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MOLECULAR DIVERSITY OF DRINKING WATER MICROBIAL COMMUNITIES: A PHYLOGENETIC APPROACH
Citation:
REVETTA, R. P., J. W. SANTO-DOMINGO, C. A. KELTY, B. W. HUMRIGHOUSE, D. B. OERTHER, R. LAMENDELLA, M. KEINANEN-TOIVOLA, AND M. WILLIAMS. MOLECULAR DIVERSITY OF DRINKING WATER MICROBIAL COMMUNITIES: A PHYLOGENETIC APPROACH. Presented at AWWA/IWA/PWEA Disinfection 2007 - Current Practice and Future Trends in Disinfection: Water, Wastewater, Stormwater, Water Reuse and Biosolids, Pittsburgh, PA, February 04 - 07, 2007.
Impact/Purpose:
To inform the public
Description:
Culture-based methods are traditionally used to determine microbiological quality of drinking water even though these methods are highly selective and tend to underestimate the densities and diversity bacterial populations inhabiting distribution systems. In order to better understand the effect of different disinfection treatments on the bacterial diversity of water distribution systems (WDS) we have focused our efforts using 16S rDNA PCR-based techniques. 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. Also, since it is possible for DNA to persist in the environment after cell death additional studies were performed using 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 alpha-Proteobacteria and Mycobacterium spp. were the predominant bacterial groups identified in both biofilm and planktonic samples. Some of the clones obtained in these studies were also shown to be closely related to Legionella spp. While members of the Mycobacterium and Legionella genera are known to be pathogenic and have been isolated from drinking water samples and drinking water biofilms, the public health relevance of these two bacterial groups has yet to be determined. Differences in biofilm community structure between disinfection treatments were evident as biofilm exposed to chloramine primarily consisted of Mycobacterium spp. and Dechloromonas spp. In contrast, a variety of alpha- and beta-Proteobacteria dominated the DNA-based clone libraries of biofilm exposed to chlorine or inactivated chlorine residual. Sequence analysis of RNA-based clones derived from biofils exposed to chlorine suggested that the active bacterial fraction consisted of a few dominant bacterial groups related to Nevskia ramosa, a member of the gamma-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 with 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.