Metagenomic Profile of Microbial Communities in a Drinking Water Storage Tank Sediment after Sequential Exposure to Monochloramine, Free Chlorine, and Monochloramine

Sediment
accumulation in drinking water storage facilities may
lead to water quality degradation, including biological growth and
disinfectant decay. The current research evaluated the microbiome
present in a sediment after sequential exposure to monochloramine,
free chlorine, and monochloramine. Chemical profiles within the sediment
based on microelectrodes showed evidence of nitrification, and monochloramine
slowly penetrated the sediment but was not measurable at lower depths.
A metagenomic approach was used to characterize the microbial communities
and functional potential of top (0–1 cm) and bottom (1–2
cm) layers in sediment cores. Differential abundance analysis revealed
both an enrichment and depletion associated with depth of microbial
populations. We assembled 30 metagenome-assembled genomes (MAGs) representing
bacterial and archaeal microorganisms. Most metabolic functions were
represented in both layers, suggesting the capability of the microbiomes
to respond to environmental fluctuations. However, niche-specific
abundance differences were identified in biotransformation processes
(e.g., nitrogen). Metagenome-level analyses indicated that nitrification
and denitrification can potentially occur simultaneously in the sediments,
but the exact location of their occurrence within the sediment will
depend on the localized physicochemical conditions. Even though monochloramine
was maintained in the bulk water there was limited penetration into
the sediment, and the microbial community remained functionally diverse
and active.