the risk of ARG transfer and dissemination in the drinking water system.
authors.affiliation: Key Lab of Urban Environment and Health, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen, 361021, China.
authors.forename: Wenfang
authors.initials: W
authors.lastname: Lin
authors.affiliation: Key Lab of Urban Environment and Health, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen, 361021, China.
authors.forename: Shuai
authors.initials: S
authors.lastname: Li
authors.affiliation: College of Environment and Safety Engineering, Shenyang University of Chemical Technology, Shenyang, 110142, China.
authors.forename: Shuting
authors.initials: S
authors.lastname: Zhang
authors.affiliation: Key Lab of Urban Environment and Health, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen, 361021, China. Electronic address: xyu@iue.ac.cn.
authors.forename: Xin
authors.initials: X
authors.lastname: Yu
mesh_terms: D001419:Bacteria / Q000187:drug effects / Q000235:genetics* / Q000528:radiation effects; D004203:Disinfection; D060766:Drinking Water / Q000382:microbiology*; D022761:Gene Transfer, Horizontal / Q000187:drug effects* / Q000528:radiation effects*; D054879:Halogenation; D010957:Plasmids / Q000187:drug effects / Q000528:radiation effects; D014466:Ultraviolet Rays
chemical_list: D060766:Drinking Water
keywords: Antibiotic resistant genes; Chlorination; Conjugative gene transfer; UV irradiation