Analysis of the bacterial communities associated with different drinking water treatment processes.

A drinking water plant was surveyed to determine the bacterial composition of different drinking water treatment processes (DWTP). Water samples were collected from different processing steps in the plant (i.e., coagulation, sedimentation, sand filtration, and chloramine disinfection) and from distantly piped water. The samples were pyrosequensed using sample-specific oligonucleotide barcodes. The taxonomic composition of the microbial communities of different DWTP and piped water was dominated by the phylum Proteobacteria. Additionally, a large proportion of the sequences were assigned to the phyla Actinobacteria and Bacteroidetes. The piped water exhibited increasing taxonomic diversity, including human pathogens such as the Mycobacterium, which revealed a threat to the safety of drinking water. Surprisingly, we also found that a sister group of SAR11 (LD12) persisted throughout the DWTP, which was always detected in freshwater aquatic systems. Moreover, Polynucleobacter, Rhodoferax, and a group of Actinobacteria, hgcI clade, were relatively consistent throughout the processes. It is concluded that smaller-size microorganisms tended to survive against the present treatment procedure. More improvement should be made to ensure the long-distance transmission drinking water.