Microbial communities associated with the problem of bacterial regrowth in chloraminated drinkingwater distribution systems (DS) have two main components: the autotrophic nitrifiers growing onammonia released from chloramine decay; and, the heterotrophs relying on biodegradable organicmaterial. While nitrifying populations have been extensively studied, microbial ecologicalknowledge on heterotrophic populations is limited even though some studies have indicated thatheterotrophs may be the dominant component, or could even initiate regrowth in DS. The types ofheterotrophic organisms inhabiting chloraminated DS can potentially influence disinfection strategies.The objectives of this study were to: identify heterotrophic bacteria in pilot- and full-scale DS usingculture-independent methods; and, comparatively evaluate heterotrophic communities tounderstand if pilot-scale adequately represents the real scale. Monthly samples were obtained fromtwo parallel pilot-scale DS with high and low chloramine dose, and three full-scale systems at ageographically different location, which included finished water and two separate tanks indownstream DS. Two additional pilot systems were run for a shorter period and sampled for theobservation of early community development. Organisms in DS samples were identified based ontheir 16S rRNA sequences and community fingerprints were generated using automated ribosomalintergenic spacer analysis (ARISA). Most of the retrieved 16S rRNA sequences (95%) were relatedto heterotrophic bacteria. Both phylogenetic analyses and community fingerprints showed that theheterotrophic communities in pilot- and full-scale were significantly different. However, a significantnumber of sequences common to all systems excluding finished water indicated organisms that arewell-adapted to chloraminated environments. These included bacteria from the Sphingomonadalesorder, Mycobacterium and Curvibacter genera, and an uncultured lineage of Rhizobiales. In addition,there were full-scale distribution system sequences, previously not reported in other environmentsrelated to drinking water. In conclusion, pilot-scale DS are useful for investigating certainsubpopulations of microbiota in chloraminated distribution systems, but are not perfect models thatcan simulate the overall microbial dynamics in the full-scale. Culture-based methods are needed todetermine the potential environmental roles of the chloraminated distribution system organismsdiscovered in this work using molecular techniques. Includes 32 references, tables, figures.
Keywords: Bacteria; Distribution Systems; Chloramines; Cultures
