Investigating Bi-directional Impacts of the Microbiome and Drinking Water Quality in Drinking Water Distribution System Water Mains and Storage Facilities

Abstract

The microbial communities that live in the biofilms of drinking water distribution system (DWDS) environments can exert significant impacts on drinking water quality before it reaches the consumer. The relatively recent advent and accessibility of powerful culture-independent techniques, such as high-throughput sequencing, have enabled characterization of diverse microbial communities; however, the difficulties of accessing DWDS infrastructure has hindered many efforts to study the health-relevant DWDS microbiome. In this work, high-throughput sequencing and quantitative real-time polymerase chain reaction (PCR) techniques were leveraged to characterize the biofilm communities of simulated and full-scale water mains, as well as the in situ suspended and biofilm communities of elevated water storage towers and underground reservoirs in a chloraminated DWDS. Seasonal variability and drivers of community composition were assessed in the simulated DWDS biofilms and in full-scale drinking water storage facilities. Among other examined drivers of community, the presence and concentration of disinfectant was an important selective pressure that impacted community composition. Communities in the simulated and full-scale DWDS biofilms were generally dominated by bacteria that live preferentially in, and form biofilms, exhibit increased resistance to disinfectant concentrations, or display versatility in substrate-utilization. These included genera that contain opportunistic pathogens, such as Mycobacterium, Pseudomonas, and Stenotrophomonas, genera implicated in microbiologically-caused corrosion of infrastructure (sulfate-reducing Desulfovibrio), - as well as ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) that catalyze nitrification processes and can cause reoccurring, problematic decreases in chloramine residual concentrations. Species-level taxonomic resolution of DWDS Mycobacterium, achieved by sequencing a mycobacterial heat shock protein gene, indicated that the bulk of these bacteria were not disease-associated strains. Early stages of community succession occurred rapidly for biofilms on new surfaces that were in proximity to more established biofilms – within a month, the biofilms on new surfaces exhibited similar compositions to neighboring, older biofilms. Apart from early changes in composition indicative of an initialization stage, biofilm communities in water storage facilities were temporally stable, although somewhat spatially heterogeneous. In contrast, suspended communities showed seasonal changes and were heavily influenced by water chemistry. Additionally, suspended communities were spatially homogeneous within a facility, and even at different facilities within the DWDS. In storage facilities that experienced problematic nitrification episodes and decreases in chloramine concentrations, suspended AOB concentrations increased as chloramine concentrations decreased. Notably, decreases in disinfectant were not accompanied by increases in the growth of other bacteria. Rather, as AOB concentrations increased, the total biomass of suspended communities actually decreased. During nitrification events, biofilm and suspended community compositions were most similar, lending further support to the concept that biofilms may act as reservoirs for nuisance and pathogenic bacteria in the DWDS. Abundant taxa were consistent with other studies of DWDSs that maintain chloramine, which provided support for the applicability of these findings to other systems, especially as there are no studies to compare to, to-date, of the microbiome in elevated storage towers.