Composition and Dynamics of Bacterial Communities of a Drinking Water Supply System as Assessed by RNA- and DNA-Based 16S rRNA Gene Fingerprinting

Abstract

Bacterial community dynamics of a whole drinking water supply system (DWSS) were studied from source to tap. Raw water for this DWSS is provided by two reservoirs with different water characteristics in the Harz mountains of Northern Germany. Samples were taken after different steps of treatment of raw water (i.e., flocculation, sand filtration, and chlorination) and at different points along the supply system to the tap. RNA and DNA were extracted from the sampled water. The 16S rRNA or its genes were partially amplified by reverse transcription-PCR or PCR and analyzed by single-strand conformation polymorphism community fingerprints. The bacterial community structures of the raw water samples from the two reservoirs were very different, but no major changes of these structures occurred after flocculation and sand filtration. Chlorination of the processed raw water strongly affected bacterial community structure, as reflected by the RNA-based fingerprints. This effect was less pronounced for the DNA-based fingerprints. After chlorination, the bacterial community remained rather constant from the storage containers to the tap. Furthermore, the community structure of the tap water did not change substantially for several months. Community composition was assessed by sequencing of abundant bands and phylogenetic analysis of the sequences obtained. The taxonomic compositions of the bacterial communities from both reservoirs were very different at the species level due to their different limnologies. On the other hand, major taxonomic groups, well known to occur in freshwater, such as Alphaproteobacteria, Betaproteobacteria, and Bacteroidetes, were found in both reservoirs. Significant differences in the detection of the major groups were observed between DNA-based and RNA-based fingerprints irrespective of the reservoir. Chlorination of the drinking water seemed to promote growth of nitrifying bacteria. Detailed analysis of the community dynamics of the whole DWSS revealed a significant influence of both source waters on the overall composition of the drinking water microflora and demonstrated the relevance of the raw water microflora for the drinking water microflora provided to the end user.

Bacterial community change through drinking water treatment processes

“…Bacterial community change through the drinking water treatment units has still been poorly characterized. Eichler et al (2006) found that no major changes of bacterial community structures occurred after flocculation and sand filtration. In contrast, Pinto et al (2012) found that filtration by dual media rapid sand filters could shape the bacterial community in waters.…”

“…Since the presence of certain bacteria may lead to water quality problems in the downstream DWDS, knowledge of the bacterial ecology in the effluents of drinking water treatment units will be of practical importance. Unfortunately, only very few works have investigated the microbial communities in the effluents of drinking water treatment units (Eichler et al 2006;Poitelon et al 2010). Therefore, the bacterial community in the effluents of drinking water filters remains poorly understood.…”

“…It is generally accepted that chlorination can result in a dramatic shift in the composition of the bacterial community (Norton and LeChevallier 2000;Eichler et al 2006;Kormas et al 2010;Poitelon et al 2010), yet little information is available on the bacterial community change through other drinking water treatment units. Pinto et al (2012) found that filtration by dual media rapid sand filters in a drinking water plant played a primary role in shaping the bacterial community in DWDS.…”

“…However, only a small fraction of the viable bacterial cells present in drinking water could be identified using the traditional culture-dependent methods (Eichler et al 2006;Sartory et 2008). Molecular methods have been widely used to characterize the microbial community dynamics in drinking waters in DWDS (Berry et al 2006;Revetta et al 2010), and drinking water biofilters (Kasuga et al 2007;Feng et al 2012;Liao et al 2012).…”

Antibiotic resistance in urban aquatic environments: can it be controlled?

“…Therefore, it is expected that in drinking water, both the diversity of bacterial species and the possible occurrence of antibiotic resistance will have different characteristics of what can be found in wastewater. Water disinfection is known to cause a dramatic bottleneck on bacterial diversity (Hoefel et al 2005;Eichler et al 2006;Vaz-Moreira et al 2013) and bacteria ubiquitous in aquatic environments, such as members of the genus Aeromonas, may be reduced to levels below the limit of detection by culture-dependent methods (Figueira et al 2011). However, other groups that comprise bacteria with recognized ubiquity and genome plasticity, demonstrated by the acquired capacity to degrade xenobiotics or to resist to some antibiotics, such as members of the genera Pseudomonas, Acinetobacter, or family Sphingomonadaceae, are commonly found in tap water (Vaz-Moreira et al 2014).…”