Spatial Description of Drinking Water Bacterial Community Structures in Bulk Water Samples Collected in a Metropolitan Distribution System

The description of microorganisms inhabiting drinking water distribution systems has commonly been performed using techniques that are biased towards easy to culture bacterial populations. As most environmental microorganisms cannot be grown on artificial media, our understanding of the microbial community structure of drinking water is very limited. To circumvent some of the problems associated with culture-based techniques, sequence analysis of 16S rRNA gene clone libraries was used in this study. Genomic DNA was extracted from bulk phase water from sampling sites within the distribution systems (WDS), and used to develop 16S rRNA gene clones libraries. Water samples were collected from areas within the distribution system fed by two distinct raw water sources. Over 2300 16S rDNA clones were analyzed in this study from a total of 31 different sites. Phylogenetic analyses showed that ?-Proteobacteria and Actinobacteria represented more than 90% of the total clones examined. In general, similar bacterial groups were observed in sites receiving groundwater and surface water sources suggesting that chlorination is an important selective force in shaping up the overall microbial community structure. While the communities were similar at the general bacterial group, there were some differences at finer phylogenetic levels. This is important as it suggests that differences in the sources and treatment technologies could select for different populations. Since more than half of the clones were associated with yet to be cultured bacteria, and in many cases with novel bacterial groups, the results further substantiate the need for the development of culture-independent methods to better identify drinking water and to study their in-situ spatial-temporal dynamics