Resilience of microbial communities in a simulated drinking water distribution system subjected to disturbances: role of conditionally rare taxa and potential implications for antibiotic-resistant bacteria

Abstract

Many US water utilities using chloramine as their secondary disinfectant have experienced nitrification episodes that detrimentally impact water quality in their distribution systems. A semi-closed pipe-loop chloraminated drinking water distribution system (DWDS) simulator was used to evaluate the biological stability of the system and describe the response of microbial communities in the bulk water (BW) and biofilm (BF) phase to a disturbance caused by changes in the operational parameters. The DWDS simulator was operated through five successive operational schemes, including an episode of nitrification, followed by a ‘chlorine burn’ by switching the disinfectant from chloramine to free chlorine. Community comparisons showed significant differences in the structure based on disinfectant and phase (e.g., BW and BF). Both disturbances created changes in the relative abundances of the core microbiome and some members of the rare biosphere (i.e., conditionally rare taxa); however, the microbial community was resilient and returned to its stable state. Genes associated with multiple antibiotic resistance mechanisms were found to be a component of the core genomes of waterborne isolates. These results provide evidence of variations in the bulk water/biofilm microbial community structure during episodes of disturbance (e.g., disinfectant switching practices, nitrification) and its recovery after disturbance.