Molecular diversity of drinking water microbial communities: a phylogenetic approach
The microbiological quality of drinking water is assessed using culture-based methods that are highly selective and that tend to underestimate the densities and diversity of microbial populations inhabiting distribution systems. In order to better understand the effect of different disinfection treatments on the bacteria in water distribution systems (WDS) we have used 16S rDNA PCR-based techniques. 16S rDNA clone libraries were developed using DNA extracted from samples collected at different times and locations in a metropolitan distribution system derived from different source waters. Since it is possible for DNA to persist in the environment after cell death we also used rRNA (instead of DNA) as the target molecule to study the active bacterial fraction in drinking water biofilms. Phylogenetic analyses and sequence comparisons with existing databases revealed that α- and β-Proteobacteria were among the most predominant bacterial groups identified in both biofilm and planktonic communities. Clones closely related to Mycobacterium spp. and Legionella spp. were also obtained in these studies. While members of the Mycobacterium and Legionella genera are known to be pathogenic, the public health relevance of these clones has yet to be determined. Differences in biofilm community structure between disinfection treatments were evident as biofilms exposed to chloramine primarily consisted of Mycobacterium spp. and Dechloromonas spp. In contrast, a variety of α- and β-Proteobacteria dominated the DNA-based clone libraries of biofilm receiving no disinfectant and biofilm exposed to chlorine. Sequence analysis of RNA-based clones derived from biofilms exposed to chlorine suggested that the active bacterial fraction consisted of a few dominant bacterial groups related to Nevskia ramosa, a member of the γ-Proteobacteria group frequently found in the air-water interphase (i.e., neuston). Some of the bacterial groups identified in the latter clone libraries are affiliated with yet to be cultured organisms suggesting that a significant fraction of drinking water communities cannot be studied using culturing methods. The results from these studies suggest that we have a limited understanding of the molecular diversity and population dynamics of WDS microbial communities. Future studies will focus on expanding sequencing databases to more accurately characterize potential differences between disinfection treatments and to better understand the microbial diversity in drinking water systems.
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Document Type: Research Article
Publication date: 2007-01-01
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