The health challenges posed by microbial pathogens in water and biofilms are of great global concern. It is important to understand the impact of different disinfection strategies on microbiomes to facilitate water quality control. This work demonstrated the yearlong impacts of ultraviolet light-emitting diodes (UV LEDs) versus chlorine disinfection on microbial communities in water and biofilms at a rural water treatment plant. Using 16S RNA gene sequencing, we found that Proteobacteria was the most abundant phylum in UV treated biofilm and water samples, and chlorine treated biofilm samples (65% ,45% and 49% relative abundance, respectively), whereas Firmicutes was the most abundant phylum in chlorine treated water samples (50%). Considering both biofilm and water samples, Chlorine resulted in higher observed alpha diversity than UV disinfection. Within each disinfection strategy, there was no significant difference between water and biofilm samples (Wilcoxon rank-sum test). Quantitative beta diversity analysis indicated that microbial communities significantly differed between UV and chlorine treated biofilm samples, but were similar between UV and chlorine treated water samples. UV treated samples were more similar than chlorine treated samples to the shared disinfection influent, indicating less selective pressure by UV than chlorine disinfection. The average relative abundance of genera that can contain opportunistic pathogens (Legionella, Mycobacterium and Pseudomonas) collected from filter effluent, chlorine effluent, and UV LED effluent was 2.3, 2.2, and 1.8%, respectively. Analysis of the impact of environmental conditions and water quality parameters in addition to disinfection strategy on the microbial taxa in water and biofilms over time is ongoing. Together, these data indicate the potential for targeted implementation of disinfection methods to fight particular waterborne pathogens and nuisance microorganisms and minimize the risks to human health.
