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

Abstract

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.

Composition of active bacterial communities and presence of opportunistic pathogens in disinfected and non-disinfected drinking water distribution systems in Finland

“…However, in DWDSs B and D the water temperature was a less dominant factor as compared to the difference between groups of active bacteria (RNA) and total bacteria (DNA). Total bacterial communities in drinking water distribution systems based on DNA methods have been more often described in publications ( Potgieter et al, 2018 ; Bruno et al, 2018 ; Waak et al, 2019 ; Rosenqvist et al, 2023 ) compared to hot water systems and active RNA-based communities. Earlier studies show that raising the temperature in hot water systems shifts bacterial composition ( Ji et al, 2017 ; Dai et al, 2018 ) and bacterial communities are less diverse in hot tap water than in cold tap water ( Zhang et al, 2021 ).…”

“…The nitrification process may decrease water quality, cause corrosion, decrease disinfectant residue, and increase growth of bacteria ( Hossain et al, 2022 ). Bdellovibrionia was active in cold water in chlorinated DWDS C and in cold and hot water in chloraminated water in DWDS D. Some species of Bdellovibrio (such as B. bacteriovorus and B. exovorus ) belonging to Bdellovibrionia have been found to be natural predators of Gram-negative human pathogens and have also been found in chloraminated drinking water and in disinfection residue-free DWDS ( Bautista-de los Santos et al, 2016 ; Atterbury and Tyson, 2021 ; Rosenqvist et al, 2023 ). In hot water systems, Acidobacteriae were present and active in DWDS A and Deinococci in DWDS E. Acidobacteriae have been found in hot water system studies ( Ji et al, 2017 ).…”

“…The selection of drinking water treatment techniques and disinfection affects the microbial content of the water going from the waterworks into the distribution system, but microbial nutrients from source water, pipe material, temperature, and the age of the water may also affect the microbiome composition and activity in water and biofilms on the inner surfaces of the pipes in many complex ways ( Potgieter et al, 2018 ; Neu and Hammes, 2020 ; Leslie et al, 2021 ). Biofilms also give shelter to bacteria, including opportunistic pathogens, that may not be detected abundant in water when DWDS is well maintained ( Waak et al, 2019 ; Leslie et al, 2021 ; Rosenqvist et al, 2023 ).…”

“…Disinfection residual is used to maintain good quality ( WHO, 2022 ) and disinfection is always required when surface water is used as source water in Finland ( STM, 2015 ). While most of the published results about bacterial communities in DWDSs concern chlorinated drinking water systems, bacterial communities in non-chlorinated DWDSs are less studied ( Potgieter et al, 2018 ; Bruno et al, 2018 ; Rosenqvist et al, 2023 ). It is known that disinfection residual in DWDSs causes selective pressure on microbiota and decreases diversity in bacterial communities and their functional potential compared to non-disinfected water systems ( Waak et al, 2019 ; Dai et al, 2020 ).…”

“…An RNA-based approach gives an estimation of live (either dormant or metabolically active) members of the bacterial community, as ribosomal RNA is actively produced and regulated by living cells and it degrades more quickly than DNA after cell death ( Li et al, 2017 ). In DWDSs, living members of bacterial communities and their activity are less studied compared to studies using DNA-based methods ( Potgieter et al, 2018 ; Bruno et al, 2018 ; Waak et al, 2019 ; Rosenqvist et al, 2023 ).…”