Succession of bacterial biofilm communities following removal of chloramine from a full-scale drinking water distribution system

Monochloramine is used to regulate microbial regrowth in drinking water distribution systems (DWDS) but produces carcinogenic disinfection byproducts and constitutes a source of energy for nitrifying bacteria. This study followed biofilm-dispersed microbial communities of a full-scale DWDS distributing ultrafiltered water over three years, before and after removal of monochloramine. Communities were described using flow cytometry and amplicon sequencing, including full-length 16S rRNA gene sequencing. Removal of monochloramine increased total cell counts by up to 440%. Increased abundance of heterotrophic bacteria was followed by emergence of the predatory bacteria Bdellovibrio, and a community potentially metabolizing small organic compounds replaced the nitrifying core community. No increased abundance of Mycobacterium or Legionella was observed. Co-occurrence analysis identified a network of Nitrosomonas, Nitrospira, Sphingomonas and Hyphomicrobium, suggesting that monochloramine supported this biofilm community. While some species expanded into the changed niche, no immediate biological risk to consumers was indicated within the DWDS.

Automated summary

This study tracked the biofilm-dispersed microbial communities of a full-scale drinking water distribution system (DWDS) for three years, before and after the removal of monochloramine. The removal of monochloramine increased total cell counts and led to the emergence of predatory bacteria Bdellovibrio, as well as the replacement of the nitrifying core community with a community potentially metabolizing small organic compounds. However, no increased abundance of Mycobacterium or Legionella was observed in the drinking water distribution system. Co-occurrence analysis revealed a network of bacteria, including Nitrosomonas, Nitrospira, Sphingomonas, and Hyphomicrobium, suggesting that monochloramine supported this biofilm community.