UV light at 254 nm (here referred to as UV) has been widely applied in (waste)water disinfection, providing effective inactivation of microorganisms (including antibiotic resistant bacteria, or ARB) primarily via damage to their nucleic acids. Relatively less knowledge is available on the fundamental kinetic parameters governing sensitivity of specific nucleic acid sequences (including antibiotic resistance genes, or ARGs) to degradation and deactivation (i.e., biological activity loss) by UV, and on applying them in modeling gene fate during bench/full-scale UV disinfection. In this work, a suite of model genes including pathogen-related ARGs (blt, mecA, vanA, tet(A), ampC, bla_NDM, and bla_KPC) and variable-length 16S rRNA gene segments were employed as disinfection targets to investigate gene degradation kinetics during bench/full-scale treatment of (waste)water with UV light.
Degradation kinetics of 21 amplicons (143-1509 bp) of these genes were examined in extra- and intracellular forms, with experiments conducted in phosphate buffer (PB) and/or wastewater (WW) matrixes. The degradation of extracellular genes followed linear kinetics up to UV fluences of 50 mJ/cm², followed by regions of decelerating kinetics (tailing) until apparent photostationary states were reached. These trends were successfully described using a kinetic model incorporating three reaction components: cyclobutane pyrimidine dimer (CPD) formation, CPD photoreversal, and irreversible (6−4) photoproduct formation. The measured rate constants of the 21 amplicons correlated predominantly with their 5’-TT-3’ doublet contents, with lesser contributions from 5’-TC-3’, 5’-CT-3’, and 5’-CC-3’ doublets. Rate constants for various DNA segments could in turn be accurately predicted from their contents of each doublet. Using the modeling approach and predicted rate constants, kinetics of extra- and intracellular ARG and 16S rRNA gene degradation were well modeled during bench-scale UV irradiation in PB and/or various WW matrixes over fluence ranges typical of WW treatment (up to 50 mJ/cm²). The host ARB strains (B. subtilis, S. aureus, E. faecium, E. coli, and P. aeruginosa) exhibited varying inactivation kinetics, with cell inactivation outpacing intracellular gene degradation. Bench-scale experimental results were validated by using the above modeling approach to predict ARG fate during full-scale disinfection at a local WWTP, where UV yielded ~1-log₁₀ elimination of detectable ARGs.

Huan He

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