Metagenomic Profiling of Pathogens in Simulated Reclaimed Water Distribution Systems Operated at Elevated Temperature Reveals Distinct Response of Mycobacteria to Filtration and Disinfection Conditions

Distribution of reclaimed water presents
distinct challenges for
pathogen control relative to the distribution of conventional potable
water. The elevated temperatures common in arid regions can exacerbate
such challenges by accelerating disinfectant decay and increasing
microbial growth rates. Here, we carried out a controlled, continuous-flow,
head-to-head study of six simulated reclaimed water distribution systems
(RWDSs) in order to assess whether treatments identified to be effective
for microbiological control at a lower temperature (22 °C) were
also effective at 30 °C. Shotgun metagenomic sequencing was carried
out to comprehensively profile fecal pathogens (FPs) (e.g., Escherichia and Klebsiella spp.), non-FPs (non-FPs) (e.g., Legionella and Mycobacterium spp.), and antibiotic-resistance
genes (ARGs). Consistent with prior studies, generally, all FP, non-FP,
and ARG markers were lowest when the influent water was biologically
active carbon (BAC) filtered and disinfected. However, in contrast
to observations at the lower temperature, where BAC filtration combined
with chlorine disinfection effectively controlled Mycobacterium spp., they were markedly elevated in BAC-filtered and chlorine-
or chloramine-disinfected conditions. This study highlights the need
for further research to improve the understanding of conditions that
select for different mycobacterial species and identify strategies
to effectively control them in RWDSs under elevated temperature conditions.