Combined Transcriptomic and Metabolomic Analyses of Fungal Spore Inactivation in a Continuous UV-LED Reactor: Kinetics, Mechanisms, and Batch Reactor Comparison

The contamination of water by fungi poses a potential threat to water quality and safety. UV light emitting diodes (LEDs) have become commercially available, while the majority of studies utilize static batch reactors rather than continuous flow reactors. In this study, the inactivation of three dominant waterborne fungal species by UV-LEDs and their combination with chlorine (Cl-2) was conducted in a continuous reactor. The results revealed that the continuous reactor showed lower inactivation rate constants (k) than the batch reactor due to the heterogeneous hydraulic conditions. Specifically, the addition of Cl-2 in the UV-LED continuous reactor enhanced the disinfection efficiency and inhibited photoreactivation; the survival ratios (8 h photoreactivation) of the three fungal species after UV-LED/Cl-2 inactivation were lower than 10% in the continuous reactor. Cultivability of fungal spores inactivated by UV-LEDs and UV-LED/Cl-2 in a continuous reactor was destroyed first, followed by the loss of membrane integrity. Simultaneously, the intracellular reactive oxygen species (ROS) level increased, disrupting cellular antioxidant functions gradually and ultimately leading to complete cell inactivation. Analysis of transcriptomics and metabolomics indicated that there was an upregulation of cytochrome c in the inactivation of Aspergillus niger by UV-LEDs and UV-LED/Cl-2, corroborating the apoptosis of fungal cells during these disinfection processes.