Characterization of bacterial community composition in drinking water

the goal of this study was to investigate the bacterial community shifts during production and distribution of drinking water, by studying a full-scale drinking water production and distribution facility that uses two series of multi-step treatment processes starting from the same source water (surface water). Furthermore, we investigated the presence and abundance of Acinetobacter at each step of the treatment chain using both culture-dependent and culture-independent methods (quantitative real-time PCR (qPCR)). Finally, we studied the importance of the physicochemical characteristics of the drinking water on the bacterial community composition in the water delivered to the end user (household tap water). Quantification of total bacteria revealed that for both production lines the amount of bacteria decreased when a treatment was applied, and the lowest amount of bacteria were detected after chlorination. There was a clear difference between the bacterial community composition in both production lines. In the first line (line A; applied treatments: rapid sand filtration, slow sand filtration, activated carbon filtration, UV treatment and chlorination), a substantial community shift was observed after slow sand filtration, resulting in a large increase in richness in operational taxonomic units (OTUs; an operational definition used to classify groups of closely related individuals) defined by a standard cut-off of 97 % 16S rRNA gene sequence identity. In the second production line (line B; applied treatments: flotation, double layer filtration, activated carbon filtration, UV treatment and chlorination), OTU richness gradually increased after every treatment step. For both lines, OTU richness decreased after chlorination. Taxonomy assignment of the OTUs revealed that Proteobacteria was again the most abundant phylum, although changes in the relative abundance of phyla was observed between treatment steps. Strikingly, the bacterial community composition of the waters sampled at the tap (originating from line A) or in the storage tank (originating from line B) were highly similar. Seasonal effects showed to be of minor influence in shaping the bacterial community composition. In contrast to Chapter II, Acinetobacter was found at low relative abundance in the water samples investigated in this study, reaching a maximum relative abundance of 2.8 %. Absolute abundance of Acinetobacter was the lowest after chlorination for both lines. Yet, for line A, a significant increase of Acinetobacter was observed in the household tap water. Plating of the water samples on agar media revealed a total of 14 different species (based on rpoB (RNA polymerase beta subunit) gene similarity), among which three potential pathogenic Acinetobacter species (i.e. A. guillouiae, A. johnsonii and A. lwoffii) were found in finished drinking water or household tap water. Water chemical parameters were more significantly different between seasons than between sampling locations, with the exception of trihalomethanes. Trihalomethanes concentrations were lower in one of the tap water samples originating from line A. Interestingly, the bacterial community in the drinking water sampled at this location was enriched in Methylophilus species which are capable of utilizing chlorinated methanes.