Spatial and Temporal Dynamics in Attached and Suspended Bacterial Communities in Three Drinking Water Distribution Systems with Variable Biological Stability

Microbial
presence and regrowth in drinking water distribution
systems (DWDSs) is routinely monitored to assess the biological stability
of drinking water without a residual disinfectant, but the conventional
microbiological culture methods currently used target only a very
small fraction of the complete DWDS microbiome. Here, we sequenced
16S rRNA gene amplicons to elucidate the attached and suspended prokaryotic
community dynamics within three nonchlorinated DWDSs with variable
regrowth conditions distributing similarly treated surface water from
the same source. One rural location, with less regrowth related issues,
differed most strikingly from the other two urban locations by the
exclusive presence of Pseudonocardia (Actinobacteria) in the biofilm and
the absence of Limnobacter (Betaproteobacteriales) in the water and loose deposits
during summer. There was a dominant seasonal effect on the drinking
water microbiomes at all three locations. For one urban location,
it was established that the most significant changes in the microbial
community composition on a spatial scale occurred shortly after freshly
treated water entered the DWDS. However, summerly regrowth of Limnobacter, one of the dominant genera in the distributed
drinking water, already occurred in the clean water reservoir at the
treatment plant before further distribution. The highlighted bacterial
lineages within these highly diverse DWDS communities might be important
new indicators for undesirable regrowth conditions affecting the final
drinking water quality.