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Assays for the detection of total coliforms and E. coli are used in the United States as a tool for the detection of fecal contamination in finished drinking water, as a measure to prevent illness. However, based on statistics published by a number of researchers, as many as 764 documented waterborne outbreaks occurred between 1971 and 2002, which resulted in over half a million cases of illness and 79 deaths (Reynolds, Mena, & Gerba, 2008). Also, it has been theorized that as many as 19 million cases/year of waterborne illness are caused by public water systems fed by ground water and surface water in the US. Therefore, it has been argued that coliforms are not good indicator organisms for predicting risk of waterborne illness. In order to gather more microbiological information regarding drinking water, much research has been conducted on microorganisms in planktonic phase, as well as in biofilms present in drinking water distribution systems (DWDS). Different species of bacteria may colonize surfaces (internal or external) and begin to proliferate and form biofilm (Zhang, Choi, Dionysiou, Sorial, & Oerther, 2006). Due to the fact that biofilms are consistently being established, maturing, and sloughing off, it seems reasonable that the bacteria in planktonic phase, in a distribution system, would be ideal for microbial community analysis. With this in mind, we decided to analyze bacterial genomic DNA in order to gain knowledge of the current community structures present in drinking water samples, to serve as a base for measuring future differences or shifts in community structure. Although biofilms and planktonic populations may differ to some degree i.e.: culturability, activity, etc. (Boe-Hansen, Albrechtsen, Arvin, & Jorgensen, 2002) and may be very similar in terms of phylogeny, we decided to analyze the planktonic bacteria present in 31 sampling sites within a DWDS in order to characterize the bacterial community structures in these areas of the distribution system. Through analysis of bulk water samples, this study aims to identify and compare the microbial communities that are present in a DWDS fed by ground water and surface water. This study was conducted in order to gain a better understanding of the bacterial communities that are present within a municipal DWDS at Points of Use (POUs), with the focus of the study being a phylogenetic comparison between those communities found in different areas of the DWDS based on source. A total of 2786 16S rDNA clones were analyzed in this study. We found that Actinobacteria (mainly Mycobacterium sp.) and Alphaproteobacteria represented nearly 46% and 36% of the total clones examined, respectively. Other bacterial genera identified in this study include Betaproteobacteria, Gammaproteobacteria, Cyanobacteria, Firmicutes, Planctomycetes, and others. While Alphaproteobacteria has been shown to be a numerically dominant group in chlorinated drinking water system simulators (Williams, Domingo, Meckes, Kelty, & Rochon, 2004); (Williams, Santo Domingo, & Meckes, 2005), the surprising abundance of mycobacterial sequences recovered in this study indicate significant differences in microbial community structure between the WDS analyzed in this study as compared to others in the literature. |
