Assessing the potential of biologically-activated carbon treatment, pasteurization, and particle filtration as pre/pro-biotic controls on premise plumbing microbiomes

The potential for “probiotic” and “prebiotic” controls for opportunistic pathogen growth in premise (i.e., building) plumbing has been hypothesized but not demonstrated in practice. Here, we employed convectively-mixed pipe reactors (CMPRs) to compare the effects of common building influent water treatments for probiotic (i.e., release of beneficial microbes) and prebiotic (i.e., manipulation of water chemistry to cultivate beneficial microbes) effects on corresponding microbiomes in distal hot water plumbing experiencing warm temperatures suitable for pathogen growth. Specifically, biologically-activated carbon (BAC) reduced influent total organic carbon (TOC) and elevated (potentially probiotic) total and intact bacterial cell counts (TCCs/ICCs). Particle filtration of the BAC-treated water depleted both microbes and the nutrients embedded in their biomass. Pasteurization of BAC-treated water converted live TCCs/ICCs into bioavailable organic carbon capable of supporting necrotrophic growth. 16S rRNA gene amplicon sequencing revealed that a substantial portion of influent bacteria were able to establish in the bulk water and biofilm of the CMPRs, with a surprisingly rare relative abundance of taxa only found in the biofilm. This was especially true for CMPRs receiving BAC-treated influent water without secondary filtration or heat treatment. In aged CMPRs with 3+ year aged biofilm, the Probiotic condition contained the lowest relative abundance of amplicon sequence variants (ASVs) annotated as Legionella , whereas the aged Control CMPRs contained the highest Legionella abundances. The microbiome composition of CMPRs constructed from new polyvinyl chloride pipe largely mirrored that of aged CMPRs, although Legionella ASVs were generally lower in relative abundance across all conditions. This study illustrates that pro/pre-biotic controls can be successfully imposed on premise plumbing through strategic implementation of existing building-level drinking water treatment technologies to intentionally manipulate the microbiome.